FOUNDATIONS OF BRIDGES AND BUILDINGS BY HENRY S. J^COBY PROFESSOR OF BRIDGE ENGINEERING, CORNELL UNIVERSITY AND ROLAND P. DAVIS PROFESSOR OF STRUCTURAL AND HYDRAULIC ENGINEERING WEST VIRGINIA UNIVERSITY FIRST EDITION MCGRAW-HILL BOOK COMPANY, INC. 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1914 s COPYRIGHT, 1914, BY THE McGR/w-HiLL BOOK COMPANY, INC. THE. MAPLE. PRE8Q. YOUR. PA PREFACE In preparing this volume the aim of the authors has been to treat in a systematic manner the entire subject of foundations for bridges and buildings as represented by American engineer- ing practice. Only occasional references are made to foreign practice. It was hoped, at first, to accomplish this task within the limits of about 300 pages, but as the work progressed it became evident that this could not be done without abbreviat- ing the treatment of many topics so much as to become un- satisfactory. In many cases, space has been economized by inserting additional illustrations and reducing descriptions in the text. A large proportion of space is devoted to piles and pile driving, since young engineers are more likely to obtain their early experience with pile foundations than with any other class of foundation construction. Many facts derived from experience are given to emphasize and illustrate the application of funda- mental principles and to form a rational basis for that kind of judgment which is such an important element in an engineer's professional practice. The undesirable features of considerable pile driving in this country have been due as much to the as- sumption that the art of pile driving is so simple that the aid of science is not essential, as to the attempt of some engineers to base the art upon theoretical rules which fail to take into account many practical factors of the problem. Another reason for extending the treatment is due to the recent intro- duction of concrete piles which will help to retain the dominant place that pile foundations have held heretofore among other classes of foundations. The attention of engineering teachers is called to the arrange- ment of the topics in the first five chapters. Instead of combin- ing the treatment of all kinds of piles in chapters on descriptions, v VI PREFACE equipment, driving, and bearing power respectively, the subject is developed in accordance with pedagogical principles for the benefit of students who approach it without any previous knowledge of the subject. It is believed, however, that practicians will find this arrangement equally useful for their study and reference. The full discussion of the bearing power of timber piles before considering that of concrete piles, conforms also to the order of historical development. The treatment of the pneumatic process and its application, to both bridges and buildings, is supplemented by a chapter on pneumatic caisson practice by T. KENNARD THOMSON, an experienced consulting engineer who has specialized in founda- tion construction. The results of his experience and ob- servation should be helpful to all engineers and contractors of lesser experience. ' Three chapters on piers and abutments are incorporated in this work since courses of instruction in technical colleges frequently include these topics in masonry construction with foundations. During the past decade considerable improve- ments have been made in the design of piers and abutments by the introduction of new types, including hollow and arched forms, in order to reduce the loads upon foundation beds and to eliminate a large part of the lateral thrust of embankments, as well as to decrease the volume of masonry in some cases. The limits of the volume precluded historical notes in con- nection with every class of foundation, but they are introduced in certain cases relating to new types of construction, or where the process of development indicates the features which are likely to persist in the future. Since a subject embracing so many details of design and construction cannot be exhaustively treated in a single volume of convenient size to meet the needs of all practicians, a chapter has been added which contains a large number of carefully selected and classified references to the vast amount of illus- trative material on foundations contained in engineering periodicals and the proceedings of engineering societies. It is hoped that young technical graduates will form the habit of PREFACE Vll consulting the article? referred to, making suitable abstracts, and filing them for future use. To compare the manner in which different designers have solved a given problem is a most valuable study. Grateful acknowledgments for photographs are due to S. W. BOWEN, A. S. CRANE, A. 0. CUNNINGHAM, Dravo Contracting Co., Lackawanna Steel Co., RALPH MODJESKI, C. K. MOHLER, J. H. PRIOR, J. R. RABLIN, E. J. SCHNEIDER, H. E. STEVENS, F. L. THOMPSON, and M. M. UPSON; to J. Q. BARLOW, J. D. ISAACS, and H. K. SELTZER for permission to reproduce draw- ings; to R. A. CUMMINGS, Engineering News, Engineering Record, Engineering and Contracting, and Railway Age Gazette for permission to reprint illustrations; to C. W. REINHARDT for the excellent drawings from which a number of illustrations were reproduced; and to E. H. CONNOR, L. L. DAVIS, WALTER FERRIS, J. E. GREINER, H. IBSEN, A. R. RAYMER, R. TRIMBLE, and many other engineers who have kindly furnished information. Acknowledgment is made for several photographs on the half-tones themselves, or their titles. April 15, 1914. CONTENTS PREFACE PAGE v LIST OF FULL-PAGE ILLUSTRATIONS xv CHAPTER I TIMBER PILES AND DRIVERS ART. i. Foundations PAGE i 2. Classification of Piles 2 3. Timber Piles 6 4. Form and Dimensions 9 5. The Phenomena of Pile Driving n 6. Ordinary Pile-drivers 14 7. Track Pile-drivers 16 8. The Drop Pile-hammer 20 9. The Steam Pile-hammer 21 10. Advantages of Steam-hammers 24 11. Rings, Caps, and Followers 27 12. Points, Shoes, and Splices 3 2 CHAPTER II DRIVING TIMBER PILES ART. 13. Observations in Practice PAGE 37 14. Driving Piles Butt Down 40 15. Driving Batter Piles 41 16. Use of the Water-jet 43 17. Equipment for Water-jet Process 48 18. Overdriving Piles 49 19. Spacing of Piles 55 20. Cutting off and Removing Piles 58 21. Chemical Preservation 63 22. Mechanical Protection 66 23. Cost of Pile Driving 71 CHAPTER III BEARING POWER OF PILES ART. 24. Piles Acting as Columns PAGE 75 25. The Goodrich Formula 77 26. Engineering News Formula 82 ix X CONTENTS ART. 27. Weight and Fall of Hammer PAGE 85 28. The Restrained Fall 87 29. Final Penetration per Blow 88 30. Formula for Steam-hammer 90 31. Tables and Diagrams 92 32. Effect of Rest on Bearing Power 95 33. Effect of Sub-surface Conditions 97 34. On Total Penetration 100 35. Degree of Security 101 36. Test Piles 105 37. Pile Records and Performance no 38. Specifications 112 CHAPTER IV CONCRETE PILES ART. 39. Introduction and Classification PAGE 116 40. Relative Advantages 118 41. Unpatented Pre- molded Piles 122 42. Patented Pre- molded Piles 127 43. Form and Construction 130 44. Design of Pre-molded Piles 134 45. Cast-in-place Piles 136 46. Precautions Against Injury 142 47. Composite Types and Combination Piles . 144 48. Drivers, Hammers, and Caps 147 49. Driving Concrete Piles 152 50. Analysis of Time and Cost 157 51. Formulas for Bearing Power 161 52. Choice of Type 163 53. Effect of Taper 166 54. Driving and Loading Test Piles 169 55. Specifications 172 CHAPTER V METAL AND SHEET PILES ART. 56. Tubular Piles PAGE 174 57. Disk and Screw Piles 178 58. Sand Piles 180 59. Timber Sheet-piling 181 60. Steel Sheet-piling 184 61. Concrete Sheet-piling 189 62. Driving Sheet-piling 190 63. Design of Sheet-piling 194 CONTENTS XI CHAPTER VI COFFERDAMS ART. 64. The Cofferdam Process PAGE 198 65. Earth Cofferdams 199 66. Wooden Sheet-pile Cofferdams 203 67. Single Wall with Guide Piles 206 68. Sheet-piling Supported by Frames 210 69. Sheet-piling Supported by Cribs .' 214 70. Steel Sheet-pile Cofferdams 216 71. Self-supporting Steel Sheet-pile Cofferdams 221 72. Crib Cofferdams 226 73. Movable Cofferdams 228 74. Miscellaneous Types. 232 75. Puddle and Leakage 234 76. Design of Cofferdams 235 77. Cost of Cofferdams 236 78. Choice of Type 238 CHAPTER VII BOX AND OPEN CAISSONS ART. 79. Definitions and Classification PAGE 239 80. Box Caissons of Timber 240 81. Box Caissons of Concrete 243 82. Miscellaneous Types 245 83. Single- wall Open Caissons 246 84. Cylinder Caissons 251 85. Metal Cylinder Caissons 254 86. Reinfo reed-concrete Cylinder Caissons 257 87. Open Caissons with Dredging Wells 262 88. Construction with Timber 263 89. Construction with Metal 270 90. Construction with Concrete 272 91. Sinking Open Caissons ' 277 CHAPTER VIII PNEUMATIC CAISSONS FOR BRIDGES ART. 92. The Pneumatic Process PAGE 280 93. Caisson Roof Construction 283 94. Sides of Working Chamber 293 95. Details of Cutting Edge 294 96. Bracing of Caisson 296 97. Crib Construction 298 98. Cofferdam Construction 300 Xll CONTENTS ART. 99. Pneumatic Caissons of Concrete PAGE 301 100. Pneumatic Caissons of Metal 302 101. Cylinder Pier Caissons 304 102. Combination Cylinder Caissons 307 CHAPTER IX PNEUMATIC CAISSONS FOR BRIDGES ART. 103. Shafts and Air-locks PAGE 309 104. Design of Caissons 313 105. Building and Placing the Caisson 315 106. Sinking the Caisson 317 107. Removing Spoil from Working Chamber 319 108. Concreting the Air Chamber ,'. ",;- 322 109. Rate of Sinking 3 23 no. Frictional Resistance 326 in. Physiological Effects of Compressed Air 329 112. Prevention of Caisson Disease 333 CHAPTER X PNEUMATIC CAISSONS FOR BUILDINGS ART. 113. General Development PAGE 338 114. Caissons of Timber 340 115. Caissons with Metal Shells 345 1 1 6. Caissons of Wood and Steel 347 117. Caissons of Reinforced Concrete 349 118. Crib and Cofferdam 350 119. Shafts and Air-locks 352 120. Sinking the Caisson 356 121. Rate of Sinking 359 122. Filling the Air Chamber 360 123. Water-tight Dam of Wall Piers 361 CHAPTER XI PIER FOUNDATIONS IN OPEN WELLS ART. 124. Open Wells with Sheet-piling PAGE 366 125. Open Wells with Sheeting; the Chicago Method .... 370 126. The Grouting Process 373 127. Applications and Tests 376 128. The Freezing Process 379 129. Hydraulic Caissons 382 CONTENTS Xlll CHAPTER XII ORDINARY BRIDGE PIERS ART. 130. General Requirements PAGE 384 131. Definitions 386 132. Form and Dimensions 388 133. Materials and Construction 394 134. Examples of Solid Piers 398 135. Examples of Hollow Piers 403 136. Stability of Piers 409 137. Example of Pier Design . . 411 CHAPTER XIII CYLINDER AND PIVOT PIERS ART. 138. General Arrangement PAGE 417 139. Metal-shell Cylinder Piers ... 418 140. Design and Construction 423 141. Reinforced-concrete Cylinder Piers 426 142. Large Cylinder or Pivot Piers 428 CHAPTER XIV BRIDGE ABUTMENTS ART. 143. Form and Dimensions PAGE 433 144. Design and Construction 436 145. Wing-wall Abutments 439 146. U-abutments and T-abutments 441 147. Buried Abutments 447 148. Reinforced Arch Abutments 449 / CHAPTER XV \/ SPREAD FOUNDATIONS ART. 149. General Considerations PAGE 452 150. Early Types of Footings 453 151. Modern Types of Spread Foundations 457 152. Construction of I-Beam Grillages 458 153. Design of I-beam Grillages 459 154. Design of Double-column Footings . 464 155. Distribution of Pressure on Base 468 156. Steel Grillage Foundations 469 157. Design of Reinforced-concrete Spread Foundations. . . . 474 158. Design of Reinforced-concrete Column Footings .... 477 159. Concrete Spread Foundations 481 XIV CONTENTS CHAPTER XVI UNDERPINNING BUILDINGS ART. 1 60. Needle-beam Underpinning PAGE 490 161. Examples with Needle-beams 493 162. Supporting Wall below Beams 495 163. The Cantilever Method 497 164. Figure-four Needles 501 165. Placing the New Foundation 503 166. Joining to the Old Wall 506 167. The Breuchaud Process 507 168. Method of Sinking Cylinders 511 169. Concreting the Cylinders 513 170. Transferring Load to Cylinder 514 171. Other Modern Methods 515 v CHAPTER XVII EXPLORATIONS AND UNIT LOADS >/ ART. 172. Test Pits and Sounding Rods PAGE 518 173. Borings with Augers , 5 T 9 174. Wash Borings 5 20 175. Core Drillings with Diamonds 524 176. Core Drilling without Diamonds 527 177. Need of Sub-surface Explorations 529 178. Tests for Bearing Capacity 531 179. Values of Bearing Capacity , 534 CHAPTER XVIII PNEUMATIC CAISSON PRACTICE ART. 180. Historical Notes PAGE 538 181. Results of Evolution 539 182. Construction of Caissons , 54* 183. Caulking, Shafts and Lighting 544 184. Methods of Launching 547 185. Placing and Sinking 549 186. Excavating and Sealing 552 187. Joints between Caissons 554 188. Plant and Equipment 555 189. Air-locks and Concrete 55 6 190. Allowable Bearing under Caissons 559 191. Remarks on Underpinning 560 CONTENTS XV CHAPTER XIX REFERENCES TO ENGINEERING LITERATURE ART. 192. Literature on Foundations PAGE 562 193. Timber Piles and Pile Driving 567 194. Bearing Power of Piles 572 195. Concrete Piles 573 196. Metal and Sheet Piles 575 197. Cofferdams 577 198. Box and Open Caissons 580 199. Pneumatic Caissons for Bridges 582 200. Pneumatic Caissons for Buildings 585 201. Pier Foundations in Open Wells 587 202. Bridge Piers 588 203. Bridge Abutments 591 204. Spread Foundations 592 205. Underpinning Buildings 593 206. Explorations and Unit Loads . 595 INDEX. PAGE 599 LIST OF FULL-PAGE ILLUSTRATIONS A Standard Type of Contractor's Pile-driver PAGE 15 Self-propelling Track Pile-driver X i6 Self-propelling and Convertible Crane Pile-drivers 1 i7 Locomotive Crane Used as Traveler and Pile-driver 18 Driving Batter Piles for Trestle at Dumbarton Point X 42 Examples of Overdriven Piles Exposed by Excavation J 43 Steel Pile-driver and Sections of Reinforced Steel Shells ^36 Sections of Patented Steel Sheet-piling . 186 Driving Wakefield Sheet-piling for a Cofferdam *I9O Cofferdams with Single Walls of Timber Sheet-piling 207 Self-supporting Timber Sheet-pile Cofferdam ^14 Timber Bracing of Steel Sheet-pile Cofferdam 1 22o Self-supporting Steel Sheet-pile Cofferdam : 222 Bulging Walls of Steel Sheet-pile Cofferdam ^23 Box Caisson for Pivot Pier of Highway Bridge 241 Open Caisson for Pivot Pier of Railroad Bridge 256 Reinforced-concrete Cylinder Caisson and Forms 260 Open Caisson of Timber with Two Dredging Wells 265 Open Caisson of Timber with Six Dredging Wells 267 Open Caisson of Concrete with Four Dredging Wells 273 Open Caisson of Concrete with Three Dredging Wells ^76 1 Half-tone illustration facing the page indicated. XVI ILLUSTRATIONS Forms for, and Cracks in, Open Caissons of Concrete PAGE '277 Pneumatic Caisson for Pier of Bellefontaine Bridge 285 Pneumatic Caisson for Pier of New Quebec Bridge 286 Pneumatic Caisson for Pier of Municipal Bridge 290 Pneumatic Caisson for Cylinder Pier 305 Material Lock for Pneumatic Caisson, Memphis Bridge ...... 310 Caissons on Launching Ways and Supported by Barges ^id Launching a Caisson from a Pontoon X 3 1 7 Pneumatic Foundation with Wells below Caisson 325 Sinking Caissons for the Municipal Building ^46 Sinking Open Wells for Column Piers of Kinney Building ^70 Open Well with Sectional Lining for Bridge Pier I 3?i Pier of Gray's Ferry Bridge, Philadelphia, Pa ^oo Pier of Cantilever Bridge at Thebes, Illinois 1 4oi Pier of McKinley Bridge at St. Louis, Missouri *402 Pier of Victoria Bridge near Montreal, Ontario . ^03 Pier of O.-W., R. & N. Co. at Portland, Oregon 408 Cylinder Piers of C. & N. W. Ry. Bridge at Clinton, Iowa .... J 4i6 Cylinder Piers of Avon River Bridge, Windsor, N. S 422 Railroad Bridge with U-abutments at Melrose, Mass ^36 U-abutment with Unequal Bearing on Foundation X 437 Diagram of Forces Acting on an Abutment 438 Abutments of Bridge over Colvin St., Buffalo, N. Y : 440 Abutments of Railroad Bridge near Mandan, N. D J 44i Reinforced-concrete Abutment, Wabash R. R., Monticello, 111. . . . ^40, ^41 Typical Plain Concrete U-abutment, C. M. & St. P. Ry 442 Bridge Abutment with Reinforced-concrete Deck 444 T-abutments of Single-track Railroad Bridge ! 446 Concrete Arch Abutments of C. M. & St. P. Ry. Bridge : 45o Reinforced-concrete Arch Abutment of Lind Viaduct *45 1 Column Footings of Plate Girders and I-beam Grillages 473 Reinforced-concrete Spread Foundation with Arch Inverts 487 Arrangement of Underpinning, 92 Maiden Lane, New York .... 499 Underpinning with Figure-four Needle Method 502 Use of Long Shores for Cross Building, New York *502 Details of Cylinder for Underpinning Stokes Building 510 1 Half-tone illustration facing the page indicated. FOUNDATIONS OF BRIDGES AND BUILDINGS CHAPTER I TIMBER PILES AND DRIVERS ART. i. FOUNDATIONS A structure usually consists of two parts one of which is sup- ported by the other; the upper part being known as the super- structure and the lower part as the substructure. In a bridge the superstructure is composed of the beams, girders, or trusses, together with the floor system and bracing which they carry; while the substructure consists of the piers and abutments, including their supporting bases. . The substructure frequently consists of two parts which differ more or less in form and character, the lower part being called the foundation which supports the rest of the entire structure. Sometimes the term foundation is used without regard to any substructure; as, for example, when it is applied to the independ- ent structure which supports a machine. The foundation of a structure may then be defined as that part of it which is usually placed below the surface of the ground and which distributes the load upon the earth beneath. Foundations are divided into various classes. The simplest form is obtained by widening merely the base of a wall or pier, so as to distribute the load over a sufficient area on the foundation bed of earth. Another form is known as the spread footing, in which the bearing area is enlarged, either by reinforcing the concrete base with steel bars or by inserting one or more tiers of steel beams. I 2 TIMBER PILES AND DRIVERS CHAP. I Pile foundations consist of a base of concrete or of timber grillage, supported by piles which distribute the load to the earth through a considerable depth, either by friction alone or by friction combined with bearing on the ends of the piles. When the bottom of the foundation has to be located on a bed of hard material at a considerable depth below the surface of the ground, the classes of foundations are distinguished by the respective methods required to sink them into position. Foundations built in open wells are used when the excavation can be made either in the dry or with no more interference by water than may be controlled by a reasonable amount of pumping. When open caissons are employed, the excavation is made through the water under ordinary atmospheric conditions, and after the bottom is sealed by concrete the rest of the foundation is built in the open air. Pneumatic foundations are those in which the excavation is made by working in compressed air in the chamber of a caisson, on the roof of which the concrete or masonry is built up in the open air during the operation of sinking. Many kinds of foundations also require the use of a temporary structure known as a cofferdam in order to exclude the water from the site of the foundation during its construction. The character of the earth at the site, extending down to the bed on which it is to be founded, and the influence of water, if any, determine the kind of foundation to be employed in any given case; with due regard, however, to economic limitations. These general classes of foundations and their subdivisions will be described and illustrated in the subsequent chapters of this volume, together with the general methods of placing them in position. Occasional notes on some of the special equipment required will also be given. ART. 2. CLASSIFICATION or PILES A pile is an element of construction placed in the ground, either vertically or nearly so, to increase its power to sustain the weight of a structure, or to resist a lateral force. ART. 2 CLASSIFICATION OF PILES 3 Piles are designated by the material of which they are com- posed; as, for example, timber piles; by their form of cross-sec- tion, as round or octagonal piles; by their inclination, as batter piles; by their use, as guide piles, sheet piles or fender piles; or by some attachment to their feet in order to increase their bearing power, as screw piles or disk piles. A bearing pile is one which carries a superimposed load. Its form of cross-section depends upon the material of which it is composed, and may be round or circular, square, hexagonal or annular. Its longitudinal section is frequently tapering, but sometimes its cross-section remains uniform throughout the length of the pile. The head of a pile is its upper end; the foot of a pile is its lower end; the butt of a pile is its larger end; the tip of a pile is its smaller end. These definitions show that the terms head and foot relate to the pile in its final position only, while the terms butt and tip apply to a tapered pile either before or after it is placed in position. The term ' top' is often applied to one end of a pile but this is ambiguous, since the upper end of the pile in the tree may be either the upper or the lower end after the pile is driven; its use should therefore be discouraged. The same objection holds with respect to the term ' point,' which is often used to desig- nate the small end of the pile, which may be either point- ed or left blunt by cutting off the end perpendicular to the axis of the pile. A batter pile is one driven at an inclination to resist forces which are not vertical. They are sometimes called spur piles. When a pile structure is built to resist lateral pressure, expe- rience has proven the importance of relying chiefly upon batter piles, rather than upon the cross-bracing of vertical piles, to insure lateral stability. When piles are employed to resist the lateral pressure of earth and to form a wall which is intended to be water-tight, they are called sheet piles. Their form usually differs from that of other piles, there being a considerable va- riety in their cross-sections both for timber as well as steel sheet piles. The subject of sheet-piling is discussed in Chap. V and 4 TIMBER PILES AND DRIVERS CHAP. I various applications are given in subsequent chapters. Short piles are sometimes driven in order to compress and consolidate the ground over a considerable area to increase its bearing power, but usually this result is more economically attained by means of sand piles, perhaps combined with sand or cinder filling on top. Bearing piles are used in foundation construction under two typical conditions: first, when the piles are driven through soft or fluid material into or to a stratum of firm or practically unyielding material; second, when no hard bottom can be reached by any reasonable length of pile and the friction of the pile in the ground is sufficient to support the load with safety. In the first case, the pile receives little if any lateral support and therefore acts as a column; while in the second case, the true pile action occurs and the load is either limited by the adhe- sion of the ground to the surface of the pile or the compressive resistance of the material in the upper part of the pile. Bearing piles located in streams often have to resist lateral forces due to the impact of drift, ice, etc. As far as possible such forces should be provided for by sway or lateral bracing. The most favorable condition for the use of bearing piles occurs when a firm stratum can be reached by piles of ordinary dimensions, and therefore easily obtainable in the markets, and the overlying material is compressible, so as to be readily pene- trated by piles, but sufficiently compact to prevent the piles from bending and lateral displacement. Guide piles are used to support the horizontal timbers or wales which in turn guide and support the vertical sheet-piling. Their principle application occurs in cofferdam construction (see Art. 67), but they are also used in ferry slips, and to aid in locating and sinking open and pneumatic caissons in streams or lakes. Fender piles, as their name implies, are driven at wharfs or in front of large masonry structures or other important works, to protect them from sudden blows by vessels. In addition to the uses of piles mentioned above, they are employed in dikes, jetties, and other structures. AST. 2 CLASSIFICATION OF PILES 5 Timber piles are very extensively employed in railroad con- struction and maintenance; for trestle bridges, either as tem- porary structures until the filling in of embankments or more permanent bridges of steel or concrete can be built to replace them, or until they are reconstructed of the same material. Trestle bridges with pile foundations are generally built in emergencies resulting from washouts, fire, or accidents of any kind. This is due to the rapidity with which the pile foundation can be put in place and the rest of the structure built; piles and large dimension timbers for framing being regularly carried in stock. Guide piles, fender piles, and in fact all piles used in temporary structures are likewise composed of wood. It will hence be noted that piles are very extensively used in modern engineering construction. While it is certain that timber piles were known as long ago as the early lake dwellers of Europe, they have been used continuously since that time, for foundation purposes. On the contrary, concrete piles were introduced in the opening years of the twentieth century. Metal piles were first used in 1838. The materials employed for piles include wood, concrete (either plain or reinforced), cast iron, wrought iron, steel and sand. Sometimes two materials are used in combination; as. for example, in a wooden pile surrounded by a protection of reinforced concrete, or in a hollow metal pile filled with concrete, either with or without reinforcement. Piles composed of sand are made in place in the earth in a vertical cavity formed for the purpose and hence serve chiefly to compact the earth and thereby increase its bearing power. In practice, a pile is usually placed in position in the ground by driving it with a steam-hammer or a drop-hammer, either with or without the aid of one or more water -jets. In rare instances, a pile may be sunk in place by static pressure, either by means of block and tackle or a weight of some kind. Sand piles or certain types of concrete piles are, however, cast directly in place. The principal use of piles occurs in the foundations of bridges, buildings and other structures in which they act simply as bearing piles. ^ 6 TIMBER PILES AND DRIVERS CHAP. I ART. 3. TIMBER PILES In the specifications for timber piles adopted in 1909 by the American Railway Engineering Association, the following kinds of wood are included for piles intended for standard construction purposes and designated as 'railroad heart grade': white, burr, and post oak; longleaf pine; Douglas fir; tamarack; eastern white and red cedar; chestnut; western cedar; redwood and cypress. For temporary construction, the following kinds of wood are included for piles designated as 'railroad falsework grade': red and all other oaks, not included in railroad heart grade; sycamore; sweet, black and tupelo gum; maple; elm; hickory; Norway pine or any sound timber that will stand driving. The principal difference between these two grades relates to durability, although the former includes several of the most valuable species of wood used in modern engineering construc- tion, as longleaf yellow pine, Douglas fir and white oak. Cedar piles are noted for their long life or durability. Spruce is not specifically mentioned in these specifications, although spruce piles are extensively used, especially in New England, both for railroad structures and other buildings. Spruce from certain localities has unusual toughness, giving the piles increased resist- ance to the tendency to split and broom when driven. Among other species which have been used to a very limited extent for piles may be mentioned beech, ash and basswood. In Florida, palmetto piles are used, as this wood is comparatively free from attacks of marine borers, known as the teredo. White pine piles were used in the northern central states before the close of the nineteenth century, but since then this species has become too valuable on account of its demand for other uses in building construction. Yellow pine, Douglas fir, spruce, cedar and other conifers have increased value for piles because they are so straight and free from large branches, and can be obtained in greater lengths. The longest piles used in single sticks are Douglas fir. Oak piles are hard and tough, but are not so straight and smooth and have the added disadvantages on ART. 3 TIMBER PILES 7 account of weight, of increased cost of transportation, and of liability to sink in water unless lighter logs are used in rafts to buoy them up. The specifications of the American Railway Engineering Association also include the following requirements, for the railroad heart grade: Piles shall be cut from sound trees; shall be close grained and solid, free from defects, such as injurious ring shakes, large and unsound or loose knots, decay or other defects, which may materially impair' their strength or durabil- ity. Piles must be cut above the ground swell and have a uni- form taper from butt to tip. Short bends will not be allowed. A line drawn from the center of the butt to the center of the tip shall lie within the body of the pile. Unless otherwise allowed, piles must be cut when the sap is down. Piles must be peeled soon after cutting. All knots shall be trimmed close to the body of the pile. Square piles shall show at least 80 percent heart on each side at any cross-section of the stick, and all round piles shall show at least loj inches diameter of heart at the butt. Piles of the railroad falsework grade, however, need not be peeled, and no limits are specified as to the diameter or propor- tion of heart. These specifications as revised, from time to time, are published in the Manual of the American Railway Engineering Association. The provision regarding the lateral curvature of a pile is modi- fied by some engineers so that the center of any cross-section shall not depart more than one-eighth of its diameter from the straight line joining the centers of the butt and tip. In another specification, this distance is made i percent of the length of the pile. When a pile has bends in two directions, it is regarded as a sufficient cause for rejection on first-class work. It has been found by experience that spruce piles selected for their straight- ness and smoothness could be driven satisfactorily where it was impossible to drive oak piles, which were irregular in shape and covered with knots. Timber piles are driven with the butt down under some conditions, this topic being discussed in Art. 14. The time of year in which timber is cut for piles does not 8 TIMBER PILES AND DRIVERS CHAP. I receive the degree of attention which it deserves. It affects both the strength of the timber and its durability. Tests made in Germany on four spruce trees, growing close together in the same soil, showed that if the strength, when cut in December, is taken as 100 percent, those cut in January, February, and March had strengths of 88, 80, and 62 percent respectively. "Beech timber cut in December and January gave an average mechan- ical life of six years, whereas the same kind of timber cut in the same location in February and March gave a service of only two years." Experience in this country has also shown conclusively, that the use of piles of the best species of wood may lead to serious loss when it is cut in the summer and left only a short time before the bark is peeled. Decay due to fungi and the ravages of worms, which became manifest when the sapwood began to decay, required in one case involving a very large number of piles, the replacement of the whole lot within four years, some of them being eaten through entirely within two years (see Rail- road Gazette, vol. 31, page 865, Dec. 15, 1899). Foundation piles when cut off below the ground-water level, apparently have an indefinite life. For example, in recon- structing a bridge, timber piles were removed which indicated no material decay after being in service 600 years. A still more conspicuous example was brought to the attention of engineers and architects, when the Campanile of St. Mark's in Venice fell in 1902. The piles in the foundation which had been in service for 1002 years were found to be in such a good state of preservation that they were allowed to remain to support the reconstructed tower. A lagged pile has pieces of timber bolted around the sides of the pile, in order to increase its bearing power. It increases the area of cross-section and also the surface of the sides of the pile which is of more importance, since such piles are used only in very soft material. The New York City Dock Department made a test in 1902 of the relative bearing power of lagged and unlagged piles driven in North River mud, the results of which are recorded in Trans. Am. Soc. C. E. (1905), vol. 54 F, pages 8 ART. 4 FORM AND DIMENSIONS 9 and 27. The discussion by the author of the paper implies that the ultimate bearing power was increased about 50 percent. The total penetration of the piles ranged from 47.1 to 52.6 feet, while the lagging was only 30 feet in length. Although it is not stated what position vertically the lagging occupied, it appears that the surface in contact with the mud was increased about 70 percent. An expert on pile driving has expressed the opinion that the lagging of piles is unnecessary and relatively costly. In general practice, lagged piles are rarely ever used, and it may therefore be concluded that they are not desirable. ART. 4. FORM AND DIMENSIONS Since a timber pile generally consists of the lower portion of the trunk of a tree, after its branches and bark are removed, .and the knots trimmed close to the body, its cross-section is round or approximately circular. Square piles are rarely used as bearing piles, and only to a limited extent for special purposes, one of which is to form large timber sheet piles by the addition of scantlings on two sides to form tongue-and-groove joints. Since the introduction of steel sheet-piling, there is but little need for framing sheet piles out of 1 2 by 1 2-inch, or even larger, timbers (see Art. 59). The specifications referred to at the beginning of the preced- ing article contain the following paragraph, relating to dimen- sions: For round piles, the minimum diameter at the tip shall be 9 inches, for lengths not exceeding 30 feet; 8 inches for lengths over 30 feet but not exceeding 50 feet; and 7 inches for lengths over 50 feet. The minimum diameter at one-quarter of the length from the butt shall be 12 inches, and the maximum diam- eter at the butt 20 inches. The same requirements apply to the square pile, by substituting thickness for diameter. The relation between the diameters of butt and tip depends upon the length of a pile and naturally varies for different spe- cies of wood. The diameters of piles for ordinary buildings are usually somewhat smaller than for bridges and very heavy buildings, but the diameter of tip should not be less than 6 inches 10 TIMBER PILES AND DRIVERS CHAP. I in any case. When a pile acts principally as a column, it should have a larger tip than if its resistance depends mainly on friction. The clearance between the leads of pile drivers, and between which piles must be placed to drive them, is ordinarily 2 2 inches and it will be noted that the maximum limit placed upon the diameter of butt, in the specifications quoted above, is 2 inches less. It may be stated that the diameter of butt usually ranges from ii to 1 6 inches in foundations which are neither intended for very light not exceptionally heavy structures. The length of a pile necessarily depends upon the character of the earth into which it is to be driven. Piles as short as 10 feet have been used but it is questionable whether this is not too low a minimum. In ordinary construction, the length of piles varies roughly from 20 to 40 feet. As an illustration of the use of long piles, Douglas fir piles ranging in length from 60 to 120 feet were driven in 1907 for the trestle approaches of the Dumbarton bridge at San Francisco Bay, the penetrations in some cases being as great as 60 feet. The tip was not less than 9 inches, while the butt was limited to 22 inches. In the jetty construction at the mouth of the Columbia River piles 130 feet long were driven 50 feet into the bed of the river; they were 30 inches in diameter at the butt. Even greater lengths up to 175 feet were formerly used on the Pacific Coast, but since the best timber next to the coast or navigable streams has been cut, the available lengths are limited by the conditions of railroad trans- portation. Where the character of the earth or of the several strata to be penetrated is fairly uniform over the area of a given site, it is desirable to use piles as nearly alike in diameter and length as can be secured economically in the available markets. Where the driving is easy a small pile is frequently as advantageous as a large one; but where the driving is hard a large pile is required so as to have the necessary strength and stiffness to stand the driving. The principles of good design and economic construction require the proper lengths of piles to be determined in advance. In the absence of definite knowledge by previous pile-driving experience at the same location or contiguous to it, a careful ART. 5 THE PHENOMENA OF PILE DRIVING 1 1 exploration of the ground should be made by means of auger or wash-borings or by means of test piles. Tests should be made at certain intervals along the line of a trestle bridge, at the loca- tions of piers and abutments, or at several places distributed over the area of a building foundation. Driving test piles is advantageous, since it furnishes information at the same time on the number of blows required to secure the necessary total pene- tration and hence, the approximate time for the subsequent work. This item alone is frequently worth far more than the cost of the investigation. On the other hand, emergencies may arise in which the value of such preliminary tests in saving material and labor in construction may be offset by a greater loss due to delay in resuming traffic operations. Methods of making explorations by different appliances are described in Chap. XVII. If some other method is used to determine the supporting power of the earth, and it is proposed to compute the size of pile, it is well to consider that " with the usual methods in vogue, in which large initial stresses are to be expected, it is not safe to use piles of diameters which would be just large enough to sup- port the developed supporting power of the earth, nor would it be practicable to secure or drive them." A convenient table prepared by E. O. FAULKNER, for cal- culating the volume of piling in cubic feet, and which is based on the prismoidal formula, may be found in Eng. News, vol. 54, page 170, or in RICKEY'S Building Foreman's Pocket-book. ART. 5. THE PHENOMENA OF PILE DRIVING The term pile driving is applied to the operation of taking a pile and forcing it into a definite position in the ground without previous excavation. A number of different methods are employed for this purpose which require different kinds of equip- ment. Historically the oldest method of driving a pile is by means of a hammer. While very small bearing piles, or posts, were doubtless driven at first by hand with a maul or beetle, those of larger size usually designated as piles required the use of 12 TIMBER PILES AND DRIVERS CHAP. I a machine by which a hammer was raised with the aid of a pulley and rope and allowed to drop on the head of the pile. A weight used in this manner was hence called a drop-hammer. At first men, then horses, and afterward the steam engine were used to raise the hammer. After the invention of the steam engine, steam-hammers were designed in which the driving weight is lifted a short distance by steam pressure and allowed to fall by gravity, the rapidity of action being greatly increased. Subsequently steam-hammers were invented in which steam pressure reinforces the action of gravity on the down stroke. At one time pressure due to the explosion of gunpowder was used to drive piles but that method is now regarded as antiquated. To a very limited extent pile driving has been accomplished by placing a static weight upon a pile and rocking it to and fro in soft ground, to which condi- tion this method is practically limited. Another method of more recent discovery which has greatly advanced the art of pile driving consists in the use of the water- jet to aid in displacing the earth at the foot of the pile and to lessen the friction of the pile as it descends through the surround- ing material. This method is generally employed in conjunc- tion with the use of a hammer, although occasionally the hammer may serve merely as a Static weight during a portion of the time required to sink the pile. The phenomena of pile driving may perhaps be most readily understood by the student by considering the case in which a timber pile is driven vertically into the ground by means of a drop-hammer. After the piles are delivered on the site within reach of one of the lines of the pile-driver which is used to handle the piles, the line is made fast to a pile near its head and first dragged, if necessary, close to the front of the pile- driver, and then hoisted until it is suspended in the air. It is next placed and held laterally between the pair of tall parallel members of the pile-driver known as the leads and between which the hammer is guided in its movements. After lowering the pile until its foot rests on the ground, the line is released. The hammer, being held at the top of the leads by the other ART. 5 THE PHENOMENA OF PILE DRIVING 13 line, is now released and in falling strikes the head of the pile. It is then raised again and released for the second blow, and so on for successive blows until the required penetration of the pile is obtained. During its fall the velocity of the hammer is accelerated until the instant when the hammer and the pile, in connection with a certain mass of earth beneath and around it, move together. When the hammer strikes the head of the pile the pressure between the pile and hammer increases from zero up to a certain value when the pile as a whole begins to move. After all the compression in both hammer and pile has taken place they will move together. Their velocity is then gradually reduced to zero by the varying resistance of the earth during the time of pene- tration for the pile. Some of the work done by the falling ham- mer is consumed in overcoming friction, in crushing and heating the head of the pile, and in compressing the pile and hammer, while the remainder causes the penetration of the pile. In careful experimental investigations conducted by ERNEST P. GOODRICH, with an apparatus designed to show the exact vertical motion of the pile, the time occupied by this motion, the velocity of the hammer as it strikes the pile, the velocity of the pile at each instant of its movement, and the amount of compression suffered by the head of the pile from the blow of the hammer, it was found that on the average the penetration, meas- ured from the deepest point, varies practically as the square of the time measured from the final instant. The autographic records showed also that, in the majority of cases, the final mag- nitude of the force acting on the pile is the same as its initial magnitude when the pile and hammer move together; and prove conclusively that the hammer remains in contact with the pile until the motion of the latter has ceased. Small- sized experiments on pressing sticks with blunt\ips into sand and other kinds of earth, as well as observations of regular piles, show that a conical mass is formed at the tip and pushed along while curved flow lines of earth appear as the material is pushed aside and compressed. The extent of the movement depends upon the compressibility of the earth. 14 TIMBER PILES AND DRIVERS CHAP. I Often some of the material near the sides of the pile will move upward slightly. It is thus seen that the supporting power of the ground penetrated is one of the elements which determines the load which a pile can bear. In most cases this supporting power of the ground increases more or less with the depth, and hence the load depends upon the total depth of penetration. Sometimes the larger part of the superimposed load is trans- mitted by the pile through its foot to a hard substratum, and therefore acts like a column. When the pile is supported entirely by the frictional resistance between its sides and the earth, the load is transmitted 'to a deep ground level in a conoid of pressure through the earth above it. Usually these two methods of transferring a load from a pile to the earth act together in varying proportions. ART. 6. PILE-DRIVERS A pile-driver is a machine for driving piles. Its characteris- tic feature consists of the leads, which are upright parallel mem- bers to support the sheaves used to hoist the hammer and piles, and to guide the hammer in its movement. The leads are held in position by being framed with back stays and other bracing into the form of a tower supported on horizontal sills. In a standard form of contractors' pile-driver the bed frame con- taining the sills is extended back far enough to support the hoist- ing engine and boiler, and the whole outfit is mounted on rollers as illustrated in Fig. 6a. Pile-driver towers are constructed either of timber or steel, and are built in a variety of forms for different purposes, or conditions. Rungs are attached to the rear inclined posts, or back stays of the tower, to form a ladder. The bracing consists of horizontal and diagonal members. In the figure two long diagonal braces are shown in addition to the diagonals in each panel. Sometimes the long diagonals are omitted and only short diagonals are placed in every panel, while in the smaller towers all diagonals may be omitted. Occasionally the lower diagonals are extended over two panels, or long diagonals may ART. 6 PILE-DRIVERS Head Block ollers - FIG. 6a. A Standard Type of Contractor's Pile-Driver 1 6 TIMBER PILES AND DRIVERS CHAP. I be employed without any short ones. The tower is braced laterally either by guy ropes attached to the rings near its top or by long inclined posts, or wind braces, in which case the bed frame is generally widened to support these braces. Leads as long as 100 feet and i inch under the head-block have been built. See also Fig. 620,. By the addition of roller bearings a driver may be moved for- ward, backward, and sidewise. When it is mounted on a turntable it is called a swiveling pile-driver, and combines swing- ing to the right or left with the motions noted in the previous sentence, the movement sidewise being made however by chang- ing the rollers. The inner faces of wooden leads are protected by channel-iron liners, in order to reduce friction and wear. A driver intended to be used in excavations to drive piles below the level of its supporting track, sometimes has rigid detachable leads which extend to the required depth. A better arrangement consists in the use of telescopic leads which slide inside of the stationary leads, and are handled by an extra line to a third hoisting drum. By this means piles may be driven without the aid of a follower in deep trenches or through con- tracted openings, or in the bottoms of cofferdams containing a large amount of internal bracing. Floating pile-drivers mounted on scows have had, in exceptional cases, loo-foot telescopic extension leads working within zoo-foot fixed leads. With such equipment it has been possible to drive piles 35 to 40 feet below the water surface with the aid of a follower that was thus guided at its lower end as well as at its upper one. Hang- ing leads, which can also be used for the same purpose as exten- sion leads, are often used in connection with ordinary derricks or cranes. ART. 7. TRACK PILE-DRIVERS Pile-drivers of recent design for railroad service have been developed to a high degree of efficiency. In the report of the Committee on Wooden Bridges and Trestles of the American Railway Engineering Association in 1911 (see Proceedings, vol. 12, part i, page 290), are contained the following: ART. 7 TRACK PILE-DRIVERS 17 DESIRABLE FEATURES OF A TRACK PILE-DRIVER (i) Steam-hammer. To secure greater rapidity in driving and with less injury to the pile than that secured by the drop- hammer. (2) Water- jet apparatus. (3) Turntable allowing practically a complete rotation. In most cases the work can be done from either side, and in many of the remaining cases it is possible to foresee the nature of the work and to head the driver in the proper direction at the nearest Y or turntable. Sometimes, however, turning facilities may be far distant, or a pile-driver may be caught between two washouts when it becomes essential to be able to turn the machine to perform the work at both places. (4) Swinging leads. The leads require an efficient rigging to permit driving piles with a batter in either direction. When driving across the track on such work as driving bents for an adjacent track, it is convenient to be able to drive with the leads not fully raised, so as to secure the proper batter. (5) Self-propelling mechanism. The greater the tract- ive force and speed the more independent is the pile-driver from locomotive service. They should preferably be sufficient to dis- pense with a locomotive except for long hauls. (6) Restricted projection on the side opposite the leads when swung across the track and without unnecessary weight. (7) High- speed power service for raising the leads. On a main line it is frequently possible to drive only one or two piles before running to a siding. In some cases the character of this apparatus to raise the leads determines whether a single pile can be driven between trains or will delay a train. (8) Adequate overhang. To enable machines to drive piles as far ahead of the leading wheels and as far sidewise as possible. On work for double- tracking the sidewise reach should be sufficient to drive a bent on the new track from a position on the old track. (9) Facili- ties for driving below the track. (10) Ability to shift the ham- mer when the leads are down, (n) No obstructions in the view of the engineman and niggerhead operator. (12) Length of leads. To accommodate the longest piles practicable. (13) Strength and/igidity of supports for leads and hammer. They i8 TIMBER PILES AND DRIVERS CHAP. I FIG. "jd. Locomotive Crane Used as a Traveler and Pile- Driver in Building a Pile Trestle. The 25-foot leads swing freely on the bolt by which they are suspended from the boom; when driving they are braced by struts to some of the finished work. Cross pieces on the back of the leads and an iron bar placed across the front on two hooks at the bottom of the leads hold the pile in position. The drop hammer is operated by the regular hoisting rope, and the same rope is used to hoist the pile into the leads, the hammer meantime being held at the top of the guides by a bolt. ART. 7 TRACK PILE -DRIVERS 1 9 should be adequate to handle the hammer and the heaviest wooden pile without damage. It is now becoming important to be able to handle concrete piles. (14) Stability. The driver while standing on its own wheels, without any jacks or special supports, should be able to pick up and drive a pile in any position within its reach. (15) Flush ends. For convenience of transportation in freight trains, no part project- ing beyond the drawheads. Otherwise an idler is required which then may be used as a tool car. (16) No lengths of steam hose that might be replaced by pipe. No single make or design of driver has incorporated every one of these desirable features. Those which come nearest to doing so are not of the combination type but are designed especially for exclusive use as pile-drivers. In different makes the reach ranges from 15 to 21 feet ahead of the wheel base, the reach side- ways from 20 to 33 feet from center of track, while the longer leads are from 40 to 47 feet. Some drivers are equipped with both steam- and drop-hammers and the best ones have a water- jet outfit. The turntable is usually on top of the car body but in one case a hydraulic turntable is provided which takes bearing on the track, raises and turns the entire car (Fig. 70). Those which are self-propelling have a speed from 8 to 25 miles per hour. In one typical form the aim has been to combine the functions of a pile-driver with those of a steam-derrick car in the erection of small bridges, the maintenance of bridges and culverts, pulling down temporary structures and old bridges, or clearing up a wreck. A boom is therefore provided of sufficient capacity for such work. In some instances it is placed in front of the leads when in use, while in others the boom always remains in place, being connected by blocks and tackle to a transverse frame and mast, the pile driving being done by leads hanging from the boom. In transit the boom is down and extends over the length of a flat idler car coupled ahead. In another typical form the leads and their supporting truss and braces are replaced by other appliances to convert it into a locomotive crane or excavator. 20 TIMBER PILES AND DRIVERS CHAP. I ART. 8. THE DROP PILE-HAMMER A drop-hammer is one which is raised by means of a rope and then allowed to drop. It consists of a solid casting with jaws on each side which fit into the guides of the pile-driver leads, with a pin near the top for the attachment of the rope or of the nip- pers, and with a broad base on which it strikes the pile. Fig. Sa shows a drop-hammer of modern design with all cor- ners rounded. It is made as long as practicable to increase the bearing in the leads, while the jaws have as little play as possible between the leads and hammer to reduce the jar on the driver when the pile is struck. The form is arranged to have its center of gravity as low as possible. When the hammer is to hit the head of the pile directly, its base is made slightly con- cave, but when a pile cap is employed, as is done in the best practice, the base is made flat. When the hammer is to have a free fall, as may be required on test piles or for very light hammers raised by horse power, the pin is triangular in section with its lower face horizontal, to engage the 'nippers' auto- matically. The upper ends of the nippers are curved so that when the trip is reached, they are drawn together and thus release the hammer for its drop on the pile. When the ham- mer is to be raised by a hoisting drum with a friction clutch, a round pin is used to which the line is attached directly. The latter method affords the following advantages for regular work: More rapid operation; facility in regulating the height of drop; and avoiding the danger of losing the hammer if it should pass out of the leads. The weight of drop-hammers most generally used in American practice to drive timber piles ranges from about 2000 to 3800 pounds. For posts and very small piles the weight runs as low FIG. 8a. Drep- Hammer. ART. 9 THE STEAM PILE-HAMMER 21 as 500 pounds, while for heavy construction requiring very long piles it runs as high as 5200 pounds. For very light service a heavy block of oak wood is sometimes employed. The weight of drop-hammers to be adopted depends upon the weight of the piles and the character of the ground to be penetrated. The relation of the weight and fall of the hammer to the bearing power of piles and to success in securing adequate total penetra- tion without injury to timber piles is discussed in Art. 27. The weight of hammers to drive concrete piles is referred to in Art. 48. ART. 9. THE STEAM PILE-HAMMER A steam-hammer is one which is automatically raised and dropped a comparatively short distance by the action of a steam cylinder and piston supported in a frame which follows the pile. It was invented in England by JAMES NASMYTH in 1845, an< 3 was first used on October 6, 1846, to drive piles for a bridge foundation. One type of steam-hammers has been built in this country since 1875 and after various improvements has continued in use, being known at present as the Warrington hammer. Steam-hammers are of two general classes single acting and double acting. In the former and older class the steam pressure is applied to raise the striking part of the hammer, while it falls by gravity. The force of the blow depends upon the length of stroke and the movable weight, the number of blows depending upon the steam pressure. In the latter class the steam pressure raises the hammer and also reinforces the action of gravity dur- ing its descent, the force of the blow, as well as the rapidity of action, being functions of the pressure. The latter apparatus is more compact, lighter and operated with greater rapidity. The Warrington and Cram hammers are single acting, while the Arnott, Industrial Works, New Monarch, Goubert, and McKier- nan-Terry hammers are double acting. Another classification may be based upon whether the striking part is attached to a movable piston or to a movable cylinder. The Warrington, 22 TIMBER PILES AND DRIVERS CHAP. I Arnott, New Monarch, and McKiernan-Terry have the former arrangement, while the Cram, Industrial Works, and Goubert have the latter. The latter arrangement is also incorporated, however, in the McKiernan-Terry hammer since it contains an auxiliary fixed piston which operates in a cylinder bored out of the upper end of the main piston. This novel feature forms a device to accelerate and intensify the down-stroke. FIG. ga. Warrington. FIG. 96. Cram. Steam Pile- Hammers. FIG. qc. Goubert. The following table gives weights, dimensions and other data for the largest regular size of hammer for each of six differ- ent makes. It is noted that in the double-acting hammers the weight of striking parts is only about one-half to one-fourth as great as in the single-acting ones. The table also indicates the steadily increasing number of blows, as well as the reduced height, thus requiring less space in the leads. The piston speed is nearly uniform. The Arnott and the McKiernan-Terry ham- ART. 9 THE STEAM PILE-HAMMER mers may also be operated by compressed air. steam-hammer is illustrated in Fig. 6a. The Arnott LARGEST SIZES OF VARIOUS STEAM PILE-HAMMERS Trade designation Warrington B S Arnott Industrial Works New Monarch Goubert McKiernan- Terry Size number. . I B o I . -2 Total weight in pounds 10 150 8 400 12 IOO 6 400 7 ooo < OOO 8 IOO Weight of striking part, pounds. Total height in inches 5000 i?o 5 5oo 14.4 2 550 118 i 900 lie i SOQ QO I 500 76 I 250 77 Diameter of cylinder, inches. . . . Stroke in inches 13-5 42 i5 4O 10.5 24 8 24 9 14 'g 14 15 12 Total downward force, pounds. . Number of blows per minute Boiler pressure, Ibs per sq in 5 ooo 60 SSoo 60 7 800 IOO 80 6 175 IOO IOO 6 200 125 80 6080 ISO 80 7 loo 200 80 Boiler required, HP 40 2030 CO (TO 2C 60 The total weights of the smallest sizes are respectively 1350 1000, 365, 750, 950, and 175 pounds. The number of blows per minute for the double-acting hammers for the same sizes are 300, 350, 200, and 500. Generally the lightest hammers are used for light sheet-piling only. Additional data may be found in the illustrated catalogues published by the manufacturers. During the operation of driving, the steam-hammer and its frame rest upon the pile, the head of which is trimmed to fit into the recessed or open base of the frame. The frame has channel or angle guides on the sides which engage the leads of the driver. The frame in turn guides the hammer in its movement, and in several makes entirely encases it. While the weight of the striking parts is only a fraction of the total weight, the extra dead weight of the frame helps to keep the pile in motion after it is started by the blow. Generally the blows follow each other so rapidly that the pile is in continuous motion. The limited vibration thus developed in the pile is also an aid in securing its penetration, particularly in ground containing a large percent- age of sand which otherwise offers considerable resistance. The vibration is limited by the weight which constantly rests upon TIMBER PILES AND DRIVERS CHAP. I the pile. The effect of the short quick blow in securing pene- tration is analogous to the method of driving an ordinary pin into a block of lead by many light taps with a very small ham- mer, which could not be done by fewer but heavier blows. FIG. gd. New Monarch. PIG. ge. McKiernan- Terry. FIG. gf. Industrial Works. Steam Pile-Hammers. ART. 10. ADVANTAGES OF STEAM-HAMMERS The following selected records of actual experience are pre- sented in order to indicate the relative values of steam- and drop-hammers when used under practically the same conditions. The interests of good practice would be materially aided if more tests of this kind were made under a wide range of conditions. In driving piles for cylinder piers 20 feet in diameter for a bridge on the Norfolk and Western Railroad, at Norfolk, Va., the piles in one cylinder were driven by a 3300-pound drop-hammer with a fall of 10 feet, while those in the twin cylinder of the same pier 33 feet away and in the nearest cylinder ART. 10 ADVANTAGES OF STEAM-HAMMERS 25 of the next pier, 44 feet distant, were driven by a steam-hammer with striking parts weighing 3000 pounds, a total weight of 6000 pounds, a normal stroke of 36 inches and an effective fall of 30 inches. The following record relates only to the averages for the first six piles driven in each cylinder respectively. In the first cylinder the average penetration under the last blows was | inch, and for each of the other cylinders the average penetra- tion under the last 100 blows was 7 inches or practically 14 blows per inch. The total penetrations averaged 28, 36, and 26 feet respectively for the three cylinders. The drop-hammer broomed the heads of the piles and no increase in penetration was secured by increasing the drop above 10 to 15 feet. With the steam-hammer no brooming occurred and the full force of the blow was effective at all stages of the driving. The piles were driven in about 38 feet of water, about 16 feet of the soft silt having been dredged out so that all the penetration secured was through firm blue mud and sand in layers of varying thickness. On the Chicago and Eastern Illinois Railroad the perform- ances of a steam-hammer and drop-hammer were compared by using them on the same pile, changing the hammer in the leads as quickly as possible. The former had a total weight of 5170 pounds, and striking parts of 2840 pounds, while the latter weighed 2900 pounds. The former had a drop of 28 inches, and the latter of 32 feet. With the steam-hammer 66 blows produced i foot of penetration in i minute, and another foot by 83 blows in if minutes; the next foot of penetration was obtained by the drop-hammer with 12 blows in 2 minutes, and the following 4 feet respectively by 12, 10, 10, and 12 blows in 2, 2, 3^, and i\ minutes; the steam-hammer being replaced caused the next foot of penetration with 203 blows in 3 minutes, and the following 9 feet by 341 blows in 5 minutes. In driving piles for a large wharf and warehouse at Pensa- cola, Fla., requiring 7000 piles, two piles 75 feet long were driven 3 feet apart, one by a drop-hammer and the other by a steam-hammer. The former was driven by 120 blows in 50 minutes, dropping the hammer from the top of the 7 5 -foot leads; 26 TIMBER PILES AND DRIVERS CHAP. I and the latter by 130 blows in 90 seconds. As should be ex- pected under such abnormally high falls the former pile was broomed for a depth of over 3 feet at the head, while the one driven with the steam-hammer was not broomed at all. The piles were creosoted and cost 40 cents per linear foot delivered. On the North River at New York City piles from 55 to 60 feet long were driven from 43 to 50 feet below low water through a lo-foot layer of cobble stones, and layers of very fine sand, coarse gravel, and sand gravel, as shown by test borings. To drive 12 piles in 10 hours by a crew of 10 men was regarded as a good day's work, an average of 175 blows with a 33oo-pound drop-hammer falling 10 feet being required, at a rate of 15 blows per minute. With a crew of 2 or 3 men less, 18 piles per day could be driven by a steam-hammer and braced, some of the piles requiring over 1200 blows at the rate of 60 per minute without showing any sign of brooming. The hammer had a total weight of 8400 pounds, and a striking weight of 4000 pounds. A contractor endeavored to drive some 45-foot piles through sand, gravel, and boulders, for bridge piers on the New York, Westchester and Boston Railroad at Pelham, N. Y., using a 3ooo-pound drop-hammer falling 20 to 40 feet, but did not succeed. A steam-hammer was then obtained with a 3000- pound striking weight, which secured the full penetration with- out brooming or splitting any piles. The following advantages are claimed for the use of the steam-hammer by those who have also had experience with the drop-hammer : (i) The pile is held in position and guided more firmly while driving, thus keeping the pile from dodging, or getting out of line, and avoiding the labor of toggling. (2) Serious damage to the pile such as brooming, splitting, etc., is avoided. Hence piles of softer wood may be employed. (3) Extra time and cost for the use of a ring on the pile head is saved. (4) The driving is equally effective for any position of the pile head in the leads. (5) A pile may be driven several feet (7 or 8 feet with some hammers) below the bottom of the fixed leads without the use of extension leads. A few feet may ART. ii RINGS, CAPS, AND FOLLOWERS 27 often be saved in cut-off by thus driving below the elevation of rail. (6) When driving into soft material or into sand, the rapidity of action keeps the pile in motion and prevents the earth from recompacting around the pile until the driving ceases, thus reducing the frictional resistance. (7) More piles can be driven in a given time and often with a smaller crew. (8) The steam-hammer has been used effectively in places and under con- ditions where it was found to be impossible to use a drop-ham- mer successfully. This relates to cases of limited head room as well as to difficult subsurface conditions. (9) Less injury is caused to adjacent foundations, and less breaking of glass and plastering in adjoining buildings. (10) The leads last about three or four times as Jong as when a drop-hammer is used, (n) On track pile-drivers less injurious strains are caused in the car and machinery, thus reducing the cost of mainte- nance. (12) Although the first cost of the steam-hammer is much greater the total cost of driving is reduced. The teaching of experience is indicated by the fact that in the city of Chicago, where perhaps more piles are driven for foundations than in any other place in the United States, steam-hammers, are used almost exclusively. Those who have had considerable practice in the use of both kinds of pile- hammers do not as a rule wish to go back to the drop-hammer. Exceptional cases have been reported in which a steam-hammer has been unable to force a pile through a hard crust. A drop- hammer may succeed in such a case because of its heavier blow, but it is more likely to break the pile. Perhaps a pointed shoe may be needed on the pile, or a charge of dynamite, or a dredge. Sometimes more caution is needed with a track driver when the track is out of level if the heavier steam-hammer is near the top of the leads. Art. ii. RINGS, CAPS, AND FOLLOWERS It is important to cut off square the butt of a pile, so that the impact of the hammer may be distributed uniformly over the surface. Since the butt tends to change its position slightly in the leads during driving, it has been found advantageous by 28 TIMBER PILES AND DRIVERS CHAP. I experience to make the lower surface of the drop-hammer slightly concave. This provision counteracts the tendency to- ward lateral movement of the pile to some degree. When the pressure on any fibers exceeds their ultimate resistance in com- pression they will yield by bending, buckling, or crushing, after their adhesion to adjacent fibers is destroyed. When the fibers are once broken down every blow of the hammer tends to injure the fibers further down. As wooden fibers are far more compressible when a force is applied on their sides instead of their ends, the bruised head of the pile thus becomes more elastic, and acts somewhat like a spring or cushion. When the height of fall for the hammer exceeds a certain value, a part of its energy is expended in destructive work like that just indicated, leaving less for useful work, reducing its ef- ficiency in forcing the pile to penetrate the ground. This breaking down of the fibers is called 'brooming.' The fall of the hammer may be so great that nearly all of the energy is used up in brooming the pile. The relation of the weight of the hammer and the height of its fall to the bearing power of a pile is discussed in Art. 27. It is often found that no increase in penetration is secured by increasing the fall or drop above 10 to 15 feet. It is possible to estimate approximately the loss of energy due to brooming by comparing the number of blows required per foot of pene- tration before and after cutting off the broomed top. From the record of a pile driven by a steam-hammer, under the direction of D. J. WHITTEMORE, it is observed that in driving the pile from the i2th to the 22d foot of penetration, 4682 blows were struck or an average of 468 blows per foot. Immediately after cutting off the broomed top at two different times, only 275 and 213 blows respectively were required to drive the pile the next foot. Their average of 244 blows indicates the number required under the condition of a sound head, and accordingly it appears that on the average only about 52 percent of the available energy was consumed in securing the penetration of the pile. The loss in this case is considered excessive. The progressive effect of brooming is shown in the number of blows ART. ii RINGS, CAPS, AND FOLLOWERS 2Q required for the zoth to the i4th foot of penetration respectively: 73> I0 9' J 53> 2 59> 68 4- The brooming and splitting of pile heads varies for different kinds of wood. The record of pile driving for the foundations of a building in Chicago, shows that for pine 12.5 percent of the heads were crushed and 5 percent broken; for gum, 7 per- cent crushed and 0.6 percent broken; for oak, 5 percent crushed and 0.8 percent broken; for hickory, 3 percent crushed and none broken; and for basswood, 8 percent crushed. In several of the oak piles the sapwood and heart separated, the heart core being driven through the shell. A cast-iron cap was used in driving, but in spite of this, an average of 8 percent of the heads were crushed or split; but when it is considered that the fall of the hammer for each pile was permitted to reach the magni- tude of 35 and 40 feet when the driving ceased, it is surprising that these percentages were not larger. The penetration at the last blow averaged 3 inches. The percentages of piles used on the work of the different species of wood named above and in the same order were 22, 32, 21, 15, and 7 respectively. The crushing of the fibers is frequently followed by the splitting of the pile head. This tendency is promoted by fail- ing to cut off enough of the butt as it comes from the forest to cover the entire section area of the pile, for if the hammer hits only one-half of the area it will force that part down into the head and split it. To prevent splitting and to reduce brooming, the head may be hooped by a pile ring. The sizes range from 2 by f to 4 by i inches. The diameters vary to suit different sizes of pile. They are .made of the best quality of wrought iron that can be obtained. Rings of the best bar iron usually last to drive 50 oak piles or 200 cedar piles; those of the best hammered iron for 75 oak piles or 300 cedar piles. Rings made out of old car axles have been used for 250 oak or 6000 cedar piles. In fitting the ring the pile is neatly chamfered down at least 5 inches from the end so that the ring will just catch on; a blow of the hammer puts it into place. To remove the ring a cant-hook or pevee is used, the pile line being fastened TIMBER PILES AND DRIVERS CHAP. I -Hammer _ on Block to its end to apply steam power. If the pile brooms too much in spite of the ring, the recognized remedy is to saw off the broomed part, so as to present a solid surface to the hammer and put the ring on again. A more effective and less expensive method of protecting the head of a timber pile from brooming and splitting is the use of a pile cap as shown in Fig. ..-Lead)-. na. It consists of a cast- ing with a tapered recess above and below. The chamfered head of the pile fits into the lower recess and a short cushion block of hard, tough wood is fitted into the upper one. The block is frequently provided with an iron hoop or ring around its top. The cap has jaws on the sides like the hammer which engage the leads, and hence the head of the pile is held in position and guided while driving. After the pile is driven the cap is hooked to the hammer by ropes and pins and raised with it. While the cap protects the pile head the short cushion block requires frequent renewal since it gets the direct impact of the hammer. Sometimes a rope mat is placed on top to protect it. White, live or swamp oak, rock maple, and blue gum have given good service for cushion blocks. When both drop- and steam-hammers are used on the same work it is often found that the drop-hammer causes brooming when the steam-hammer gives no indication of it. In hard driving, however, it becomes important to protect the pile head. Sometimes this is done by spiking a flat steel plate on the pile to receive the blow, or a dished or cupped striking plate may be substituted for the flat plate. A better arrangement is adopted for some motces of steam-hammers. The Warrington hammer FIG. iia. Casgrain's Pile Cap. ART. ii RINGS, CAPS, AND FOLLOWERS 31 substitutes for its ordinary base what is known as the McDer- mid patent base in which a recess is provided for a thick steel plate inserted through a slot in the side, covered by a door. The plate is held in place by the base and thus avoids the danger to the crew which occurs with the separate flat or dished plate. The Goubert and the McKiernan-Terry steam-hammers are provided with an anvil block in the base and which rests on the pile. When a pile has to be driven below the leads, or below the ground or water surface, a follower is generally employed. A follower is a member interposed between the hammer and a pile to transmit blows to the latter when below the foot of the leads. In its simplest form a follower may consist of a short pile or stick of white oak of the requisite length and diameter. To keep its lower end in position on the pile a follower band may be used which is flared both upward and downward, but it is better to use a follower cap. This is a cylindrical casting with a horizontal diaphragm at the middle, which is bolted to the lower end of the timber follower, and fits over the head of the pile. The upper end of the follower is held in position by the recessed base of the steam-hammer or by a pile cap if a drop-hammer is in use. A better kind of follower consists of an extra strong pipe cast into the base, so as to avoid the objections to the use of bolts. A stick of turned hard wood is driven in to the pipe. An iron band is shrunk on the pipe so as to project beyond the top into which is fitted a hooped oak driving block that may be replaced when worn out. Patented followers are also used, to which pipes are attached by which steam or air may be intro- duced on top of the pile to release the follower when such aid is needed in certain soils. When followers are used to drive piles through a considerable depth of water the base of the follower should engage extension leads so as to hold and guide the head of the pile properly. In deep water with a swift current it may not be possible to handle the follower effectively. In such cases long piles are driven while their heads remain above the sur- face; afterward they are cut off at the proper ele 32 TIMBER PILES AND DRIVERS CHAP. I The use of a follower generally absorbs a considerable per- centage of the energy of the hammer, frequently amounting to 50 percent. The loss is greater when the lower end of the follower is not guided by the leads and the pile is set into unu- sual vibration. The following record by J. E. CRAWFORD shows, however, that under proper conditions there may be no appreciable loss in the effect of the blow. The pile sank of its own weight 6 feet then the hammer with its housing- weighing 6000 pounds was put on it, and it sank 5 feet further. The number of blows for each succeeding foot of penetration were 9, 5, 13, 20, 14, 16, 17, 15, 3i 40, 47> 6 5> 45> 26, 22, 33, 60, 55, and 55. Then the follower was put on and the number of blows required by foot were 55, 75, 56, 60. 73, 90, 113, 115, and 102 blows for the last 7 inches, giving the pile a pene- tration of 39 feet 7 inches. ART. 12. POINTS, SHOES, AND SPLICES The foot of a timber pile should always be cut off perpen- dicular to its axis, since it facilitates driving it true to line or position. In soft and silty ground or where the driving is easy, it is not necessary to sharpen or .point the pile. If a pile penetrates soft material and rests upon a hard stratum, thus acting as a column, the unpointed foot has the additional ad- vantage of providing a larger bearing area. The blunt end on striking a root or any small obstruction will generally break the obstruction without deflecting the pile. In driving a pile with a blunt end a cone of compressed earth forms under it and acts in most respects as if the pile were pointed. It is frequently claimed that even in driving through hard material a pile will keep more nearly to the required position than if it is pointed. This implies that the cone of earth is more likely to have the form of a fairly good cone or pyramid than the wooden point made by sharpening the pile. Such a contention can hardly be maintained if the point- ing is properly done. When coarse gravel or boulders are en- countered which destroy the cone of compact earth, crush the ART. 12 POINTS, SHOES, AND SPLICES 33 fibers of the timber and wedge them apart, it is desirable to reduce the area of the foot by pointing. In general, when the ground is at least moderately compressible and the driving is not hard the foot of the pile may be left unpointed. When the driving is hard for most of the penetration, as in stiff clay or in material that is but slightly compressible and hence must be displaced, it is advisable to point the pile that it may separate the material at the foot like a wedge. In FIGS. 1 2a, b, and c. Shoes for Timber Piles. pointing a pile it is preferably sharpened to the form of a trun- cated pyramid, the end being from 4 to 6 inches square. If the end is too small the fibers lack the necessary strength to resist brooming. The length of the point may be from one and a half to twice the diameter of the foot. Another advan- tage of pointing is to increase the rate of penetration, or to reduce the energy required. In compact material the bearing power of a pile is practically the same with or without the point. Experience has also shown that piles with pointed ends may be successfully driven through old timber cribwork while attempt- ing to drive them with blunt ends resulted in broomed tips, split and broomed heads. 3 34 TIMBER PILES AND DRIVERS CHAP. I Sometimes the timber point is replaced or protected by a metal shoe. Fig. 1 20, shows an undesirable form which tends to split the pile when the side of the shoe strikes an obstruction. Figs. i2b, c, and / illustrate the best forms, since the timber has a square bearing on the upper flat surface of the shoe and the sides of the socket or the straps permit such a firm fastening as to make the shoe act like an in- tegral part of the pile. Those in Figs. i2d and e are not quite so effec- tive unless a close fit is secured in the socket at an increased labor cost. Shoes are used by some engineers when piles are driven into material containing boulders, rip rap, coarse faf/> shoe has 3ho/es. I for boat spikes. FIGS. i2d, e, and /. Shoes for Timber Piles. gravel, shale, slate, hardpan, buried timber, very hard clay, and coral rock. Another use is to penetrate a thin hard stratum (2 feet or less) which overlies a softer one. They are also at- tached to piles for bridge falsework in order to gain a foothold on rock bottom. In one case it was thus possible to secure sufficient penetration to hold the piles against a 2o-foot rise in the river and a swift current. On the Key West Extension of the Florida East Coast Rail- way where numerous pile foundations are built on coral rock containing pockets of different sizes, a hole was made by driving a steel punch with the pile-hammer and then driving in the timber pile with a few light blows. In order to permit the ART. 12 POINTS, SHOES, AND SPLICES 35 punch to be readily withdrawn, it was provided with a foot slightly larger in diameter than its body. Some engineers and contractors condemn the use of shoes unqualifiedly because of their unsatisfactory experience, but in many cases such experience is probably due to employing shoes which were improperly designed or constructed, while in others the piles should have been omitted since the ground was hard enough to support the substructure directly. It is occasionally necessary to use longer piles than can be obtained in single sticks. It becomes necessary therefore to splice two piles together end to end. For this purpose a fish-plate joint is usually the ; best since it provides lateral resistance. Either four or six timber fish plates may be used as illustrated in Figs. i2g and h. For the falsework to erect the Poughkeepsie bridge 55- I FIGS. i2g and h. Fish-plate Splices for Timber Piles. foot piles were spliced to 75- foot piles by means of fish plates 20 feet long, eight fish plates 4 by 5 inches in section being fastened to the piles with J-inch wr ought-iron spikes 8 inches long. The water was 55 feet deep. Wrought-iron fish plates may be employed instead of wooden ones and thus reduce the sectional area at the joint. Another method is to use a metal sleeve consisting of a piece of heavy pipe as indicated in Fig. 122. Half-lap joints fastened either with bolts, bands, or wire wrapping are often used but they are deficient in lateral strength and stiffness. TIMBER PILES AND DRIVERS CHAP. I In rebuilding the fender piers of the Thames River bridge in 1902, 400 piles were driven formed by splicing spruce piles 35 to 40 feet long to creosoted yellow pine piles from 50 to 65 feet long. The water was 50 feet or less in depth, so that the spruce piles are below the bottom of the river and hence free from the attacks of the teredo. Pile splices may also be required where piles have to be driven in sections on account of limited clearance under a bridge. Piles in three sections have thus been placed with pile-drivers having short leads. The sections were joined together with iron sleeves, the piles being found satisfactory under test loads. In swampy places one pile is sometimes driven on top of another with only a dowel connecting the two. Such a joint affords practically no lateral stiffness and the upper section is liable to bounce off while 'driving unless the dowel is very long. In pile trestles where the upper portions of long piles are decayed repairs may be made by cutting out the decayed section and inserting new timbers. In one case four steel angles were used as fish plates for each pile. They were well fastened with spikes, and each end of the joint was wrapped with a band of heavy wire, while spiral wrapping extended between them. A shell of concrete was then cast around the joint to protect the metal. The repairs cost about 15 percent of the cost of the piles in place. FIG. 12*. Tubu- lar Splice for Tim- ber Pile. CHAPTER II DRIVING TIMBER PILES ART. 13. OBSERVATIONS IN PRACTICE As a general rule a heavy hammer with a low fall secures greater penetration with less expenditure of power than a light one with a high fall; it is also less injurious to the equip- ment. More blows can be given in the same time with a low fall and hence less time is given between blows for the ground to compact itself around the pile. In quicksand it is especially necessary to have the blows follow each other as rapidly as the operation of the hammer permits. In silt the rapidity of blows need not be quite so great as for quicksand. When a pile sinks at a uniform rate it is less apt to jam, buckle, or split than when driven with heavier blows and with marked intervals of time between them. This statement is confirmed by observations in putting down steel sounding rods by hand. For example, through soft gravel mixed with quicksand, one man may be able to push a rod down 5 or 6 feet, and if quick enough may pull the rod up again with the same expenditure of power. If, however, the rod is allowed to rest no longer than 15 seconds the sand packs against it so that two men are scarcely able to pull it up. A pile which is left standing for a few minutes in some kinds of sand may be packed so hard as to resist further penetration, or at least to require a much larger impact to start it again. A very slight bounce of a drop-hammer occurs at every blow under good conditions for driving, but decided bouncing of the hammer may occur when the penetration ceases, or when the hammer is too light, or the fall too great, or both; or when the head of the pile is crushed or .broomed so as to cushion the blow. 37 38 DRIVING TIMBER PILES CHAP. II In certain kinds of soil a pile may sink some distance and then refuse to go further, but will resume penetration when driven after an interval of rest; or it may refuse to sink under a heavy hammer and yield under the more rapid blows of a lighter one. The driving of one pile may cause adjacent piles to rise, and in soft ground or mud often causes an adjacent pile previously driven to move away slightly. The great variety of experiences which may occur on a simple work of construction may be illustrated by those encountered in driving piles for the Odgen-Lucien Cut-off of the Central Pacific Railway. The nature of the bottom of Great Salt Lake was found to be so variable that at times a blow of the hammer drove a pile only i or 2 inches, and at other times i or 2 feet; or a pile seemed to strike a hard stratum and refused to sink farther under many blows, but after being forced through, the pile sank as much as 2 or 3 feet per blow. Frequently a pile with a penetration of 30 to 50 feet would suddenly rise 2 or 3 feet during a short delay of the hammer. At the end of the temporary trestle, to be later replaced by a rock fill, a new difficulty was encountered. The first pile 26 feet long was driven out of sight by a single blow, and when another pile 28 feet long was placed on top of it, the next blow of the hammer sent both out of sight. The formation was found to be a deep mud deposit due to the Bear River. As the mud was 50 feet deep, two 40-foot piles were driven on top of each other. The trestle supported by these spliced piles supported the trains until the rock fill was completed and settled. In certain kinds of clay the lateral spring of a pile under the hammer blows makes a hole slightly larger than the diameter of the pile, allowing surface water to find its way to the foot of the pile thus reducing both the skin friction and the bearing power of the clay under the foot of the pile. This action ex- plains why cases have been observed where piles settled under moving trains after a rain although the resistance of the pile when driven was considered satisfactory. The treatment of such conditions is indicated in Art. 16. ART. 13 OBSERVATIONS IN PRACTICE 39 The principle involved may be advantageously applied in some cases to reduce the resistance in pile driving when there is no available water-jet equipment. For example, by discharg- ing water on the surface of the ground at the pile with an ordi- nary garden hose, without a nozzle, the number of blows by a steam-hammer was reduced from 296 to 164 for a 45-foot pile in a Chicago building foundation. One engineer declared in a discussion on this subject that sometimes hardly a day passed but someone rushed into the office to state that in a certain place the piles were being driven too deep; that they had gone through a hard stratum into a weaker one, forgetting that in ground where its supporting power depends mainly upon skin friction the total penetration must be large. A frequent cause of small penetrations per blow is the crookedness of a pile which produces a lateral spring under the hammer blow, and thus dissipates some of the energy. Occa- sionally it is due to the head of the pile being cut off improperly so that the hammer strikes on one side only. Perhaps the most common cause is due to setting the pile out of plumb in the leads, on account of undue haste or carelessness. It is equally as important to keep the leads plumb by leveling up the tracks on which the pile-driver moves. Under- ground conditions sometimes force a pile out of line in spite of ordinary efforts to control its movements in the leads. A block and tackle or a jack screw may be required to force it back. If it is desired to compact the ground in a given area uni- formly, it is best to begin driving piles at the center and work outward to the perimeter. If the order of procedure is reversed, it becomes more and more difficult to drive the piles toward the middle to secure the same penetration and usually the adjacent outer piles will be forced to rise more or less. It is often instructive to notice the effect on piles in place when additional ones are driven near-by. One may observe piles which were cut off to grade rising from 2 to 3 inches when adjacent piles are driven, showing that the ground between 40 DRIVING TIMBER PILES CHAP. II the piles is thoroughly compacted and that its vertical motion indicates the line of least resistance. If time permits they may be given some extra blows to settle them, or they may be cut off again to grade since the phenomenon shows that the full supporting power which the nature of the ground permits is being applied to the pile. On foundation work for the Illinois Central Passenger Sta- tion at Chicago a group of eight piles had been driven, sawed off to a uniform height, and wales drift-bolted to them. Upon driving a group of 16 piles 15 feet away, the piles in the former group rose 4 inches next to the driver and i inch on the opposite side. In a group of 72 piles observations were taken daily on the head of the first pile while the rest were being driven. The pile sank \ inch during the first two days, then rose steadily until 50 piles were in place when it was 3 inches above the original elevation, the greatest rise in one day being f inch. The pile was 55 feet long, and had a total penetra- tion of 45 feet. The distance to which vibration was felt at the same site varied with the height of fall of the hammer, the nature of the ground and the spacing of the piles. The vibration was easily felt at a distance of 400 feet and was quite marked at 75 feet. In doing instrumental work it was sometimes observed that the vibration within 25 feet of the pile-driver was less severe than at several times that distance. ART. 14. DRIVING PILES BUTT DOWN It is the general practice to drive piles with the tip downward. Occasionally, however, special conditions make it advisable to drive them with the butt downward. It has been found diffi- cult at times to keep a pile down after being struck by the hammer, the pile beginning at once to rise, lifting the hammer with it; and upon raising the hammer the pile may shoot up- ward 5 feet or more, or the pile may exhibit this tendency but slightly when driven, but the following morning will stand with its head a number of feet higher than before. This be- ART. 15 DRIVING BATTER PILES 41 havior is ascribed to a substratum of quicksand, and the difficulty is usually overcome by driving the pile 'butt down.' Another condition occurs when piles are driven through very soft ground and the load has nearly all to be borne by the foot. The substratum may require the larger bearing area afforded by the butt of the pile to carry the load. Some engi- neers recommend that tall pile trestles which are to be filled should have the piles driven butt down, thus leaving no hollows to cause trouble as the embankment settles. The bracing can be removed as the filling rises. In hard material the butt may have to be pointed to a smaller diameter to facilitate pene- tration. Great care must be exercised in driving on account of the smaller area of the tip, which receives the blow, the smaller percentage of heartwood in that area and the weaker fibers of the wood which grows in the upper part of a tree trunk. In some cofferdam construction on the Ohio river where it was necessary to drive about 600 oak guide piles into hard gravel it was found that the best way to secure adequate pene- tration was to drive them with the butts down. In this manner the resistance encountered due to the wedge action of piles as usually driven was avoided, and the useful effect of the blow was all transmitted to the foot of the pile. An interesting example relates to piles driven 4 to 6 feet apart both ways in the embankment of the Yazoo canal near Vicksburg, Miss., to stop the bank from sliding on the adja- cent railroad track during the low- water stage of the river. By driving the piles butt down advantage was taken of the larger cross-section at the lower elevation where the bending moment was a maximum. Pile trestles have resisted the pressure of ice going out by having extra flexural strength due to the piles being driven butt down. When piles have to be driven into sand with their butts down the water-jet should be employed (Art. 16). ART. 15. DRIVING BATTER PILES A batter pile is a pile driven at an inclination to resist forces which are not vertical. It is sometimes called a spur pile. 42 DRIVING TIMBER PILES CHAP. II When a pile-driver is designed to drive batter piles as well as the ordinary vertical piles, its leads are suspended from a horizontal pin to permit them to be swung laterally like a pendulum. Hence they are known as swinging leads and sometimes as pendulum leads. The pivot is attached to the top of a tower, the front timbers of which are inclined laterally to provide the requisite transverse bracing. Fig. 150 shows batter piles being driven in the trestle approach of the Dum- barton bridge across San Francisco Bay. Although this illus- tration is that of a track driver, the arrangement of swinging leads shown is the same as for ordinary land drivers or for floating pile-drivers. Occasionally drivers are arranged to drive batter piles by having a removable section at the bottom of the back stays, so that the tower revolves backward about hinges located near the foot of the leads. Another scheme consists in taking a separate set of leads and temporarily bracing them to the tower of a pile-driver. In this manner, batter piles 60 to 70 feet long were driven for car dump foundations at the Erie Rail- road Dock at Cleveland, the piles sloping downward toward 'the driver. An interesting form of pile-driver was used in 1904 to drive piles for a permanent extension on the Ogden-Lucien Cut-off which crosses the western arm of Great Salt Lake. It was de- signed to operate from a low falsework built alongside, the tower overhanging the track. The leads were arranged to swing forward below to drive the piles and whenever a train came along they could be swung back between the timbers in the tower corresponding to fixed leads. The king pin support- ing the leads was placed directly over the center of the track, so that the leads had their correct position and direction to drive the respective piles of each bent when the proper pins were inserted in the struts holding the leads. Two sets of rollers were set under the sills of the driver, the lower set to allow the driver on the falsework to move parallel to the trestles and the upper to move at right angles to it, to place the driver in the clear of passing trains. FIG. 150. Driving Batter Piles on the Trestle Approach to the Central California Railway Bridge over San Francisco Bay at Dumbarton Point, August, 14, 1907. (Facing p. 42.) FIG. 1 8a. Examples of Overdriven Piles Exposed by Subsequent Excavation. ART. 1 6 USE OF THE WATER- JET 43 Batter piles are used under arch abutments to resist the horizontal component of the reaction, and sometimes several are employed under each side of piers for simple truss or girder spans when the weight of the pier is not sufficient to provide adequately for the effect of traction. Quay walls are provided either with batter piles or with rods to anchor piles, or both. Many accidents to such structures have occurred because of a failure to provide batter piles to relieve the vertical piles from flexural stresses. Vertical piles in permanent structures should be protected against the action of lateral forces whenever possi- ble either by sway bracing or by batter piles. See Fig. 13 5<; for an illustration of the use of batter piles in the foundation of a bridge pier. ART. 1 6. USE OF THE WATER- JET A method of placing a pile in position, which differs radically from that of driving it with a hammer, consists in displacing the material by means of one or more jets which discharge water under pressure at or near the foot of the pile. As the water comes up around the pile carrying with it some of the material it also diminishes the frictional resistance of the pile. In some kinds of earth the hammer is merely placed on top of the pile to increase the pressure by its weight, while in other cases the hammer is operated with a restricted fall to secure a greater rate of penetration. In soft ground one jet may answer the purpose, but in most cases two jets, used on opposite sides of the pile, give better results. As the pile tends to move toward the side where the jet is operated, the use of two jets usually enables a pile to be placed more accurately in position. Sometimes a third jet is employed, discharging at a higher elevation than the others, if difficulty is experienced in keeping the ground from packing against the sides of the pile. The water has a puddling action upon the adjacent earth and after the jet is removed the earth packs closely around the surface of the pile, thus securing a greater skin friction 44 DRIVING TIMBER PILES CHAP. II than if the pile is driven by means of the hammer alone. In order to secure better bearing at the foot, it is customary to shut off the water just before the pile reaches its intended total penetration, and to complete the driving by a few blows of the hammer. This procedure presses the pile firmly into the softened earth and tends to avoid any arching action of the earth that might prevent the material from filling every cavity when it settles into place. The water-jet may be used advantageously in any material that will settle around the pile after the flow of water ceases. The best results are obtained in pure ocean or river sand. In this material the simplest form of jet may be used, only a moderate pressure is required, a single jet will generally answer, the time of sinking is very short, and the sand packs quickly after the water is shut off, while no blows of the hammer are needed except for the purpose stated in the preceding para- graph. It is fortunate that this is the case for pure sand offers very high resistance to a pile when driven with the ham- mer alone, especially with a drop-hammer. Even in quicksand this is frequently found to be true. With the jet a pile may be sunk in sand without danger of injury, while it is difficult to avoid injuring piles when driven into sand without the aid of the jet; more time and a larger expenditure of energy are also required. Piles have been driven with the aid of the water-jet process in mixtures of sand and silt or gravel, if the latter is not too coarse; in loam, clay, marl, and even 'gumbo' in pockets, al- though a special nozzle is required for the material named last. Some of the most experienced engineers ,in the use of the jet have driven piles with its aid in "sand and clay and the hardest kind of bottom," and in "almost any material except hard-pan and rock." In hard ground the jet process may be used advan- tageously in case sufficient volume and pressure of water be provided. In clay it may be economical to bore several holes in the earth before driving the pile, thus securing the accurate location of the pile and its lubrication while being driven. Where the material is of such a porous character that the ART. 16 USE OF THE WATER- JET 45 water from the jets may be dissipated and fail to come up in the immediate vicinity of the pile, the utility of the jet process is uncertain except for a part of the penetration. In mixtures with gravel or coarse material the water will often wash out the sand and finer material leaving the stones in the hole to interfere with the penetration of the pile. This action may often be remedied, however, by increasing the volume and pressure of the water. In driving in sand the jet should be hung on a rope passing over a pulley in the driver so that it may be kept moving up and down with its point near the point of the pile. If this is not done the pipe is likely to 'freeze' fast and cannot be moved. After the pile reaches a depth of 10 or 15 feet the water will sometimes fail to come up around it, breaking out on the surface at a considerable distance, perhaps around a pile driven previously. When this occurs it indicates that the jet has not been kept moving sufficiently, or an auxiliary jet may be needed discharging at some intermediate depth. In any case the jet should be withdrawn at once and immediately put down again, thus usually reestablishing the flow of water along the pile. Where piles are sunk 20 feet or more into sand it is advisable to have two jets. One is to be kept moving with its nozzle slightly ahead of the pile, while the other is slowly raised and lowered between the foot of the pile and the surface to maintain the flow along the pile. On the other hand, when the material is soft and readily compressible as in silt, or in fine sand mixed with silt or a small percentage of clay, it may not be economical to use a jet since the pile may be driven quickly without risk of injury by means of a steam-hammer. The effectiveness of the water-jet is demonstrated at times during the operation of sinking a pile when a break-down occurs, and an attempt is made to drive temporarily without its aid. So frequently will the piles broom or split, or give other signs of injury before reaching the full depth of penetration, as to preclude further driving. When piles were first driven at Atlantic City prior to 1890, a contractor became bankrupt by attempting to drive piles in the wet sand by means of the ham- 46 DRIVING TIMBER PILES CHAP. II mer alone. A score of years later when the water-jet was gen- erally used in that locality contractors were wont to consider it as an ordinary performance to sink 100 to 120 piles in a half day. This fact illustrates the saving in time and money which is made possible by the aid of the jet. In Florida palmetto piles are sometimes used since they are comparatively free from the ravages of the teredo. This wood has a hard shell and a soft interior, and cannot stand heavy blows with a hammer. Such piles may be easily sunk into hard sand by a water-jet, the hammer resting on top and occasionally tapping the pile, the fall being only 3 to 6 inches. By keeping the pile and jet pipes constantly moving the sand is kept from closing in on the pile until it occupies its final position. With the aid of the jet, piles may be sunk as readily with the butt down as with the tip down. In general the water-jet should not be attached to the pile, but handled separately. The nozzle is usually extended a small distance, not exceeding a foot, below the foot of the pile, but sometimes it is necessary to move it up and down to reduce the frictional resistance on the pipe, or to change its position if a boulder is encountered, so as to excavate an opening into which the boulder may he pushed by the p^e. If this is not sufficient to displace an obstruction the pile may be raised a little and dropped with the hammer resting upon it. It is not desirable to bend the pipe, as is sometimes done just above the nozzle. For depths not exceeding 15 to 20 feet and when the ground does not consist of layers differing materially in character, the average rate of penetration is often found to be remarkably uniform, independently of the depth. At the Brooklyn anchorage of the Manhattan bridge 2500 piles were driven, about 40 feet long and 14 to 16 inches in diameter at the butt. Great difficulty was experienced in driving them on account of the numerous large and small boulders encountered and a thin stratum of hard-pan that had to be penetrated. With the hammer alone test piles could be driven only 8 to 10 feet, but with the aid of a powerful hydraulic jet they could be driven to a depth of 40 feet. When a boulder ART. 16 USE OF THE WATER-JET 47 was encountered the jet was worked around its edges until it was moved aside, or until it was undermined and finally sunk to a position below the foot of the pile at its desired elevation. The continued use of the jet softened the ground when it could not excavate it so that the pile could be driven further to its final grade. In this manner piles were driven where it would have been impossible to do so without the jet. Boulders two cubic yards in volume were sometimes displaced. In using the water-jet, the quantity of water should be ample. In most cases volume rather than velocity is necessary. The velocity must be sufficient to excavate the sand below the foot of the pile and to make it 'live' or 'quick,' while the volume is large enough to force the water to escape by rising along the sides of the pile to bring the material to the surface, and at the same time to reduce the surface friction, if it does not entirely eliminate it. In beach sand, piles have been jetted down within 18 inches from adjacent piles without disturbing them, showing that in this material the movement of the water is confined to a small radius horizontally. In cities the water-jet cannot be used as freely as elsewhere on account of the danger of settlement to adjacent foundations and injury to the heavy structures supported by them. Where piles are to be driven to the uneven surface of an underlying ledge of rock the proper length of pile may be de- termined conveniently by running the jet down to the rock and measuring the penetrating length of pipe. The bearing power of piles sunk by the water- jet process is determined by test blows of the hammer after the material has had time to settle or pack around the pile. In pure sand the pentration per blow is so small that the bearing power of the pile is limited either by the safe compressive strength of the wood of which it is composed, or by its' strength as a column in case the total pene- tration is only a part of its length. The earliest authenticated use of the water-jet in sinking piles appears to have been introduced on the construction of a wharf at Decrow's Point, Matagorda Bay, Texas, in 1852, and to have arisen from a suggestion made by Lieut. GEORGE 48 DRIVING TIMBER PILES CHAP. II B. McCLELLAN, Corps of Engineers, U. S. A. The water was pumped by an ordinary hand pump through a rubber hose with a gas-pipe nozzle, the nozzle being placed close to the tip of the pile. The historical development of the water-jet process is described at length in an article on The Water -Jet as an Aid to Engineering Construction, by L. Y. SCHERMERHORN, in Pro- ceedings of the Engineer's Club of Philadelphia, 1900, vol. 17. The use of the water-jet in driving concrete piles is treated in Art. 49. ART. 17. EQUIPMENT FOR WATER- JET PROCESS The water-jet consists generally of a straight pipe with a nozzle at its end, connected by some length of flexible hose to the discharge pipe from the pump which provides the water under pressure. The suction pipe connects the pump with the source of water supply. The pump is operated by steam, being connected either with the boiler for the pile-driver or with a separate steam supply. Sometimes a short piece of curved pipe is coupled between the straight jet pipe and the hose. The pipe can be raised and lowered by a line attached to the top leading over a snatch block to be operated by hand power on the ground, or to a spool on the hoisting engine. The diameter of the jet pipe is either 2 or i\ inches. The discharge pipe of the pump is in most cases 4 inches in diam- eter while the diameter of the suction pipe is 6 inches. To increase the velocity of the water and thus increase its power to loosen the earth, the size of the pipe is drawn down at the end to form a nozzle. The nozzle is usually circular in section and its diameter varies from f to \ inch. In a few cases a rose-jet has been employed, the nozzle having one central opening at the end and five openings around the sides with their axes inclined about 45 degrees to that of the axes of the pipe. (See Fig. gib.) Another form of nozzle is made by flattening the end of the pipe until the opening is reduced to \ inch. This nozzle has given better results than a round one, especially in stiff material, it being rotated back and forth about its axis. ART. 1 8 OVERDRIVING PILES 49 The quantity of water to be discharged varies from 50 to 250 gallons per minute. It must be sufficient to bring to the surface the material which is next to the pile. The pressure ranges from 65 to 200 pounds per square inch although the hose and fittings are sometimes designed to resist a pressure of 250 pounds per square inch. The higher pressures are required especially when gravel and boulders are encountered. Recipro- cating pumps are employed, either single acting or double acting, and sometimes compounds. The error which is most frequently made is to use pumps of insufficient capacity, leading to ineffective work with the jet and loss of time. Un- satisfactory results with the water-jet due to inadequate and inefficient equipment is doubtless one of the main reasons why the water-jet process has not come into more extensive use in pile-driving practice. A device has been invented by which the jet pipe is handled by means of the water pressure, thus reducing hand labor to a minimum. By turning a valve the operator who guides the pipe near the pile can control the direction and pressure of the water so as to raise or lower the jet or to hold it in any given position. The jet pipe acts as a plunger inside of a larger pipe which acts as a cylinder, the latter being suspended from a derrick pile-driver. ART. 18. OVERDRIVING PILES Examples of piles which were injured by overdriving are occasionally exposed by subsequent excavation. In Jersey City some piles were driven into the surface of a street to sup- port temporarily a large water pipe, and afterward the street had to be excavated for the passage of a railroad. It was thought that the piles were well driven and in good condition. It was discovered that about one-half of them were ruined in driving, some being broken off square across and the upper piece driven alongside the lower piece. One pile encountered a large flat rock about 16 feet below the surface, and the fibers of the tip were found to have turned aside horizontally to a distance' of 15 feet. 4 50 DRIVING TIMBER PILES CHAP. II In Brooklyn before making certain subway excavations timber piles had been driven on the sides of the street to sup- port temporary plank roadways. When they were exposed by the steam shovel it was seen that very many of them were broken, splintered, or sheared. It was known from their be- havior during driving that some of the piles were overdriven, but the injuries proved to be more numerous than had been supposed. The piles were mostly spruce as yellow pine would not stand the hard driving. The average diameter at the butt was 12 inches and after a preliminary test 20 feet was found to be the most satisfactory length. A 2ooo-pound drop-hammer was used with a fall ordinarily of 25 feet. Although a water- jet aided in driving, it was difficult to secure the desired total penetration. The pile fractures had a variety of forms; some were splintered and broomed, others burst and were spread out, while others were sheared apart, and the upper end driven past the stub. In western Massachusetts where a new railroad passed under an old railroad embankment, temporary bents of piles were driven about 22 feet deep through fine compact sand. The driving was hard and no water-jet was employed. The ex- cavation of the bank showed over half of the piles to be seriously damaged, being split or broken at distances exceeding 8 feet below the surface. In most cases the break was a double shear, the upper part acting as a wedge to split the lower piece; some failed by a single inclined shear, and a few by bulging. Some- times bulging assumes the condition of collapsing like an accordion. In 1907 while sinking a pneumatic caisson for the Vancouver bridge over the Columbia River some piles were removed which had been driven in 1890. Their tips were found to be broomed and shattered by driving into the compact gravel which they did not penetrate. During excavation for a building in New Orleans it was seen that not all the test piles previously driven had pierced the sand stratum. Those with knotty ends had broken off some dis- tance from the tip, and the new tip thus formed reached the sand. ART. 18 OVERDRIVING PILES 51 In some instances two such breaks had occurred. One of the test piles had not even penetrated to the depth of cut-off for the foundation piles to be driven later. Some feet in length above the tip showed a mass of fibers, resembling worn-out rope, of about the same shape and size as a barrel. The effect of continuing to drive temporary piles after the tip reaches rock was clearly shown during excavation at a tunnel portal in New York. Piles were furnished to the fore- man in charge of the excavation somewhat longer than neces- sary to reach rock at the elevation indicated by the borings, and he was instructed to drive them to rock. The foreman reported that he had driven the piles as far as possible without bringing the butts below the upper wales which they were intended to support, and that they had not reached rock, insisting that they had moved quite uniformly until he stopped driving. For a number of feet the lower ends of the piles were badly shat- tered and broomed as revealed by the subsequent excavation, although the heads were not broomed materially. A contracting engineer of large experience has expressed his conclusion that more piles are dangerously injured by improper driving than are rendered unsafe through insufficient driving. Another engineer concludes that, in general, piles are apt to be overdriven and much of their value lost. The former believes that this is due largely to the use of drop- hammers with excessive weights and undue heights of fall. He reported a case where ten successive piles in an important foundation were driven in hard material with a 3ooo-pound drop-hammer and a fall of 30 feet and after practically reaching 'refusal' suddenly moved several inches at the head. The inspector in charge accounted for the resumption of penetration by assuming that the foot of the pile had met and passed through a layer of hard material. The subsequent removal of these piles showed that every one had been broken near mid-length. He also had frequent occasion in the removal of timber -pile piers to examine the piles after they were withdrawn and found that when driven to hard bottom they were generally either broken at a considerable distance above the foot, or else the 52 DRIVING TIMBER PILES CHAP. II foot had split and spread out so as to resemble an inverted mushroom several feet in diameter. He claimed, moreover, that excessive driving results in a degeneration of the fiber which reduces the strength of the piles acting as columns and hastens decay materially. A contractor, having noticed the apparently injurious effect on piles due to very heavy blows, ordered experiments to be made to learn just what damage was done and the proper remedy. Spruce and yellow pine piles 40 to 50 feet long, 1 2 to 15 inches at the butt and 6 to 8 inches at the tip were driven into a mixture of clay, sand, gravel, and small cobble stones, and which offered a gradually increasing resistance to penetra- tion. A drop-hammer weighing 3000 pounds was used with the hoisting rope attached. The object was to determine what height of fall could be safely adopted without impairing the in- tegrity of the pile either by brooming its head or its foot, or by breaking it at some intermediate point. The first piles were driven according to the former custom of raising the hammer to the top of the leads until the fall reached about 25 feet after which it was not increased. The fall was gradually di- minished as successive piles were driven. Each pile was pulled up by a loo-ton derrick and examined. Nearly every pile .driven with a fall exceeding 10 feet was found to be more or less injured, either by badly brooming at the foot or by breaking at some distance higher. A fall of 10 feet could be depended upon not to injure the pile. To make sure that the fall should not exceed this distance the instructions to the foreman placed the limit at 8 feet for a 3ooo-pound hammer, the driving to be continued until the penetration should not exceed i inch in the last three to five blows as circumstances might warrant. Extensive subsequent experience in pile driving under many other conditions confirmed the results of the experiments that a greater fall than 10 feet for a 3ooo-pound hammer is uncertain m its results and more likely than not to injure the pile. The effect of a heavy drop-hammer, weighing 3800 pounds, is seen from the results in driving 34 piles for a temporary trestle at an under-crossing of a railroad near Columbus, 0., 13 piles ART. 1 8 OVERDRIVING PILES 53 or 38 percent being more or less damaged. Several were even telescoped, buckled and bent almost beyond belief, so as to be practically without value to sustain loads. The following example illustrates conditions which too fre- quently prevail and lead to overdriving. No provision was made for an adequate exploration of sub- surf ace conditions. It was known, however, that the soft mud was interspersed with layers of gravel hard-pan of varying thickness. It was there- fore decided to drive the piles so hard that it might be safely concluded that they rested upon a stratum thick enough to carry the required load. Ordinary spruce and hemlock piles split and smashed. Finally Nova Scotia spruce piles full of solid knots were obtained, which were said to be so tough as to resist splitting, and yet soft and elastic enough to absorb the blows of the hammer. It was claimed that a satisfactory pile foundation was made with them. Unfortunately the opinion prevails too widely that several extra blows at the end of the driving generally secure extra resistance of the pile or extra bearing capacity. The limit of safe driving depends chiefly upon the weight and fall of the hammer, the material penetrated, the species of wood in the pile, its diameter and length, and the protection given to the head of the pile while being driven. Whether the timber pile is dry or green or improperly creosoted will also need con- sideration. Two piles have been driven side by side through the same ground and under the same conditions, so far as this is practically possible; one pile penetrated to its full length without apparent damage while the other " burst all to pieces," the difference in behavior being due to the fact that the first pile was sound while the second one had incipient decay called 'red heart.' The pile which failed appeared to penetrate the ground rapidly and easily, but the head showed signs of dis- tress at an early stage of the driving. The elements affecting safe driving are discussed further in Arts. 27, 28, 29, 33 and 35. Another fruitful reason for overdriving piles is the unreasonable specification that is frequently adopted which requires driving to refusal. This is considered in Art. 38. 54 DRIVING TIMBER PILES CHAP. II There is danger from overdriving when the hammer begins to bounce. Overdriving is also indicated by the bending, kick- ing, or staggering of the pile. When a pile has not penetrated very far and the hammer begins to bounce and the pile to shiver and spring near the ground, it is time to stop driving, unless the pile is disproportionately long for its diameter. In fairly homogeneous ground, if the driving becomes hard and the hammer starts to bounce it is usually wise to stop driving. If driving is continued and the rate of penetration is irregular, it is probably safe to assume that the pile is either brooming at the tip or fracturing at some intermediate portion of its length. If a pile suddenly changes direction, there is but little doubt that it has broken. In general, when a pile is sinking easily and suddenly stops, and the hammer commences to bounce, the driving should cease, as it is probable that the pile has struck a boulder or some other obstruction. The quality of a pile can usually be judged by the behavior of its head under moderate driving. As the driving progresses, the condition of the head also gives some indication regarding the action of the pile below the surface. The best measures to adopt to prevent injury to piles by over- driving include the use of a cap to protect and guide the pile head; the substitution of the steam-hammer for the drop-ham- mer; the use of the water-jet whenever practicable; and an ade- quate exploration of the ground to be penetrated. The steam- hammer is more effective than the drop-hammer in securing the penetration of a pile without injury, because of the shorter interval between blows. Some piles have taken over 1200 blows without any sign of the head being broomed. The use of the water-jet is one of the most effective means to avoid the danger of overdriving since it reduces the resistance to pene- tration. Preliminary exploration of sub-surface conditions is necessary to interpret properly the behavior of a pile while being driven, as well as to determine the proper length of pile and whether it is to act as a column, or to support its load by skin friction. In the preceding paragraph a reference was made to the significance of an irregular rate of penetration; it would ART. 19 SPACING OF PILES 55 be entirely different in stratified material where the pile con- tinues to break through one thin stratum into another one of different density. If a hard crust has to be penetrated and the piles cannot do so without injury, it is better to use dyna- mite to break it up, placing it by means of a pipe. Or, a double-strength wr ought-iron pipe, with a steel point and cap, may be driven until it penetrates the hard stratum, and after withdrawing it, the timber pile may be inserted in the hole and driven to the proper depth. This method has been used to penetrate a hard embankment under railroad tracks. In other cases the hard overlying stratum may be removed by dredging or otherwise, and replacing the material if it is needed to provide lateral resistance. Attention is called to the ref- erences on this topic in Chap. XIX, especially to the Proceedings of the American Railway Engineering Association. It is often remarked that judgment based on experience will dictate when to stop driving. The training of the judgment depends not so much on the amount of experience as upon the habit of care- ful reflection on the results of observations in pile driving and of the probable causes in each case. It is most earnestly to be hoped that the time will come soon when it cannot be truth- fully said that "the most prevalent bad practice in pile driving is overdriving." See Fig. 130 facing page 43. ART. 19. SPACING OF PILES In good practice timber piles are never spaced closer than i\ feet between centers, and preferably not closer than 3 feet. When piles are supported by frictional resistance they should be driven so far apart, or to such a depth, that the increased area of bearing developed by the conoid of pressure, which has the required altitude to contain the frictional resistance, reaches a level whose material will afford the required support before it intersects the corresponding conoid of an adjacent pile. This indicates that the character of the ground at different depths should be known before the number of piles is deter- mined and any of them are driven, or else the number required 56 DRIVING TIMBER PILES CHAP. II to support the given load must be changed and hence the spacing required. When an important function of the piles is to compress the ground penetrated by them a closer spacing may afford larger bearing power at a given level, while on the other hand, in some kinds of material one or more extra piles in a small group may reduce the supporting power at the same level. If piles are spaced too close together the entire mass of earth enclosed by the group tends to sink as a unit. In discussing this subject GOODRICH states that "the best practice is to assume a given load per pile, to design all footings accordingly and to require the superintendent of construction to provide and drive piles which will sustain this assumed load. In that case the designer's care will be to provide just the proper number under each footing and to space them so that each pile will develop its full proportion of the given load. To this end, groups should be made as nearly circular as possible, especially when they consist of any considerable number of piles. The corner piles of square groups of 16 piles might just as well be omitted. It is of the utmost importance not to space piles too closely together; or if close spacing is necessary, to drive them all to such a depth that the bearing power of the earth at that depth is sufficient to provide the necessary sup- port. All the piles under a building should be driven to the same depth, if possible, and the areas of groups should be care- fully proportioned to the loads to be carried, unless the spacing is large enough for each pile to develop its full supporting power independently. Tests made by the Department of Docks and Ferries of New York City prove conclusively that piles driven in North River mud, even to considerable depths, influence each other to some extent when 6 feet apart, and are practi- cally a unit in their action when only 3 feet apart. A group of two piles thus spaced had a supporting power only about if times what a single pile developed when properly spaced. "Earth with 35 percent of voids, if compressed so that all voids are filled, will increase in density only 54 percent. From quite a number of tests of the compressibility of soils made by ART. 19 SPACING OF PILES 57 the writer, it is evident that a tremendous amount of energy is wasted in pile driving if the piles are spaced so closely that any great compressing of the soil must be done. This wasted energy is not disclosed in any pile formula, and serves to give exaggerated values when such formulas are applied. Con- siderable practical experience also confirms this and all the other theoretical results given above. Thus, it is evident that, even with piles spaced 2^ feet apart, the amount of compres- sion suffered by the earth is more than one-quarter of the maxi- mum possible amount in many cases and that considerable energy must be wasted in driving so closely. A spacing of 3 feet is much to be preferred, especially when it is seen that the theoretical depths to which it is necessary to drive the piles, in order to develop a safe bearing power of 40 ooo pounds, are 16 feet for the 3-foot spacing and 26 feet for the 2^-foot spacing. The writer [GOODRICH] thinks that a minimum spac- ing of not less than 2.7 feet should ever be allowed and that 3 feet should be used whenever possible" (see Trans. Am. Soc. C. E., vol. 54, page 448, June, 1905). In discussions on pile driving one may find such examples as that in which 100 timber piles 60 feet long and 12 inches in diameter at the butt were driven into soft material, 2 feet apart each way, to sustain a static load of 600 tons, followed by the remark that no settlement was observed. In this connec- tion it may be well to quote the following statement by WELL- INGTON: " Bearing piles should be spaced at least 3 feet center to center each way if this gives a sufficient number to carry the load, and they are worse than wasted if driven less than 2\ feet center to center." Bearing piles may be located in plan either at the vertices of a series of squares, or of a series of equilateral triangles. When a considerable area is covered the piles are located thus in parallel lines on the plan, being opposite to one another in one scheme, and staggered in the other. Where the piles are staggered the alternate piles in alternate rows are sometimes omitted over a part of the area instead of slightly increasing the spacing throughout some rows. As stated in a preceding 58 DRIVING TIMBER PILES CHAP. II paragraph, groups of piles under column footings should be arranged in plan as nearly circular as possible (see Fig. 159^). Since it is not always an easy matter to hold a pile closely to line it is of especial importance to use range boards and transits when necessary to line up the leads of a floating pile- driver so that the pile may be started in correct position. Telescope leads may be used to hold piles against the action of the current until the penetration is sufficient to hold them. Piles which are so crooked that they cannot be held fairly to line should not be used. The stresses which are produced in some piles in trestle bents or other structures by forcibly bending them, before the cap and bracing are attached, are often so great that their supporting power as columns is con- siderably less than that for which they were designed. ART. 20. CUTTING OFF AND REMOVING PILES When the heads of piles are to be imbedded in a footing of concrete it is unnecessary to have them cut off at exactly the same level; in fact it is often specified that a certain proportion of them shall be cut off at a higher level than the rest. The heads should be cut off approximately level in this case but great precision is not required. When timber caps or timber grillage, however, are to transfer the load from the substructure to the piles it is important to cut off the piles at the elevations marked on the plans and that concave, convex or inclined heads will not be accepted. In the open air the cut can be made by an ordinary cross-cut saw upon two straight-edge guides attached to the piles. The next best method is to use a circular saw mounted upon a vertical shaft which is rigidly supported by a movable frame. The piles should be cut at such an elevation that the top of the timber grillage is below the ground water at its lowest stage. Changes in this level due to probable changes in the drainage system should receive due consideration. Where tide water has access to piles it is often customary to keep the timber of the foundation below half tide rather than below low ART. 20 CUTTING OFF AND REMOVING PILES 59 tide, since it will be kept wet continuously by the rise and fall of the tide. The same conditions hold with respect to the heads of piles imbedded in concrete, otherwise they will suffer from dry rot. When timber piles have to be cut off below the water surface to a given elevation special care is necessary as well as properly designed equipment. At Portland, Ore., 256 piles for the pivot pier of the Morrison Street bridge were cut off as close as pos- sible to the bed of the river. The rig designed for this pur- pose consisted of a carriage running on tracks supported by solid falsework. On top of this was placed a second carriage working across the first one. Suspended from the upper car- riage was a four-post steel frame built of angles and rods, which extended down to the required depth, and upon one corner carried the shaft to which a 5-foot circular saw was attached. The saw was operated by an electric motor. By careful op- eration the piles were cut off to a practically true level. At the Cambridge bridge over the Charles River the contract- ors used a heavily constructed machine to cut off foundation piles from 15 to 34 feet below the water surface. The scow sup- ported regular pile-driver leads 60 feet high. The saw is 42 inches in diameter and attached to a 4-inch hollow shaft, the bearings of which are supported by a spud or vertical timber 14 inches square which can be easily raised or lowered between the leads. The driving pulley occupies a fixed position arid engages a continuous spline or key attached to the shaft. The saw is operated at a speed of 400 to 500 revolutions per minute by means of a 40-HP. engine and a boiler of still larger capacity. The usual rate of cutting lo-inch spruce piles is 600 to 800 per day of 10 hours, with a maximum of 600 in a half day. Hori- zontal range sights were established and lines painted on the spud to determine the proper elevation of the saw as the tide changed. The Department of Docks and Ferries of New York City has an equipment especially designed and constructed for rapid and economical operation. It has cut 115 piles 14 inches in diameter in five hours, and a maximum of u piles in seven 60 DRIVING TIMBER PILES CHAP. II minutes. Its capacity is only limited by the ability of the crew to remove the butts. The special engine has a vertical shaft, double-acting cylinders, cranks set 180 degrees apart, and a 5-foot fly-wheel. The engine operates at 300 and the saw at 1000 revolutions per minute. The driving pulley has a key, engaging a seat cut 25 feet long in the 3! -inch saw shaft, which is 34 feet long and has its bearings bolted to a spud 52 feet long suspended between the leads. The saw avoids danger of bind- ing or jamming by cutting off a pile before it can be stopped by an ordinary obstacle. At Superior Entry, Wis., where foundation piles were cut off 2 feet above the bottom of the lake and 35 feet below low water, it was necessary to secure accurate cutting to grade to provide a uniform bearing for the timber cribs. The piles had been driven butt down without extension leads and a follower, and hence their heads projected above the water surface. In order to hold the saw at the exact elevation a guide bracket was attached to the saw shaft whose trolley with double- flanged wheels took bearing upon an 8 by 8-inch timber cap tem- porarily placed on the adjacent line of piles. To cut the last row the cap was placed on three piles driven for this purpose. Errors discovered by measuring the lengths of cut-off were limited to J inch. With good weather and quiet water the machine frequently cut 45 piles per hour, and occasionally a bent of 10 piles was cut in six minutes, the diameters at the cut being n to 1.9 inches. The crew consisted of seven men on the scow and five men who removed the parts cut off and placed the temporary caps in position. Allowing two hours to transfer and set up the machine, in addition to the actual time for cutting 230 piles, the work was done at an average cost of 13.75 cents per pile. For additional details and illustrations see Engineer- ing News, vol. 63, page 696, June 16, 1910. Where only a small number of piles have to be cut off or in locations where equipment like that previously described cannot be used on account of interference with structures, a simple device may be adopted and operated by hand. A rig- ging used on the Chicago and Northwestern Railway consists ART. 20 CUTTING OFF AND REMOVING PILES 6 1 of a triangular frame in which a saw 4 feet long is held between the ends of a bent iron bar 2 by J inches in section which forms the other two sides of the triangle, each 8 feet long. The frame is suspended at its apex from a stick fastened to the lower surface of the stringers of a pile trestle, and operated by hand near the water surface. Another device consists of a vertical frame formed by two timbers crossing each other like the letter X; at the crossing a pin is driven into the pile to be cut off; the saw is held between the lower ends of these timbers and the upper ends are braced by a horizontal timber bolted on just below the handles by means of which it is operated. At New Orleans a floating pneumatic caisson has been em- ployed to cut off the piles and to construct the timber grillage upon them for terminal piers in the harbor. The caisson is surmounted by a tank for water ballast, and is partly supported by two barges on its sides which are rigidly connected by a framework of Howe trusses. The lower edges of the working chamber were submerged from 15 to 18 feet. The construc- tion of the pneumatic caisson is described and illustrated in Engineering Record, vol. 54, page 125, Aug. 4, 1906. Piles are often used for temporary construction, such as to support falsework for the erection of a bridge, and have to be removed afterward. If its penetration is not too large a pile may be pulled by the pile line of a pile-driver or with the aid of block and tackle. To reduce the initial resistance the pile should be tapped by the pile-hammer before pulling it; or if the water-jet equipment is available it may be used to loosen the pile so that it can be easily removed. In tide water piles are sometimes fastened by a chain to a scow at low tide and thus pulled by a rising tide. If hard ground surrounds a pile it may be started by securely spiking a block of wood on each side and lifting it by the aid of two screw jacks. To remove the falsework piles of the Municipal bridge at St. Louis, a heavy timber tower formed of two bents battered in both directions and thoroughly braced was constructed on two barges. "The barges were placed about 10 feet apart in 62 DRIVING TIMBER PILES CHAP. II the clear so as to straddle the double line of piles forming a bent. Two sets of falls, composed of four-sheave steel blocks, reeved with .wire rope, were used and attached to the pile by means of chains. After the pile was lifted about 20 feet by the main falls, they were disconnected and the pile lifted clear by means of a ranner passing through a snatch block attached to the lower chord of the bridge span. From 30 to 45 piles per day of nine hours were pulled with this rig." In excavating for a foundation on reclaimed land in Kansas City it was necessary to pull some old piles which averaged 18 inches at the butt and 40 feet in length. The rig employed consisted of four triple and four double blocks in combination, the if inch hoisting line being run to a 25-H.P. hoisting en- gine. A water-jet from a 7-5-10 duplex pump was also used. An illustrated description of a sweep pile puller and of a tripod pile puller to be used on land or in very shallow water together with a statement of costs may be found in Engineer- ing News, vol. 49, page 338, April 16, 1903. Another method of removing piles as an obstruction in a water-way is to cut them off with dynamite. A hole about i^ inches in diameter is bored down along the axis of the pile with a ship auger and one or more sticks of dynamite inserted and exploded. In some cases 75-percent dynamite has made a clean cut. In one instance where a foreman was instructed to use 70-percent dynamite he used 40-percent dynamite as that was more easily obtainable. As a result the piles were merely shattered and not cut off. Later on using two | -pound sticks of 7o-percent and one of 4o-percent dynamite the largest timber pile was cut off and the top hurled over 50 feet into the air. The holes bored were 4! feet deep, and the cost was 55 cents per pile for labor, dynamite, fuse and cap. Dry sand may be used to fill the hole after inserting the dynamite, but does not need to be tamped. In a report on the removal of a temporary pile bridge to clear the river for floating ice and logs in the spring, 40-percent dynamite was stated to be effective. A ring was formed of telegraph wire which was large enough to slip over a pile, three ART. 21 CHEMICAL PRESERVATION 63 half sticks of dynamite were fastened equidistant on the wire with a percussion cap in each. A fuse was attached long enoagh to reach the bottom of the river when the wire was dropped over the pile, and was connected to a battery. All of the piles were cut off clean at the bottom, making this method the cheapest and quickest way to remove the obstructing piles. To remove a cluster of 13 large pine piles at Leavenworth, Kans., which had been sunk by a water-jet, and could not be palled on account of high water and floating ice, a 3 -gallon jug was placed in hot water and partly filled with hot sand so as to store as much heat as possible. The remaining space was filled with 30 pounds of dynamite. After arranging an exploder and battery, the jug was corked and lowered through a small opening in the center of the cluster and on reaching the sand bottom at a depth of 14 feet it was exploded, thus cutting off the piles at the level of the jug. ART. 21. CHEMICAL PRESERVATION Where the waters are infested by marine borers timber piles which are not chemically treated or mechanically protected have a very short period of usefulness. The average life of a timber pile on the Coasts of the South Atlantic, Gulf and Pa- cific states ranges from about eight months to two years. The development and activity of the borers is stimulated by high temperatures, and hence in some of the more northern coasts the average life may extend to three or more years. The mini- mum life of service is considerably shorter. For example, on the coast of California, where the average life of a pile is esti- mated at about two years, a pine pile 15 inches in diameter has been eaten off entirely within eight months; and on the Gulf Coast in Texas, where the average life ranges from one to one and one-half years, piles have had to be replaced in within 8 to 30 percent of that time. In very salty water and a hot season a pile 1 8 inches in diameter may be entirely honeycombed in three months. It is claimed that in the vicinity of Puget Sound, "a stick of timber, rough sawed, will last about eight 64 DRIVING TIMBER PILES CHAP. II months, a peeled pile will last a year, a pile with the bark on will last a year and a half, while a creosoted pile will last from 15 months to 15 years." The durability of creosoted timber piles depends upon several elements. The timber must be of good quality, free from decay, and should have sufficient sap wood to take the requisite amount of creosote oil. Timber may be of such high grade according to standard specifications for structural timber as to be unfit for chemical treatment. The creosote oil must be high grade, with the proper chemical constituents and physical properties, and the artificial seasoning and chem- ical treatment have to be conducted so as to secure the re- quired impregnation. The artificial seasoning and treatment of material is a con- tinuous operation and occupies from 24 to 36 hours. After the green material has been placed in the cylinder, the doors are closed and steam is admitted into the cylinder until the required steam pressure is indicated by the gage. This pressure is maintained until the wood is thoroughly sterilized and the sap liquefied; the steam pressure is then relieved and both air and the remaining steam are exhausted from the cylinder by means of a powerful vacuum pump. The temperature in the cylinder during this portion of the treatment is kept above the vaporization point corresponding to the degree of vacuum, so that the liquefied sap is vaporized and passes off from the timber to the vacuum pump. After all the moisture has been ex- hausted from the cylinder and the wood is perfectly dry, the cylinder is filled with oil from an elevated tank. The oil pres- sure pump is then started and kept in operation until the oil in the cylinder is under a specified pressure. This pressure is maintained until the established system of measurement in- dicates that the timber has been impregnated by the required amount of oil. After relieving the pressure the cylinder is opened and the timber withdrawn. When the treatment is carefully done and the full amount of impregnation with the best quality of creosote, or dead oil of coal tar, is secured, the timber will not be materially reduced ART. 21 CHEMICAL PRESERVATION 65 in strength and it will be protected effectively from the teredo navalis and the limnoria terebrans. At an inspection made in 1905 of over 4000 creosoted piles in the railroad pile trestle connecting Galveston Island with the mainland, which had been in service for 10 years, no traces of decay or deterioration could be found (see Railway Age Gazette, vol. 45, page 1270, Oct. 30, 1908). In 1904 and 1905 it became necessary to replace the truss spans of the bridges over East and West Pascagoula rivers, and of the Rigolets and Chef Menteur crossings on the New Orleans and Mobile Division of the Louisville and Nashville Railroad, by new girder bridges and truss swing spans to ac- commodate the heavier rolling stock. Examinations by bor- ing showed so many of the creosoted piles which had been driven in 1876-78 to be still perfectly sound that it was decided to use them in the new structures. Intermediate pile piers were driven and the old ones reinforced by additional piles, many of which were sunk by jetting. In the Chef Menteur bridge not a single pile was replaced on account of defects, and in the other three bridges the proportion was less than 10 percent. Of those rejected and replaced by new piles not one had been damaged by the teredo, nor had the outer ring penetrated by the creosote shown any signs of deterioration, nor was a single pile seriously decayed. The rejected piles showed an interior dry rot which indicated that they were not perfectly sound when treated. As the new cut-off level was several feet lower than the old, and below the extreme high- tide level, there was oppor- tunity for a thorough examination of each pile's condition (Engineering News, vol. 61, page 277, March n, 1909). These results are more favorable than can usually be expected. Ex- tended experience shows, however, that creosoting may be depended upon to protect timber piles in gulf waters from 10 to 15 years, after which it is generally necessary to furnish- ad- ditional protection by enclosing the piles with terra cotta, con- crete, or steel pipes as described in the next article. When this railroad was built in 1869-70, untreated piles and timber were used to build the trestles which cross numerous 5 66 DRIVING TIMBER PILES CHAP. II arms of the Mississippi Sound. Before trains had been run- ning six months an engine was precipitated into Biloxi Bay where the green piles had been eaten by the teredo. The unsatisfactory results obtained by mechanical protection of piles in other trestles whose piles were also attacked led to the decision in 1875 to rebuild with the creosoted piles referred to in the preceding paragraph. The piles were treated in a plant owned and controlled by the railroad company. Of 5093 piles driven in 1877-78 in 19 pile trestle bridges 617 were still in service in 1908 as they were originally driven; on account of settlement 868 were either redriven or were cut off to place framed bents upon them in the years 1904, 1906 or 1908; 95 were replaced from time to time, including 70 in three trestles which had been cut off by the teredo; while 3513 piles were protected mechanically in 1892-93 in five trestles where the action of the teredo was especially severe, and in which the 95 piles had been replaced. The limitations of space prevent the insertion of specifica- tions for the chemical preservation of piles, and a discussion of various methods of treatment, and of the tests to be applied to the oil, etc., and hence the student is referred to the reports of the Committee on Wood Preservation of the American Railway Engineering Association, to the Proceedings of the American Wood Preservers' Association, and to some investi- gations by the United States Forest Service. In these publi- cations the discussions of the subject are kept up to date, and the results of good practice are recorded. ART. 22. MECHANICAL PROTECTION The marine wood borers are almost invariably confined to salt water. The portion of the pile commonly attacked lies between mean tide level and about 4 feet below low tide. The extent of the ravages inside is not indicated by the position of the entrance hole. Experience has shown that any protec- tion applied to the surface of a pile must extend for a short dis- tance above the high-water line to an elevation below the mud ART. 22 MECHANICAL PROTECTION 6 7 line, due consideration being given to the probability of a change in the elevation of the mud line. Since chemical treatment must be applied to the entire length of the pile, and is accordingly quite expensive, various FIG. 22, a to j. methods of mechanical protection have been devised which are applied only to the vulnerable surface of the pile. Fig. 22 is reproduced from Circular 128 of the United States Forest Service entitled Preservation of Piling against Marine Wood Borers, by C. STOWELL SMITH 1908, to which reference is 68 DRIVING TIMBER PILES CHAP. II made for further information. Fig. 220, illustrates a pile with the bark left on it, which affords protection against marine borers provided it remains absolutely intact. Above the water line, however, it offers an excellent place for insects and fungi which hasten the destruction of the pile. In Fig. 226 an arti- ficial bark is provided consisting of thin plank with close joints, which partially eliminates the danger from insects and fungi. In Fig. 220 the exposed surface is completely covered by nails with large square heads as illustrated directly below the pile. Fig. 22^ shows a coating of various mixtures of coal tar, pitch, asphalt and other ingredients, protected by a cover- ing of burlap soaked in the same mixtures. Figs. 220 and / illustrate a metallic sheathing consisting of riveted thin sheets of copper, yellow metal, or zinc, which is held in place by copper nails. Fig. 22g illustrates a casing of cement mortar or concrete in contact with the timber pile. The results obtained and the cost depend largely upon the design of the forms and the method of handling the concrete. In one case the forms are made of sheet steel in sections 18 inches long, and split longi- tudinally into halves. Vertical angles are riveted to these halves so that they may be clamped together with rubber gaskets between them to make tight joints. The lower end of each section is slightly reduced in diameter and fits tightly into the slightly enlarged upper end of the next lower section. The mortar consists of one part cement to two parts of sand and by means of a double-end scuttle is placed by a diver into each section of the form before the next section is placed in posi- tion. The lowest section is placed in an excavation in -the bottom, the mortar is extended up to mean- tide level, and the remainder of the pile painted with a wash of neat cement. This method has produced good results although it is more expensive than some others. In another device which is patented the vertical edges of the semi-cylindrical sections of galvanized iron are covered with compressible material and are held together on each side by a sliding clamp with a ring at the top. In operation, the sec- ART. 22 MECHANICAL PROTECTION 69 tions are put together on top of each other near the head of the pile and gradually lowered until the form extends to the bottom and is pumped out. After the form is rilled and the concrete set, the chain of clamps is pulled up by the rings, thus releasing the halves of each section which are then hoisted by the attached ropes. Shells of concrete without reinforcement should not be placed around the piles until they have been long enough in place so that no further swelling will occur, otherwise it will crack the concrete. A different method which can only be used on new construc- tion consists in pre-molding a tapering reinforced-concrete shell long enough to reach from above high water to a short distance below the bottom, and lowering it over the pile by a hoisting line of the pile driver. The weight of the hammer, or light taps with it on a suitable cap, serve to sink the shell to its desired elevation. After wedging the shell in a concentric position about the pile head the bottom is scaled with rich concrete and after two or more days the enclosed water is pumped out and the space filled with lean concrete. This construction has been used where the wharf superstructure is of reinforced concrete and the column reinforcement is carried down into the upper end of the annular space between the pile and the shell and into which a richer mixture of concrete is placed. In the harbor at Seattle, Wash., a lot of piles were protected by a coating of cement mortar. After fastening a wrapper of poultry wire netting about each pile, the covering was deposited on the surface to a thickness of if to 2 inches by means of a cement gun. The gun was operated between tides and the 'gunite' set up so quickly that no trouble was experienced from the rising tide. A coating of gunite rein- forced by longitudinal rods and wire fabric has also been applied to new piles over a part of their length, before being driven, to serve as a mechanical protection against marine borers. In one case the coated lengths were less than 40 percent of the lengths of the piles. Another type of protection consists in slipping sections of vitrified clay pipe or of reinforced-concrete pipe over the heads DRIVING TIMBER PILES CHAP. II of piles and filling up the intervening space with sand. To protect piles in this manner after the cap or superstructures are in place requires the use of pipe divided longitudinally into halves. Fig. 22 k gives the dimensioned plans of a patented concrete pipe of this kind known as the lock-joint pipe. The two halves are placed around the pile and locked together by inserting wooden keys, soaked in hot tar, in the scarf joints. The pipes are molded in iron forms and after seasoning are placed in position from a raft moored alongside of the piles. Vitrified pipe is sometimes used in a similar manner, but as these halves have butt joints they must be wired together and it is difficult to get tight joints to hold the sand. Section C-D. Side Elevation. FIG. 22k. Section A-B. The use of natural bark, nails and burlap soaked in various compounds for protection is unsatisfactory since they are easily injured by floating debris or by impact from the waves. The artificial bark is attacked by the borers and must be re- placed before it becomes so weak as to be knocked off by drift- wood. The metallic sheathing is more expensive than chemical preservation for the entire length of piles and requires costly repairs. The sheathing of reinforced concrete has sufficient strength to resist the impact of driftwood, and the mesh rein- forcement usually holds it in place even if it should become cracked. Better results are obtained with concrete than with cement mortar. The mortar or concrete filled between the removable form and the pile mixes with the mud at the bottom ART. 23 COST OF PILE DRIVING 71 to such an extent that the lower part of the protection frequently breaks off. It is impossible to prevent this entirely without considerable expense. A more serious fault is the cracking and breaking off of the upper part of the encasement. Scour at the bottom exposes the unprotected wood. These defects are avoided by the use of pipe with a sand filling, as the pipe slips down and one or more sections can be added above when this is observed. If an intermediate section is broken attention is called to it by the sand running out. Repairs are easily made by removing the broken pieces, lower- ing the upper sections, adding a new section on top, and filling in the sand as before. This method of protection has been suc- cessfully used for pile trestles on some railroads since 1893. Reinforced-concrete pipe is superior to vitrified clay pipe on account of its greater resistance to accidental or other blows. In unusually exposed situations cast-iron pipes have been used. When creosoted piles have been standing in salt water so long as not to be immune any more from marine borers, they may be protected mechanically to prolong their service. Figs. 221 andy illustrate the protection of piles by boring holes into them and filling the holes with a poisonous substance. This treatment has been discontinued. For additional details the student is directed to the references on this subject in Chap. XIX. See also the combination piles which are described in Art. 47. ART. 23. COST OF PILE DRIVING So many elements enter into the cost of driving piles that it is difficult to give costs that are of real value in estimating unless the record is more complete than is customary in practice. Some statements of the cost of driving piles for the founda- tions of buildings, trestles, docks, bridge piers and abutments, are given in handbooks of cost data and in engineering period- icals, but they can only be used with extreme caution since the local conditions and the methods of doing the work are usually not given in sufficient detail, if they are given at all. 72 DRIVING TIMBER PILES CHAP. II The time and cost depend upon whether a steam-hammer or a drop-hammer is employed; whether a suitable cap is used to protect the pile head and guide its movement, or merely a pile ring; whether the water-jet is employed to sink the piles, or to aid the hammer in driving; whether the foot must be pro- tected by a shoe; whether the piles are driven below the water surface by means of a follower; whether extension leads are used; whether the pile-driver must be moved over the timber bracing of an excavation, or directly on the surface of the ground; whether the piles are creosoted or not, long or short, of hard or soft timber; driven with the butt or tip down, vertically or on a batter. The cost also depends upon the type of pile-driver, the magnitude of the job, and the organization and experience of the crew; but especially upon the sub-surface conditions, whether the driving is easy or hard, and whether special pre- cautions are needed to avoid overdriving. The following is a brief summary of driving piles for 41 trestle bridges averaging 101 feet in length on the Omaha and St. Louis Railway in the late fall of 1889. In 46 days 1267 piles were driven ranging in length from 14 to 52 feet, the average being 24 feet. The penetration varied from 10 to 18 feet, or an average of 14 feet. The working time each day with the leads of the track driver in position averaged six hours and 32 minutes, and the time to raise and lower the leads, 14 minutes. The average time required to drive a pile was 15 minutes and to raise or to lower the leads, 2.5 minutes. The average cost per linear foot of the piles was 15 cents, and the average cost per pile in place was $5.14. The cost of labor for the 46 days was $1683.72; and for fuel and supplies $262.28, or 15.6 percent of that for the labor only. The following gives an analysis of the cost per pile for the 4383 piles in place which support the timber grillage and masonry of Fort Montgomery on Lake Champlain, the piles being driven in 1844-46: Net cost for machinery, $1.22; cost of piles, $1.40; driving, 40 cents; measuring, hauling, securing for winter and sharpening, 18 cents; pile rings, 10 cents; cutting off piles to receive grillage, n cents; net cost for other machin- ART. 23 COST OF PILE DRIVING 73 ery than pile-drivers, 4 cents; contingent services and contin- gencies for this part of the construction, 43 cents; total, $3.88. Such an analysis in still valuable although prices have changed. In the spring of 1902, on the Chicago and Eastern Indiana Railway, 436 piles were driven varying in length from 14 to 42 feet, aggregating 10 535 linear feet at a total cost for driving of $466.35 or of 4.4 cents per linear foot. In 1906, on the Chicago, Milwaukee, and St. Paul Railway, the average cost of driving foundation piles on 150 jobs was $2.45 per pile. In different classes of work the cost ranged from $0.75 to $7.15; for piers and abutments, $3.84. This variation shows the effect of differences in local conditions including the size of the job. In building the railroad trestle to the Sandy Hook Proving Ground, the cost of which was about $10.60 per linear foot of track for a length of 4494 feet, the cost of driving creosoted piles was about 15 cents per linear foot. Three land and two water drivers were employed with drop-hammers weighing 1800 to 3000 pounds. The averages for several hundred piles observed were: Fall, 14 feet; number of blows, 175; time, 20 minutes; penetration per blow, i inch. The minimum total penetration was 15 feet, and when the penetration was over 20 feet, the water-jet process was used. The piles were driven during the last quarter of 1904. In the construction of the viaduct approaches of the Southern Railway over Chattahoochee River, completed in 1907, the cost for the piles under the viaduct footings was found to be as follows: 13 750 linear feet of creosoted piles, $3812.50; pile shoes, spikes and rings, $352.33; coal, oil, waste, rent of driver, etc., $758. 72; labor for pile driving, $3186.31; labor for sharpen- ing piles, $83.70; making the total cost per linear foot 59.6 cents, which includes 27.7 cents for the cost of the creosoted piles. The cost 01 freight and of train service is included in the items for materials, etc. "The high cost of pile driving was due to the fact that one row of pedestals came beneath the old trestle and thus required considerable manipulation of the driver and loss of time in working around the bents. The 74 DRIVING TIMBER PILES CHAP. II actual labor of driving piles for the outside row of pedestals was only a little over 9 cents per linear foot of piles in leads." In some estimates of cost, the cost of driving is taken from 65 to 100 percent of the cost of untreated piles. CHAPTER III BEARING POWER OF PILES ART. 24. Pif,ES ACTING AS COLUMNS When piles on land project some distance above the surface they are usually held in position laterally by diagonal bracing whenever there is sufficient room for it so that the pile is not subject to direct bending. An example of this construction oc- curs in pile trestle bents. If the vertical distance between points of connection for the bracing is large, the pile must be designed to provide for column action. Piles driven in water are frequently not braced and hence it is essential to design them with regard to their strength as long columns since this may be the limiting condition, rather than the bearing power, of the ground penetrated. If the sub- structure placed upon the piles is not held laterally except by vertical piles, then the piles act like columns with the upper end practically free and the lower end fixed at some elevation which depends upon the material penetrated. To determine this elevation is the principal problem. Usually, it cannot be taken at the bed of the river or lake, since the material there is soft or yielding. Even if the bottom consists of firm gravel and sand the required elevation is one or more feet below its surface. When the material is mud or silt grading slowly into more compact material the upper strata give relatively little resistance to the lateral deflection of the pile. That the re- sistance of such material is greater than may be naturally in- ferred from its consistency is proven by the fact that at New York piles frequently break off in case of trouble at approxi- mately the mud line of North River silt. It has been proposed (see Eng. News, vol. 60, page 18, July 2, 1908) as a reasonable assumption to consider the lower third of the softer strata, which overlie the hard stratum, to be effect- 75 76 BEARING POWER OF PILES CHAP. Ill ive in lateral resistance and to ignore that of the upper two- thirds. This makes the assumed free length of the pile column equal to the distance from the pile cap to the river bottom plus two-thirds of the penetration in distinctly soft ground. The strength of such a column is equivalent to that of a column of double the length with both ends round. It must also be re- membered that the strength of a group of pile columns has only the strength of one column multiplied by their number, since there is no provision made to resist their movement longi- tudinally with respect to one another. In this respect they are analogous to composite posts. See JACOBY'S Structural De- tails, Arts. 49 and 50. It frequently happens that bearing piles transmit nearly or all of their vertical load to a hard substratum, overlaid by softer material, which will yield laterally under pressure. In all such cases the piles should be designed as columns. If the foot of a pile bears on rock and the overlying material is not able to resist its lateral displacement it may be necessary to drill shallow holes into the rock. In shelving rock this method of preventing displacement is of especial importance. Sometimes riprap is used for this purpose, but its uneven weight upon the material overlying the rock has been known to cause sliding with disastrous results. The section area of the post should be large enough to pro- vide adequate bearing area and the taper of the timber pile should be as small as possible. In some cases it may be desir- able to place the butt at the foot of the pile. The foot should not be pointed unless it is necessary to secure penetration for a short distance into material like hard-pan, to prevent its lateral displacement. The greatest care should be taken in driving piles which are expected to rest in bed rock or penetrate slightly into hard- pan, in order to prevent shattering or crushing the feet of piles, otherwise their supporting power may be seriously impaired. When the overlying material is muck or silt, or soft, yielding material it is preferable to omit the resistance, if any, due to skin friction in designing the pile. ART. 25 THE GOODRICH FORMULA 77 The conditions described in the preceding paragraphs often apply to falsework piles used to erect bridges. In any case it is desirable to brace the piles effectively by means of sway bracing, but in rivers which carry a large amount of driftwood during flood seasons, or large masses of floating ice, it is essential to provide the piles with carefully designed sway bracing and to add lateral bracing. Experience amply justifies special cau- tion in design and construction for this purpose. The unit-stress in the outer fiber which may safely be allowed depends upon the species of wood as for ordinary wooden columns, but some reduction is usually made on account of the piles being water soaked. Sometimes its value is reduced further on account of a lower grade of timber being employed having more knots and other defects than are permitted by specifications for structural timber. When no account is taken of the species of wood, specifications sometimes give the working unit-stress in the outer fiber as 600 pounds per square inch, reduced for pile columns to 600 (i l/6od), in which / is the unsupported length in inches and d the diameter at the middle of the unsupported length (see Art. 38.) When piles act as columns or are subject to bending moment especial care should be taken to drive them accurately in posi- tion; for if they have to be forced laterally into line account must be taken of the initial flexural stress thus produced. In case it is necessary to deposit riprap to give lateral support to piles or to prevent scour it is better practice to deposit the riprap first and drive the piles through it, because filling in afterward has been known to bring such great lateral pressure upon piles as to cause their failure by bending. ART. 25. THE GOODRICH FORMULA The most elaborate attempt which has been made to deduce a general theoretical formula for the final resistance of a timber pile when subjected to the blow of a drop-hammer is that of ERNEST P. GOODRICH, the results of which are contained in a paper entitled, The Supporting Power of Piles, published in 78 BEARING POWER OF PILES CHAP. Ill Trans. Am. C. E., vol. 48, page 180, Aug., 1902. The phe- nomena of pile driving which are taken into account mathemat- ically in deducing the formula, in accordance with the princi- ples of physics and mechanics, are those described in the fifth paragraph of Art. 5. It is then shown how fourteen other pile-driving formulas may be derived from this general one, by stating the various assump- tions with respect to its elements or terms which are made in each case. That some of the assumptions are seriously in error is proved conclusively by the wide variations in results obtained by the application of the formulas. The true values of some of the terms con be determined only by experimental investigation. The general formula consists of twenty-five terms besides several numerical coefficients and exponents, and is therefore too complicated and unwieldy for practical use. For this pur- pose, a number of terms were evaluated with the aid of experi- ments conducted under proper conditions for pile driving in good practice. One of these is referred to in the sixth para- graph of Art. 5, and another in the third paragraph of Art. 28. By substituting the values thus obtained, and inserting suit- able numerical values for the dimensions and weights of the pile and hammer, an expression was derived giving a direct relation between the pressure on the head of the pile when it comes to rest, and the penetration. From this relation, it was found that for an allowance of 3 percent error in the observation (which, for example, is a variation of f inch for a penetration of 4 inches), the corresponding error involved in the pressure on the pile is 3.1 percent when the penetration is 4 inches and 23 percent when the penetration is i inch. Hence any terms in the formula which involve a change of less than 3 percent in the pressure on the pile may be advantageously omitted, and no penetration much less than i inch can be trusted to give the corresponding pressure within a reasonable per- centage of error. An extreme variation in the elastic shortening of the hammer is found to produce a change of only 0.07 percent in the pressure on the pile, and hence the four terms relating to the deformation ART. 25 THE GOODRICH FORMULA 79 are omitted. The difference between the elastic shortening of a long soft-wood pile and that of a short hard- wood pile may cause an extreme variation in the pressure on the head of the pile of about 25 percent, and hence this term is retained. After introducing the experimental values, and making the other changes mentioned, the formula for- the final pressure on the head of the pile, as it comes to rest, is reduced to i;'J (i) in which p denotes the penetration of the pile under a single blow, C the elastic shortening of the pile due to longitudinal compression, W w the weight of the hammer, h the fall of the hammer, R h the ratio of the weight of the hammer to the com- bined weight of hammer, pile and earth moved in connection with the pile, and v r the ratio of the work done in crushing and heating the head of the pile, to the total work done by the hammer exclusive of losses before it strikes the pile. The coefficient 1.15 in this expression relates to the velocity of the hammer, it being found by experiment that when the hammer is operated in the customary manner with the line from the engine attached to it, v 2 =i.i$ gh, instead of v 2 = igh for a free fall (see Art. 28). This loss of energy may be computed by formula (i) from two sets of observations on the same pile for falls of the hammer which do not differ widely, provided it be assumed that both the total pressure or resistance of the pile and the loss of energy are the same in the two cases. From observations made on a number of piles GOODRICH found that the loss of energy v' rarely exceeded 5 percent and in most cases was nearly 2 per- cent for piles that were sound and well driven. From a given numerical example in which ^ = 3000 pounds and A=i8o inches, the value of F is found by computation to be 134 400 pounds when z/ = o, and 124 800 pounds when z/ = 5 percent, or a reduction of about 7 percent. Without such observation- and computations, it is absolutely impossible to form any reas sonable judgment of the value of v', or of its effect. To eliminate the value of C in formula (i), the same data 80 BEARING POWER OF PILES CHAP. Ill are used and the values of if computed from the formula but with C omitted. The value V thus obtained for each pile in- cludes losses due to the compression of the pile, as well as to heating and crushing its head. The values thus found vary greatly but average less than 10 percent, even with some very badly broomed piles. By plotting the percentage of energy losses due to all causes for the different falls of the hammer used in the experiments, the curve shows that the loss of energy increases with the height of the fall. The author of the for- mula states, however, that his observations tend to show that the terms involving the compression of the pile can be neglected and proper compensation be made by taking if as 2 percent in the formula, provided the piles are sound and well driven; but the formula is liable to be in error about 20 percent, if the piles are poorly driven and the fall is much less than 15 feet. By making these further substitutions, the formula becomes F = o.$i$W h h(R w o.o2)/p. The term R w involves the un- knowable quantity W g or the weight of the ground moved in connection with the pile. It was estimated that for piles 700 inches long and weighing 2000 pounds, W g should not be taken less than 1000 pounds, this estimate being based on observa- tions of minature. piles driven in a box of sand with glass sides, and of the ground found clinging to actual piles withdrawn from the earth. In special cases, such an assumption may in- volve an error of 33 percent and, if combined with other cumu- lative errors, the final value of F given by the formula may be 50 percent in error. The opinion was expressed by its author, however, that if a sound well-driven pile weighing somewhat less than the hammer be tested by a fall of about 15 feet and shows a penetration of about i inch, the formula in its final shape will give the supporting power of the pile immediately, after driving with a probable error of considerably less than 10 percent. Inserting the value of ^ = 0.5, the formula finally reduces to the expression/? = 0.2 76 Whh/p, or by chang- ing the height of the fall from inches to feet, it becomes ART. 25 THE GOODRICH FORMULA 8 1 in which F denotes the ultimate bearing power in pounds imme- diately after driving; WH the weight of the drop-hammer in pounds; H the restrained height of fall in feet, the line being fastened to the hammer; and p the final penetration per blow, expressed in inches. GOODRICH recommends "that in making tests for the sup- porting power of piles, a standard fall of hammer be adopted and specified for making all determinations, and that 15 feet be adopted for the following reason: (a) This height of fall produces good observable penetration with any but very light hammers, or for piles in extremely compact soils; (b) the pene- tration is not excessive for any but very heavy hammers or for piles in very light soils; (c) all frames are large enough to afford this fall; (d) the lost energy is comparatively small; (e) nearly all formulas give nearly the same values through this region of variation; (f) the writer's formula is especially built for this fall." After recommending a specification relating to the weight of hammer, height of fall and final penetration, he adds "that designers can more easily determine the necessary pile spacing and the most desirable factor of safety to be used in individual cases, and make the pile-drivers follow a standard specification, than otherwise." The description in this article is given at such length because it properly emphasizes certain phenomena of pile driving which are often not fully appreciated, and in order that every one who uses the Goodrich formula may know all the elements in- volved in its deductions, the values determined by experiment, the methods of determining certain approximations, the practical basis for certain assumptions, the relative effect of different elements upon the bearing power, and the general limitations under which it may be used properly as recommended by its author. If, for example, someone should pay no heed to these limitations, and proceed to substitute a value of zero for the penetration p, an infinite value would be obtained for the ulti- mate bearing power F, which is manifestly absurd. See the discussion on the final penetration per blow in Art. 29. It must not be forgotten in this connection that all formulas 6 82 BEARING POWER OF PILES CHAP. Ill for bearing power are deduced under the fundamental hypo- thesis that the material of which the pile is composed can trans- mit a load of this magnitude through its head and at least a part of its length. Therefore, the strength of the pile under longitudinal compression invariably limits the load which it can support, if this value is less than that given by the formula. ART. 26. ENGINEERING NEWS FORMULA The Engineering News formula for pile driving was developed by A. M. WELLINGTON in an approximate and simple manner as compared with that of GOODRICH, by considering the subject more from a purely practical standpoint. The work done by the hammer having a weight W, in falling freely through the height, h, is Wh. The useful work done upon the pile is the prod- uct of its resistance multiplied by its penetration under the last blow. The ratio of these two products measures the effi- ciency of the hammer blow, and depends likewise upon the pro- portion of work wasted. The penetration was called the 'set' by WELLINGTON and hence designated by 5. Practically, the energy stored in the hammer during its fall may be absorbed in four different ways: (a) In brooming and mashing the pile either visibly at the head or invisibly at the foot or at some other part of its length; (b) in bouncing, and thus striking two or more light blows instead of one heavy one; (c) in compressing elastically the material of the pile and ham- mer; and (d) in causing the pile to penetrate against the resist- ance of the surrounding earth. As indicated in Art. n brooming constitutes a serious loss of useful work whenever it occurs both directly in crushing the fibers of the wood and in cushioning the blow. Brooming at the foot does not diminish the effect of the blow on the pile head but dissipates it more or less without useful result. It can frequently be detected by a skilled operator by a change in the behavior of hammer and pile, but not always. Bounc- ing of the hammer invariably means a waste of energy, either because the pile has struck a solid obstacle like a boulder, which is soon detected, or because the hammer is too light, or ART. 26 ENGINEERING NEWS FORMULA 83 the velocity is too great, or both, to get the pile in motion before it reacts elastically with more force than the hammer is exerting to push it down. A very slight rebound is a necessary accompaniment of good pile driving, due to the elasticity of the pile. Both brooming and bouncing of the hammer cannot be pro- vided for by any formula to determine the bearing power of a pile. When the pile is nearly home and the average penetra- tion is to be observed for this purpose, the broomed top should be sawed off to enable a fresh surface of unbroken fibers to receive the blow. Bouncing is remedied either by providing a heavier hammer or by diminishing the fall. The, elastic compression of the pile and its effect upon the bearing power was fully treated in the preceding article. In the formula now under consideration it is provided for in the margin of safety. At the instant when the hammer strikes the pile the resist- ance of the pile and earth is relatively very large, but as the pile acquires velocity the resistance rapidly diminishes and then continues at some more or less uniform value until the motion of the pile ceases. The reasons for the high initial resistance are the grip of the earth upon the surface of the pile, due to its settling against it during the interval since the last blow, and the excess in the coefficient of friction at rest or at a very low velocity over that at a relatively high velocity. The approximate measure of the static bearing power of the pile immediately after driving is the comparatively uniform frictional resistance to penetration after the high initial resist- ance is overcome. The initial resistance is more difficult to overcome, since the impact of the hammer occurs so suddenly and it requires time for the stress to be transmitted through the fibers of the pile. These relations are indicated graphically in Fig. 26 a. The initial ordinate OY represents the initial resistance and the final ordinate XB represents the final resistance as the pile comes to rest. The area of the taller rectangle represents the work done by the hammer, and its altitude is the mean resistance Wh/s. The area enclosed by the full lines has the 84 BEARING POWER OF PILES CHAP. Ill some area Wh as the rectangle, provided no energy is wasted, and its ordinate X B represents the bearing power of the pile. The probable ultimate bearing power is accordingly equal to Wh/(s-\-c), the term c being some empirical value to be added to the penetration. It is thus seen that to overcome the large initial resistance is equivalent to causing some extra penetration. The value of c is doubtless as variable as the character of the ground in which piles are driven but it was taken by WELLINGTON as i inch, a value which he claimed to be "based on extensive obser- vations of the behavior of piles in driving, and on many years' experiment and study as to the general laws of friction." This value means practically that the initial resistance is about equivalent to an extra inch of penetration after the pile is set in motion. For convenience of observation the fall is expressed in feet and denoted by H, and the penetration in inches, FIG. 26a. whence the expression becomes i2WH/(s-\-i}. A so-called factor of safety of 6 was then as- sumed since it was found to give loads as large as were custo- mary in practice based on precedent. The author made a statement four years afterward that he had discovered no cases where the factor 6 had proved insufficient, either ex- perimentally or in service; and that since it will in no case require piles to be driven closer together than is customary and reasonable he should advise adhering to it in all cases unless under some very exceptional circumstances, where the engineer may see that he has special cause and justification for taking more chances. Accordingly, the Engineering News formula for pile driving with a drop-hammer is , f } ^WH Safe load= rr H-i VpL Wh s+c ART. 27 WEIGHT AND FALL OF DROP HAMMER 85 in which W denotes the weight of the drop-hammer in pounds, H the height of fall in feet, provided the hammer falls freely, and ^ the average penetration in inches under the last few blows. For a discussion of the limitations of W, H, and s, see Arts. 27, 28 and 29. This formula was first published in Engineering News, vol. 20, page 511, Dec. 29, 1888. It has been used more extensively in American practice than all other formulas and at present (1914) is widely adopted as standard. The formula is modified for use with steam-hammers by substituting o.i in place of the constant i in the denominator, as explained in Art. 30. ART. 27. WEIGHT AND FALL OF DROP-HAMMER In 1897 a Committee of the American Association of Rail- way Superintendents of Bridges and Buildings recommended 3300 pounds as the best weight of drop-hammer for general railroad service. In hard driving, experience has frequently proved that piles can be successfully driven with a 4ooo-pound hammer when a 2oco-pound hammer fails to do so. In general, the hammer must be heavy enough to put the pile in motion after allowing the pile to absorb its share of the energy developed in the fall. The weight of the hammer should never be less than the weight of the pile and should preferably weigh about twice as much. In one example of piles failing to sustain without settlement half the load they were designed to carry, the hammer used in driving was only 56 percent of the weight of the pile. In the best practice the height of fall for a drop-hammer is limited to about 20 feet. While a fall of 5 feet or even less may be used in soft ground, its value will most frequently range between 10 and 15 feet. If occasionally a fall exceeding 20 feet be used to penetrate a hard stratum, it should not be continued long on the same pile for fear of damag- ing it. A low fall, or short drop, has the additional advantage of securing a more rapid succession of blows, which in most kinds of earth is advantageous in securing penetration, and thus economizing time. If W denote the weight of the hammer in pounds, and H 86 BEARING POWER OF PILES CHAP. Ill the height of its fall in feet, WE will represent closely the work done by the hammer in a single blow for free fall. It is con- sidered that 30000 foot-pounds is about as small a value for WH as it is economical to use in work of any magnitude and that 50000 foot-pounds should rarely be exceeded on account of the limited strength of timber. The only drawback that may be alleged against a heavy hammer is the increased capacity required for the hoisting engine and equipment, but in work of any magnitude it is economical to provide the equipment required to do the work expeditiously and well. If the fall is too low, then nearly all of the energy developed is absorbed by the pile without produc- ing motion; and on the other hand, if the fall is too high, its, effect is analogous to that of a bullet, too large a percentage of the energy being expended in crushing the fibers in the head of the pile, or possibly damaging it elsewhere. The resistance of the pile varies greatly from the time it is struck by the hammer until its motion stops. The mass of the pile and the higher static friction cause a high resistance at the start, while afterward the kinetic energy of the pile and the decreased friction in motion cause a much smaller resist- ance. On this account a heavy hammer with a low fall is more effective in securing the penetration of a pile than a light hammer with a high fall and its accompanying high velocity. In the latter case there is not sufficient time allowed to transmit the stress through the fibers of the pile and hence too large a percentage of the energy must be expended at its head with consequent destructive effect. From another point of view, when the pile is ready to give out the energy received from the hammer, to produce further penetration at the foot, it is necessary to have a weight on the head to serve as an additional reaction; and a heavy hammer performs this function better than a light one. The facts given above indicate that the height of fall should be adjusted to the resilience of the timber composing the pile as well as to some of its other qualities, including the strength in tension across the fiber, which measures resistance to split- ART. 28 THE RESTRAINED FALL 87 ting. This fact was recognized practically when the com- mittee, referred to at the beginning of this article, recommended that the fall should not exceed 1 2 feet for cedar piles, and 20 feet for oak piles. It materially facilitates the progress of the work if a prelimi- nary test is made to discover the best height of fall for the con- ditions existing at the given site. In one instance where it was found that the penetration was not increased by a higher fall, the average for several hundred piles observed was: fall, 14 feet; number of blows, 175; time, 20 minutes; penetration per blow, i inch. When the rope is fastened to a drop-hammer and the falling hammer must pull the rope with it and thereby also revolve the drum of the hoisting engine } a considerable correction must be applied to the height of the restrained fall to reduce it to an equivalent free fall. This subject is discussed in the next article. It is the universal practice to make no allowance for the effect of wind pressure on the hammer, nor for the friction between hammer and guides when the leads are vertical and in good order. ART. 28. THE RESTRAINED FALL In most of the formulas for the bearing power of piles it is assumed that the drop-hammer falls freely. When the hammer is operated by keeping the line fastened to it so that the hammer in descending must overhaul the line from the drum, it is neces- sary to apply a correction to the height of fall to reduce it to an equivalent free fall. The following table gives the penetrations of three piles, driven by different pile-drivers under both conditions of free and restrained fall, as reported by G. B. NICHOLSON. See Trans. Am. Soc. C. E., vol. 27, page 172, Aug., 1892. Penetration in feet Weight of Height Restrained Free Pile No. hammer of fall fall fall 1 2470 Ibs. 40 ft. 0.5 0.7 2 2750 Ibs. 45 ft. 0.7 0.9 3 2500 Ibs. 46 ft. 0.32 0.4 88 BEARING POWER OF PILES CHAP. Ill On applying the Engineering News formula for the bearing power of piles driven with a drop-hammer, it is found that the restrained falls are equivalent to the following percentages of the corresponding free falls: 74.5, 79.6, and 83.4; the average being 79.2. If the Goodrich formula is applied, in which the bearing power is inversely proportional to the penetration, pro- vided penetrations less then J and preferably less than J inch be excluded, the corresponding percentages are 71.4, 77-8. and 80.0; the average being 76.4. From these data GOODRICH computed the coefficients of the final velocity of the hammer in each case to be 1.02 and 1.28, instead of 2 in the well-known formula v 2 = igh. Their average is 1.15 which agrees with that obtained by him in some exper- iments in which the velocity of the hammer was obtained di- rectly, the time on the recording device being measured by a tuning fork chronograph (see Trans. Am. Soc. C. E., vol. 48, page 202, Aug., 1902). Instances have been observed with new equipment, in which the conditions were unfavorable, where the required correction required for restrained fall was found to average 50 percent. When it is known how readily the resistance of the rope and drum may be increased by the operator of the hoisting drum, and which it is difficult to guard against by inspection, it is best to disconnect the rope from the hammer and to employ nippers to secure a free fall when testing the penetration for bearing power. ART. 29. FINAL PENETRATION PER BLOW Formulas for the bearing power of piles are not designed for the case where a pile is driven through soft yielding material, like silt and wet clay, to a hard stratum of sand, gravel, hard- pan or rock, for then it acts like a column and must be designed accordingly. Column action also exists where a pile is driven through strata of varying consistency and the lower part of the pile penetrates a stratum which is more compact than those which lie above it. In this case the lower end may be almost ART. 29 FINAL PENETRATION PER BLOW 89 completely restrained while the upper end may be restrained but slightly. Formulas for bearing power are intended primarily for the general case in which the support of a pile is due to frictional resistance between the surface of the pile and the surrounding earth. Extended experience has proved, however, that their use may properly be extended to a pile which receives some additional resistance in bearing at its foot. The value of the penetration to use in the formula is gen- erally taken as the mean for the last five or ten blows. When the drop-hammer is employed no value less than J inch should be considered in any case for timber piles, and usually not less than J inch for hard-wood piles, nor less than i inch for soft-wood piles. When the penetration is smaller than the values just given it is highly probable that the true penetration of the foot of the pile is not equal to the movement of the head of the pile where the measurement must necessarily be made. Even the average penetration under the last five blows is not a fair measure of the bearing power of the pile at that time, unless the penetration has been either uniform for a number of blows, or decreasing at an approximately uniform rate, and that it would continue in the same manner for a short distance farther. The last condition mentioned should be known from previous explorations of the ground. It is pre- supposed that the head of the pile is sound, that the weight of the hammer and height of fall conform to the limitations indicated in Art. 27, arid that the operation of driving is not interrupted materially. In practice a penetration of less than f inch should be regarded with far more suspicion than is frequently accorded to it. An apparent penetration below this limit is more likely to be merely a sinking of the head due to crushing the foot or crippling the pile in some other part of its length. In hard driving experienced inspectors are often misled when they do not know the character of the different strata from previous explorations. Whenever the observed penetrations pO BEARING POWER OF PILES CHAP. Ill are quite irregular caution is especially necessary. It is by no means difficult to get an apparent penetration with the foot on solid rock for a spruce pile under a 2ooo-pound drop-ham- mer by continued driving. Damage due to overdriving is discussed at length in Art. 18. The value of the final penetration per blow depends upon the nature of the ground, the size of the pile, the smoothness of its surface, its taper, the form and diameter of the tip, and the total penetration, as well as upon the weight and fall of the hammer and some other minor factors, but extensive tests have shown that the final penetration under a given energy of the hammer is practically as good in determining the bearing power of the pile as a test by actual loading. Whenever a follower has to be used on top of a pile as it is driven home and it is desired to compute its bearing power, it is necessary to apply a correction to the observed average penetration. For this purpose some bests should be made under fairly comparable conditions when each pile may be driven alternately with and without the follower. ART. 30. FORMULA FOR STEAM-HAMMER It is observed that the dynamic effect of the short quick blows of a steam-hammer exceeds that of the slower blows and higher falls of a drop-hammer more than a mere comparison of the relative energy developed seems to warrant. This is readily seen if a 3000-pound drop-hammer is operated with a fall equal to that of a steam-hammer having the same weight of moving parts. The greater efficiency of the steam-hammer is due primarily to the rapidity of its blows, which does not permit the material penetrated to settle back against the pile after being shaken up, or pushed away. As indicated in Art. 32, ex- perience shows that 12 to 24 hours rest requires the number of blows per foot of penetration to be increased from 6- to 10- fold. Another effect of rapid blows is that before the pile comes fully to rest the next blow is delivered, hence the varia- tion in resistance is not so marked as that illustrated in Fig. ART. 30 FORMULA FOR STEAM-HAMMER 91 26 a. Accordingly, the value of the constant in the denominator of the Engineering News formula is dependent chiefly upon the magnitude of the time interval between blows. When, there- fore the method of pile driving is so radically changed as by substituting a steam-hammer for a drop-hammer, the constant must be reduced materially. WELLINGTON adopted the value of o.i. The Engineering News formula for pile driving with a steam-hammer is therefore 2WH Safe load = the significations of the terms being the same as those given in the sixth paragraph of Art. 26. When its author published this formula he expressed the opinion that it was probably too conservative, but that the experimental data on which to base a closer estimate were not available. Since that time the subject seems to have received but little experimental study by engineers. However, as the result of some observations in pile-driving practice and of special tests, the engineering department of the Norfolk and Western Railroad has adopted the constant of 0.3 instead of o.i. At the Brooklyn Navy Yard two test piles were driven under probably as nearly equal conditions of the ground penetrated as may be possible in practice. One was driven by a steam- hammer with moving parts of 3 tons and a stroke of 3 feet, and the penetration per blow decreased steadily from 4 inches to J inch. The pile was 20 and 14 inches in diameter at the butt and tip respectively and was driven to a total penetration of 43 feet in seven minutes by 373 blows. The other was driven by a i-ton drop-hammer which started with a fall of ^ foot and gradually increased to 35 feet as the pile went down in the leads. It was driven to a total penetration of 45 feet with 735 blows in 166 minutes. The final penetration was ij inches. This pile had an iron shoe while the one driven by steam-ham- mer had none. According to the Engineering News formulas the corresponding safe loads are 30 and 31.1 tons. Another pile with a penetration of 33 feet driven by the drop-hammer with a 92 BEARING POWER OF PILES CHAP. Ill fall of 30 feet developed an ultimate resistance of 125 tons. Such close agreement is, however, by no means common between the results of driving by both types of hammer, since the effect of rest on the bearing power varies in different material and between slow and rapid driving. Whether it is possible to make any close comparison between the effect of driving by steam- and drop-hammers in all kinds of earth is an open question, since so few observations have been made with reference to this problem. ART. 31. TABLES AND DIAGRAMS A convenient table for the safe load on piles, for a given weight of drop-hammer, may be prepared by placing the fall in feet at the top of a column, and the penetration in inches at the left end of a line. The falls may include each foot between suitable limits, while the penetrations begin with } inch and vary by quarter inches at first, and then by half inches, to the desired limit. The loads may be expressed in units of i kip = 1000 pounds, or in tons as preferred, and then inserted in the table within practical limits. In practice diagrams have been found more convenient than tables and a number of different forms have been devised. In one diagram the fall is laid off as an abscissa, and the safe load as an ordinate, the value of each penetration being marked on a line connecting the proper points of intersection of vertical and horizontal coordinates. For the Engineering News formula, or GOODRICH'S formula, these lines are straight. A very simple one for use with a given weight of hammer and a standard height of fall may be constructed by laying off the average penetration as an abscissa and the safe load as an ordi- nate. A curve is then drawn connecting the proper points of intersection of horizontal and vertical coordinates. The dia- gram shows at a glance what penetration is required for a given safe load, or vice versa. For a steam-hammer the penetration is preferably expressed by the number of blows per inch. When driving test piles for foundations on the New York Barge Canal rectangular diagrams were used based on the Engineering News ART. 31 TABLES AND DIAGRAMS 93 formulas for drop-and steam-hammers respectively. On the first one the fall of the hammer is laid off along the bottom from zero at the right end to 50 feet at the left. The safe load is laid off along the top from zero at the left end to 100 ooo pounds at the right. The values of 2WH are laid off on the left side from zero at the bottom to 168 ooo foot-pounds at the top. A series of lines radiating from the lower right corner are drawn for weights of hammer from 1000 to 5200 pounds. Another series h s Drop of Hammer, Feet. o ro 4. oo o o-jootoo f3<5?ui 4- X "v ^5 ^ ^ N, x .^* s ! f; \ X, ^ S ^s x k ^ *, \, . v - ^ ^ jfe ' x V, v ^ *: **< '"'>. * ( 15 20 25 30 35 40 45 5( Bearing Power irTTons. FIG. 316. A diagram which contains no radiating lines, and is very easy to read with precision, may be constructed on logarithmic paper, as shown in Fig. 316. The vertical coordinates give the total penetration in inches for the last ten blows of the steam- hammer, while the horizontal coordinates give the safe loads. A similar diagram for a drop-hammer with falls of 20 feet and less is given in an article by E. F. KRIEGSMAN in Eng. Rec., vol. 65, page 417, April 13, 1912. ART. 32 EFFECT OF REST ON BEARING POWER 95 ART. 32. EFFECT OF REST ON BEARING POWER In some kinds of material like sand or gravel if a pile be partly driven one day and driving is resumed the next day, the resistance as measured by the average penetration per blow at the beginning of the second day's driving is generally found to be practically the same as that at the close of the first day. This is not the case with other kinds of material, for which increases in resistance within 24 hours of more than 1000 percent have been observed in extreme cases. An old contractor reports an illustration of this phenomenon: An attempt was made to reach hard bottom through a very deep marsh. After driving a 35-foot pile another one of equal length was spliced to it and also driven without finding a hard stratum, sinking 4 or 5 inches per blow. After driving the next pile to a penetration of 25 feet it was time to quit work, hence the pile was left in the leads in that position. The next morning five or six blows of the hammer failed to produce any appreci- able movement and accordingly the engineer concluded to drive piles about 35 or 40 feet long and depend upon the friction in the soft meadow muck to support them. The trestle bridge thus supported carried its traffic safely for years, the locomotives and cars becoming much heavier than it was originally expected would ever be used upon it. On the 6-mile pile trestle bridge of the New Orleans and Northeastern Railroad crossing Lake Pontchartrain the piles were from 45 to 70 feet long. The longer piles often penetrated 5 feet under their own weight, 3 feet more when the hammer rested on top, 20 feet additional at the rate of about 2 feet per blow for low drops, and finally from 10 to 15 feet deeper with a penetration of about one-half to i foot for a 3Ooo-pound hammer dropping 10 feet. The driving was done rapidly by means of a friction drum. It was observed that if a pile was allowed to stand several hours owing to a breakdown or some other cause, several blows were required to start it, but later the penetration resumed the same rate as before the period of rest. The engineer in repeating the facts 15 years later stated that none of the piles had settled under the traffic. 96 BEARING POWER OF PILES CHAP. Ill At Fort Point Channel, Boston, borings 65 feet below low water showed only soft blue clay changing in a few instances to soft yellow clay. Tests were made to determine the increased frictiona) resistance after a period of rest. A spruce pile 35 feet long, 17 inches at the butt and 7 inches at the tip was driven 20 feet into the clay by a 236o-pound hammer falling 8 feet. The average penetration for the last five blows was 5.5 inches. After four days rest, the pile was struck 20 blows, giving an aver- age penetration of 0.9 inch for the first five blows and 1.5 inches for the 20 blows. With another pile in slightly softer material the average penetration for five blows before and after four days rest decreased from 7.6 to 1.6 inches. In the upper San Francisco Bay is a deposit of very soft silt due to the finest and lightest tailings from hydraulic mining in the Sacramento and San Joaquin rivers. A pile sinks 20 to 27 feet in it by its own weight, but with a total penetration of- 40 to 55 feet will later support 40 ooo pounds. If a pile is allowed to rest only 15 minutes a heavy blow from a drop-hammer will not move it perceptibly, but a few blows in rapid succession will start it at the old rate. While attempting to splice a pile on one occasion the mud settled against it so that it could not be driven further and a scow with a displacement of 30 tons could not lift it. The friction developed was 200 pounds per square foot. These examples show why it is possible to sink piles in soft ground by a static load placed upon them which afterward will safely support a load several times as great. Instead of superimposing a static load, the pile may be pulled down by means of a block and tackle operated from a scow. It is also instructive to reflect upon the fact that a pile driven to a pene- tration of 90 feet in 10 minutes with apparently small resistance, a few days later supported a test load of 40 tons, whereas a pile of this length could not support it without lateral support if its foot stood on solid rock. A similar decrease in penetration after rest over night has often been observed in ground where the average penetration per blow was less than an inch. In one instance the penetration ART. 33 EFFECT OF SUB-SURFACE CONDITIONS 97 was reduced in the ratio of 2.3 to i and in another from 2.8 to i. At the Brooklyn anchorage of the Manhattan bridge it was noticed frequently that after a number of days rest the resist- ance of piles would develop to meet the requirements, although the driving was regarded to be hard. The increase in supporting power of plastic muds or clays is due to the material settling back against the surface of the pile which was disturbed in driving, the vibration of the pile tem- porarily enlarging the hole and thus releasing part of the frictional resistance. This curious physical property is analo- gous to that of India rubber. If a pin be forced into a solid India-rubber ball, the same force which pushed it in can pull it out again, provided it be done immediately, but after waiting 24 hours the force required will be about five times as great. A similar effect is produced in sand which for certain properties of moisture will temporarily arch itself laterally over small areas so that the pile will not receive pressure until some time after driving. ART. 33. EFFECT OF SUB-SURFACE CONDITIONS When a pile is held in position entirely by frictional resistance the load is transferred to the adjacent ground and transmitted down to different levels in widening areas until a level is reached where the earth can readily support the unit bearing value. The mass of ground thus transmitting the load may be said to form approximately a conoid of pressure, the slope of which depends upon the nature of the ground with respect to both the kind of material and its degree of compactness. When the coefficient of frictional resistance is small the total penetration must be larger or the pile will settle under the load, sometimes slipping through the surrounding material and at other times carrying a mass of the earth with it. When the bearing power of the earth chiefly supports the pile at its foot it should be designed as a column as described in Art. 24. When the support is due mainly to friction an impor- tant criterion of its magnitude is the final penetration per blow 7 98 BEARING POWER OF PILES CHAP. Ill of the hammer; but in first-class practice this is supplemented by a knowledge of the characteristics of the ground at the site. It is important to know, for instance, whether the resistance will increase for some time to a maximum, whether it will remain nearly or quite the same, or whether there is any possibility of its diminishing. An instructive example is that of six yellow pine piles driven into the wet alluvium of New Orleans which supported a turntable. Their diameters were 14 and 12 inches at the butt and tip respectively, and the average length was 31 feet below the cut-off. When driven by a 2825-pound hammer falling from 30 to 35 feet, penetrations 9.5 to 18 inches were obtained under the last blow, or an average of 12.1 inches. The total number of blows for each pile averaged 27, showing that there was prac- tically no appreciable compacting of the ground. The weight of the turntable and the two courses of creosoted timber grillage to which it was bolted was 36 100 pounds, and the weight of engines and tenders ranged from 116000 to 156000 pounds. No settlement had been observed during the nine years of operation after its construction, when the case was reported. In another instance piles 60 to 70 feet long were driven into mud with a final penetration of 2 feet or more per blow, but examinations for a number of years failed to give any evidence of settlement under traffic. These piles were used in some bridge foundations on the Boston and Maine Railroad near Conway Junction, Mass. It is particularly important to know what the effect of time is upon the supporting power of piles when the penetration per blow is very large. In Art. 32 reference was made to the very fine silt in upper San Francisco Bay. Even in that extreme case the friction was found to be about 200 pounds per square foot. The piles supporting the turntable in New Orleans cited above developed a frictional resistance of about 300 pounds per square foot under a load which was certainly safe. Whenever crusts of vegetable or of peat-like deposits cover sections of swamps which may be deep and strong enough to support ordinary ART. 33 EFFECT OF SUB-SURFACE CONDITIONS 99 highway loads it is usually necessary to penetrate them for pile foundations and extend the piles to the sand or clay bottom. Piles have been driven through 10 to 18 feet of soft mud and 15 feet into soft clay, when it took three or four blows of a 2000- pound hammer falling 6 to 1 2 feet to secure a penetration of i foot. Immediately after driving, the piles might be swayed as much as 2 feet at the head which was 15 to 20 feet above the mud line, but at the end of a week it required considerable force to move them. In attempting to pull piles which penetrated only 5 or 6 feet into the clay they frequently broke off. The effect of sand upon the settlement of piles having insufficient length, but for which the penetration per blow was very small, is described in Art. 34. By means of a steam-ham- mer aided by a water-jet, piles have been driven 33 feet into quicksand, and apparently might have been driven twice that depth, which could not have been driven to a quarter of that depth by a drop-hammer alone. In the upper drainage district of New Orleans a sand stratum underlies the silt at a depth of 40 feet. In driving piles they ' bring up' almost as suddenly as if they struck solid rock. The difficulty of driving piles in gravel increases in proportion to its fineness, if the ordinary drop- hammer method be employed. Unless sand or gravel are mixed with other material they are practically incompressible and have to be displaced in driving piles. On account of the danger of scour it is often necessary to secure a large total penetration, and in such cases it is unnecessary to consider the final penetration per blow. The strength of the material of which the pile is composed limits its bearing power. Engineers who have closely studied hard-pan and sandy clays claim that in this material the most perplexing results I of all are to be found. No two hard-pans seem to develop the\ same results. The ultimate result depends not only upon the, 1 percentage of clay and sand in the hard-pan, but also upon the solubility of the clay when brought into contact with the local ground water. Where piles are driven through ground water overlying hard-pan, the water invariably follows each pile 100 BEARING POWER OF PILES CHAP. Ill down as it penetrates the ground, softens the clay in contact with the surface of the pile, and often practically destroys all lateral friction. In such cases the only point of support is at the end of the pile, and the overhead load will be supported by a cluster of columns, the heights of which are equal to the lengths of the piles. ART. 34. ON TOTAL PENETRATION It is well known from observations in practice that piles driven in sand will sometimes settle when set in vibration by a live load. For example, in a pile trestle bridge, piles have settled under a load of 9 tons each although they had been driven to an average penetration of ^ inch with a i2oo-pound drop-hammer falling 20 feet. The final penetration is no ade- quate index of the bearing power of the pile in this case, since the hammer was too light in proportion to the pile, but apart from that, the primary reason for its settlement was its lack of suf- ficient depth of total penetration to prevent the vibration from being communicated to the foot of the pile. In another in- stance piles settled 15 inches under a load of 19 tons each, which were supposed to have been driven to absolute refusal. Observations seem to show that this tendency for piles to settle in sand is independent of the penetration under the last blow. Where the track is at a considerable elevation above the ground the specified final penetration per blow is reached when the total penetration is so small as to permit the pile to rock slightly on its foot. The effective remedy for such conditions is to drive the piles deeper. This can readily be done without injury to the pile since, fortunately, sand is so well adapted to the use of the water-jet. A total penetration of 10 feet in sand may be sufficient for piles in a building foundation, but may be insufficient for a pile trestle. It is noticed that if the longitudinal reinforcing bars of a con- crete pile are hit by the hammer instead of being protected by either plain concrete or independently reinforced concrete above it, that the foot of the pile is far more liable to be injured in ART. 35 DEGREE OF SECURITY IOI driving. The steel seems to transmit vibrations to the foot which would be dissipated otherwise before reaching it. The injury to the foot of the concrete pile implies more vibration at that point and therefore makes it somewhat analogous to the timber pile which settles by the lateral movement of its foot. All the piles under a building should be driven to the same depth if possible and the areas of groups should be carefully proportioned to the loads to be supported unless the spacing is large enough for each pile to develop its full supporting power independently. If the earth is not uniform in character, the piles should be driven preferably through the variable stratum to one which is practically uniform. When driving piles for the foundation of a cylinder pier it may not be possible to secure the same depth for all the piles in any cylinder on account of the gradually increasing compres- sion of the ground unless the piles first driven are not required to have as small a penetration per blow as that specified. In one example where the average penetration of all the piles in a cylinder 20 feet in diameter was 3 1 feet, the total penetration for the last five piles driven in the cylinder averaged 24 percent less than the penetration for the first five piles. The following sentence occurs in COOPER'S General Speci- fications for Foundations and Substructures of [Country] Highway and Electric Railway Bridges (1902): The minimum penetration accepted for the piles should be about 8 to 12 feet in wet gravel, sand, or stiff clay, and 20 to 40 feet in soft clay or silt. These values are apparently intended for foundations of substructures supporting light superstructures. Whenever pile foundations are liable to scour during excep- tional floods, provision must be made for this by increasing the total penetration beyond the depth needed to secure the specified average penetration per blow. ART. 35. DEGREE OF SECURITY The force .F in equations (i) and (2) of Art. 25 represents the final pressure on the head of the pile as it comes to rest after 102 BEARING POWER OF PILES CHAP. Ill any blow of the hammer, but since an average value of the final penetration is used for a certain number of blows, it is assumed to equal the ultimate bearing power immediately after driving. This bearing power is liable to change in most cases for earth of different kinds. Generally it increases after driving up to a maximum and this maximum does not increase with time. In Art.' 3 2 a number of examples were cited to show how large an increase may occur in short intervals of time, but on the other hand, a change in the moisture conditions due to hydraulic constructions may transform a stratum of clay into a slowly yielding mass which permits piles to sink into it that before appeared to have a solid support, or deformation in the ground of a contiguous site may reduce the bearing power in a given site. When a pile acts as a column the stress in the outer fiber due to its safe load must be less than the elastic limit of the material under a long time test irrespective of the relation between the elastic limit and the ultimate strength of the mate- rial for direct compression in an ordinary test of a short specimen. The safe load for a pile in which the resistance depends upon friction only is analogous to that of a column and must be less than a load which will cause settlement under a long time test. In some instances it may be difficult if not impossible to deter- mine how much of the supporting power is due to bearing on a solid sub-stratum and how much to friction alone. In others there is no guarantee that a pile will not steadily sink under a heavy quiescent load applied continuously, although it with- stands satisfactorily the specified test of driving. This result is especially to be feared in clays. Experience in testing piles by static loads placed upon them shows that a load may cause settlement if left on for several days or a week which produced no settlement when first applied or even during the first day, or a load may cause increasing settlement for a time but after a while no further settlement will take place. What margin of security is to be allowed between this load and the safe load for which the pile is to be designed depends on a number of factors. Sometimes the load to be supported by piles is a dead load ART. 35 DEGREE OF SECURITY 103 while in others it is a live load. The live load itself may increase during the life of the foundation as, for example, that of loco- motives and trains passing over a railroad structure. In pile trestles it is none too great an allowance to assume that the entire weight on the driving wheel base falls upon each bent in succession. In addition to the static weight of the live load some provision must often be made for the dynamic effect due to a moving load or to the vibration of machinery. At a factory on Fort Point Channel, Boston, the movement of piles may be observed when the machinery is in motion. The allowance thus made for foundations is usually less than for the superstructures or for parts of the substructure. If a building is adjacent to a railroad some account must be taken of the fact in designing its pile foundation. In some structures like that of a wharf the failure of piles may cause serious loss of property or even loss of life, and hence a larger margin of security is needed. In other cases it is difficult to estimate the probable load. A higher load may often be used for piles under temporary structures than that allowed for permanent structures. A building may be subsequently used for a different purpose than that for which it was designed. The building itself may be readily strengthened on this account but it may be impracticable to increase the strength of the foundation without excessive cost. Such contingencies are provided for only in special cases, for it is not generally economical to make the additional invest- ment required. It makes a decided difference whether the structure to be supported is permanent or merely temporary. The most important factor is that relating to the nature of the ground which is penetrated by the piles. The more uncertainty which exists in regard to it, the larger the margin of security must be. The character of the earth also determines whether the bearing power of all the piles in a foundation, or in some portion of it, equals the bearing power of one pile mul- tiplied by the number of piles. Extra caution should be used when the penetrations of piles are quite variable. Some engineers after evaluating these several factors in a given case, determine the safe load with reference to the ulti- 104 BEARING POWER OF PILES CHAP. Ill mate strength as obtained by a formula for the bearing power, while others fix it with reference to the value obtained from a formula that has been divided by a factor to make it certainly safe for the most unfavorable conditions met in ordinary prac- tice. The latter hold the opinion that it is better in principle to be obliged to consider carefully whether the conditions relat- ing to the foundation have been so fully investigated as to justify any increase in the working load per pile for adequate security, rather than to start with a value which is certainly unsafe and reduce that, thus enabling a man to deceive himself with the notion that he is cautious, when he is really rash. These conflicting opinions lose their force when adequate tests have been made to determine the character and the behavior of the earth to be penetrated. Uncertainty with respect to the load to be supported by the foundation is best provided for by the addition of some esti- mated percentage, after due consideration of all the facts and probabilities. The statement is frequently made in engineering literature that pile driving is largely a matter of judgment and that theo- retical considerations have practically no part in it. It should be remembered, however, that foundation failures and lack of economical design are most frequently due to a failure to explore the sub-surface conditions. Under this condition, the so-called exercise of engineering judgment is practically equivalent to guessing. It is interesting to note the results of this method as indicated in engineering periodicals: "It is an established custom among engineers to restrict the loading of timber piles within the range from 6 to 1 2 tons." " I note that there is a pretty general work- ing rule among engineers throughout this country to allow a load of 20 tons each on all piles driven to practical refusal." The art of pile driving at its best is based on science. Scien- tific method consists mainly in the solution of a problem by analysis into its component parts and by treating each part separately. With the diminishing supply of good timber piles and their increasing cost, the methods of design for pile founda- ART. 36 TEST PILES 105 tions should have approximately the degree of precision which is applied to the design of the superstructure. The margin of security is well illustrated in the following record regarding timber piles driven in 1908 to support the false- work of Bridge No. 5 of the Norfolk and Western Railroad over Elizabeth River at Norfolk, Va. "The falsework piles were driven with a 33 50 cts $10.00 14 cu. yds. portland cement concrete @ $6.50 91.00 8 concrete piles @ $22.00 ; 176.00 $277.00 Estimated saving on each footing $36.48 The concrete piles were 20 feet long, 20 inches in diameter at the head and 6 inches at the foot. On account of the size and taper of the concrete piles a smaller number could be used. The reduced amount of excavation and of concrete in the footings effected the balance of the saving in cost. The size of the con- 122 CONCRETE PILES CHAP. IV crete cap and footing was in both cases 4 by 6 feet on top and 8 by 10 feet on the bottom, but the height was reduced from n to 6 feet. ART. 41. UNPATENTED PRE-MOLDED PILES A pre-molded pile is a reinforced concrete pile which is molded to a regular form and after curing and seasoning is handled and driven like a timber pile. In order to indicate the principal variations in form and reinforcement which have been developed by different designers of pre-molded concrete piles, brief descrip- tions are given either of standard designs or of those adopted for the foundations of particular structures. The bridge department of the Chicago, Burlington & Quincy Railroad was a pioneer in the design and construction of low reinforced-concrete pile trestles for steam railroads. In con- nection with the thorough studies and tests made for this purpose, an unpatented type of pre-molded pile was developed in 1905 which together with the Chenoweth rolled pile (Fig. 41 b), has been extensively used in construction by that railroad. The piles used in the first of these bridges are 16 inches square at the butt, have a 4-inch chamfer at each corner, a taper of 4 inches in 30 feet on each face, and are pointed at the tip. The rein- forcement consists of four f -inch square corrugated bars, hooped with No. 12 steel wire, wound at close pitch near the butt and tip, and at 3-inch pitch over the greatest part of the length of the pile. Since the cost of making the reinforcement units was one of the principal items, experiments were made to reduce it by mold- ing a pile without taper, and using a wire netting which could then be simply folded into a square prismatic form and wired together at the lap, thus greatly lessening the labor involved. The cost of forms was thereby also materially reduced. Fig. 410 shows the details of the form and reinforcement of this later design. It will be observed that the corners of the pile are rounded and that the loi)gitudinal bars are wired to the fabric at its corners. At the point, the transverse wires were cut and ART. 41 UNPATENTED PRE-MOLDED PILES I2 3 the longitudinal wires brought together and tied securely with small wire. The concrete piles driven in 1909 in the foundations of eight of the piers of the Erie Railroad viaduct over Penhorn Creek in Jersey City, have the re : markable lengths of 55 to 65 feet. They are square in cross-section, tapered from 1 6 inches at the butt to 8 inches at the tip, and have a 2-inch hole- through the axis from end to end. Each corner is reinforced by a single f-inch round steel rod. Especial pains were taken to design them so that no patented features were incorporated. Reinforced- concrete piles were designed by the Penn- sylvania Lines for their ex- tensive docks at Cleveland, 0., and which were con- structed by the Great Lakes Dredge and Dock Com- pany. They are octagonal in shape, without taper, pointed at the foot and have a cast-iron shoe which was made an integral part of the pile. As indicated in Fig. 4 id, the reinforcement con- sists of 8 longitudinal rods securely bound together at regular intervals throughout the body of the pile by tie rods. They are also spirally wrapped for short distances at both head and foot. The dimensions in Fig. 4 id refer to piles 30 to 40 feet long, the longitudinal rods being i inch in diameter, while the ties and k- FIG. FIG. 416. 124 CONCRETE PILES CHAP. IV wrapping are f inch in diameter. Over 3500 octagonal piles were used on the dock foundations and all of them were cast in vertical molds. The weight of the largest pile is 6 tons. The standard design of the Chicago, Rock Island & Pacific Railway adopted in 1910 is illustrated in Fig. 416. The form FIGS. 4ic and d. is octagonal, without taper and pointed at the foot. The rein- forcement occupies a cylindrical form in the body of the pile, and consists of 6 longitudinal corrugated bars and spiral wrap- pings of wire with a small pitch, which is slightly modified near the head and foot. The bars extend to the point but not quite to the upper end and are wired to the helical reinforcement at intervals not exceeding 12 inches. ART. 41 UNPATENTED PRE-MOLDED PILES 125 A similar design was adopted for some pile foundations in the approaches of the Municipal bridge at St. Louis, Mo., in 1911. The least diameter is also 14 inches and the reinforcement con- sists of six f -inch round rods, and a helical winding with No. 9 wire on a pitch of 4 inches, reduced to i inch for about 18 inches at the head of the pile. Concrete Pile Devotion Section D-D FIG. 4ie. Concrete Pile and Forms. The pre-molded piles designed for the Government Pier at Halifax, N. S., are 24 inches square in section with the corners slightly chamfered. The 8 reinforcing rods are i inch in diame- ter for piles under 60 feet in length, i J inches for lengths of 60 to 70 feet, and i \ inches for lengths over 70 feet. In addition to these rods which extend from the pyramidal point to 3 feet above the head so as to bond into the superstructure, four rods 8 feet long extend from the point upward about midway between 126 CONCRETE PILES CHAP. IV the axis and the full-length corner rods. Helical wrapping with |-inch wire and a pitch of 2 inches is used for a distance of 5^ feet above the point. Beyond that the wire hoops are spaced 12 inches apart except at the head where the spaces are reduced to 9 and 6 inches respectively. The reinforced-concrete piles used in 1906-07 in the founda- tions of the steamship terminal of the Atlanta, Birmingham and Atlantic Railway at Brunswick, Ga. ? were tapered for a length of only 10 feet from the tip. Their length ranges from 30 to 51 feet and their weight from 3 to 5 tons each. They are 16 inches square from the shoulders to a section 10 feet from the tip and 8 inches at the tip. Above the shoulders, they have a projecting tenon, 8X16 inches and 16 inches long to permit concrete fillers to be placed in the shoulders to increase the bearing area of the packed timber beams used in the floor of the pier. The rein- forcement consists of four ij-inch bars placed in the corners of the pile and tied together at 1 2-inch intervals by J-inch round steel clips. At the head electric-welded wire fabric is placed for a length of 4 feet to aid in withstanding the shock from hammering. A i^-inch jet pipe was cast into the lower part of the pile for subsequent use in sinking. The piles used in 1907 at the Charles town Navy Yard were noteworthy on account of their size and weight. In design, they are similar to those described in the preceding paragraph. They are 55 feet long and 18 inches square to within 8 feet of the tip and then tapered off to 1 2 inches square. The reinforcement consists of four ij-inch twisted bars and two f -inch bars. The larger bars are placed in the comers of the pile 2\ inches from the surface, and the smaller ones are placed between the others and on a line across the pier transversely. A 2-inch pipe 22 feet long was cast in the pile for use as a water-jet. As the weight of a pile is 10 tons, a bridle which picked up a pile at two points, 1 8 feet apart, was employed in lifting them. Pre-molded round piles, 12 inches in diameter but having a bulb-shaped foot 30 inches in diameter and 24 inches high, were used on some new work for the reconstruction of the ' old steel pier' at Atlantic City, into a reinforced-concrete pier. The ART. 42 PATENTED PRE-MOLDED PILES I2 7 longitudinal reinforcement consists of six f -inch bars, and these are splayed out at the bottom to reinforce the foot, which is intended to increase the bearing power in the sand. A 2-inch jet pipe was cast in the pile and extends throughout its full length. ART. 42. PATENTED PRE-MOLDED PILES The corrugated pile is hexagonal or octagonal in cross-section with grooves approximately semi-cylindrical on each face, has a round hole along the axis, both pile and hole being tapered from butt to tip, and is reinforced with electrically welded wire fabric (Fig. 420). The hole or central bore is used to permit a water- jet to pass through it, and it is tapered to increase the section - Wire Mesh '-Reinforcing Bars- i '*iy ^Reinforcement FIG. 42a. Section of Corru- gated Pile. End- Cross Section for All Piles. Middle Cross Section for Long Piles. FIG. 426. Sections of Chenoweth Pile. area of concrete at the tip and to permit the plug used to cast the hole to be easily withdrawn. The object of the corruga- tions is to increase the pile surface for skin friction, and to fur- nish convenient outlets for the escaping water from the jet, thus reducing the friction during the operation of sinking. They are not extended, however, along the head or tip, to avoid reducing the full section area of both parts. When the piles are intended to project above the ground level, the corrugations are designed not to extend above it. The Chenoweth concrete pile is a rolled pile. The machine used for this purpose has a moving platform, a number of rolls and mechanism to turn the tubular mandrel, about which the pile is formed. The reinforcement consists of a number of lon- gitudinal corrugated bars, wired to transverse strips of wire 128 CONCRETE PILES CHAP. IV mesh. This reinforcement is laid out on the platform and the ends of the wire mesh attached by wire clips to the key ways of the mandrel; the concrete is property spread over it and then by simultaneously turning the mandrel and moving the platform, the pile 'is coiled and rolled into a cylindrical form which is compacted and shaped by means of the adjustable rollers. At the same time, the pile is wound by wire at about 6-inch inter- vals during the entire process of rolling. After fastening the ends of these wires, the central tube is withdrawn, and the pile is removed to the drying table. A concrete point shaped like the frustum of a cone is constructed around the projecting reinforcing bars with the aid of a suitable form, and the head is perfected in a similar manner. The wire netting in the finished pile is located in a spiral surface, as indicated in the cross-section shown in Fig. 426, while the longitudinal bars are equidistant near the surface of the pile. In making these piles, a very dry mixture has to be used; otherwise, the cement will be squeezed out with the water in rolling. If the mixture is too wet, the piles will also lose their shape and become oval on the drying table. On some railroads, it is the practice to omit pointing the rolled piles, leaving the tip, just as it comes from the rolls. The largest pile of this type employed prior to 1913, was used in a coal dock at Havana, the length being 76 feet, diameter 18 inches, and weight 12 tons. At the end of the dock, the piles are unsupported for a length of 40 feet and their penetration extends 2 feet into the coral rock. Piles 50 feet long and only 12 inches in diameter have been successfully handled. Piles of the same length but 14 inches in diameter and weighing 3^ tons have been hauled four miles to the site of the foundation. The reinforcement of the Cummings concrete pile is illus- trated in Fig. 420. Four of the longitudinal bars do not extend the full length of the pile. The other four are welded together at the point, and welded to a conical sheet-metal point protector or shoe. They are also bent over at the head and welded together in pairs. The longitudinal rods are held in position, at intervals of approximately 5 feet, by flat rings of |-mch metal ART. 42 PATENTED PRE-MOLDED PILES 129 K 14'- with notches cut in the circumference to receive the rods. The body of the pile has a helical wrapping of wire to perform the function of hooping and to aid in resisting diagonal stresses. At the head there is also a series of horizontal bands closely spaced to give special lateral support to the concrete under the driving shock and each of the upper four of these contains a horizontal spiral as shown in the sketch plan. Sometimes seven are used in large piles. This arrangement for re- inforcing the pile head has proven to be very resistant to the impact of the pile- driver hammer. It is claimed, that in driving thousands of piles with this resilient head, that in no case was the head of the pile broken. Fig. 420 shows the ta- pered form which is always made with an octagonal cross-section and a tip 9 inches in diameter; the diameter of the butt de- pending upon the length of the pile so as to preserve a constant taper of 2 inches in 10 feet in the standard designs. When a pile of uniform section is used, the form of the cross-section is circular. Sometimes both the tapered and un- tapered piles are molded with annular grooves to increase the frictional resistance. The ordinary form of the Hennebique pile is usually con- structed as a square pile without taper, with the reinforcing bars near the four edges which are slightly beveled and tied 9 i Shoe FIG. 42C. Reinforcement of Cummings Concrete Pile. 130 CONCRETE PILES CHAP. IV together by wire collars or binders at short intervals. The standard form has a cast-steel shoe at the foot forming an inte- gral part of the pile. To support a reinforced-concrete quay, at Key West, piles 16 and 20 inches square and from 25 to 60 feet long were driven through marl and sand into the coral rock ; all of them being provided with metal shoes. The longitudinal reinforcement consisted of four rods i| inches in diameter, with extra rods in the middle third of the longest piles. The J-inch wire collars were spaced 12 inches apart in the body of the pile, 4 inches in the head, 6 and 3 inches in the tip. A pile of this kind, which was constructed as a hollow pile to reduce its weight, and was filled with concrete when in place, is described in Art. 47. Further details as to sizes of piles, sizes and disposition of reinforcement, and methods of construction may be found in the elaborately illustrated catalogues which are published by the construction companies. ART. 43. FORM AND CONSTRUCTION The prevailing form of cross-section for pre-molded piles is octagonal. Practically all of those with square sections approximate toward the octagonal form in that their edges are beveled to a width of 2 or 3 inches, although occasionally they are merely rounded (see Fig. 410). The circular cross-section is used but seldom, in which case the piles must be cast in a vertical position. The diameter varies from 10 to 25 inches but it is rarely below 12 or above 18 inches. The length varies from 8 to 76 feet, but it is questionable whether any length less than 15 feet should be employed in any pile foundation. In most cases the length ranges from 20 to 40 feet. The longest piles are used in dock construction where the piles are located in deep water. It would be difficult to say whether more pre-molded piles are constructed with taper than without it, for both forms are in extensive use. A number of railroads have adopted the straight or untapered pile as standard, and in a considerable number of important works, each one requiring thousands of piles, half ART. 43 FORM AND CONSTRUCTION 131 of them use the form with uniform cross-section. This form should always be used when conditions require the pile to act chiefly as a column. The tendency is to use a decidedly smaller taper in pre-molded piles than that for cast-in-place piles. It may be stated that except for very short piles in the foundations of buildings, the taper does not exceed i inch in 4 feet, is frequently i inch in 5 feet and sometimes as low as i inch in 7.5 feet. The influence of taper on the bearing power of piles is discussed in Art. 53. As indicated in Arts. 41 and 42, pre-molded piles are most frequently designed with a point at the foot. Its length often exceeds but is sometimes less than the diameter. Even in tapered piles experience has shown the advantage of a point. In driving piles for the Kentucky shore pier of the Kentucky and Indiana bridge at Louisville in 1910 the 9-inch tip of the pile was made square ended to insure straight driving. But as driving through the hard clay proved to be so difficult the last batch of piles for the pier footing was provided with pyramid points, which increased three-fold the number driven per day. In some experiments reported in 1908 made by THOMPSON and Fox with tapered piles 30^ feet long it was found that the 8-inch tip required less time to drive the piles than 9 or lo-inch tips, although in this case the result was complicated by the effect of difference in taper. The use of metal shoes in pre- molded piles is referred to in Arts. 41 and 42. See Fig. 4id for an illustration of one form. Sometimes the foot of the pile has been enlarged in diameter in order to increase the bearing area of the pile in the lower stratum. One example of this practice is found in the 1 6-inch reinforced concrete piles for the Atlantic City boardwalk built in 1908 which were formed with a base 26 inches in diameter. See also Art. 41. It is customary in good practice to fabricate the reinforce- ment as a unit so that it can be easily handled and placed quickly in the form when the process of casting is under way. The reinforcement unit is held in accurate position in the 132 CONCRETE PILES CHAP. IV forms by suitable hangers and separators, so that the con- ditions assumed in designing the pile shall be realized in its construction. If the pile is to have a hole in the center for the insertion of a jet pipe to be used in sinking, which is more economical than to cast a jet pipe in the pile, either a tapered wooden core may be used, or preferably a collapsible form; or a tin tube may be used instead and left in the pile. The objection to the solid core is that it requires occasional turning to prevent its sticking to the concrete, and its removal later. The composition of the concrete consists of i part portland cement, 2 parts of sand and 4 parts of broken stone or gravel. This mixture is so generally employed that it may be regarded as standard. Occasionally it is modified to 1-2-3. In large hollow piles the molded portion may have a composition of 1-1.5-3 and a leaner mixture like 1-3-5 or 1-3-6 employed in filling the interior after they are in place. Usually the size of the crushed stone or gravel is limited to f inch. Investigations relating to the effect of sea water on concrete piles have not resulted in definite conclusions. Experience has shown however that it is important to make as dense a mixture of concrete as possible. At first piles were molded in forms laid horizontally on the ground or on suitable platforms. Later the practice of molding piles in a vertical position was introduced in order that the sur- face of the concrete as it is deposited in batches shall always be perpendicular to the direction of the load to be supported by the pile, or to the force applied by the hammer in driving. When piles are molded in a horizontal position special care should be exercised to provide an unyielding base so that the concrete may not be subjected to flexural stresses while in the process of set- ting. When the forms are vertical special precautions must be observed in tamping or puddling the concrete to eliminate all voids. In one case where 361 piles were cast vertically in lengths of 28 and 32 feet, not one unsound pile was found when the forms were removed. Both positions of the molds have been used on large constructions where adequate equip- ment was provided. ART. 43 FORM AND CONSTRUCTION 133 With horizontal molds the sides may be removed in from 24 to 48 hours, but the pile is allowed to rest on the base about a week longer during which time it should be copiously showered with water to permit complete chemical action for the setting of the cement. In very warm weather some protection from the sun may be required. After this the piles may be removed and piled in stacks to continue seasoning, using an equalizing spreader and bridle, if necessary to handle them. They are usually allowed to harden for at least three weeks more before they are driven. The actual time to be allowed in each case depends upon the temperature and humidity of the atmosphere, while the age at which piles may be placed in position depends also upon the character of the ground and the method of driving. The hardening of the concrete may be materially hastened by curing with live stream under cover. The piles for the docks of the Pennsylvania Lines at Cleveland were cast vertically in steel forms. The pile forms were then closed at the top and placed horizontally on a floor of cross timbers. On account of the late season, it was found necessary to use some method of artificial seasoning and this was done by piling up the newly filled forms and covering them with canvas. A steam-pipe line provided with outlet pipes was laid to discharge steam under the cover, and to maintain a temperature of about 80 degrees. The forms were removed in from 12 to 18 hours, thus leaving the concrete piles exposed directly to the steam for three or more days afterward until they were set sufficiently to be handled by a derrick. They were afterward placed by derricks in the stor- age yard to be kept at least 30 days before driving. It may be added that on other works concrete piles have been allowed to set for from five to six days in the ordinary manner and then gently hoisted to the curing bed with 25 or 30 stacked together in a pile with wooden spacing blocks between them where they were subjected to live stream for two or three days. They were then driven within three or four days in summer, or within ten days in winter. As soon as pre-molded piles are driven they are ready to receive their load from the superstructure above. 134 CONCRETE PILES CHAP. IV ART. 44. DESIGN OF PRE-MOLDED PILES The steel reinforcement of a concrete pile is intended to resist the stresses due to handling and driving the pile, and to the load which may come upon it in its final position. The longitudinal bars receive their greatest stresses when the pile is lifted from a horizontal position. Unless the pile is exceptionally long or heavy it is often picked up at or near the middle in going to or from the seasoning yard, or a line may be attached near one end to drag it to the pile driver. In the former case the pile must be strong enough to resist flexure due to its own weight, while in the latter case the pile must not only sustain its own weight but also shock or the impact due to meeting obstacles, which sets it into active vibration. When so handled concrete piles rarely fail by compression, but cracks develop on the tension side which sometimes may be due to the rods slipping. Twisted or deformed bars are preferable to plain rods on account of their increased bond resistance. Large cracks may endanger the permanency of the reinforcement by permitting corrosion to occur. It is also important that uniform circumferential spacing of the bars be maintained in construc- tion as any side of an octagonal pile, for example, may become subject to tension. Some designers add 100 percent to the weight of a pile to provide for the shock due to handling. This may be excessive in cases where special provision is made for proper handling, 50 percent being a more reasonable allowance. Very long piles have extra longitudinal reinforcement provided in the middle third or half of the length. Sometimes short lengths of additional longitudinal bars are inserted in the head, to aid in resisting the impact due to the hammer, but additional hooping is more frequently provided for this purpose. The lateral reinforcement is of two distinct types: One con- sists of separate wire hoops or binders either approximately square or circular in shape, and spaced at intervals which vary more or less along the length of the pile; the other consists of a continuous spiral wrapping which varies in pitch at the head and ART. 44 DESIGN OF PRE -MOLDED PILES 135 foot of the pile. It is primarily intended to increase the resist- ance of the concrete to longitudinal compression, but the latter form may also aid in resisting diagonal tension. The lateral reinforcement is equally as important as the longitudinal. The percentage of steel in the section area of the pile varies considerably in practice, ranging from about 0.6 to 2.8 percent. In the pre-molded piles for the approach of the Municipal bridge at St. Louis, the total reinforcement amounted to i| per- cent of the volume of the pile. Experiment has shown that hair cracks develop in handling when the reinforcement is less than i percent. The section area of the head must be sufficient to support in direct compression the safe load for which the pile is designed. The safe unit-stresses to be adopted should depend upon the quality of the concrete, the percentage of reinforcement, and its arrangement, as well as the character of the loading. If the pile is tapered the critical section for direct compression is not at the butt or top of the head but at some distance below the surface of the ground. The additional allowance for hard driving in any case is pre- ferably made by a direct addition to the section area or by adding extra cement to the batch of concrete to be placed in the head of the pile. It is, of course, understood that when a pile acts as a column that it is to be designed as a column. The New York City building code as recommended by the National Board of Fire Underwriters, allows a maximum load of 25 tons per square foot of cross-section and an additional load of 6000 pounds per square inch of steel reinforcement in the section. The unit-stress on the concrete is therefore nearly 350 pounds per square inch. In a given railroad pier foundation the piles were designed for a safe load of 50 tons. They are octagonal in form, the least diameter is 12^ inches and the reinforcement consists of four | -inch square bars. If in this case the compression on the steel bars be assumed as 10000 pounds per square inch, the compression in the concrete is found to be 534 pounds per square inch. 136 CONCRETE PILES CHAP. IV As the design of reinforced- concrete piles is so comparatively new, engineering practice in regard to safe unit-stresses is not reduced to such narrow limits as in many other divisions of structural design. For a discussion of the principles involved and their application to illustrative examples the student is referred to standard text-books on mechanics and on reinforced concrete. The method of computing the lateral resistance of a pile is similar to that for the lateral resistance of a track spike as deduced in JACOBY'S Structural Details, Art. 8. In that case the maximum unit-compression on the wood is located at the upper surface but for a pile the bearing resistance of the upper strata of the ground may be less than that of the lower strata. Therefore, while using the same general method, the formulas given cannot usually be employed without some modi- fication. It may be sufficient for practical purposes in many cases to assume the surface of the ground to be lowered more or less so as to make the resultant moment of the actual pres- sures equivalent to that of the theoretic pressure used in deducing the formula. Under retaining walls where the piles receive a lateral thrust as well as a vertical load it is necessary to use reinforced piles to resist the flexure thus produced. The distribution of bend- ing moments indicates that at least the upper part of the pile should have a uniform section. ART. 45. CAST-IN-PLACE PILES A cast-in-place pile is a concrete pile which is built in its permanent place in a hole prepared for the purpose. While only some types of the class of pre-molded piles are patented, all types of cast-in-place piles have been patented. The characteristic features of the latter class relate more specifically to the method of construction for each type and the appliances used for that purpose. In making the type known as the Raymond pile (see Art. 39) a tapering sheet-steel shell or casing is driven into the ground by means of a collapsible steel core FIG. 450. Two Sections of Reinforced Sheet-steel Shell and ' Boot' Section. FIG. 456. Steel Pile Driver of the Raymond Concrete Pile Company. (Facing p. 136.) ART. 45 CAST-IN-PLACE PILES 137 which acts as a form to support the shell. After the desired penetration is reached the core is collapsed and withdrawn, and the casing filled with concrete. The core when dressed with the shell is driven by means of a pile-driver with a heavy steam- hammer. On account of the great weight of the core the pile- driver is of heavy construction, steel leads and bracing being always used for the largest cores. The driver illustrated in Fig. 456, is equipped with leads measuring 57 feet from the top of the turntable I-beams to the head block. The shell of 18 to 20 gage sheet steel is made in various diameters and in conical sections about 8 feet long which overlap tightly (in telescope fashion) when in place, but enable them to be shipped 'knocked down/ and to be readily slipped over the core in regular suc- cession. The very short section closed at the bottom is called the 'boot/ and is made of pressed steel to withsand the cutting effect of stone or other obstacles encountered in driving. The object of the casing is to prevent the earth and water from mixing with the concrete and to act as a mold that shall pre- serve its shape until the concrete is set. Before placing the concrete, the interior of the shell can be inspected, by means of an electric light, by light reflected from a mirror, or by the light reflected from the surface of water thrown into the casing. More or less difficulty has been met when the hydrostatic pressure collapsed the thin shell, and sometimes several shells were driven inside of one another. In 1911 their construction was improved by reinforcing a 24-gage shell with a J-inch wire spiral, as illustrated in Fig. 450, thus materially increasing its strength. The concrete is either a 1-2-4 or a I ~3~5 mixture, using respectively f-inch and if-inch stone or gravel, and mixed rather wet. The piles are occasionally reinforced by longitudinal bars but usually no such reinforcement is employed, unless short rods are inserted to assist in bonding the tops of the piles to the concrete footing. Lateral reinforcement is, however, provided by the spiral wire used to stiffen the casing, since the concrete of the finished pile is wrapped by it. Since reinforcement is seldom used in these piles it is easy to place the con- 138 CONCRETE PILES CHAP. IV crete in the smooth shell so as to obtain good concrete with- out voids. The standard sizes of Raymond piles have a diameter of 20 inches at the head for lengths of 20 to 30 feet, and 18 inches for lengths of 35 to 40 feet. The tip has a diameter of 6 inches for a length of 20 feet, and 8 inches for greater lengths. This type of pile has been very extensively employed in America, especially for the foundations of buildings. The special advantage claimed for it over those of other concrete piles are speed of placement, and economy due to the large taper (see Art. 53 for discussion of taper) whereby the length is materially reduced. The taper adopted is greater than that for any other type of pile. Additional advantages over those of other types of cast-in-place piles are the inspection of the form in which the concrete is deposited, and the testing of bearing power for every pile by the average penetration of the steel core under the final blows of the hammer. On account of using a steel core it is claimed to be possible to drive through very hard material which cannot be penetrated by any other kind of pile at reasonable cost. Occasionally a steel core is broken in such material as compact earth containing boulders. The Simplex pile introduced in 1903 is made by driving a steel pipe, with a special shoe or 'jaw' to close the bottom, in the same manner as a pile, and then filling the hole with concrete as the pipe is gradually withdrawn. The pipe must be extra heavy and at least as long as the pile to be formed, and the pile-driver must have extra strength and equipment to pull out the pipe. Sometimes a cast-iron or concrete shoe is used with a projection which fits into the pipe. The shoe remains in place and hence a new one is needed for each pile. Where the earth is firm and compact an 'alligator jaw' attached to the pipe by cable hinges is used which opens automatically when the pipe is withdrawn to permit the concrete to flow through it. A ram is generally employed to force each batch of concrete into place against the surrounding earth until the hole is completely filled; this increases the diameter of the pile somewhat beyond that of the pipe driven. In some cases the pipe is first filled with con- ART. 45 CAST IN PLACE PILES 139 crete and then slowly withdrawn at a uniform rate, without ram- ming the concrete. The concrete is made of a fairly wet 1-2-4 mixture using J-inch stone or gravel, and which by its weight is expected to resist the pressure of the soil. It is claimed, since the concrete is forced into the surface irregu- larities of the compressed earth, that its frictional resistance is greater than for any other kind of pile of equal diameter and length. The indentations, however, become filled with com- pressed earth and become a part of the pile thus changing the frictional or shearing surface to a more regular form. The con- crete may also adhere to some stone or gravel contained in the surrounding material. Where the earth penetrated does not have sufficient stability to retain its form when the pipe is withdrawn this method cannot be used without modification. Such a condition has been met by dropping into the hole, after the first batch of concrete was placed an auxiliary cylindrical form of sheet metal of slightly smaller diameter than the pipe. After this form is filled with concrete the pipe is withdrawn. This leaves some voids outside of the sheet metal form which will only be filled by adjustment of the surrounding earth. As an illustration of the time saved in construction, it is noted that about 4800 Simplex piles from 30 to 45 feet long and aggre- gating about 162 ooo linear feet were driven through filled material for the Terminal Warehouse Building at Pittsburgh in 76 days by 7 pile-drivers. In another location piles 48 feet long were used. The practical limit to the length is the strength of the equipment provided to pull out the pipe. It is impossible to inspect the integrity of the pile, and it is a question as to what extent its strength may be reduced by some admixture of the concrete with adjacent earth. In stiff, non- water bearing, or clay soils, where the ground has no tendency to flow, this is claimed to be the cheapest system of installing concrete piles. The 'pedestal pile' invented by HUNLEY ABBOTT may be regarded as a modification of the Simplex pile by the addition of a bulb-shaped base or pedestal at the foot. Its form is intended 140 CONCRETE PILES CHAP. IV to take a larger measure of advantage of a lower stratum of higher bearing capacity than is done by piles of the ordinary form. By thus increasing its bearing area at the foot it imi- tates the metallic disk and screw piles (Art. 57) which doubt- less suggested it. The pedestal pile requires the same equipment as the Simplex pile except the shoe or jaw, and in addition a steel core which fits inside of the pipe with its enlarged head engaging the top of the pipe, and its lower pointed end projecting several feet below Ground FIG. 45c. The Process of Forming Pedestal Concrete Piles. the pipe. As illustrated in Fig. 45^, the steel pipe and core are first driven into the ground and a charge of concrete dumped into the pipe. The core is next used as a rammer to enlarge the hole below the pipe laterally by pushing aside the concrete, repeating the process until the concrete base has the required volume. Finally, the pipe is filled with concrete and then withdrawn. The pipe employed is usually 16 inches in diameter and f inch thick, while the core projects 4 or 5 feet below the pipe. The cylindrical stem of the pile is hence about 17 inches in diameter and the base roughly 3 feet in diameter, the volume of the base being about 16 cuoic feet. The diameter of the base, for a given volume of concrete used in making it, depends upon the nature of the ground and its homogeneity. If for any reason the earth should resist unequally on opposite sides of the hole ART. 45 CAST-IN-PLACE PILES 141 the resulting form of base would make its reaction eccentric. The concrete is usually a 1-2-4 mixture with the broken stone or gravel limited to a diameter of i| inches. The pedestal piles under the retaining wall of the Oregon- Washington Railroad and Navigation Co. at Seattle, Wash., were reinforced by six f -inch rods 15 feet long in order to provide against bending moments due to the horizontal component of the earth pressure. Cast-in-place piles except the Raymond type cannot project any distance above the ground without the use of special forms at increased cost. The Gow and Palmer pile is made by driving a metal casing or pipe into the earth, the inside of which is kept empty by a stream of water under pressure until it reaches the required depth. The casing is then withdrawn a few feet and a lozenge-shaped cutter lowered to the bottom of the hole. By turning this tool and at the same time opening it gradually the chamber is hol- lowed out and the earth removed by the current of water. The casing and chamber are then pumped out, filled with concrete and tamped, the casing being gradually withdrawn as the con- crete fills the hole. Reinforcing bars are pushed down into the concrete to reinforce the stem of the pile when desired. This pile was originally designed in 1904 to underpin a building, the enlarged base being located in the clay stratum which was over- laid by filling and soft material to a depth of 20 feet. The casing was in that instance put down in 5-foot lengths. In one location where the original surface of stiff clay had been covered by 15 feet of clay fill from adjoining excavations it was deemed best to carry the load to the underlying stratum. For this purpose holes 10 inches in diameter were excavated by means of a post-hole auger and then filled with concrete, the clay sides being stiff enough to retain the form of the holes. The piles were spaced 3 feet between centers, and the cost of the piles was 33 cents per linear foot, 60 percent of which represents the cost of digging the holes. This extremely low cost is due in part to the absence of any charge for the installation of plant. The chief objection to all cast-in-place piles has been based 142 CONCRETE PILES CHAP. IV upon the probability of injury to the green concrete by driving the forms for adjacent piles. There are other disadvantages which pertain only to certain types. The precautions which may be adopted to obviate these difficulties are discussed in the next article. ART. 46. PRECAUTIONS AGAINST INJURY Since pre-molded piles cannot be driven until they are suffi- ciently seasoned, they may be placed in any order in the required foundation. This cannot safely be done with cast-in-place piles. When the core or the pipe is driven for a given pile, it displaces and compresses the earth adjacent to the hole which is formed, and the elastic earth tends to relieve its stress by crowding back. Even if the shell, which is left in the hole, or the weight of the concrete, when no shell is employed, is able to resist this outside pressure until the cement is set, it is very probable that the green concrete will be injured by the vibra- tion and additional earth pressure due to driving adjacent piles, after the setting of the cement has progressed to a certain extent and before its completion. To determine its effect, two tests were made before beginning the pile work in the foundations for the north abutment of the Pittsburgh and Lake Erie Railroad bridge over the Ohio River at Beaver, Pa. The first test consisted of a pile driven with four others around it, spaced as in the proposed foundation work, the four being driven while the test pile was still soft. The second test differed from the first only by allowing the test pile to set partially before the four piles around it were driven. The working conditions on a large foundation are such that the second test more nearly represents the actual conditions than the first. After both test piles were allowed 30 days to set, the first test pile supported a load of 60 tons for 72 hours with a settlement of Vr inch, which was recovered almost wholly after the load was removed, while in the other case, the results, as expected, were not good enough for approval. To meet the difficulty developed by the conditions of the second test, and ART. 46 PRECAUTIONS AGAINST INJURY 143 which apply to all kinds of concrete piles formed in place, thus recognizing the well-known limitations of concrete, the following specifications were adopted in 1908, probably for the first time on such work, and were strictly observed: The setting of the concrete in any pile must not, under any considera- tion, be disturbed by driving another pile or piles within a radius less than 9 feet from it, center to center, after a minimum interval of three hours or before the expiration of seven days from the time the concrete was mixed with water for that pile. The contractor may, however, at his own op- tion drive pile forms within the g-foot radius to a depth not more than 3 feet from the total estimated penetration, inside of the three-hour limit; and then after the three-hour limit and before the expiration of the seven- day limit, complete the driving and filling of these forms. The extent to which such damage may occur has been proved by subsequent excavation in a number of cases, owing to changes in plan or to building adjacent structures. In one example, failure was due to the fluid alluvial soil penetrating between batches of concrete, thus separating the pile into sections about 5 feet long. In another, the cement failed to set on account of certain chemical constituents in the ground water, ascertained later by analysis. In still other cases, piles had their section areas reduced from 20 to 100 percent; and were bent out of line. The liability of the green concrete to suffer injury by driving adjacent piles is increased when thin hard strata alternate with soft ones. Material, which is lighter than concrete, may transmit pressures which displace concrete when it is soft, and injure it after the initial set. In boulders or gravel, a shearing effect may be produced instead of merely a direct pressure. Unless protected by a shell, there is more or less danger of some of the cement being washed out by underground flowing water, or on the other hand, that the cement may be deprived of some of the water which it needs to set completely, by the absorbent earth. It should be added that the construction of cast-in-place piles requires more careful supervision to secure good results, on account of the manner in which the concrete is deposited, and the surrounding conditions which preclude inspection of the 144 CONCRETE PILES CHAP. IV pile after the concrete is all in place. When it is deemed neces- sary to put reinforcement in a cast-in-place pile throughout its length, it should be fabricated as a unit and properly put in position. It is impracticable to place bars separately, so that they shall occupy specified positions in the finished pile. ART. 47. COMPOSITE TYPES AND COMBINATION PILES Hollow pre-molded piles, which were filled with lean concrete after they were placed in their final positions were driven in 191 1, for the foundations of the ocean pier at Long Branch, N. J. The piles are of the Hennebique type and range in length from 45 to 68 feet, with an average penetration of 22 feet. Near the shore, some 1 8-inch square piles were used but the rest are hol- low square piles 24 inches square on the outside and 13 inches on the inside, in order to reduce their weight for handling. The reinforcement consists of ij-inch round rods tied together at intervals with J-inch wire collars, while the longer piles have additional reinforcement in the middle to provide against break- age by handling. They were handled by a special form of sling or bridle, to reduce the stresses due to bending. The ' peerless' concrete pile has a sectional reinforced con- crete shell, which is driven down together with a steel driving pipe, both of which bear on a pointed cast-iron shoe, which is left in the ground. After the steel pipe is withdrawn, the shell is inspected, and filled with concrete by a special tremie de- signed for the purpose. The use of the steel pipe protects the concrete shell from severe stresses due to driving. Reinforced-concrete piles, with the unprecedented diameter of 25 inches, were placed under the Music Hall at the reconstructed pier in Atlantic City in 1906. Since the largest of these piles were nearly 50 feet long, it was deemed impracticable to mold them complete before sinking them in place. Accordingly, the lower portion, 12 feet long, which included an enlarged foot, 3^ feet in diameter and 2 feet high, was molded in a wooden form with the jet pipe and steel reinforcement in place. When the concrete was hardened, a T \-inch galvanized steel shell ART. 47 COMPOSITE TYPES AND COMBINATION PILES 145 was slipped a little distance over its top, and the joint made water-tight by calking with oakum. The steel shell was made water-tight by close riveting and calking, and was long enough to reach above the water when sunk. After the reinforcement of the upper part of the pile was hooked on- and the jet pipe extended, the pre-molded pile and casing were swung into place and sunk about 16 feet in the sand by the water-jet. The steel form was then filled with concrete. Where the conditions are such that the water-jet cannot be used to sink them and there is danger of damage to pre-molded piles by driving, the following method may be adopted: A steel shell and cast-iron shoe are driven to the proper penetra- tion by the method used for Simplex piles; some concrete is then placed in the shell and a molded reinforced-concrete pile is inserted and imbedded firmly in the concrete in the bottom of the hole, after which, the intervening space is filled with a strong grout and the shell is withdrawn. The quantity of grout used is to provide some excess over that required to fill the space between the molded pile and the sides of the hole after the shell is withdrawn. This method was specified for the pile foundations of a rein- forced-concrete structure of the Pittsburgh and Lake Erie Railroad at Youngstown/ Ohio. The molded piles were octag- onal in form, \2\ inches thick, of uniform cross-section through- out and the lengths were determined by driving test piles. The molded piles were varied in length by steps not exceeding 5 feet and generally smaller; and the top of the molded pile was brought to the proper elevation by adjusting the quantity of concrete filling, which ranged in depth from 2 to 5 feet after the shell was withdrawn. The reinforcing rods extended 2 feet below the bottom of the molded pile. It was specified that the Simplex forms and shoes were to be driven to a penetration of \ inch per blow from a 3ooo-pound hammer, falling 15 feet. No inserted pile was to be exposed to stresses due to driving adjacent piles, until it had been in place 15 days. The piles were designed to carry 50 tons per pile safely, and those selected for testing were to settle not more than 146 CONCRETE PILES CHAP. IV a half-inch under a load of 60 tons. It was estimated that the use of molded piles thus inserted, at an increased cost per pile, would reduce the total cost of the foundation by diminishing the sizes of the pier footings, under the assumption that their safe bearing power is 25 percent greater than that of cast-in-place piles. On the Pacific Coast, combination piles have been made for wharf construction by driving a wooden pile from 50 to 60 feet long with its head projecting 10 feet above the mud line, which is 20 or 30 feet below the top of the wharf. A hollow reinforced- concrete pile 2 to 3 inches thick and 24 inches in diameter is then FIG. 470. Ripley Combination Pile. driven over the wooden pile to a good bearing in the mud. After removing the mud and water inside, the hollow pile is filled with concrete. Such combination piles can also be used in foundations on land, and are considerably cheaper than very long concrete piles. Similar combination piles were used in the Delaware Lacka- wanna and Western Railroad Terminal at Hoboken, N. J., but in this case the form for the concrete top was attached to the pile and carried down with it into position so as to avoid the necessity of pumping out the form. The forms were filled after the follower was withdrawn. Occasionally the durability of concrete piles is combined with the lesser weight and cost of timber piles, in a single building foundation by placing concrete piles on top of timber piles, which ART. 48 DRIVERS, HAMMERS, AND CAPS 147 are driven below ground water level with the aid of a follower. In case the concrete pile is built in place, a waterproof tube or container is put on top of the timber pile, filled with concrete, and after the concrete is hardened sufficiently, the upper end of the container is cut away at the lower surface of the concrete cap or footing. The Ripley combination pile, shown in Fig. 470 is composed of a timber pile encased in concrete. The reinforcement con- sists of wire mesh wound spirally with the concrete around the pile to which it is attached by staples, the final lap being tied with wire. Before concreting, spikes are driven into the timber at intervals on its surface. The concrete is a 1-2-3 mixture of cement, sand, and broken stone. ART. 48. DRIVERS, HAMMERS, AND CAPS To drive pre-molded piles the pile-driver and its equipment have to be strong on account of the greater weight to be handled, and the heavier hammers used. Piles weighing from 2 to 4 torts are quite common and those of 6 to 8 tons are employed on heavy construction. On this account the steel pile-driver is growing in favor. It is found to be stiffer, more durable, and lighter for the same strength than those built of wood. The necessity for dragging the piles from the casting platform or from the unloading platform to the driver develops stresses in the tower for which special provision must be made in the design. Concrete piles should be driven wherever possible with the aid of the water-jet so that the duty of the hammer becomes secondary. However, in some kinds of earth it is necessary for the hammer to do very effective work either with or without the aid of the water-jet. Under such conditions it is uneconom- ical to use a light hammer which may answer very well for a timber pile but which itself is considerably lighter than a con- crete pile. Otherwise the temptation is constantly present to use too high a fall and thus expend too large a part of the energy in useless or destructive work. 148 CONCRETE PILES CHAP. IV In driving concrete piles into hard clay for the foundations of the Kentucky and Indiana Bridge to which reference was made in Art. 43, a steam-hammer was at first used in which the striking parts weighed 3000 pounds. Upon substituting another one with a 6ooo-pound striking weight the results were far more satisfactory. Although drop-hammers weighing less than 4000 or 5000 pounds have been employed to drive concrete piles successfully the time required was unnecessarily large to secure the required total penetration. Very satisfactory results have been secured on some building foundations in Pittsburgh by using hammers weighing from 7000 to 12000 pounds each. Such hammers are handled by three-part crucible-steel lines rove at the lower end over sheaves set in the hammer casting. The fall of the largest hammer is limited to about 8 feet, but is usually less, and it has been used to drive concrete piles weighing about 3000 pounds to an average depth of 30 feet below the surface with a penetra- tion in the gravel of i inch for the last ten blows of the hammer. Three machines operated by a total crew of 25 men, have aver- aged 15 piles per day for each machine, with a maximum of 25 piles, while driving through mud and clay which overlay a deep gravel stratum. The heaviest steam-hammer built prior to 1913 was an Arnott make with a total weight of 28 ooo pounds and with striking parts weighing 4000 pounds. Its length of stroke is 36 inches. It was especially designed to drive concrete piles 24 inches square and 47 to 77 feet long for the monolithic concrete piers, docks and breakwaters of the Canadian Government at Halifax, N. S. A single-acting hammer has been built with moving parts weighing 7500 pounds, and a total weight of 16000 pounds. Those who have had experience with both steam- and drop- hammers in driving concrete piles state that the steam-hammer drives them in less time and with less injury to the pile. Excel- lent results have, however, been obtained with the drop- hammer, the heavier hammers being the more efficient. The successful driving of pre-molded piles without injury, when it is necessary to use the hammer actively, is due mainly ART. 48 DRIVERS, HAMMERS, AND CAPS 149 to the various driving caps which have been devised as the result of experience. Fig. 480 shows the form used for the foundation pile of the Municipal bridge approach at -St. Louis. The construction is fully explained on the diagram. It was found that as long as the blow could be uniformly distributed on the pile head but little injury was produced, but when the Casi- Steel Striking Piece Drift Hole for \ removing the Oak driving BlockX when worn out Oak Driving Block - -Steel Casting irLuqs to fit Leads of Driver -Layers of Old Rubber Belting -Band of l"Steel PI. bolted around Pile to prevent spa I ling -Reinforced Concrete Pile FIG. 48a. Cap for Driving Concrete Piles. pressure was too large on the edges the pile head spalled and exposed the reinforcing bars. Hence in some cases the head had to be cut off in order to continue driving. Fig. 486 gives the details of the shells of two driving caps which have been used on the Chicago, Burlington and Quincy Railroad. The steel cap which was first used consists of a built-up shell of f -inch plate, with steel channel guides riveted to the sides. The extension guides are to keep the cap in the leads when driving below the track, thus avoiding delay in reentering it. Near the lower end of the shell is fitted a 3 -inch oak block and above that a 6-inch layer of rope ends, old rubber hose or belting. Resting on top of this cushion is a short piece of wooden pile which extends above the guides and receives the blows of the hammer. For use with the cast-iron cap, the cushion consists of two layers of old rope or a bag of sawdust. CONCRETE PILES CHAP. IV After the pile is placed in position the cushion is laid on top of its head and the cap lowered over it. The top of the cap contains a short driving block. As shown in the plan this cap is designed to fit either a round or a square pile. Its jaws are chamfered at the top to facilitate reentering the leads when it 3 Section through Extension Guides Sr Section E-E Detail of Hoist Strap Steel Driving Cap FIG. 486. Steel and Cast- Iron Shells of Pile Caps. is driven below them. The cast-iron cap was found to be more satisfactory in service than the steel cap in which the rivets holding the angles broke repeatedly. The cap used in pile driving at the Kentucky and Indiana bridge at Louisville was square in cross-section, and composed of two bent steel plates bolted together through the projecting flanges at the sides. On the other two sides channels to engage the leads were riveted ART. 48 DRIVERS, HAMMERS, AND CAPS 151 by means of two pairs of intermediate horizontal Z-bars. After a number of experiments with cushions the best results were obtained by placing three cement bags filled with coarse sawdust directly on the head of the pile which projected several inches up into the steel cap. A square block of beechwood 2 feet long was placed on top to receive the blows of the hammer. This species of wood proved better than any other. In some cases where fine sawdust was used the pile heads shattered under very hard driving. At the Cleveland docks of the Pennsylvania Lines (see Art. 41) a cast-iron cap was used with an oak filler block on top and a few coils of rope underneath. At Cambridge (see Art. 49) the steel-plate cap was 16 inches square on the inside and inclosed an oak block 18 inches high, to the bottom of which six thick- nesses of rope and four layers of rubber belting were nailed. The cap was held in the leads by two pairs of vertical oak pieces bolted through the incased driving block. At Brunswick (see Art. 41) a cast-steel cap was used with rope and rubber below and a wooden driving block above. The cap was made to fit over the tenon cast on the head and performed the important additional function of preventing the pile from turning while it was being driven. At the Chicago and Northwestern Railway bridge at Racine, Wis., the cast-steel cap was 3 feet high and had a solid horizontal diaphragm in the middle. The underside fitted the pile and rested directly on its head. On top of the diaphragm was placed a rubber cushion and driving block. In another case the cushion in the casting is composed of coarse sawdust or planing-mill shavings, above which rested a hard gum driving block hooped with a steel ring. The sawdust or shavings are quickly compressed to adhere to the casting and only need occasional renewal. The driving block proved to be very durable. Sometimes rubber-lined canvas hose is combined with rope to form a cushion. In still another example, a mat of six layers of rope was placed on the pile head below the dia- phragm of the cast-iron cap while sawdust and a hooped driving block were placed above it. Australian pine has also been employed for driving blocks. 152 CONCRETE PILES CHAP. IV ART. 49. DRIVING CONCRETE PILES Some of the difficulties encountered in keeping the pipe from clogging when the jet pipe is cast in the pile, are due to improper construction of the nozzle. In ground containing a large pro- portion of sand the sinking can be done mainly by the use of the jet, the hammer serving merely as a weight or to give occasional light blows. Where clay is the predominant constituent of the ground the nozzle clogs frequently when the hammer is actively employed. This difficulty can be overcome most readily by extending the diameter of the end of the nozzle back for 12 inches or more, thus substituting a short-pipe tip for a conical tip. For concrete piles it is generally preferable, however, to use two jets on the outside of the pile. The equipment, methods, and precautions for the use of the water-jet described in Art. 17 apply likewise topre-molded concrete piles. The use of the water-jet with adequate equipment in sinking concrete piles whenever sub-surface conditions permit, is to be urged not merely on account of avoiding any possible injury to the pile by driving with a hammer but to save time and energy. At Brunswick, Ga., after failing to make satisfactory progress by means of the jet and hammer a new scheme was adopted, in which the pile itself was used as a hammer. A wire bridle was fastened near the top of the pile by which to lift it, but the cap and hammer were allowed to remain on top to give additional weight. The pile was raised from 1 8 to 24 inches and dropped, and while this process was continued the jet was constantly operated, until the driving was nearly completed. By this means the number of piles driven per day was increased to six- fold. The water was then shut off and the last few inches driven by the hammer alone. This distance was increased to 8 or 10 inches in good clear sand, as the jet excavated deeper below the foot than in the other material. The ground penetrated varied from clear sand to hard clay. It was also necessary to penetrate a 2-foot stratum of soft rock composed of shells, sand and lime which was harder than any coral. About 50 percent of the 6000 piles had to be driven through that material. Upon taking up ART. 49 DRIVING CONCRETE PILES 153 some piles driven through it the edges at the foot were found to be but slightly rounded off. The jet pipe was not reduced in diameter at the end, and the pipe did not clog from driving more than once or twice. Their dimensions are given in the ninth paragraph of Art. 41. At the Charleston, S. C., pier the bottom consisted of marl containing a yellow clay and about 15 percent of sand, making it extremely hard and sticky. When exposed to the air for a few hours it required a hammer to break it. Some of the piles (see Art. 41) had to be driven through 38 feet of the marl, and this was accomplished entirely by the churning process until within 2 or 3 inches of the full penetration when they were driven to grade by a 45oo-pound hammer. In driving 800 3o-foot concrete piles for the Sixth Street Viaduct in Kansas City, Mo., a hole was jetted down the full length of the pile in the proper position. The pile was then inserted in the hole and churned up and down with the hammer resting on top, while the jet was used alongside of the pile. Experience showed that two jets would have been better to secure sinking accurately in position. When the hole was not first jetted down the piles had a tendency to crowd toward those previously driven since the ground on that side was still soft. At Cambridge, Mass., where a 47oo-pound drop-hammer and water-jet were used in driving piles for a building foundation, it was found best to begin driving by churning and the water-jet, and after continuing this method as long as possible the chain which connected the pile to the hammer during the churn- ing operation was disconnected and the hammer started with a drop of about 2\ to 4 feet, and increasing the fall as the driving became harder. Sometimes the churning process can be employed advantageously to start a pile in cases where the leads are not long enough, or a short wooden pilot pile may be driven first and withdrawn, and the pile then churned up and down in the hole after directing a stream of water into it with the hose. In loam and ordinary clay it was the practice on the Burling- ton Railroad, as reported in 191 1, to put down two or three holes 154 CONCRETE PILES CHAP. IV with the jet as close together as possible. The pile was then set in the leads and driven without further use of the jet. It was found that this method saves time besides reducing injury to the pile. In many cases a penetration was thus secured which could not have been reached by driving with the hammer alone. In order to save a considerable length of pipe an arrangement is sometimes adopted of casting a jet pipe only in the lower por- tion of the pile, its upper end having a reversed curve and terminating outside of the pipe. The outside pipe can then be connected to this and afterward removed. This connection may be located just above the ground level in a pile extending above the water surface. It is remarkable how well pre-molded piles usually stand the pounding of the hammer where the jet cannot be used success- fully. In one instance where piles were driven into hard clay for a bridge pier, after several piles were driven the clay became so compact that it required 5000 blows of the steam-hammer to drive some of them 20 feet. In the few piles which were broken the crushing extended only 18 inches below the top of the head. At the approach to the Municipal bridge where the driving was very hard only eight out of 767 piles were broken, due to the cold weather retarding the setting of the concrete. Apart from this the injury to other piles was confined to some spalling at the heads, and that occurred mainly in piles made in the winter. In some cases, piles stood 40 to 80 blows per inch of penetration, but most of the heads were uninjured after sustaining more than 2000 blows of a steam-hammer. Reinforced-concrete piles made in cold weather and im- perfectly set due to the cold, can be driven practically without fracture at low temperatures, or about 10 to 15 degrees Fahren- heit. When, however, the temperature rises above the freezing point, such piles will go to pieces under the hammer. But after the piles are thoroughly cured they can be driven without danger of fracture. In other words, in respect to driving, the effect of freezing is practically the same as that of thorough set- ting of the concrete. ART. 49 DRIVING CONCRETE PILES 155 In driving 675 concrete piles, molded vertically in steel forms, to a penetration of 20 to 30 feet for bridge piers in Cleveland, no failures occurred and no pile heads were battered. A five- ton steam-hammer was used. Thoroughly well-seasoned con- crete piles will stand without appreciable injury several hundred blows with a 3ooo-pound drop-hammer, the drop increasing from 10 to 30 feet as driving progresses, but comparatively green piles must be handled very carefully and the drop limited to 6 or 8 feet. Such work is slow and expensive, and it is better to season piles thoroughly. In driving 3-ton piles under bridge abutments by the Sanitary District of Chicago, the time ranged from 9 to 27 minutes per pile for the driving, with 21 minutes or more to get the next pile ready. The average number of blows was 600, and the maximum 1782. One of the piles which required over 1600 blows was cut off i| feet, and no lines of weakness due to driving could be discovered. Of 300 octagonal piles driven by the Long Island Railroad on its Jamaica improvements not a single one was broken either in handling or in driving. In 1907 a pre-molded pile 30 feet long in which the reinforce- ment was electrically welded into a unit form, was selected at random from a thousand that had been driven for a dock pier. A careful examination of the pile after it was pulled up failed to reveal any defects. The same pile was thereupon driven and withdrawn twice in different locations through 20 feet of silt, sand and gravel into soft rock, without any sign of deterioration. Finally it was driven again for permanent use in the pier. At Cambridge in 1908 a reinforced-concrete pile struck a boulder at a depth of about 18 feet and could be driven no further. The 47oo-pound hammer with drops of 18 to 30 inches had given it 735 blows, the water- jet being used also. As the head was badly crushed the driving was stopped; the pro- jecting part was cut off, its ends squared, and sent to the Water- town Arsenal for test. Its length was g\ feet, its smaller section area 128.59 square inches, and it developed a compressive strength of 3865 pounds per square inch. Since this value exceeds the usual strength of reinforced concrete columns, the 156 CONCRETE PILES CHAP. IV pile evidently suffered no injury due to hard driving except at the head which was cut off. Another method has been used in hard clay which resisted penetration by the use of the steam-hammer except at too great a cost in time. The piles were 14 and 9 inches square at the butt and tip respectively, 22 feet long and driven to rock. Holes 12 inches in diameter were bored with a post-hole auger from 1 6 to 19 feet deep in which to place the pile and start driving. The weight of the hammer would push the pile down 8 to -i i feet. In driving the piles great care was necessary to center the leads directly over the piles so as not to cause bending in the pile. Only one out of 125 piles was shattered enough to condemn it, and only three required new heads to be cast. After gaining some experience 90 percent could be driven with- out a crack, and in the balance the cracks were confined to the topmost 12 inches. It was found necessary to stop driving at intervals to permit the compressed air and water in the auger hole to escape through the gravel next to the rock. In Art. 47 reference was made to a method which avoids driv- ing the concrete pile itself, by first driving a very heavy steel tube fitted with a point or shoe. After it has penetrated to a good bearing, a few cubic feet of concrete are deposited in the bottom of the form. A pre-molded pile, slightly smaller in diameter than the tube, is then lowered to place and forced into the plastic concrete. After withdrawing the tube the remaining space is filled with grout. By this method a pile may be forced some distance into stiff clay or hard-pan which is overlaid by soft material that would not otherwise hold the pile in place 1 aterally. Concrete piles cannot be driven as rapidly as timber piles on account of the care necessary in handling the greater weights, and the extra work in getting ready to drive, as well as the necessary delays incidental to driving. In one case where three crews were working on the same foundation, one drove 41 piles aggregating 1207 linear feet in 872 hours, another 39 piles or 1130 linear feet in 9 hours, and the third 45 piles or 1064 linear feet in 10 hours. In another case 42 piles were driven in ART. 50 ANALYSIS OF TIME AND COST 157 10 hours. No soil has been encountered in which wooden piles can be driven in which it has not been possible to drive concrete piles, and in many cases with far less danger of over- driving. At Greenville, N. J., a Chenoweth pile 13 inches in diameter and 50 feet long was driven into the ground and pene- trated 8 feet into a substratum of gravel, and subsequently with- drawn. A wooden pile could be driven only 2 feet into it. Occasionally it is found to be impossible to drive a concrete pile to the proposed depth, and it becomes necessary to cut off its head to a given grade to connect with a concrete footing. A track chisel and heavy hammer may be used for the concrete and a hack saw for the reinforcing bars. A plumber's pipe cutter has also been used for round reinforcing rods. Since the concrete is usually not more than a month old when driven the task of cutting it is not as difficult as for concrete which is thoroughly seasoned. ART. 50. ANALYSIS OF TIME AND COST In order to obtain data for estimates of cost for pile driving a series of observations was made in 1908 by SANFORD E. THOMPSON and BENJAMIN Fox, of the time required for each elementary operation into which the process of pile driving was analyzed. The results in detail together with the conclusions and some recommendations intended to facilitate pile driving operations by better system and less waste of time are published in the Journal of the Association of Engineering Societies, vol. 42, page i, January, 1909. The ground at the site, as was shown by explorations, con- sisted of 6 to 8 feet of fill; and then to a depth of 29^ to 31^ feet from the surface, fine sand and mud, but which was prac- tically considered all sand; underlaid by a clay hard-pan which was tested to a depth of 13 feet. The piles were 14 and 9 inches square at the butt and tip, each one being reinforced by four | -inch corrugated bars with loops of J-inch bars spaced about 12 inches apart but reduced to 4 inches near the head. Extra longitudinal reinforcement of f - or |-inch bars 2 or 3 feet 158 CONCRETE PILES CHAP. IV long was also put in the head. A galvanized pipe was cast in the center of each pile for the water- jet. For experimental purposes the pipes were 2, ij, ij and i inch in diameter. The piles were seasoned from 30 to 41 days. A drop-hammer was used weighing 4700 pounds. " After moving the pile-driver, the usual [work preliminary to the actual] driving consisted in hooking and dragging the pile; lifting it to place and attaching the hose, or attaching the hose first and then lifting; and setting the pile in the leads. The water was then turned on and the pile usually penetrated for a short distance without the hammer. The hammer was then placed on the cap and the pile sank further to a depth depending upon the nature of the fill. Next the hammer was attached to the pile with a chain and the churning commenced. There was enough play in the chain connection to give about a lo-inch blow of the hammer each time the pile was lifted. When this churning became ineffective the chain was disengaged and the pile was driven with blows in the usual manner." The elementary unit-times were obtained in sufficient detail so that they may be recombined in any desired arrangement. "This enables the constants to be distinguished from the variables, abnormal times corrected, and lost time which will not occur on another job eliminated. Allowance can be readily made for the time which is always necessarily lost during rests and ordinary delays." The average time per pile was found to be as follows: For moving the pile driver, 29.0 minutes; placing the pile, 23.0 minutes (including delays 5.1 minutes); driving 83.0 minutes (including delays 2 1 .3 minutes) ; a total of 2 hours and 1 5 minutes. As the men became more expert in moving the driver and plac- ing the piles, their average times were reduced in the last 4 days to 27 and 13 minutes respectively, the former, however, being still unnecessarily long on account of imperfect rolls under the driver. The time of driving was greatly increased by the low pressure of the water-jet. Taking an average for 16 piles driven in less than an hour each, the time during driving was 44 minutes, making the total i hour and 24 minutes. Ex- ART. 50 . ANALYSIS OF TIME AND COST 159 pressed as percentages the three operations require respectively 32.1, 15.5 and 52.4 percent of the total time. One-half of the delays were said to be avoidable. A further analysis of the time required to get ready to drive, exclusive of delays, gives the following percentages; Attaching the rope to the pile, 14.1; dragging the pile to the driver, 30.4; attaching hose and ropes preparatory to raising 15.6; rais- ing the pile to a vertical position, 12.2; placing the pile in the leads, 15.9; and placing the hammer and cap on the head of the pile, 11.8. The number of blows of the hammer varies from 112 to 1160, the average being 589; the average range in the fall of the hammer is from i.o to 5.6 feet, exclusive of i range from 25 to 20 feet; the average fall for the last blow is 4.7 feet, exclusive of one drop of 10 feet; while the average penetration under the last blow is closely J inch, the maximum value being | inch. The total penetration varies from 25.6 to 32.0 feet, exclusive of one of 18 feet, the average being 28.7 feet. The same investigators made the analysis of the cost for making and driving the piles, expressed in cents per linear foot of piling, which is given on the next page.. Accordingly the total cost per linear foot for making and driving the piles is $1.64. The cost for items i and 28 are based on the assumption that the plank is used four times. A few of the items, such as 12 and 13 are constant per pile and independent of the length, and may therefore be modified for a close estimate. The only items depending upon the character of the ground are 22, 24, 25, and 27. The cost for these items is based on the assumption of driving five and three-fourths piles in eight hours, and hence the corresponding cost can be estimated for a harder or softer ground by as- suming the number of piles to be driven per day. To make similar records of value for other estimates the following elements must be kept in mind: (i) "To distinguish between the times which are constant for any job and those which vary with the quantity of the work; (2) to separate items which may be abnormally large or abnormally small on the 160 CONCRETE PILES CHAP. IV 1. Plank for molding platform 2 . 56 2. Lumber for chamfer 0.72 3. Spikes for platform | 4. 5. Nails (qd. and 4d.) for forms J 6. Crushed stone. . 5.12 7. Sand i . 26 8. Cement 8.64 9. Longitudinal reinforcing bars 26 . 70 10. Lateral reinforcing loops 4.01 11. Wire to bind reinforcement together o. 50 12. Extra short bars in head o- 79 13. Nipples for jet pipe o . 49 14. Ells for jet pipe 0.39 15. Jet pipe 3.46 16. Hooks to handle pile 0.82 17. Bending and placing reinforcement 8.38 18. Labor on pile platform 2 . 26 19. Labor on forms 5.72 20. Labor on concrete 7.51 21. Superintendence for making piles 2 . 13 22. Pile-driving labor 27.22 23. Cutting slot in tip of pile o. 20 24. Repairs to pile-driver and cap 1.52 25. Cutting off broken piles i . 61 26. Rent of engine 2 .07 27. Superintendence for driving piles 2 .86 Cost varying with number and length of piles. .... 117 .05 28. Plank for sides of forms $i 7 . 50 29. Plank for ends of forms 7 . 50 30. Pile-driver, 25 percent of cost 49-55 31. Getting ready, two days 60.00 32. Teaming for pile-driver, etc 34-55 33. Removing driver 34 61 Total cost for the job $203 . 71 Cost of items which are constant for each job 13 .91 Total estimated net cost per linear foot if the job has 48 piles 130 . 96 Add 25 percent for pumping, connections, contingencies and profit 32 . 74 163.70 ART. 51 FORMULAS FOR BEARING POWER l6l job in question, so that allowance may be made for these particular items in future estimates; (3) to separate the time necessarily wasted because of abnormal conditions, or because the work is of a new or untried character." ART. 51. FORMULAS FOR BEARING POWER In Art. 27 a reference is made to the relation between the weights of the hammer and pile. The formulas for the bearing power of piles given in Arts. 25, 26 and 30 do not take this into account by means of a separate term, but it is understood that this relation must be considered in any rational use of the formulas. On account of the great weight of concrete* piles this relation becomes one of increased importance, but it does not seem to be sufficiently appreciated in practice. Conservatism tends to employ the same weight of hammers for concrete piles as for timber piles, and to increase these weight for new equip- ment but slowly. Progress in this respect may be materially aided by the use of formulas in which the weight of the pile is introduced separately. Several formulas of this type are in extensive use in Europe. EYTELWEIN'S formula in its ordinary form gives the ulti- mate resistance, but if one-sixth of its value be taken as in the case of the Engineering News formula, it becomes 2W h H ! in which the W h denotes the weight of the hammer, W P that of the pile, H the fall in feet, and s the average final penetra- tion in inches. It will be noted that if the penetration is i inch, and the hammer and pile have the same weight, that the value of the denominator is the same as if it were j-f-i, but if the hammer weighs twice as much as the pile, the safe load is increased 33 percent. If the penetration be f inch, the bear- ing power by the Engineering News formula is 1.33 W\H, 162 CONCRETE PILES CHAP. IV whereas formula (i) gives 2 W h H and 2.67 W h H, for the two cases when W W P and W h = 2W P . These results indicate such radical differences that an urgent need is shown for careful comparative tests for driving concrete piles with different weights of hammers and within a limited range of fall. RITTER'S formula may be written in the following form: Ultimate load = ~ ' ~ +W h +W p (2) in which the terms are the same as those denned in the preceding paragraph. When s=i and W h = W P , one-sixth of the first term has the same value as the Engineering News formula, but when W h = 2W P its value is increased 33 percent. This formula differs from EYTELWEIN'S for the ultimate load merely in the added weights of hammer and pile. As a result of extensive experience by the Raymond Con- crete Co., in driving heavy collapsible cores for cast-in-place concrete piles M. M. UPSON states that the Engineering News formula may be safely used to determine the approximate bearing power, and that the bearing power of the core may be applied to the cast-in-place pile provided that the compression of the soil is not released by the collapse of the shell. Steam- hammers are generally employed, the heaviest hammer being used for the longest standard core. It has been truly said that no formula for pile driving can give more than an approximation to the supporting power of the special pile observed, and only at the time of driving; but with an intimate knowledge of the soil conditions, a good formula becomes valuable, and considerable money can often be saved by its proper application. In this manner the science of pile driving can influence the art. The peculiar and appar- ently erratic variations in the results obtained can be readily and satisfactorily explained by conditions in the ground, but they prove that it may be misleading to use a formula when no exploration has been made of the sub-surface con- ditions at the site. ART. 52 CHOICE OF TYPE 163 ART. 52. CHOICE OF TYPE When it is determined in any given case that the use of concrete piles is justified by considerations of economy in which due allowance is made for durability, as well as the other elements referred to in Art. 41 and the conditions at the site are known as the result of careful explorations of the ground (Art. 174), the next question is to decide what type of pile is especially adapted to these conditions, due consideration being given to the certainty of securing adequate strength at reason- able cost. It may fairly be assumed that each type of pile has some distinctive advantages which are adapted, more or less closely, to certain conditions of the ground where piles are necessary. To use a type of pile, under conditions which are not favorable, involves either an economic loss, or a smaller degree of security, or both. Naturally some types may be applicable to a wider range of conditions than others and it is the duty of the engineer to study each situation as a special problem. When piles are used to support a structure above open water, as in pile trestles, wharves, piers, etc., they are required to resist flexure, as well as to act as columns. Pre-molded piles are the only ones which are adapted for this service; and they should be molded without taper, at least for that part of the length, whjch is not in the ground. If the piles penetrate sand, which is not liable to scour, that portion may be tapered, since in sand the supporting power is almost wholly due to friction. If, however, the sand is liable to scour, or if adequate total penetration can be secured to furnish the necessary frictional surface, as well as the required horizontal reactions without exceeding the safe bearing value on the side of the pile, then a pile with uniform cross-section should be used. In ordinary sand, quicksand,, or in combinations of sand with gravel or clay, so as to produce a porous mass, in which the water- jet can be used successfully, the pre-molded pile has special advantages. When a pile is driven through soft material to a hard sub- 1 64 CONCRETE PILES CHAP. IV stratum, so that it must act as a column, it must be reinforced, and hence frequently the pre-molded pile is the only type that can be used. The pile should be uniform throughout, so as to have a large bearing area in the harder substratum. Whether other types can be used, depends upon the nature of the over- lying material. If any stratum contains quicksand or other soft material, which will not retain its form until the pressure of the concrete can resist the external pressure, then no cast-in- place pile should be used, which does not leave a casing in the ground which can retain its form until the concrete has set. If such a shell or casing is used, it should also have uniform diameter, so as to secure a larger bearing area at the foot, than that for a tapered pile. If, however, the overlying material is of such a nature that it will retain its form temporarily, until the concrete is in place, then those types in which the pipe is gradually with- drawn may be used. If the underlying stratum which is to bear a considerable part of the load is not sharply defined on its upper surface, it may be desirable to increase the bearing sur- face of the pile by means of an enlarged base. The method of forming the pedestal pile requires the material adjacent to the base to be displaced by the pressure of the concrete due to ramming. If the material is not homogenous, the base may be unsymmetrical about the vertical axis, and thereby produce an eccentric reaction on the pile column, thus causing dangerous stresses in the stem. In any case, when the load is mainly carried to its foot, the pile must be reinforced, unless the over- lying material affords good lateral support, and there should also be some limiting ratio of length to diameter. It should be remembered that if subsequent to the installa- tion of plain concrete piles, the adjacent ground is subjected to very heavy loading, that in some kinds of earth like stiff clay, lateral pressure will be developed, thereby causing serious bending moments, which piles without longitudinal reinforce- ment may be unable to resist safely. If for example, the substratum is hard clay and the foot of a pile of uniform section does not afford sufficient bearing area, ART. 52 CHOICE OF TYPE 165 then an elarged base may be formed by a tool like that referred to in paragraph 17 of Art. 45. When the ground is compressible at the top but not soft, and gradually increases in density downward, any one of a number of different types may be employed, provided proper precau- tions are taken, but all of them should be without taper, so that proper advantage be taken of the greater bearing at the foot and the greater frictional resistance of the lower surface of the pile. Pre-molded piles will probably require the use of the hammer, as well as the jet, or if conditions on adjacent property do not permit the use of the jet, the driving may be done by the hammer alone. For cast-in-place piles, the necessary pre- cautions relate more particularly to the order in which the piles are placed, so that no core or pipe is driven for another pile within a prescribed distance of any one during the setting of its cement (see Art. 46). When proper consideration is given to the importance of this matter, the relative cost of driving differ- ent types of piles assumes a different aspect. Usually the eco- nomic relation will decide the choice of type of pile, and hence it is of the utmost importance, that the same degree of security should be demanded for every one, so far as this is practicable. When the ground near the surface is not quite sufficient to carry directly the load transmitted by a wall or column, with the aid of a spread footing or when it costs less to increase its bear- ing power by means of piles, then the tapered pile of short length is most advantageous. Whether the pre-molded pile or one of the cast-in-place piles will be most advantageous, prob- ably depends upon similar considerations to those described in the preceding paragraph. If the ground consists of silt or alluvium for a great depth and increasing but slowly in density with the depth, so that the bearing power depends practically all on skin friction, the choice between a tapered and an untapered pile depends upon two factors. The pile with a uniform section has a slightly larger superficial area for a given volume, the greatest difference being practically less than 5 percent. Such a pile has .the additional advantage of having a larger proportion of its surface 1 66 CONCRETE PILES CHAP. IV in the lower part of the pile, where the friction is slightly greater. But the tapered pile has a larger section area of concrete at the top to transmit the load and that may govern in some cases. As the load is gradually transferred to the surrounding earth in passing downward through the pile, the decreasing section area of a tapered pile makes it conform more closely to one of uni- form strength throughout. If the ground is tough and leathery, so as to cause upheaval when adjacent piles are driven, it would be disastrous to use some types of cast-in-place piles ; but so far as form is concerned the piles should not have any taper. Sometimes deep beds of clay require pile foundations be- cause the upper stratum becomes soft during the flood season, while during the most favorable time for construction, the clay is so hard that it is impracticable to drive any piles. Under such conditions, a satisfactory solution consists in excavating holes by means of an earth auger of the proper diameter, and then driving a pre-molded pile into it, so as to fill the hole so prefectly that the surface water will not follow down the pile. Although some type of concrete pile may be adapted to nearly all kinds of earth, there are limitations imposed that leave a field of usefulness for the timber pile. Some black marshy land will carry timber-pile trestles safely but nothing heavier than that. Concrete-pile trestles, with their rein- forced-concrete caps and slabs require the strata below the top to contain sand, gravel or stiff clay. In other cases, combination piles are used to reduce the load as well as the cost (see Art. 47). ART. 53. EFFECT OF TAPER To indicate the relative properties of tapered and straight concrete piles let the following example be considered. Let the tapered piles be 20 feet long, and the diameters of its head and foot be 20 and 6 inches respectively, making its volume 20.2 cubic feet. Let a straight pile be taken having the same length and volume; its diameter is therefore 13.6 inches. In the tapered pile 44.5 percent of its volume is in the uppermost ART. 53 EFFECT OF TAPER 167 quarter of the pile, and 74.2 percent in its upper half; while 35.1 percent of its available surface for frictional resistance is in the top quarter, and 63.5 percent in the upper half of the pile. Since piles are frequently spaced 3 feet between centers, let it be assumed that the compression of the earth surrounding a pile, which diminishes from the pile outward according to some law depending upon the nature of the material, be equiva- lent to a uniform compression, limited to a radius of 1.5 feet from the center of the pile. Dividing the depth into four quarters the ratio of the displacement of the pile to the corresponding volume of the compressed earth is accordingly 25.8 percent for the top division 16.9 and 9.8 percent for the next two divisions and 4.7 percent for the lowest division. For the straight pile the corresponding values are 14.3 percent for each division. The proportions of the total frictional area of the tapered pile are 35.1, 28.4, 21.6, and 14.9 percent in the four divisions respectively, while those for the straight pile are each 25.0 per- cent. The frictional areas of the tapered and straight piles are 68.1 and 71.2 square feet, the difference being a little less than five percent. It should be noted especially that about 45 per cent, of the total equivalent compression of the earth was expended in the top division, and very nearly 75 percent in the upper half of the depth. It may be considered objectionable to adopt a large taper since the compression of the earth is thereby made a maxi- mum near the surface and a minimum near the foot of the pile which is contrary to the fundamental principle of pile founda- tions; and since the area available for frictional resistance is reduced near the foot where the natural compression of the earth is generally the greatest and most useful. It should be added that the highly compressed and loaded area near the head of the pile may have its supporting power reduced by subse- quent shallow excavations or by erosion in contiguous areas. Probably a more important objection to a large taper is that an increased bearing capacity is artificially created in the ground which becomes dissipated in time as the pressures are dis- tributed through a larger mass. In districts subject to floods 1 68 CONCRETE PILES CHAP. IV the bearing power of the ground near the surface is at least temporarily reduced and if a large percentage of the load is carried by the ground near the surface, serious settlement is very likely to result. . It should be remembered that in driving a straight pile the compression of the earth is done at the tip by increments as the penetration of the pile increases; on the other hand in driving a pile with a large taper the compression thus made at the tip is materially smaller, but the compression is con- tinuously increased all along the depth of penetration while the total resistance increases to its final maximum value. The tapered pile, however, causes less displacement or disturbance of the texture or internal arrangement of the material through which it is driven than the straight pile. Experience in driving concrete piles into hard clay for the foundations of the Kentucky and Indiana bridge at Louisville, in 1911, led to a change in the taper by reducing the thickness of the head from 20 to 14 inches, leaving the thickness of the foot the same as before, or 9 inches, and below which there was a pyramidal point 9 inches long. The piles were square in cross-section and 22 feet long. In some cases 5000 blows had been required previously for the 25-foot piles with the larger taper (see fourth paragraph of Art. 43). Various tests have been made to determine the effect of taper upon the resistance of a pile. In a test at Chicago in 1901 a tapered steel core and an oak pile both 20 feet long were driven within a few feet of each other. The diameters of butt and tip were 18 and 6 inches for the core; 12^ and 10 inches for the oak pile. With a 22oo-pound hammer falling 25 feet, the former penetrated an average of i inch for the last several blows, and the latter 5^ inches. The volume of the oak pile is 67.5 pel cent of that of the steel core. In incompressible but plastic clays the wedge action of tapered piles is found to be of no value according to loading tests. Extensive experience proves, however, that concrete piles with a large taper have been used successfully in compress- ible ground to form foundations without subsequent appre- ART. 54 DRIVING AND LOADING TEST PILES 169 ciable settlement. In many cases, doubtless, the spread footing would have been a more appropriate type of founda- tion. In other cases, sand piles (Art. 58) might be preferable, for if the ground is to receive its greatest degree of compression near the surface, it would apparently be a more economical arrangement to fill the conical holes made by the tapered core with sand since sand is less expensive than concrete, and the increased bearing power of the ground could be utilized equally well by the concrete cap or footing (see Art. 150). The following experiment is very instructive regarding the effect of taper. A concrete pile was driven to a total penetra- tion of 26.5 feet, the diameters at the surface of the ground and at the foot being 18.6 and 8 inches respectively. The safe load was computed to be 40.9 tons. A wooden pile was driven to a total penetration of 24 feet, the diameters at the surface and at the foot being nf and 9^ inches. Its safe load was computed to be n.6 tons. These piles were both driven in dense blue clay. They were subsequently loaded and the test loads for a settlement of J inch in each case were 44 and 32.1 tons respectively. As the frictional surfaces are 92.4 and 67.2 square feet, the resistances are found to be 0.476 and 0.478 tons per square foot respectively. No definite conclusion can be stated with respect to the effect of taper since no adequate experimental investigation has been made of the subject. Tests are needed with piles of the same length and total penetration but with gradually increasing tapers, and these tests should be repeated in several typical kinds of earth. It is also desirable to have some sets in which the volume is constant, and others in which the frictional surface is constant. The problem involves a determination of the most efficient taper to secure an adequate total penetra- tion in combination with a maximum frictional carrying capacity per unit of surface area. ART. 54. DRIVING AND LOADING TEST PILES Concrete piles have been in use so short a time comparatively that no standard practice has yet been developed with refer- 170 CONCRETE PILES CHAP. IV ence to the allowed settlement of test piles for a given loading. It may be desirable therefore to state a few examples of such specifications. In one case where the piles were to be driven through materials ranging from quicksand to stiff clay, two test piles were required for each pier, the settlement in seven days under a load of 60 tons per pile being limited to i inch. In another case test piles 35 feet long were not to settle over f inch in 24 hours under a load of 40 tons. The building code of a certain city states that the allowable load on concrete piles shall be taken as one-half of the load which shows no settle- ment for 24 hours, and a total settlement not to exceed o.oi inch per ton of test load. Still another specification requires that not more than J-inch settlement shall occur on any one of six test piles for a building foundation under a load of 40 tons each. The piles varied from 30 to 40 feet in length and pene- trated sandy soil underlaid by irregular strata of soft blue clay alternating with strata of stiff material. A load of 25 tons was assumed for the design. In 1913 the city of Chicago required that for cast-in-place piles, test loads shall be applied on at least two piles in different locations and as directed by the Commissioner of Buildings, not less than three piles being driven at each location. The pile to be loaded is to be placed first; within six hours a second pile, and within 20 to 24 hours a third pile, are to be placed at distances from the first not to exceed twice the greatest diameter of the pile, the measurements being made between centers. The tests are not to be made until ten days after the placing of those which are to be loaded. The remainder of the test is to be the same as for pre-molded piles. In order to be certain that the kind of cast-in-place pile is adapted to the local sub- terranean conditions it is necessary to excavate one or more piles. In some cases it may be necessary to drive steel sheet- piling around it to exclude the ground water in order to make the excavation. Another city adopted specifications in 1913 for the test piles of a bridge foundation, requiring a balanced platform to be built on top of each test pile, and to have level readings taken ART. 54 DRIVING AND LOADING TEST PILES 17 1 on a rod set on a steel dowel grouted into the pile. For each test nine readings are required: Before the platform is placed; immediately after a 30-ton load is placed; 36 hours after this load is placed; after the load is increased to 40, 50, and 60 tons respectively; 36 hours after the load is increased to 60 tons; after the load is reduced to 30 tons; and immediately after the entire load and platform have been removed. To be acceptable the pile is not to show a settlement exceeding J inch between the first and third readings, exceeding f inch between the first and seventh readings, or exceeding inch between the first and ninth readings. The safe load is to be taken as one-half of the load which causes a settlement of f inch, and if this load is less than that originally assumed for the design, additional piles are to be driven so as to make the combined capacity of a group of piles adequate for the imposed load. The following is the record of a loading test for a concrete pile in pier 19 of the reinforced- concrete viaduct on the Pitts- burgh and Lake Erie Railroad referred to in Art. 47. The pile was 26.2 feet long below cut-off, the length of pre-molded pile used being 23 feet. In driving the casing the average penetration under the last five blows of a 3ooo-pound hammer, falling 15 feet, was 0.45 inch. The loading was begun at 7 A. M. on Sept. 6, 1912. The loads in tons and corresponding settlements in feet are as follows: 18.5,0; 27.0, 0.003; 32.0, 0.004; 35-0, 0.006; 38.5, 0.006; 45.0, 0.006; 52.0, 0.008; 57.0, 0.008; 59.0, 0.008; 60, 0.013 (Sept. 7, 2 P. M.); 60.325, 0.013; 60.325, 0.013; (Sept. 9, 8 A.M.). After removing the load two-thirds of the settlement was recovered leaving a permanent set of only 0.004 foot or 0.05 inch. A test well 8 feet distant indicated that the pile penetrated 10 feet of cinder fill, 5 feet of dark mud, 3 feet of sand, 4 feet of gravel, 3 feet more of sand, while its foot rested on another stratum of gravel which is 4 feet deep. The loading tests of two pre-molded piles driven by very heavy drop-hammers have been published. One was driven by a 7ooo-pound hammer to a depth of 27 feet 2 inches through silt, sand, and gravel. A test load of 63 tons caused a settlement 172 CONCRETE PILES CHAP. IV of only | inch at the end of 2 weeks. Another pile driven by a i2ooo-pound hammer to a total penetration of 30 feet, upon being loaded with a weight of 72 tons showed no settlement at the end of 6 months. The use of such heavy hammers was referred to in Art. 48. While experience has shown that in most conditions of the ground the phenomena of pile driving give a fair measure of the bearing power, there are others to which this statement does not apply. Some moist clays are practically incompressible but being plastic, the piles displace the material and force the surface upward elsewhere. This movement may be so small as to escape observation unless levels are carefully taken. In such a case the loading of test piles will reveal the true condi- tions. For example, a pile required 30 blows of a steam-hammer, having a striking weight of 3000 pounds and stroke of 30 inches, to produce the last inch of penetration while the total pene- tration was only 9 feet. The ground was " ordinary yellow clay which was moist but not wet, and fairly solid." Under a load of 20 tons the settlement was 3! inches; for 25 tons, 5 inches increasing to 5! inches the next morning; and for 35 tons, 7 inches, which increased to 7J-f inches the following morn- ing. In subsequently testing a group of four piles it was ob- served that some of the adjacent unloaded piles also sank dur- ing the progress of loading, but rose after the maximum load had been in position for a time. Level readings taken over the whole area of the excavation revealed the fact that the volume of clay forced upward was practically equal to the volume of the piles beneath the surface. These tests led to a change in the type of foundation adopted. ART. 55. SPECIFICATIONS In Art. 38 extracts are given from GREINER'S Specifications which relate to timber piles; the following paragraphs are taken from the same source and relate to concrete piles. 88. Concrete piles, when reinforced and designed so that they may be handled and driven with steam-hammers in the same manner as timber ART. 55 r SPECIFICATIONS 173 piles, and when of the specified quality and sizes driven to refusal, may be subjected to a maximum load not in excess of 24 tons when used for rail- way bridges, all movable spans, arches and high abutments, and 30 tons when used for other foundations. Concrete piles molded in place without metal reinforcement should not be used in water or ground so soft as not to give firm lateral support. When they are molded in a strong metal shell, previously driven to refusal and which remains in place after concrete has set, the safe loads when piles are completely embedded in firm earth may be taken the same as specified above for reinforced piles. When their design is such or the conditions are such as to necessitate the piles being jetted down instead of driven, the safe load should be not more than specified above or more than one-quarter of the failure load as deter- mined by actual tests. When concrete piles act as columns they shall be designed as columns. 135. Concrete piles shall be of portland cement concrete in the propor- tion of i cement, 2 sand and 4 broken stone, varying in size from | inch to i inch. They shall be constructed strictly in accordance with the plans but when their construction is not shown thereon they shall be of a type suitable for the conditions, and which will meet with the approval of the engineer. Their minimum diameter at. tip and maximum diameter at butt shall be same as specified in paragraph 133 for timber piles. When driven through hard ground they shall be shod with steel points of approved design. When subjected to the maximum loads specified in paragraph 88 they shall go to rock or shall have an average penetration under each of the last twenty blows of a steam-hammer not in excess of that deter- mined from the formula S=WH/ 450000.1. In case this maximum penetration cannot be obtained without injury to the piles, or on account of the impracticable length required, the number of piles shall be in- creased until the load on each shall not exceed the amount indicated in the following formula for piles supporting railway bridges, all arches and movable spans. P _i.o6 WH JT 5-f-o.i For other structures the above load may be increased 25 percent. When concrete piles are jetted in place they shall either go to rock or to a solid stratum in which case they shall be tested with steam-hammers and the set and loads shall not be greater than above specified. When piles are placed by other means than by hammers and jetting and when they are of such design as not to permit of them being driven same as timber piles, the safe loads and numbers required shall be determined by tests to failure as directed by the engineer, the expense of the tests to be borne by the contractor and included in his cost. CHAPTER V METAL AND SHEET PILES ART. 56. TUBULAR PILES Some of the problems relating to underpinning and the foundations of buildings in New York City led to the intro- duction in 1901 of a patented pile which consists of a steel pipe filled with either plain or reinforced concrete. The steel pipe or casing can be of any diameter of which pipe and well casings are manufactured, but the most usual sizes are 12 inches inside diameter and 9 inches outside diameter. The thickness varies from i to f inch. Since in underpinning the head room is generally limited, the casings are designed to be driven in sections from 5 to 20 feet in length. The ends of the sections are machined so as to be truly perpendicular to the axis, thus securing a true alignment of the pile, and a uniform bearing of the metal. Inside sleeves are provided to hold the sections together and they have a driving fit in the pipe. Means are provided to prevent the sleeves from moving under the blows of the hammer while driving the pipe, and their length is not less than twice the inside diameter of the casing. The lowest section bears on the shoulder of a hollow conical shoe of cast iron or steel which is fitted with a hole for a water-jet, if re- quired. The casing is driven like sheet piles with a steam- or pneumatic hammer, usually without leads, the head of the casing being protected by a cap. In some ground, especially in sand, the casing is driven without a shoe, and the sand is removed through the pipe as the driving proceeds. It is claimed that such a pile has been driven to a depth of 80 feet with perfect alignment. When the casing has been driven, a hollow steel tube of con- siderable strength is thus provided which is then filled with ART. 56 TUBULAR PILES 175 concrete. When the concrete is to be reinforced, sleeves connected to the casing are provided which hold each rein- forcing rod in place without any lateral play. The pile is built up as it is driven down and if any material length projects above the ground it is cut off and used on another pile. Before the pile is filled with concrete an electric light can be lowered to ascertain if the true alignment of the casing has been main- tained. In underpinning, the casing is often forced down by means of a hydraulic or a screw jack. If driven into soft soil without a shoe the concrete may be rammed so as to form a bulbous foot to increase the bearing area. Experience indicates that if the earth surrounding the piles remains undisturbed, the casings may last for many years. These pile casings are not good, however, when exposed to the action of moving water or air, which permits the thin film of oxide forming on the surface of the metal to be removed. In designing piles careful consideration should be given also to the probability of injury due to electrolysis and methods of protec- tion against it. In the trade the casing described above is known as the Simmons sectional concrete pile casing. Piles of this kind have been used up to 85 feet in length. Fig. 56^ shows a wall pier of a 1 2-story office and loft build- ing built in 1912-13 in New York City in which three tubular piles support a wall column seated on an I-beam grillage. The inside diameter of the steel tubes is 12 inches, and they are spaced 2 feet between centers. Additional piles are driven between the clusters to carry the walls between columns. Most of the interior foundations have clusters of four piles spaced 2 feet apart. All the tubes are made in two sections, connected by a cast-steel inside sleeve tapered slightly at the ends to make a driving fit and provided with an exterior horizontal rib in the middle against which the pipes take bearing. The rate of driving with a steel hammer varied from 40 to 200 feet in one 8-hour shift. They penetrated through some sand, about 8 feet of mud, 5 feet of hard clay, 25 to 35 feet of fine wet sand and gravel; to the irregular surface of the rock which in most places was overlaid by about 2 feet of hard-pan. The interior of the I 7 6 METAL AND SHEET PILES CHAP. V pipes was cleaned out every 5 to 20 feet by the use of air pressure at 150 pounds per square inch delivered through a 2\ inch pipe without a nozzle, and which blew out the sand, lumps of clay, and ground water high into the air. From one to five 2- inch reinforcing rods were set with a clearance of about i inch from the pipe and driven to a solid bearing. Their tops were also arranged to bear firmly against the cast-iron cap. The T Wall Columns ~\ PileDetail Wall Pier FIG. 560. Tubular Piles. concrete filling is a 1-2-4 mixture, and the piles were propor- tioned for loads of from 56 to 80 tons each. The stresses allowed for the steel and concrete are 4200 and 350 pounds per square inch respectively. The section areas of steel vary from 17.8 to 30.2 square inches and of concrete from 109.9 to 97-5 square inches. A light framework containing templates at the top and bottom, and thoroughly braced was used to secure accurate location and alignment. It will be observed that the de- ART. 56 TUBULAR PILES 177 tails of these piles differ from those described in the preced- ing paragraphs. If the cleaning out of tubes or casings during the process of sinking causes trouble in the settlement of adjacent buildings, they may be driven to a firm bearing on the rock or hard-pan and cleaned afterward by the dry-blow-out process. A bag of dry cement may then be placed in the bottom and the reinforcing rods placed in position. The casing is filled with water to resist any external pressure, if necessary, and after the cement has set, the casing may be pumped out and filled with concrete. Sometimes the jet which aids in sinking the tube and scouring out the interior is immediately afterward con- nected to a tank of grout under air pressure, and by discharging it at the bottom the grout displaces the water and sediment and makes it overflow. If a pile does not extend to rock, but is jacked down to a sufficient penetration in sand or gravel, the jack is applied again after the concrete has set, in order to force it to the required resistance. Under such conditions, a pile may sink from 3 to 6 inches further. In this manner there is more certainty of distributing a given load equally among several piles. In one instance borings showed that a bed of quicksand 25 feet deep overlaid a stratum of very coarse gravel charged with water under a high head. After an 8-inch tube was driven down until it rested on the gravel and was cleaned out with a jet, a i-inch pipe perforated at the bottom for 2 feet was driven 3 feet into the gravel. Grout was forced through the pipe to form a solid footing of grouted gravel and to seal the tube which was then pumped out and filled with concrete. A test load of 35 tons caused no appreciable settlement. The diameter of tubular piles has been increased considerably over those stated in this article for use in underpinning and for some other suitable conditions. When the diameter is large enough to admit a workman to excavate the interior by hand they are generally sunk by the pneumatic process. The larger sizes are preferably regarded as pneumatic caissons rather than pneumatic piles. For further details see Chap. XVI. METAL AND SHEET PILES CHAP. V ART. 57. DISK AND SCREW PILES A disk pile is one which has a disk attached to its foot to provide a larger bearing area. Disk piles have been used prin- cipally in ocean piers and wharves, where the total penetra- tion is not large and is subject to more or less variation. The minimum penetration should not be less than about 6 feet below any possible scour. The disk is a casting which con- sists of a horizontal circular plate, stiffened by a number of radial ribs and connected to a central hollow stem, as shown in Figs. 570 and b. The former illustrates the connection of FIGS, a and 6. Two Forms of Foot of Disk Pile. the disk to a flanged cast-iron pipe which forms the body of the pile, and the latter the connection to a steel pipe. The upper part of the stem is cylindrical while the lower part is conical so as to form the nozzle of a water-jet or to permit a water-jet pipe to pass through it. Sometimes the ribs on the upper side of the disk are made higher than the lower ones, their edges being inclined at an angle of 45 degrees. The disk pile can be used only in sand or soft material which permits sinking by the water-jet. If some material is encountered which is not easily displaced by the jet alone the pile may be ART. 57 DISK AND SCREW PILES 179 rotated to cause the ribs to act as cutters. In THEODORE COOPER'S General Specifications for Foundations and Sub- structures of Highway and Electric Railway Bridges is given a table of the minimum sizes of pipe for corresponding diameters of disks. The diameters of disks range from 1.75 to 4 feet, those of the cast-iron pipe from 8 to 14 inches, with a thickness FIG. 57<;. FIGS. 570? and e. Four Forms of the Foot of a Screw Pile. FIG. 57 f. of f to i inch, and of the steel pipe from 6 to 10 inches, the thick- ness being f inch in all cases. The thickness of the disk plate, ribs and thickest part of the stem are not to be above ij inches for a diameter of 2 feet or less, and i| inches for larger di- ameters of disk. The ends of the cast-iron pipe sections are to be machined so as to secure perfect alinement. A screw pile is one which has a broad-bladed screw attached to its foot to provide a larger bearing area. The use of the l8o METAL AND SHEET PILES CHAP. V screw pile is similar to that of the disk pile. The form of the screw casting is illustrated in Figs. 57^ to/. The pitch of the screw varies from one-third to one-sixth of its diameter, the pitch adopted in any case depending upon the difficulty of securing penetration. The points of the screws are also varied, the gimlet point being suitable for gravel, the blunt point for sand, the hollow conical point for the use of a water- jet in sand and gravel, and the serrated point for soft rock or coral. The dimensions of the shaft of the pile, and of the screw and its connections, must be carefully designed to resist the torsional strength required to sink the pile into position. In one case where the frictional resistance was so great as to break several piles by torsion, it was discovered that by discharging a water- jet on the upper surface of the screw blade the friction was re- duced so that the sinking could be accomplished without diffi- culty. After using the jet only about one- tenth as much power was needed to rotate the piles. Screw piles were first used in 1838, and disk piles in 1856. They are unsuitable for deep foundations where the over- lying material is soft or liable to scour since it is impossible to brace the piles below the surface. It is quite probable that in future reconstruction these types will be replaced by reinforced-concrete piles. ART. 58. SAND PILES As stated in Art. 2 short timber piles are sometimes used to compact the soil and thus increase its bearing power. The same result may be accomplished at less cost by withdrawing the pile as soon as it is driven and filling the hole with sand. Such piles are called sand piles. They can be placed without regard to the elevation of the ground water-level, but cannot be used if there is any danger of scour, or in regions subject to earthquakes. The use of sand columns confined in wooden boxes to lower great weights has proved that they will sustain loads while developing relatively small lateral pressures. In order to have the sand pack firmly, it should be moistened ART. 59 TIMBER SHEET-PILING l8l when placed in the holes and tamped. In case there is a slight settlement, the sand will readjust itself and maintain its stability. The method of consolidating the ground by ramming its surface and mixing sand with it during the operation, is far less effective since a hard crust is thus produced which trans- mits the pressure only to a very short distance below the surface. This difference may be proved by applying test loads and noting the settlement under a time test extending over a month at least. The 'compressol system' is somewhat analogous to sand piles in first forming a hole and then filling it with a different material. The hole is made by a heavy conical perforator having a sharp point which is successively raised and dropped until the hole reaches a hard stratum. If the compressed earth does not keep the water out, the hole may be lined with clay dumped in after each fall of the perforator. Boulders are dropped into the hole and rammed with a tamping rammer which is shaped like a cartridge, thus forming a layer at the enlarged bottom of the hole. Concrete is then deposited in batches and tamped in the same way. In this way a sort of rude concrete pillar is formed. The system was originated in France and is seldom used in this country. It is more economical to use concrete in the form of concrete piles as described in the previous chapter. ART. 59. TIMBER SHEET-PILING Sheet-piling consists of special shapes of piles driven in close contact to form a reasonably tight wall, in order to prevent the leakage of water and soft materials, or to resist the lateral pressure of the adjacent ground. Sheet piles are made of timber, of steel, and of reinforced concrete. Sheet-piling is to be distinguished from 'sheeting' which is set in place or driven as the excavation proceeds, as in trenches or open wells. Sheet- piling is driven in advance of and usually beyond the final depth of the excavation. The best form of timber sheet-piling is known as Wakefield sheet-piling and has been very extensively employed in this 182 METAL AND SHEET PILES CHAP. V country. The patents secured in 1887 and 1891 have expired. It consists of three planks fastened together so as to form a tongue on one edge and a groove on the other (see Fig. 590). The planks are connected by two bolts at intervals of about 6 feet, while spikes are used at intermediate points about 18 inches apart. It has been cus- tomary to use J-inch bolts for planks from if to i\ inches thick, and f-inch bolts for planks 3 to 4 inches thick. For sheet piles made of i-inch boards, f-inch bolts may be T used. For the thin boards or planks, the tongue is made if inches longer than its thickness, while for the thickest planks, the length is the same as the thick- ness. The usual width of the planks is 12 inches except for those less than 2 inches thick. By sizing the middle planks to a uniform thickness, a good fit can be secured between the tongues and grooves. Experience has shown that these triple-lap piles are stronger to resist driving than if made of a single stick, this being due in part to the fact that cross- grain, knots, or other defects in FIG. 5905. Wakefield or Triple-lap Timber Sheet-piling. the three planks are not likely to be located at the same part of the length; and that some defects become visible and lead to the rejection of a plank which might not be visible in a single stick of the same total thickness. Other advantages of this form of pile are the absence of waste in forming the tongue and groove, and less tendency to warp or bend before they are driven. ART. 59 TIMBER SHEET-PILING Fig. 590 also shows how corners may be turned at a right angle by bolting and spiking a tongue to the face of a pile or at any other angle by fastening a tongue to a beveled side. It also illustrates how the foot of each pile is beveled on both faces, in order to drive plumb, and on one edge so as to keep in close contact with the adjacent one. The tongue should always be kept in the lead, otherwise gravel or stone may become wedged in the groove, and damage the succeeding pile. If it is desired to drive the sheet-piling each way from the corner, FIGS. 59&-. Sections of Timber Sheet-piling. the first pile should be constructed with a tongue on both sides, and sharpened so as to drive plumb longitudinally as well as laterally with respect to the lines of piling. The last pile in the center is constructed of the proper width and acts as a wedge to tighten the line if necessary. When the sheet piling is to be driven to rock bottom, the middle plank should be cut off square at the end, so that water will not readily pass underneath the piling along the rock surface. Some other sections of sheet-piling are shown in Figs. 59 b-f. In Fig. 596 a single row of ordinary planks are driven edge to edge. This arrangement cannot be used if it is necessary to secure a water-tight wall. In Fig. 59^ two rows of planks are placed in contact and breaking joints. Fig. 59^ shows the 184 METAL AND SHEET PILES CHAP. V cross-section of a sheet pile which is merely a plank with an ordinary planed tongue and groove. In Fig. 59^ the plank has a groove cut on both edges and a tongue formed by nailing a strip or spline into one groove to form a tongue. In this case, the tongue can be made of a different species of tough wood like maple or elm, and carefully selected. Fig. 59/ gives the details of construction for timber sheet- piling 4 inches thick according to the standard adopted by the FIG. 59/. Details of Timber Sheet-piling with Dovetail Joints. Southern Pacific Company. The strips nailed to the planks are beveled to form a dovetailed tongue-and-groove joint. Sheet-piling built up in a similar manner is sometimes made as thick as 12 inches, and in exceptional cases 15 inches. ART. 60. STEEL SHEET-PILING On account of the difficulties encountered frequently in driving timber sheet-piling in hard ground without injury, and the large amount of bracing required to resist earth and water pressure during excavation and construction, an effort was made naturally to devise a sheet-piling of greater strength and stiffness, without excessive resistance to penetration. The ART. 60 STEEL SHEET-PILING 185 need of this was emphasized by the increasing size and depth of foundation constructions, and the difficulty of securing water- tightness in quicksand. Rolled steel sheet-piling was intro- duced to meet these conditions. The use of standard structural shapes in building up sheet piles gave such excellent results as to demonstrate the commercial success of steel sheet-piling. The first form of this class was employed in 1901, in the foun- dations of the Randolph Street bridge in Chicago and is similar to that shown in Fig. 6oa. Alternate piles consist of standard I-beams, and the others are built up of two standard channels bolted together with pipe separators. The design is based on a foreign patent. The next step forward was taken during the following year by the introduction of the Friestedt interlocking channel-bar piling. Each alternate pile consists of a standard channel, while each of the others is built up by riveting two Z-bars to a channel. An improved form known as the symmetrical inter- lock channel-bar piling is also manufactured in which a con- tinuous Z-bar is riveted near one flange of every channel, and a short Z-bar clip is riveted near the other flange at the upper end only. This arrangement makes every pile alike and preserves its symmetrical head to receive the blows of the hammer (see Fig. 6ob). The experimental work begun by LUTHER P. FRIESTEDT in 1899 which led to his patented form, and his efforts to extend its use by others, fairly entitle him to be known as pioneer of the steel sheet-piling industry in this country. Another form which employs a standard structural shape was placed on the market in 1908. The piling consists of I- beams which are locked together by what is known as a lock- ing bar. This bar consists of a small I-beam which, by extra passes through the mill, has its flanges bent into hook shapes as shown in Fig. 6oc. One locking bar is attached to each beam at the mills by steel wedges and then the beam and locking bar are driven as one sheet pile. The beams differ slightly from the ordinary standard in having the outer corners of the flanges rounded. Another class of steel sheet piles includes those which con- i86 METAL AND SHEET PILES CHAP. V 1 ; i ; SL IT Clip Clip- Clip FIGS. 6oa-h. Sections of Steel Sheet-piling. ART. 60 STEEL SHEET-PILING 187 sist of a single shape formed by special rolls. Fig. 6od shows a section of what is known as United States sheet-piling. At one edge of the web is a flange with a bulbous section and at the other edge is an open or slotted cylindrical flange. This type was invented some years before the Jackson and Friestedt types but did not come into commercial use until a few years after their introduction. The smaller flange of one pile enters easily the larger curved flange of the next one, the slot being wide enough to allow a considerable change in the direction of the web. The Lackawanna sheet-piling introduced in 1908, is also a special rolled section as illustrated in Fig. 6oe. Both flanges are alike, the section being symmetrical with respect to a central transverse plane. The diagram shows how the flanges of adjacent piles engage each other to form a double interlock. The shorter flanges may be said to engage like hooks, while the larger ones act like guards. Where flexural strength is of primary importance, the web is curved as indicated in Fig. 6of. It will be noticed that the web is bent until a considerable por- tion of its width touches the plane which is tangent to the curved flanges of the adjajcent piles. A large bearing surface against supporting timber wales is thus obtained. Corrugated steel sheet-piling which was first used in 1907 is illustrated in Fig. 6og and permits the use of very thin plates. A double thickness of metal is provided at each joint. The width of sections can be varied to suit the conditions of driving them. Fig. 6oh shows sections of the Gould sheet pile in which alternate piles are standard channels, as in the Frie- stedt type, while each of the others consist of a channel and a plate bolted together with a spacing timber between, the timber being of such a size as to provide for the interlock at each edge. A U-shaped bent-plate shoe is bolted to the bottom of each combination pile to protect its foot during driving. There are several other patented forms which have been used to a limited extent. The general method of forming a corner pile is by cutting an ordinary sheet pile longitudinally into two halves, and 1 88 METAL AND SHEET PILES CHAP. V then riveting them to a structural steel angle. In some cases a sheet pile has its web bent to a curve of short radius to form a corner pile. At the junction between a longitudinal wall and a transverse wall on one side of it, a half section like that used at a corner is riveted to the web of a whole section by means of two angles. It will be observed that each type of sheet-piling has inter- locking edges to prevent a pile which is being driven from pulling apart from the one driven previously. This is an im- portant advantage not possessed by timber sheet-piling. The tensile strength of the interlock enables steel sheet-piling to re- sist a considerable lateral pressure without the aid of transverse bracing. In the construction of some very large cofferdams it has been possible to take advantage of this feature by con- structing a row of pockets to be filled with excavated material so as to avoid the use of transverse bracing in the large interior area (see Art. 71). The direct tensile strength of interlock for five types of steel sheet piles for sections weighing approxi- mately 40 pounds per square foot, with one exception, were found by tests in 1908 to be 9746, 7769, 3842, 3362, and 1094 pounds per linear inch. More extended tests later gave values of 9584, 7271, 6060, 3569, 2252, 2022, and 1502 pounds per square inch, the lowest three values relating to fabricated sections. Not only do the different types of steel-piling vary materially in the tensile strength of the interlock, but also in the section modulus which measures the resistance to flexure between the horizontal wales or the frames which support them laterally, as well as in their least radii of gyration which indicate the re- sistance as a column while being driven. Each type is usually manufactured in different sizes and weights; for example, the United States piling has two sections with a net width of about 12 inches with weights of 35 and 40 pounds per linear foot, and a small section about 6 inches wide weighing 1 1 pounds per linear foot. All the types permit some degree of flexibility in the interlock, being small in those using structural shapes and large in the special rolled sections, the maximum change of ART. 6 1 CONCRETE SHEET-PILING 189 direction toward either side being about 20 degrees. This arrangement permits piling to be driven in a curved line, or to avoid boulders encountered in a proposed line. Steel sheet-piling is employed in cofferdam construction, for retaining walls, to protect adjacent buildings during ex- cavation, to line shafts in quicksand, to line open wells for building piers, as well as for 'dams and other hydraulic con- structions. It is practically used for the same purpose as timber sheet-piling but the results secured by it are much more certain. Only one wall is often required to secure water- tightness which would require two walls of timber sheet-piling under the same conditions. Single lengths of steel sheet piles 52 feet long have been successfully driven with sec- tions having a weight of about 40 pounds per linear foot. Spliced lengths of 75 feet were employed in the cofferdam around the wreck of the U. S. Battleship Maine in Havana Harbor. It is not necessary to form a splice by bolting or riveting but merely to abut the pieces and break joints with the adjacent piles. Spliced lengths up to 96 feet have been employed in exceptional cases. Further details regarding the properties and uses of steel sheet-piling, proposed specifications and an account of its historical development, may be found in a paper by L. R. GIFFORD on Steel Sheeting and Sheet-piling, and its elaborate discussion, in Trans. Am. Soc. C. E., vol. 64, pages 441-525, Sept., 1909. ART. 61. CONCRETE SHEET-PILING In the construction of piers or wharves where sheet-piling forms a part of the permanent structure, reinforced-concrete sheet piles are employed. Sometimes they are rectangular in cross-section and are driven in as close contact as possible, the foot being beveled on one edge like timber sheet piles. The larger sizes have tongues and grooves on the edges, the sides of the grooves being splayed so as to engage the tongues more easily. Experience shows that it is not advisable to have a 190 METAL AND SHEET PILES CHAP. V thickness less than 8 inches when a tongue and groove are used, as it is otherwise difficult to obtain the requisite strength for these details. Another plan consists in forming a semi-circular groove on both edges, thus forming a cylindrical space with the adjacent pile, to be occupied by the water-jet pipe during sink- ing and to be filled afterward with grout. At the terminal piers at Brunswick, Ga., reinforced-concrete sheet piles 18 inches square were used for the bulkhead at the basin. They were 45 feet long, beveled at the foot to 12 by 1 8 inches and weighed 7 tons each. Four f-inch square rein- forcing bars extended the full length, and for the lower two-thirds of the length two ij-inch bars were added in trussed form to help in resisting the maximum bending moment. In 1910 at the Norfolk Navy Yard the sheet piles were 1 8 by 24 inches in section with tongue and groove, and 55 feet long. The most extensive use of concrete sheet-piling up to that date occurred in the Galveston causeway begun in 1909, 9808 piles being re- quired. They were 10 by 18 inches in section, grooved on both edges, and grouted together after being driven. To improve the protection of the reinforcing rods, it is desirable to place them farther from the surface on the water side than on the other side of a pile. In order to combine the tensile strength of the interlock for steel sheet-piling with the freedom from corrosion of concrete piles, sections have been designed in which a steel pile is cut longitudinally through the web and these halves are cast into a concrete pile on opposite edges. After the piles are driven, the grooves containing the steel interlock are cleaned out with a jet and filled with grout. Another arrangement consists in making a combination pile by enclosing an entire steel sheet pile within a concrete pile, the joints being grouted in a similar manner after driving the piles. ART. 62. DRIVING SHEET-PILING The construction of a single wall of timber sheet-piling is illustrated in Fig. 620. Each row of vertical guide piles supports ART. 62 DRIVING SHEET-PILING 191 several horizontal timbers called 'wales' against which the sheet- piling is driven. An outside wale is usually bolted to the upper inside wale in order to hold the sheet-piling in line. It will be noticed that a pair of short leads is attached in front of the ordinary fixed leads of the pile-driver in order to bring the ham- mer directly over the line of sheet-piling. The light-weight steam-hammers especially designed for driving sheet-piling give the best service, most of which are operated without any leads, being held in position by the boom of a derrick. Nu- merous illustrations and descriptions may be found in the catalogues of manufacturers. They will drive piles to a greater depth, and without brooming, splitting, or other injury. To secure a good job, the piling must be very carefully driven. If a pile is injured by some obstruction in driving, it is generally better to replace it at once, than to attempt some other means of repairing the wall to make it water-tight. In case sheet- piling has to be driven through a shallow deposit of silt or sand to a rock bottom and it is desired to secure a close fit where the bottom is not level, a sheet pile may be sharpened to a knife edge, driven until the edge is broomed to contact throughout, then pulled up, the end cut to the proper form and finally redriven. After all the sheet-piling is in place, the hammer should be placed on each pile in succession to secure closer contact with the rock by slight brooming at the foot. Timber sheet-piling is sometimes used to form cofferdams for piers, and is left in place as a protection from scour around the heads of the bearing piles which support the piers. This was done on some of the piers of the Vancouver bridge of the Portland and Seattle Railway. Wakefield sheet piles were built up to a maximum length of 68 feet. In order to secure the necessary penetration through the sand which varied from 45 to 59 feet below the cut-off, the sheet piles were sunk with the aid of a water-jet. It would have been impossible to drive them without the jet aiding the steam-hammer. An ingenious arrangement in which a guide or pilot tube is utilized both as a water-jet tube and as a guide for each pile is described in Engineering News, vol. 70, page 552, Sept. 18, IQ2 METAL AND SHEET PILES CHAP. V 1913. The tube which has a flattened oval section engages the groove in the pile already driven and the adjacent groove of the pile to be driven. The tube is afterward withdrawn and the space filled with a hardwood spline. Steel sheet piles are driven generally by steam-hammers, the weights of which are proportioned to that of the piles to be driven. The double-acting steam-hammer is very effective for this purpose on account of its rapidity of action which keeps the pile practically in constant motion, and since it can be handled for this purpose without leads. The lightest hammer of several designs can be handled by one man, and sometimes a step is attached to the hammer frame, so that the weight of the man who operates it may be added while driving. Long sheet piles with heavy sections are driven with heavy steam hammers and pile-drivers. The comparative resistance of different makes of steel sheet- piling is indicated by driving tests with five types of piling at Black Rock Harbor in 1908. The number of blows of the steam-hammer per square foot of piling was found tp be 13.9, 14.4, 12. i, 19.6, and 22.9. All of the piling weighed about 40 pounds per square foot, except one type which was lighter. To protect the head of a steel sheet pile, especially in hard ground, a cap is generally employed which contains a wooden cushion or driving block. Its base contains grooves or sockets which fit over the pile. The elaborately illustrated catalogues of manufacturers of steel sheet-piling show plans and sections of caps which are designed for each type of pile. There is usually a transverse as well as a longitudinal groove in the cap so as to fit a corner pile or a junction pile as well. In driving through material with a large proportion of sand or clay, the interlocks seal themselves with the material penetrated. Occasionally strips of wood are driven into the openings, which by swelling help to make the joint water-tight above the bottom of the water. Sawdust or wood pulp may also be used to stop leaks. The special rolled sections offer less resistance to driving on account of the absence of rivets or bolt heads; and hence they may also be pulled more easily. In ART. 62 DRIVING SHEET-PILING 193 sections like the United States piling, the bulbous flange should be kept in the lead. Under ordinary conditions steel sheet- piling may be pulled and redriven a number of times and finally has considerable scrap value, thus frequently making the cost less than for timber sheet-piling which can ordinarily be used only once. Experience has shown instances in which steel sheet piles driven into hard ground could not be used over again, and in exceptional cases, it has been impossible to pull it, making it necessary to dredge away some material alongside and to bend it down on the bottom to avoid interference with naviga- tion. Whether this result was due in any measure to improper driving remains uncertain. Under certain conditions, it is not desirable to drive each pile to its full penetration at one operation. In order to main- tain good alignment, or to facilitate closure, it is often advanta- geous to set up a considerable number of sheet piles and then drive them several feet at a time in succession, repeating the operation until the desired penetration is reached. The same method of driving ahead some distance may be used successfully in avoiding injury to piles when boulders are encountered, if they are not too large. The damage thus becomes local and limited in extent. The water-jet may also be used to aid [ir> displacing boulders. Sheet piles should be carefully handled, in transportation, for with a small clearance in the interlock, a bend or kink due to careless handling may cause so much fric- tion that the pile refuses to move on reaching a hard stratum, and may result in crippling the pile, if driving is continued. Steel sheet-piling has been successfully driven through sub- merged logs, old timber cribs, brick, stone, and other debris in made ground. If considerable cribwork or logs have to be penetrated, it may be more economical to construct a special chisel attached to the end of a timber, and to cut the timbers with the aid of the chisel and pile-hammer before inserting the sheet pile. The construction of such a tool is described in Engineering Record, vol. 66, page 704, Dec. 21, 1912. To drive sheet-piling below the leads of a pile-driver, a follower may be constructed for the purpose by riveting to the 13 IQ4 METAL AND SHEET PILES CHAP. V web of a piece of piling, of the proper length, two plates or chan- nels which project below its web and engage that of the sheet pile to be driven. Steel sheet-piling may ordinarily be pulled up by means of block and tackle. If difficulty is found in starting a pile, it may be loosened by giving ibseveral blows with a pile-hammer, or by using a pair of hydraulic jacks, one on each side. If the piling has to remain in place for a long time, the pulling may be facilitated by lubricating the joints with graphite or some other material which will prevent corrosion of the interlocking joints. If concrete is deposited next to steel sheet-piling, which is to be pulled subsequently, it is essential to prevent contact between the concrete and steel by using tar-paper, or preferably light wooden sheeting with tongue-and-groove joints. Occasionally it is necessary to cut off steel sheet-piling to an exact level. Where only a few pieces have to be cut and where time is not an important element, hack saws may be used economically. For larger quantities to be cut in the least time, the oxyacetylene flame is the most advantageous in operation and cost. The electric arc has been employed in some instances, but its cost is very high and it is difficult to handle on account of the intense light produced. ART. 63. DESIGN OF SHEET-PILING When sheet-piling is driven a short distance into the bottom and is supported at the water surface by wales and struts, as illustrated in Fig. 63 a, each pile may properly be regarded as a simple beam with a span d. Taking the weight of a cubic foot of water as 62.4 pounds and expressing distances in feet, let a sheet pile be considered i foot wide. The pressure in pounds per square foot at the depth d is 62.4 d, the total pres- sure on the pile is 31.2 d 2 , distributed as shown in Fig. 63 a; and since the center of pressure is at ^ d from the bottom, the horizontal reaction at the surface is 10.4 d 2 . By the principles of mechanics, the bending moment at any distance x below the surface is M=io.4 d 2 x 62.4 x . | x . f x=io.4d 2 x 10.4 x 3 . ART. 63 DESIGN OF SHEET-PILING 195 Placing the first differential coefficient dM/dx equal to zero, there is found x = d/ "^3 or ^ dv r $= 0.577 ^> f r the location of the maximum bending moment. The maximum bending mo- ment is accordingly 4.00 d s , expressed in pound-feet; or 48.00 d 3 , expressed in pound-inches. If the total pressure be regarded as uniformly distributed over the pile, the value of the maxi- mum bending moment is 3.90 d 3 , or 2.5 percent less than the true value. The strength of Wakefield sheet-piling must be regarded as that of three separate planks since the longitudinal shear Water Surface FIG. 630. FIG. 636. developed between them by flexure cannot be fully resisted by the bolts or spikes which connect them. Such piles are analo- gous to deepened beams which also require better means than connecting bolts to develop their strength as a unit. The tests of columns composed of two or more sticks bolted together also show that in no case is the resistance materially greater than if each stick were acting freely (see JACOBY'S Structural Details, Arts. 43, 45, 49 and 50). Let it be required to find the thick- ness of Wakefield sheet-piling for a depth of water of 10 feet, the unit-stress in the outer fiber being taken at 1000 pounds per Ip6 METAL, AND SHEET PILES CHAP. V square inch. The resisting moment of the three planks 1 2 inches wide is accordingly 1000 X 12 X 3/f/6 = 6ooo/ 2 pound-inches, in which / is the thickness of each plank in inches. Equating this to the bending moment of 48.ooX io 3 = 48 ooo pound-inches, there is found =2.83 or 2! inches. In determining the com- mercial sizes required account must be taken of the loss due to sawing as well as for planing the middle planks in the construction of sheet piles. In Fig. 63 b, the sheet pile is horizontally supported at the water surface and at an intermediate depth. Let d=i6 feet, and c = 6 feet. The pressure at a depth of 10 feet is 624 pounds per square foot, and at depth of 16 feet is 624+374.4 = 998.4 pounds per square foot. Taking a width of pile of one foot, the pressures on its lower portion, represented respectively by the rectangle and triangle of the shaded area, are 3744 and 1123.2 pounds. Treating the pile as a simple beam with a span of 6 feet, the reaction at the intermediate wale is |X3744+ ^X 1123.2 = 2246.2 pounds. The bending moment expressed in pound-feet at a distance x below this support is M = 2246.4 x (312 x 2 10.4 # 3 ). In the same manner as before the value of x which makes M a maximum is found to be 3.115 feet, while the value of the maximum bending moment is 3656.0 pound-feet. If the total load is regarded as uniformly dis- tributed, the maximum bending moment is 4867.2X3 =3650.4 pound-feet which is only 0.15 percent less than the true value. Since the error decreases as the depth d increases, it is suffi- ciently precise for purposes of design to use the simpler approxi- mate method of 'computation for all portions of a sheet pile below the top span, for which the true value of the maximum bending moment is expressed by a simple term as given in the first paragraph of this article. If the values of d and c were 16.25 and 6.25 feet respectively, the approximate value of the maximum bending moment is 3999 pound-feet which is prac- tically the same as for the upper span of 10 feet. If a timber sheet pile is built up as shown in Fig. 59 /, the small pieces spiked to the main timber to form the tongue and groove should be omitted in computing the resisting moment of ART. 63 DESIGN OF SHEET-PILING IQ7 the section. The values of the section modulus for the com- mercial sizes of steel sheet piles may be obtained from the manu- facturers. The corresponding width to be used in computing the bending moment per pile is the distance center to center of interlock when assembled. The design of sheet-piling to resist earth pressure in which the material has more or less cohesion is not on a basis that is entirely satisfactory. The conditions vary so widely and often the material penetrated in any locality occurs in layers of different density or character that it is well to make the design so as to be on the safe side. Some engineers design all sheet- piling for hydrostatic pressure, increased by 50 percent or more for wet slippery material. CHAPTER VI COFFERDAMS ART. 64. THE COFFERDAM PROCESS When, for some purpose, it is desired to exclude the water and expose a portion of the bottom of a river, lake, or other body of water, a structure called a cofferdam is employed. This cofferdam is a temporary structure, practically water- tight and large enough to provide adequate room for working. Denned, a cofferdam is a temporary structure used for the purpose of excluding the water from a given site, or area, either wholly or to such a degree that with a reasonable amount of pumping the permanent substructure may be built within it in the open air, or that other work may be accomplished. The building of the permanent substructure may include pile driving, placing grillages, building piers and abutments, etc., while other work may include the construction of dams, removal of sunken vessels, etc. Where the ground is satu- rated with water, cofferdams are sometimes used in placing foundations for buildings. Cofferdams are usually built in place. They may be self- contained or may depend for strength on the natural bottom, as is the case where guide piles are used. Bracing may be used to resist the lateral pressure against the walls. To obtain water-tightness the sides of the cofferdam must be tight and the soil on which the cofferdam rests must be impervious. If the latter condition does not exist, either the sides of the cofferdam must extend through the pervious material to an impervious stratum or else a layer of concrete must be spread over the bottom inside the cofferdam and allowed to harden before pumping is begun. Absolute water- tightness is seldom sought, it being cheaper to pump a moderate 198 ART. 65 EARTH COFFERDAMS 199 amount of leakage than to go to the heavy expense of building a structure that will not leak. The cofferdam should be so designed that the combined cost of construction, maintenance and pumping shall be a minimum. To depths of from 20 to 30 feet the cofferdam process will prove the best and cheapest method of founding bridge piers and abutments, but for depths greater than 30 feet, owing to the difficulty of properly bracing the cofferdam against the pressure of the water, as well as preventing heavy leakage, some other method is usually preferable. Cofferdams over 50 feet deep have been used in a few instances. Cofferdams may be constructed of earth, timber, steel or concrete. They may be divided into five general classes: earth, sheet pile, crib, movable and miscellaneous cofferdams. These classes will be described separately in the following articles. ART. 65. EARTH COFFERDAMS Of the five classes the earth cofferdam is the oldest in origin and simplest in construction. Its use is usually limited to shallow water with low velocities of current. It is made of a bank of earth placed around the site to be enclosed, and of a thickness sufficient to furnish the required stability and to keep the leakage down to a small amount. The earth bank should be carried up 2 or 3 feet above the water-level with a width of at least 3 feet at the top, and with side slopes corre- sponding to the natural slope of the material. The embankment should preferably be composed of a mixture of clay and sand or gravel, but if clay is scarce the bank may be composed of sand with a clay wall in the center. The amount of embankment may be somewhat reduced by using one or two rows of sheet-piling, in which case the cofferdam may resemble more or less closely the sheet-pile cofferdam described in later articles. As to whether in any given case the cofferdam should be classed as an earth or sheet-pile cofferdam will depend upon whether or not stability and water- tightness depend primarily upon the earth filling. 2OO COFFERDAMS t CHAP. VI Where the depth of water is not more than 4 or 5 feet and the velocity of the current would wash away loose material, coffer- dams may be made of ordinary canvas bags about half filled with a mixture of clay and sand. It is important that the bags shall be but partially filled for otherwise they will not pack together closely. A modern and up-to-date use of the earth cofferdam is found in the construction of the cofferdams of the West Neebish Channel of the St. Mary's River. In some places the depth of the water was far too great for the economical use of earth cofferdams and was justified here only by the extremely favor- able conditions that obtained for placing the earth. Two sub- sidiary cofferdams were first constructed across the channel about midway between the main ones in order to stop the current and divert the flow to another course. 1U These tem- porary dams were about 1000 feet apart at the site of the channel and extended across the river from the mainland to the island, varying in direction to suit the contours of the river bed. They were built in 2 to 7 feet of water flowing 3 to 6 miles an hour. The construction of these dams stopped the flow of water in the West Neebish Channel of the river, that the main cofferdams could be built in still water, and also laid bare a part of the site of the channel about 1000 feet long. In building these temporary dams, which varied from 4 to 10 feet in height, broken stone and rock were dumped from scows on the line of the dams until the force of the current was broken and the rock fill carried above the water. Sandy clay was then brought in and dumped on the upstream side of these rock embankments in order to silt up the openings and pro- duce water-tight dams." The main cofferdams which unwatered the 86oo-foot section of the work were structures of unusual size. The upstream cofferdam was 1900 feet long and was built in water from 2 to 18 feet in depth. la This cofferdam has a minimum width of 8 feet at the top, which is 7 feet above the water, and has side slopes on the water side of about i on if, and of about i on 1 Engineering Record, vol. 56, page 112, Aug. 3, 1907. ART. 65 EARTH COFFERDAMS 2OI 2 on the other side. The other main cofferdam is 8600 feet downstream from this one. It has a total length of 2600 feet, and in plan is arched slightly downstream against the water on that side of it. This cofferdam was built in water from nothing to 26 feet deep; it has a minimum width of 12 feet at the top, which is 6 feet above the water; its side toward the water is built on an average slope of i on 2, and the one on the other side of i on 2^. "The construction of the upstream main cofferdam was started soon after the current of the river had been broken by the temporary dams. Sandy clay and mud excavated by the El. 345.2-, s2xl2'Joists,2Q"c. toe. I 1 15 t'&e'o'c.toc.^ 6 ( S' 33 \ , 20'0' - * (J> \ fR- g* ^ 4 _ . Filled with 6x8 Excavated Material^ - Prota by ^ ^*J jj ~3j $ ftoj fi; K a- - fig ? ! -8"x8' ( ^ 4 # -8\IO' W5? -10'xlO' \ :;;. ^ s r About ISO 'to Bottom of Excavathn Cross Section FIG. 650. Sheeting for Earth Cofferdam on the Ohio River. dredges at work on the adjacent sections of the channel were brought to the site in bottom-dump scows and deposited in place. When the banks thus formed had been carried up until the bottom-Pump scows would operate no longer, the materials were loaded on flat-deck scows, and handled from these to place in the embankment by a clam-shell bucket on a derrick scow." French engineers have made extensive use of the earth cofferdam for work on their various canals. In some work on the Meuse Canal, described in Annales des Fonts et Chaussees, 202 COFFERDAMS CHAP. VI 1896, page 539, gravel ranging in size from about i to 4 inches being the residue, after the sand was used, of material dredged from the canal bottom was employed. Water-tightness was obtained by placing a layer of tan-bark over the water face. In some cases the head of water on the cofferdam was as much as 9 feet. In place of earth, cofferdams are sometimes made of fascines. The cofferdam for a concrete dam at Milford, Conn., was made by forming brush into mats, which were sunk by loading with rocks, the layers of brush and stone alternating. To give water- tightness a layer of earth was placed over the upstream side. Fig. 650 illustrates the cross-section of the earth cofferdam with sheeting used in the construction of the Ohio River Lock HeH vertically tyDtrrick Boar S. FIG. 656. Method of Constructing Ohio River Cofferdam. and Dam 48, where the bottom was composed of sand. To break the current a line of sheet-piling was first driven. Frames were then placed by a boat as shown in Fig. 65^ and connected to the sheet-piling. Vertical planking was placed against the frames and the interior then filled wirh dredged material. Gravel was placed along the outside of the sheet-piling up to its top and on a slope of about 45 degrees; the space between the sheet-piling 'and sheeting was also filled with earth, and finally sand was placed against the inside wall of sheeting up to the elevation of the sheet-piling tops. This sand had a very gentle slope, running approximately 100 feet before reaching the eleva- tion of the bottom of the sheeting. ART. 66 WOODEN SHEET-PILE COFFERDAMS 203 ART. 66. WOODEN SHEET-PILE COFFERDAMS The sheet-pile type may be considered as the standard form of cofferdam. It consists of rows of sheet-piling, usually not more than two, extending around the site to be enclosed. The piling is held in place in various ways as described in the fol- lowing articles. The sheet-piling serves the function of giving water-tightness to the structure, and to this end some form of intermeshing or interlocking piling is always employed. Strength to resist the pressure of the water outside is furnished by guide piles, frames, or cribs, in addition to a large amount of internal bracing. The sheet-piling may be of wood or steel; at the present time (1914) the use of various forms of steel piling is rapidly increasing. Where it is possible to drive piles some distance into the soil the sheet-piling is best supported by vertical guide piles and horizontal wales. The latter will not only furnish a guide for the sheet-piling while being driven but will also add strength to the cofferdam, thus decreasing the amount of internal brac- ing necessary. DOUBLE WALL WITH GUIDE PILES. Fig. 66a shows the de- tails of this type of cofferdam. It is composed of vertical guide piles, horizontal waling and cap timbers, vertical sheet piles and a puddle filling. Rods are usually put in near the top to connect each pair of guide piles in order to prevent the filling from spreading the walls apart. If the top of the cofferdam is but slightly above water-level, struts are often placed near and parallel to the tie rods, serving to hold the two walls apart. The bearing piles are driven more deeply into the earth than the sheet piles, the aim being to drive them far enough to develop the full transverse strength of the pile when acting as a free cantilever above the earth. The sheet-piling should be driven to a fairly impervious stratum to prevent leakage under the cofferdam. The space between the walls should be filled with earth, preferably an intimate mixture of sand and clay or gravel and clay, to form a puddle (Art. 75), which will mate- 2O4 COFFERDAMS 6 "x 12 "Sheet Pile.., ..-Strut 10 x 10 " ^ 4 Drift Bolt -\ About IZ ft. Water 5urface\ P u d d' I ' e. ' ''" CHAP. VI -Cut Washer 7 / t/&%8'%fa*'"Pc+, {BluetCtay,/////////' FIG. 66a. Section of the Double Wall of a Cofferdam Showing Puddle Chamber. Rive ?5'0"- *l rS/7rt/ce EI.+ IIO.O \0"*10"Y.P. El. +100.0 L ock ENG. Ntws, Transverse Section. FIG. 66fe. Details of Double Wall of Sheet-pile Cofferdam, Charles River, Boston, Mass. WOODEN SHEET-PILE COFFERDAMS 205 rially assist the sheet-piling in making the cofferdam water- tight. This puddle should be placed in thin layers and thor- oughly tamped in a damp state. Before placing the same it will usually be advisable to dredge out the soft material on the bottom to an impermeable stratum. This puddle filling, in addition to promoting water-tightness, will materially strengthen the structure. Clay is often banked around the outside of the cofferdam to safeguard it further against leakage. The cofferdam should have its puddle chamber wide enough to develop the required strength, furnish water-tightness, and afford sufficient space for plac- ing machinery, gangways, etc. One rule for the width of un- braced cofferdams is to make it equal to the height above the ground up to 10 feet, and when the height is greater than this, make the width 10 feet plus one-third the height in excess of 10 feet. The design of sheet- piling is considered in Art. 63. A well-designed cofferdam of the double-wall type was used in the construction of the locks for the Charles River Dam, Boston, Mass., where the length was about 625 feet and the width about 250 feet, surround- ing an area of approximately 4 acres. The maximum depth of water on the outside at low water was 20 feet. As shown in Fig. 66 b and c, the cofferdam consisted of two rows of guide piles ii feet apart, with piles spaced 10 feet on centers, which through wales supported 6 -inch splined and grooved sheet-piling. The guide piles were of spruce, 45 feet long, and each alternate pile was braced by a batter or spur pile. The sheet-piling was of yellow pine with spruce splines and was 38 feet in length. The remainder of the details are clearly shown in the diagrams. A filling of sand and clay was placed around both the inside and 206 COFFERDAMS CHAP. VI outside of the cofferdam as well as in the puddle chamber. On the inside it had a width of 25 feet at the top and then sloped down on a 2 on i slope, thus making virtually a combination pile and earth cofferdam. Although probably not an econom- ical form of cofferdam for ordinary use, yet in a case like this where the filling was permanent construction, it made an ad- mirable structure to withstand the 37-foot head, which was approximately the maximum height of high water above the bottom of the lock masonry. ART. 67. SINGLE WALL WITH GUIDE PILES Where the space available for the cofferdam is restricted or where the area of the site to be enclosed is small and the head of water not great, a cofferdam having a single wall is preferable to the double-wall type. Other conditions being the same the former type will require more bracing than the latter, but in many cases this will prove cheaper than the extra wall. Figs. 670 and b show the details of cofferdams used for the rectangular and pivot piers for the Illinois Central Railroad bridge across the Tennessee River at Gilberstville, Ky., both of which are standard types for single- wall cofferdams of moderate size. Before placing these cofferdams the bottom of the river was dredged down to about 17 feet below low water to hard gravel. Cofferdam guide piles were then driven and ioX 12-inch wales bolted to the outside, after which 9Xi2-inch triple-lap sheet-piling was driven against the latter, penetrating the gravel from 4 to 6 feet. The piers were founded on bearing piles driven from 16 to 20 feet into the gravel and cut off 2 feet above the bottom before the cofferdam was placed. Before pumping out the water a 3 -foot layer of concrete was placed on the bottom, thus preventing leakage of water beneath the cofferdam; later it served as a cap for the bearing piles. The bracing, which is clearly shown in the illustrations, was placed as the water was pumped out. The octagonal cofferdam was braced by annular trusses which, by their arch-like action, proved to be a very rigid form of bracing, and yet offered no ART. 67 SINGLE WALL WITH GUIDE PILES 2O7 B-J i Cofferdam for Center Pier No. 3 Half Plan of Lower Cofferdam Half Plan of Upper Cofferdam. Cofferdam for Piers 4, 5 and FIG. 6;a. Cofferdams with Single Walls of Timber Sheet Piling Supported by Wales and Guide Piles, for Piers of Illinois Central Railroad Bridge over Tennessee River, at Gilbertsville, Ky. See also Fig. 620. 208 COFFERDAMS CHAP. VI obstruction to the work of building the piers/ which were of concrete. The forms for these piers were braced against the trusses. A good example of a very large and high single-wall sheet- pile cofferdam, very strongly braced, is illustrated in Fig. 6yc, this structure being used to found the pier of a lift bridge for ............. , ITTJI ffffTTTrmnmT ' ' I |'l I i I II i i ! M I ! Mil I I ' ; i 1 1 [ ] i j | j 1 1 1 1 1 1 n 1 1 ; i n ; j 1 1! 1. 1 1 1 [ 1 1 1 ii ; 1 1 Section A-)V lar Coffe Rectangular Cofferdam. %&? ' Section 8-B. Octagonal Cofferdam. FIG. 676. Elevation of Cofferdam Walls. the Chicago Terminal Transfer Railroad. Two sides of the cofferdam were on land, one in water, and the other two partly in water and partly on land. A row of guide piles, from 6 to 8 feet apart and 40 feet long, were first driven. 1 " Six tiers of inside and outside waling pieces were bolted to these piles, and on the land side 370 6X1 2-inch 1 Engineering Record, vol. 50, page 636, Nov. 26, 1904. ART. 67 SINGLE WALL WITH GUIDE PILES 209 sheet piles 34 feet long were driven between the outer wales, and 6X i2-inch horizontal guide pieces at the surface of the ground and 4 feet below it. On the water sides 274 34-foot Wakefield piles 9 inches thick, made of 3Xi2-inch planks, were driven in the same manner. 210 COFFERDAMS CHAP. VI "The piles were driven as the excavation progressed inside of the cofferdam, and at the same time rows of transverse and longitudinal 12X1 2-inch horizontal braces, about 6 and 8 feet apart on centers and from 4 to 6 feet apart vertically, were set with their ends engaging the round piles on the center lines of the walls. At intersections these braces were supported on 8X8- inch vertical timbers; one of them was continuous and the other was cut to clear it, with the square ends abutting against the sides of the first piece and spliced across it with two side fish plates. . . . The inside wales were of 12X1 2-inch timber (except in the upper two tiers, where 8X 1 6-inch timber was used because it was conveniently available from the contractor's stock), all of them being lapped and halved at intersections. The outside wales were uniformly 6X12 inches. The round pile caps and the two upper rows of wales on the water side were made of gX i3-inch timber. All wales were bolted through the round piles, and the oblique joint in the Wakefield piling was tied by bolts through both faces. "In the longest dimension of the cofferdam, the six tiers of horizontal struts in each longitudinal line were divided into seven panels by the vertical posts supporting them at the intersections of alternate transverse braces. Each panel thus formed on three of the long lines and one short line was X-braced with 2Xio-inch planks, spiked to the longitudinal struts at all intersections and overlapping in the centers of the panels, as shown in the longitudinal sectional elevation. Six lines of similar bracing were provided for the transverse struts, but varied from that in the longitudinal direction in that the upper and lower pieces of the bracing overlapped each other by the width of the space between two transverse struts, thus increasing the amount of bracing and the rigidity at a point half way between the top and bottom of the cofferdam." ART. 68. SHEET-PILING SUPPORTED BY FRAMES Where the nature of the bottom is such that piles cannot penetrate the same it is necessary to employ a frame to hold the ART. 68 SHEET-PILING SUPPORTED BY FRAMES 211 sheet-piling in place. These frames are usually built on shore, floated to the site, and sunk. Where piers are to be built under an existing bridge it is sometimes possible to suspend the frame from the bridge. SINGLE-WALL TYPE. At the site of the bridge piers of the Chicago, Milwaukee & St. Paul Ry. near Kilbourn, Wis., Sectional Side Elevation. FIG. 68a. Cofferdam for Pier of Chicago, Milwaukee, and St. Paul Railway, Kilbourn, Wis. only a few feet of sand covered the rock bottom on which the piers were to rest. As the channel was narrow and the current swift it was essential that the current be obstructed as little as possible, and for this reason the single-wall type was chosen in preference to that having a double wall. On account of the slight depth of sand, guide piles could not be used and so 212 COFFERDAMS CHAP. VI recourse was had to a frame. As shown in Fig. 68 a, the coffer- dam had V-shaped ends to diminish the force of the current against the structure and was held in place by wire guys an- chored to the rocks on the sides of the river. The frame, the details of which are shown in the illustration, was sunk by weight- ing with scrap rails. The covering consisted of gXi2-inch Wakefield sheet-piling; in driving this piling care was taken to broom the lower ends to give a close fit to the irregular rock surface. To aid in giving water- tightness to the structure canvas was placed around the outside of the cofferdam, and was so arranged that the lower part rested flat on the river bed for a distance of 8 feet out from the dam, while the upper part extended above water-level. The lower part of the canvas was first weighted down with iron rails and sand bags to make it fit closely, after which about fifty car loads of gravel were placed upon it. As the water was pumped out the structure was thoroughly braced as shown, but on building the pier this bracing was removed and the cofferdam walls braced against the pier. One of the largest and highest cofferdams ever built of wood was of the single- wall sheet-pile-on-frame type, and was used for the Mare Island Dry Dock No. 2. For a complete descrip- tion of this structure see Engineering Record, vol. 57, page 428, April 4, 1908. The cofferdam was approximately 150 by 800 feet in plan and the maximum head of water on it was 48 feet. The framework and bracing consisted of five horizontal courses of transverse and longitudinal timbers, the timbers of each course being con- nected to those of the adjacent courses by posts, the whole struc- ture being built as one unit which rested on bearing piles previously driven and sawed off under water. These longitudi- nal and transverse rows were 12 feet apart on centers. In the bottom course all timbers were 16X16 inches in section, while those in the next two courses were 14X14 inches, with 12 X 12- inch timbers for the two upper courses. The rangers, i.e., the horizontal pieces forming the frame proper which holds the sheet-piling in position, were 20X24 inches in section for the ART. 68 SHEET-PILING SUPPORTED BY FRAMES 213 bottom course and 12X12 inches for the top course, the other courses having intermediate sizes between these limits. The distance between courses was approximately 10 feet. In addi- tion to the members mentioned, a large amount of bracing in both horizontal and vertical planes was used. The sheet-piling units were formed of two 12 X 1 2-inch timbers fastened together side by side and were 60 feet long, this length being obtained by using two pieces, one 34 and the other 26 feet long. A tongue-and-groove joint was made by spiking to each piece of piling three 3 X4-inch sticks, two on one side and one on the other, thus making each piling unit 30 inches wide. To give additional water-tightness to the cofferdam a large amount of filling was banked around the outside. DOUBLE-WALL TYPE. This is a form but little used since it offers but slight advantages over the single- wall type and is con- siderably more expensive. It is more easily made water-tight than the single- wall form, but on the other hand, it is very little stronger because strength is almost entirely dependent on the amount of internal bracing used. Where strength must be obtained without the use of bracing the type described in Art. 69 should be used. The cofferdams for one of the piers of the Chattahoochee River Viaduct had an inside framework, 39 feet long by 15 feet wide, which was composed of horizontal frames of 6X8- inch pine timber braced with one set of longitudinal and two sets of transverse timbers. These frames were spaced from 2 feet center to center on the bottom to 3 feet centers at the top and were held in place by vertical posts between them, the total height of the framework being 9 feet. The outside frames were sufficiently large for a 4-foot thickness of puddle and were connected to the inside frames by braces and rods. The framing was partly built on shore, launched, floated to place and there completed. The bottom of the river had a seamy ledge covered with a layer of sand varying in depth from 6 inches to 3 feet. As soon as the framework was sunk two rows of sheet-piling, each row consisting of a double thickness of 2-inch pine plank, 214 COFFERDAMS CHAP. VI were driven, care being taken to break joints. The bottom of the puddle chamber was then covered with two layers of sacks loosely filled with sand, after which the remainder of the chamber was filled with clay puddle. Considerable trouble was caused by water coming up in the cofferdam through the seamy ledge and this leakage was stopped only after a 2-foot layer of concrete was deposited through the water and allowed to harden before pumping out the water. ART. 69. SHEET-PILING SUPPORTED BY CRIBS For cofferdams which rest on hard bottom and are too large to employ internal bracing economically, a series of cribs, laid up log-house fashion, are used to hold the sheet-piling in place. Each crib unit is made as long as can be conveniently handled and as wide as is necessary to develop the required stability. Rough logs are generally used although in some cases they may be squared, but the latter offer only a slight advantage over the former. In building these cribs the bottom courses are usually started on land and the crib is built to a height sufficient to permit the top part being well out of water when it is first launched; after this it is launched, floated to place and com- pleted. Where the stream is low at certain times of the year the cribs may sometimes be built in place. The bottom of each crib should be shaped to fit the rock bottom, and if a few feet of sand or other material overlies the bedrock this should be dredged out before placing the cribs. A part of the bot- tom of the crib is usually floored to permit placing stones so as to sink it. After all the cribs are sunk the remainder of the space inside of them may be filled with stones or earth. The latter material possesses the advantage of not only giving the cribs great sta- bility but also to secure water-tightness. After the cribs are placed sheet piling is driven around the outside and banked with earth. This type of cofferdam is very widely used in build- ing dams for hydro-electric plants. Fig. 690 shows a view of the cofferdam employed in the con- ART. 69 SHEET-PILING SUPPORTED BY CRIBS 215 struction of a dam for the Connecticut River Power Co., near Vernon, Vt. The width varied with the height of the coffer- ,dam; for the upstream one the maximum width was 35 feet, while the maximum height was 42 feet, or 16 feet above normal water-level. The structure was of the rock-filled type made of round logs in 7-foot checks, with the face logs slabbed on the sides to give good bearing for the sheet-piling. The top of the cribs were floored with logs to serve as a walk and also as a protection against ice pressures. On the outside the cribs were sheet-piled with 3-inch spline-and-grooved spruce, and this in turn was banked with earth up to normal water-level. k - 4610 Section C~D. FIG. 696. Typical Section of Crib Cofferdam. Niagara Power Plant, Electrical Development Company of Ontario. The cofferdams for the Niagara Power Plant of the Electric Development Co. of Ontario furnish an example of exceedingly strong and rigid cofferdams placed under the most trying conditions. In some places the current had a velocity as high as 17 feet per second which made it difficult to study the nature of the bottom and the depth of water previously to placing the cofferdams. The widest part of the cofferdam consisted of two lines of parallel, rock-filled timber cribs with a space between, sheet- piled and filled with puddle as shown in Fig. 696. Both cribs 2l6 COFFERDAMS CHAP. VI were built of squared timber with the outside wall of the outer crib laid solid. The width of the cribs varied to meet the variation in depth and the bottom of the cribs was made to fit the irregularities of the rock surface. In shallow water the cribs were built in place but elsewhere they were constructed in the river upstream, and by means of cables from the shore they were floated into place and were sunk by filling with rocks the wells which had bottoms. For further details of this in- teresting cofferdam the reader is referred to Engineering News, vol. 54, page 561, Nov. 30, 1905. ART. 70. STEEL SHEET-PILE COFFERDAMS The advantages which steel sheet-piling possesses over the wooden type are discussed in Art. 60. On account of these advantages steel-piling is being used more and more in coffer- dam work. The details of the structures differ but little from those using timber sheet-piling, the main difference being that the steel type, on account of the greater strength and positive interlock of the piling, requires less bracing. Fig. joa indicates a good example of a steel sheet-pile coffer- dam with guide piles. In the illustration the guide piles and the outer course of wales are not shown, however. The bottom at the site of the pier consisted of hard-pan to an un- known depth covered with about 6 inches of mud. The depth of water was about 9 feet at mean tide, which had a rise and fall of about 6 feet. 1(t Round wooden piles were driven 8 feet apart enclosing the site of the 83Xi5-foot cofferdam; 6X 1 2-in inside waling pieces were bolted to them above high water. " Spacing blocks 4 inches thick and i2Xi2-inch inside wales were bolted to the outside wales, forming guides, between which were driven a single row of Lackawanna 1 2-inch, 40- pound steel sheet piles 35 feet long. These were all assembled together before driving .... and then driven ... by one McKiernan-Terry steam-hammer weighing 5000 pounds and making about 225 strokes per minute. It was handled by the 1 Engineering Record, vol. 67, page 268, March 8, 1913. ART. 70 STEEL SHEET-PILE COFFERDAMS 217 boom of a floating derrick and went round and round the coffer- dam, driving each pile a foot or two at a time until the work was completed. The driving was very hard, many boulders being encountered, some of which were displaced and others broken by the piles. When they could be neither displaced nor broken, driving on the piles that encountered them was discontinued, and adjacent piles were driven down to subgrade about 6 inches below the bottom of the footing. Plan EL7655 3 -s i. M\ \ M.HW-^ n, | -,.\M.LW M I I2"x/?" \ \ - * n K- d'O" * KSfre/ 'Piling m a Stone Facing Concrete Backing a i y tm ___. _.. !_^ _L Concrete Base ^ 30 I3'0" 1 Section A-A FIG. 7oa. Cofferdam for Highway Bridge Piers in Passaic River, at Bridge St., Newark, N. J. "As the bottom was excavated inside the cofferdam, some of the boulders which obstructed the sheet piles were left in position and the sides of the excavation below them were closed as well as possible with bags of cement. The cofferdam resisted a pressure head of about 28 feet with very little leakage through the pile joints, which were packed with oakum. . . . The long sides of the cofferdam are braced with 12X1 2-inch horizontal transverse struts 9 feet 7 inches apart on centers, 2l8 COFFERDAMS CHAP. VI in four tiers about 6 feet apart. At the rounded ends the in- side waling pieces are made like arch centers of 12X1 2-inch double-scarf pieces, with radial braces to the middle of the adjacent cross- strut."- Some of the concrete piers for a bridge ocross the Illinois River at Peoria, 111., were founded on bedrock 20 feet below the bottom of the river, where the depth of water was approximately 20 feet. To build these piers, cofferdams of steel sheet-piling on frames were used. By means of an orange-peel bucket the material of the river bottom was first dredged down to a layer of slate and soapstone, about 3 feet thick, which overlaid the rock. The excavation was made over a large area so that the material overlying the slate' would stand at its natural slope and still leave an area on the slate of sufficient size for the cofferdams, one of which was 39 by 40 feet in plan. l "The steel-piling forming the sides and ends of the coffer- dam was braced across the latter with five longitudinal and six transverse rows of 12X1 2-inch timbers to hold it in place when the water had been drawn down in the cofferdam. These timbers were placed in nine horizontal layers, varying from i\ to 5 feet apart from the bottom to the top of the cofferdam. The horizontal layers were held apart by a vertical i2X 1 2-inch timber at each intersection of the rows of braces. The timber crib formed by these braces and verticals was built in the water approximately over the site. The horizontal layer which would come at the level of the top of the slate and soapstone in the cofferdam was first assembled as a raft on which the verticals were erected and then the second horizontal layer was placed, sinking the crib thus formed to the water-level. The various horizontal layers were thus added in succession and when they had been completed the crib was towed over the site, sunk in position and anchored." The steel-piling, of the Friestedt form, was driven around this framework through the slate and soapstone to rock, after which the material which had been previously dredged was backfilled around the cofferdam up to low water-level. After 1 Engineering Record, vol. 55, page 247, March 2, 1907. ART. 70 STEEL SHEET-PILE COFFERDAMS 2IQ pumping out the cofferdam the layer of slate and soapstone was removed and the pier built. Among the deepest cofferdams that have ever been placed are those used in founding the piers of the Tunkhannock Via- duct of the Delaware, Lackawanna & Western Railroad. These were land cofferdams ' and had a maximum depth of nearly 100 feet, with a depth of 65 feet below ground water- level. In principle they closely resemble the method used in placing piers for buildings as described in Art. 124, and differ from the regular caisson since excavation took place simul- taneously with the driving of the sheet-piling, and since the lower part of the sheet-piling served as a form for the pier footing. lu The cofferdam for pier 4 is typical of those of piers 3, 5, 6, 7 and 8 and was commenced by assembling on the surface of the ground a 43X49-foot rectangle made of 12X1 2-inch horizontal timbers spliced together to form one course of inner wales. Vertical posts were set up on this course and supported a second similar course about 16 feet above it, and two corresponding courses of exterior wales were erected outside of these and about 6 inches in the clear from them." Lackawanna steel sheet-pile units 30 feet long were then placed between the outer and inner wales and driven by a steam-hammer going round and round the cofferdam driving each pile unit 2 or 3 feet at a time. As the piling was driven the interior was excavated and the cofferdam braced with succes- sive tiers of 12X1 2-inch longitudinal and transverse struts. After driving this set of piling to its full length an exterior row, concentric with the inner row and 4 feet 8 inches beyond the same, was assembled and first driven to a penetration of about 12 to 15 feet. The space between the two rows was then excavated and at the same time the inner row was also driven, the upper tiers of bracing of the latter being transferred to the bottom and new sets of bracing furnished to the outer piling. In this way, by driving both outer and inner rows to their required positions, the excavation was carried to rock. 1 Engineering Record, vol. 67, page 485, May 3, 1913. 220 COFFERDAMS CHAP. VI The advantage of two rows of piling was in the easier driving thereby obtained. The lower part of the excavation was com- pletely filled with concrete, the steel-piling serving as a form; DL^J^L^ /d^^'^'--^'^*^ -.(),&- ^ I f 6 b o o O OjO O O 1 i o o o! oi T vw s b o o o ^ io o! s i oi oi t *sl i of 0| oi i ("0660 io jo p o // \ -,_ o o n ^ OjO i o CO |0 io >' B 1 ! O |o i O action at E 10 io [p |p o o o x \;\ x'^ \'-y'"' o|<>'--'b o 0000 i o jo o o oi o ' c/) .6,02-- H the surface of the piling was protected from the concrete by tarred paper, thus permitting the piling to be with-drawn later. Fig. 706 illustrates a somewhat similar type of cofferdam used ART. 71 SELF-SUPPORTING STEEL SHEET-PILE COFFERDAMS 221 in the reconstruction of the Union Pacific Railroad bridge at Kansas City. The upper tier of sheet-piling was of wood. The details of the bracing are clearly shown in the illustration. Fig. ;oc is a half-tone showing the details of the bracing used for the steel sheet-pile cofferdam at the Loomis St. tunnel, Chicago. The cofferdam was 75 by 53 feet in plan and the maximum head of water on it was about 53 feet. The bracing consisted of i2Xi2-inch timbers, spaced 8 feet apart hori- zontally and 4 feet vertically. Few examples exist of the type of cofferdam consisting of steel sheet-piling on cribs. The reason for this lies in the fact that almost all the crib and sheet-pile cofferdams have been built in localities where timber is abundant and for this reason sheet-piling of wood is cheaper than that of steel. ART. 71. SELF-SUPPORTING STEEL SHEET-PILE COFFERDAMS There is a type of cofferdam using steel sheet-piling which has almost no parallel in the wooden sheet-pile cofferdam; this is the cofferdam without horizontal guides or bracing. Two reasons may be given for this fact: First, with the positive form of interlock which most forms of steel sheet-piling po- sess, sufficient guidance is furnished by the interlock to do away with the necessity of horizontal guides; and second, the higher strength lessens the amount of bracing necessary. The two most notable examples of this type of cofferdam are those used for the United States Government lock at Black Rock Harbor, Buffalo, N. Y., and for raising the United States Battleship " Maine" in Havana Harbor, Cuba. Both of these structures rank high as daring pieces of cofferdam work, the former on account of its great size and the latter because of its great height. The Black Rock cofferdam was built to permit the construc- tion of a ship lock, and was rectangular in plan, 260 by 947 feet over all as shown in Fig. 710. The depth of water at the site varied from 2 to 15 feet, averaging about 8 feet, while the solid rock on which the lock was built was about 40 feet below mean water-level. As shown in Fig. 716 the sides of the cofferdam 222 COFFERDAMS CHAP. VI were made of two walls of steel sheet-piling, the space between the two walls being divided into pockets 30 feet square by transverse walls of the same piling as that used for the main walls, which served to connect the latter. A horizontal 15- inch, 40-pound channel was bolted to the tops of the piles of the inner wall and a similar channel was bolted at an inclination across the transverse walls as shown in Fig. yic. The piling was driven to rock and at first wooden guide piles and wales were used to maintain the alignment of the steel sheeting, but eventually these guides were dispensed with, the 3 Q UA W ISLAND h 947' - H i I5| is i |7 1 |9K/| i i i mi i i i IZQI i i i |g| | | | 13 ff-ED:' M 1 1 i M 1 1 MI 1 1 i isoi n i kimnifc ^sK^^Sr~-5SS^iri^^^^^s^ i FIG. 710. Plan of Black Rock Cofferdam. only ones used being ioX3o-foot floating forms having one edge in the plane of the sheeting. The fine alignment at- tained by this simple method may be seen in Fig. jib. After driving the piling the pockets were filled with clay and to further strengthen the structure, as the inside was excavated, a bank of earth 25 feet high was maintained on the inside as shown in Fig. jic. But in spite of this bank of earth the material in the pockets caused the inside wall to bulge badly between the cross walls in both a horizontal and vertical direction. It is instructive to observe the plans of different pockets of the cofferdam, and the curvature of vertical sections after the steel sheet-piling adjusted itself to the pressure of the clay filling by developing tension in the interlock. Fig. 71 d gives the ART. 71 SELF-SUPPORTING STEEL SHEET-PILE COFFERDAMS 223 results of a careful survey of pocket No. 35 in which the maxi- mum bulging of sides occurred. It should be noted how short a distance the bulging extended below the sand and gravel bank which was allowed to remain inside of the cofferdam. The diagram also shows vertical sections at the middle of pock- ets Nos. 30, 52, and 75, the relative location of the pockets being indicated in Fig. 710. See also the half-tone view, Fig. 7 ic. Section A-B. FIG. 7 id. Diagram Showing Deformation of Steel Sheet Piling. In all 6589 tons of steel sheet-piling were used in this coffer- dam, there being 6870 linear feet of piling wall from 45 to 50 feet high, which makes this the largest piece of cofferdam sheet- piling work on record to 1914. The price paid the contractor for building the cofferdam, which included furnishing all material, pumping out, and maintaining the same, was $408 830. The type of piling used was that known as the Lackawanna, and which had a web thickness of J inch and weighed 40 pounds per linear foot. 224 COFFERDAMS CHAP. VI The cofferdam for raising the " Maine" represents a special type of steel cofferdam, very large and strong. l "The problem was to surround the wreck of the vessel, lying in about 29 to 37 feet of water, with a cofferdam, which when unwatered would be tight enough to prevent leakage, strong enough to resist outside water and mud pressures, and a protection that would assure safety during the work. The cofferdam should be self- sustaining, if possible. Bracing by struts across its interior to resist the water and mud pressures might be difficult to install and would interfere with the operation of removal. The bor- ings indicated bad conditions for foundations. The building of a cofferdam without internal bracing, which would withstand pressures from a head of 37 feet of water and practically 21 to 23 feet of mud, was an unprecedented task. "The cofferdam should be not only self-sustaining and safe against the pressures to which it was to be exposed, but it should also be capable of complete removal after it had served its purpose. It should be able to support more or less superim- posed loads, for working platforms had to be built upon it. The work of unwatering the area enclosed had to be carried on from the top of the cofferdam; and afterward, men and materials had to be transferred from there to the interior, for work upon the wreck. . . . The cofferdam decided upon consisted of 20 equal cylinders, 50 feet in diameter, and composed of steel- piling 75 feet long. . . . " A plan is shown in Fig. 710. "The length of the major axis of the cofferdam was prac- tically 399 feet, and of the minor axis 219 feet, leaving a 2o-foot clearance at the submerged bow of the ship and a i4-foot clearance at the stern, with 45 feet at the side cylinders. Such clearance was necessary to avoid portions of the wreck which had been blown beyond the position occupied by the hull. "The units of the cofferdam were made cylindrical for the reason that the extremely high pressures, which would be exerted by the mud rilling, would act radially and uniformly on each pile, straining each joint to the same amount at equal depths, 1 Bulletin No. 102, Lackawanna Steel Co., Buffalo, N.Y. ART. 71 SELF-SUPPORTING STEEL SHEET-PILE COFFERDAMS 225 FIG. jie. Plan of Cofferdam for Raising the "Maine." FIG. 7 if. Connection of Cofferdam Cylinders. L FIG. 7ig. Filling Clay into Cylinder A . Part of B in Foreground. 226 COFFERDAMS CHAP. VI and in the entire cofferdam cylinders would deform least from play in the piling interlocks." The cylinders were driven tangent to one another and to in- sure their stability and prevent leakage of water through them when the cofferdam was pumped out they were filled to the top with clayey material that was dredged from the bottom of the harbor. A curved diaphragm of steel-piling, as shown in Fig. 7 if, was driven to connect adjacent cylinders, and the space between this arc and the outer surfaces of the large cylinders was likewise filled with dredged material. The piling used was the Lacka wanna section, weighing 35 pounds per linear foot, and had a web \ inch thick. The piles were driven so that their tops were 2 or 3 feet above normal water-level (Fig. yig) and the 75-foot length of piling, which penetrated the harbor bottom to a distance of approximately 35 feet, was made of two lengths spliced together with channels. ART. 72. CRIB COFFERDAMS Where the cofferdam is to rest on bedrock which is ap- proximately smooth and level, a crib cofferdam, formed with one or two walls of squared horizontal timbers laid closely, may be used in place of the sheet-pile cofferdam. Where the single- wall type is used it is ordinarily made an integral and permanent part of the pier, and as such is not a cofferdam, but a caisson. For a description of this type see Art. 83. In his book on Sub-aqueous Foundations, FOWLER describes a double- wall crib cofferdam used by the C. B. & Q. R. R., which was made from 2X8-inch and 2Xio-inch fence boards laid flat. The two walls were thoroughly tied together and the space between filled with puddle. Fig. 72 a shows a polygonal cofferdam of the crib type which was used for the center pier of the Arthur Kill Bridge. At the site of the cofferdam the depth of water at high tide was about 28 feet, with about 4 feet of mud and clay overlying bedrock. This mud and clay was dredged out previously to placing the cofferdam. The latter had twelve sides with walls 4 feet apart in the clear, and in this space puddle was dumped. All courses ART. 72 CRIB COFFERDAMS 227 of timber were thoroughly drift-bolted together and all joints caulked with cotton wicking. No internal bracing was used. Before pumping out the water a 4-foot layer of concrete was deposited all over the bottom and allowed to harden for a week. The cofferdam for the new inlet tower of the St. Louis Water- works was of the double-wall crib type, 38 by 76 feet in plan and 22 feet high. The walls were composed of horizontal 12 X i2-inch material and were 3 feet apart in the clear. The joints between all courses were carefully caulked. The cofferdam was braced transversely by three vertical rows of M.H.W. nearfy Level. Section of Dam. Plan of Dam. FIG. 720. Cofferdam for Pivot Pier of Arthur Kill Bridge. horizontal 12X1 2-inch timbers spaced 4 feet apart vertically, and extending from outside wall to outside wall, thus tying the walls together as well as bracing the cofferdam. The ends were braced by similar horizontal i2Xi2-inch diagonal timbers, running at an angle of about 45 degrees from the center of the ends to the sides. The river bottom was bedrock and the depth of water about 15 feet, the current having a velocity of from 6 to 8 miles an hour. The cofferdam was held in place by three triangular 228 COFFERDAMS CHAP. VI cribs filled with rocks and sunk upstream from the cofferdam and tied to the latter by cables. The puddle chamber was partly filled with concrete in sacks and puddle placed on top. Sacks of clay were also banked around the outside. Cofferdams are widely used as temporary adjuncts to open and pneumatic caissons, but as the details differ widely from the types described in this chapter and resemble closely the caissons themselves they will be described in the chapters dealing with such caissons. ART. 73. MOVABLE COFFERDAMS Unless it forms an obstruction to navigation only that part of the cofferdam above low water is sometimes removed. This is because the salvage value of the material is less than the cost of getting it out, except where steel sheet-pil- ing is used. Where the same size and style of cofferdam is to be used for a number of piers it will often prove advantageous to so construct a cofferdam that it can be used over and over again. In one type, that of the cofferdam on grillage, it is so easy to make its sides removable that it is universally done, even though they may not be used a second time. A movable cofferdam consisting of sheet-piling supported by a crib was used in constructing the piers of the Falls-of- Schuylkill Bridge, of the Philadelphia & Reading Railroad. When in position the cofferdam was 62 feet long, 36 feet wide and 16 feet high. The cribs were 10 feet thick, making the inside dimensions 42X16 feet. The cofferdam was divided vertically through each short side into two parts of equal size and these were floated separately to the site, joined together and sunk. Each section had water-tight compartments to assist in floating and these were filled with water and stone, while other non-water-tight compartments were filled with stone, when it was desired to sink the sections. On reaching the rock bottom sheet-piling of jointed planks, 3 or 4 inches thick, was placed on the outside and spiked there. Puddle was then placed around the outside, after which the cofferdam was ART. 73 MOVABLE COFFERDAMS 229 pumped out. Two sets of horizontal bracing connecting the long sides were placed as the water was removed. In placing cylinder piers for the Queen's Bridge, Melbourne, Australia, square movable cofferdams of the sheet-pile-on-frame type were used. One side opened outward as a door, thus per- mitting the cofferdam to be removed on completion of a pier. la The dam was built on shore complete, and launched ready for immediate use on the site of a cylinder. The sheet-piling was vertical and consisted of i2X4-inch rough-sawn Oregon planks, supported by horizontal frames of 12X1 2-inch Oregon timber, spaced close together near the bottom of the river, to 3"x8" 6x8" 25' 0" 6"xlO" 6"x8' Longitudinal Section. Cross Section. BothSidet ? Smoothed andEdges Beveled PI ah. Corner Details. FIG. 730. Cofferdam Used on Key West Extension of Florida East Coast Railway. carry the greater pressure of water. Up the four corners of the dam were i2Xi2-inch Oregon timbers,^into which the frames were checked and by which they were kept to their proper spacing, and which formed supports for the door. Outside the sheet-piling, at the top and bottom frames there were outside wales, 12 by 6 inches (keeping the sheet-piling in place), bolted to the frames inside by i-inch bolts, two to each waie, passing between two sheet piles." The sheet-piling was flush 1 Engineering News, vol. 33, page 230, April 4, 1895. 2 3 COFFERDAMS CHAP. VI with the bottom of the frame and extended a few feet above the top. At the site of the piers there was about 3 feet of soft silt covering the rock. This silt was covered with puddle before placing the cofferdam. After sinking it by weighting, the sheet- piling was driven through the puddle and silt. On pumping out the cofferdam much of the silt ran into the interior and the clay took its place, thus sealing the structure. To remove the cofferdam the sheet-piling was first drawn up, the loading taken off, the door opened, and the cofferdam floated out. At \ffemove fhis Top Cross- Brcrce erncf Base of Rail El. +11.05 -,.\ brace Concrete Form from Side +IW5 \ ] Posts as indicated in dotted Lines^~K'fiT] i \before Coping-Course is put on ,!<-"- /-"" >]' & I eTI ! ' o. Part Sectional Side Elevation. Sectional Side Elevation. FIG. 73&. Cofferdam for Rest Pier of Chicago and Northwestern Railway Lift Bridge at Kinzie Street, Chicago. first tarpaulin was placed around the outside of the cofferdam but it was later found that this was unnecessary since the sheet-piling was water-tight without it. Fig. 730 illustrates the form of a movable cofferdam used in constructing the piers of the Key West Extension of the Florida East Coast Railway, where the depth of water did not exceed 8 feet. The two sides and the two ends formed independent portable sections which were connected together by means of ij-inch vertical rods running down through the overlapping rangers at the corners of the cofferdam. ART. 73 MOVABLE COFFERDAMS 2 3 I Detail at A 4x6 'about 6'0'cJoc. At the site of the piers sand overlaid the coral rock. Piles, for the foundation of the pier, were first driven until the tops were 2 feet below low water, after which the cofferdam was assembled on a barge, lifted from the same and set in place. The sand was then pumped out by a centrifugal pump, after which a 2-foot seal of concrete was placed over the whole bottom. After allowing this concrete to harden for seven days, the cofferdam was pumped out, forms placed and the pier built. On completion of the pier the rods were withdrawn, which allowed the sections to float free. MOVABLE COFFERDAMS ON GRIL- LAGE. On account of its conven- ience and ease of manipulation a movable cofferdam is almost uni- versally employed where a timber grillage foundation on piles is used for the pier. The grillage and the cofferdam form an open box con- structed on shore or on a barge or raft, launched, floated to the site, and sunk on the pile foundation by building the pier in the box. This type differs from the box caisson, described in Art. 80, since the sides of the former are not a permanent part of the pier. After the pier is built to above high-water level the cofferdam is removed, the sides being so fastened to the grillage that this can easily be done. Fig. 736 shows the details of the movable cofferdam used for the i2X4il*-foot pier of the Kinzie St. drawbridge, in Chicago. This cofferdam was connected to the grillage by 28 vertical i-inch rods, 2 if feet long. To sink the structure, concrete forming the pier was placed in the same, the cofferdam itself serving as a form for the concrete up to an elevation shown in the drawing, and above this regular forms were used. On com- Sect ion of Cpisson FIG. 73 if' ,o ff ) j Diaphragms and Anchored to5ideWat/,ai 6K. ;i I Shown ^ ! N -4s * s \ _Q> ^ A - i. : --A Spacedsame asHor.Rods, \-l'6"long. ) ^?77rc-"-ra; I . va _ Note:. All 8'x 12 "Caissons to be Built in Sections the Height of which should not exceed 10 ft The Reinforcement of Bottom Walls and Diaphragms will be same as Indicated on the Detail of 12'* 12 'Caisson. The Height will vary as Shown. r.r::cK:.'-''.'j'.::::j:r^T^"r j "- j T'''''rx""--.i ' : V N <"4"*24" Dia- phragm in ! each Section \ ,<^> ^Q n'o"- '- ..... I2'0~ Horizontal Section B-B. Plan. 12-Ft.x 12-Ft. Caisson. 8 ~ ftx "^ Ft. Caisson. FIG. 8ia. Box Caisson of Reinforced Concrete near Glen Cove, Long Island. water, after which they were towed to position and sunk. Some of the upper sections were placed on the scow and lifted directly from there upon the lower sections already in place. In the ART. 82 MISCELLANEOUS TYPES . 245 bottom sections a 3 -inch hole was cast, which was closed while the caisson was being towed to position. When directly over the site of the foundation bed, water was let in by unplugging the hole to sink the structure, after which the same was filled with sand and gravel. For a very complete discussion of the subject of concrete cais- son construction for breakwaters the reader is referred to a paper by Major W. V. JUDSON in the Proceedings of the Western Society of Engineers, vol. 14, page 533. An abstract of this paper may be consulted in Engineering News, vol. 62, page 34, July 8, 1909. ART. 82. MISCELLANEOUS TYPES A metal box caisson, composed of a vertical cylinder 9 feet in diameter and nearly 13 feet high, having sides formed of |-inch steel plate and a bottom composed of a ribbed and flanged cast- ing, slightly convex downward, was sunk about 13 feet through quicksand to form the foundation for some machinery at the General Electric Company's Plant at Schenectady, N. Y. Through the bottom there were forty -four if -inch holes, each hole being tapped for a vertical pipe, which in turn was connected to a 3-inch main which provided water at 80 pounds pressure. Valves were so placed that any combination of streams could be used at once. The caisson was sunk by opening the valves, thus forcing the water through the pipes to scour out under the bot- tom of the cylinder. At the same time the caisson was heavily weighted with pig lead. Some little trouble was experienced in keeping the caisson plumb but by using certain jets at certain times and by placing the loading material mostly on the high side the structure was finally brought to bearing on the firm material The pipes were then disconnected near the bottom and concrete placed in the caisson. Another modified form of box caisson used at the same place to avoid danger of undermining adjacent structures resting on the quicksand, was sunk by boring out the quicksand from under the caisson. A pile foundation was to be used and as it was desired to cut off the piles at an elevation well below ground 246 . BOX AND OPEN CAISSONS CHAP. VII water -level, a box caisson 4 feet high and 16 by 40 feet in plan, inside dimensions, was constructed with a large number of i2-inch holes cut through the bottom. Twelve-inch vertical wrought-iron pipes, 4 feet long and open at both ends, were fitted into these holes, after which the caisson was filled with con- crete to the top of the pipes. After this had set 3600 tons of pig iron were loaded on the caisson between the pipes. The quick- sand would not rise in the pipes but by means of post-hole augers the material was raised and removed. Care was taken to remove but a slight amount from a hole at any one time in order to prevent unequal settlement. After sinking the desired amount, about 4 feet, piles of about 1 1 inches diameter at the top were driven through the pipes to a distance of about 19 feet below the bottom of the caisson and were then cut off level with the tops of the pipes, after which the latter were grouted and the foundation completed. In both the foregoing cases the problem was to sink a founda- tion through quicksand without disturbing adjacent structures founded on quicksand. Success was due to weighting the cais- son so heavily that quicksand could not flow under the same from outside and at the same time providing means to remove the sand under the caisson. ART. 83. SINGLE- WALL OPEN CAISSONS An open caisson is a box-like self-contained structure' either partly or entirely open at both top and bottom, and forming an integral and permanent part of the pier. The open caisson which forms one of the most important classes of structures used for subaqueous work and has the distinction of being employed for the deepest foundations, may be divided into three types: First, the single-wall timber cais- son consisting of a frame with solid walls and without top, bottom, interior chambers, or cutting edges; second, the cylin- der caisson consisting of open cylinders of iron or masonry; and third, the caisson with dredging wells consisting of a struc- ture partly closed both at the top and at the bottom, with open ART. 83 SINGLE- WALL OPEN CAISSONS 247 wells running vertically through it. The first type is used where little or no sinking is required, while the second and third are employed where sinking is necessary; the second where the required cross-sections of foundations are small and the third where they are large. In the details of construction the single-wall open caisson of timber resembles the single- wall crib cofferdam (Art. 72) and differs from it chiefly in that it is an integral part of the founda- tion. The caisson usually consists of a solid framework of 12X1 2-inch timbers thoroughly caulked. It is used only where little or no sinking is required or else where the material to be sunk through is very soft. This is true since sinking must be done by artificially weighting the structure with removable material, such as iron rails. If soft material covers the site, as much of it as possible should be dredged out before placing the caisson. Removing the material from within the caisson after it is placed, and also using the water-jet along the sides will greatly facilitate sinking. On reaching its final position con- crete is deposited through the water to a depth of several feet and allowed to harden. This virtually forms a box caisson which is then pumped out and filled with concrete, placed in the dry, to make the foundation for the pier. It is customary to add a cofferdam on top of the caisson so that the latter may not extend above low water. Fig. 83 a shows the details of the caisson used for one of the piers of the French River bridge of the Canadian Pacific Rail- way. The lower part was built on shore, the structure then being launched and completed in the river. Rolls of canvas were attached to the inner faces along the bottom and as soon as the caisson was lowered to the bottom, divers went down and spread out the canvas, and on it laid bags of cement to close the openings under the walls. A layer of mortar was then de- posited through the water on the rock bottom, after which the remainder of the caisson was filled with concrete. The cais- son was surmounted with a cofferdam of exactly the same construction as the caisson. Fig. 836 shows the details of the caissons used in the substruc- 248 BOX AND OPEN CAISSONS CHAP. VII ture of the Columbia River bridge of the Oregon- Washing ton Railroad & Navigation Co. The river bed was composed of very firm soapstone, overlaid in places with cemented boulders, v 30 -> ( 1 Cement \ 3 Sand ( S Rock H-Kl t-ftl- 17-H III 1 1 Sectional Side Elevat 4*9 xlO Sectional End Elevation. 25- 2** 6'0'S <3T(? ^A/'/fea' J Projecting 3' up into Concrete, cvj Sectional Plan. FIG. 830. Open Caisson for Canadian Pacific Railway Bridge over French River. gravel and sand. The maximum depth of water at the usual stage of the river was about 30 feet, with a maximum velocity of current of 7 miles per hour. ART. 83 SINGLE-WALL OPEN CAISSONS 249 The caissons after being framed were floated to place and sunk by loading with steel rails, the latter being placed in the racks shown on the drawings. All concrete was placed through the water, no attempt being made to pump out the caisson. Upon completion of concreting all timbers above low water- level were removed. Some of the piers of the Fraser River bridge at New West- minster, British Columbia, were founded on caissons, 14 by Cross Section. 1 Side Elevation. |~| 7 Plan. -\ ' u u FIG. 836. Open Caisson for Piers of Oregon- Washington Railroad and Navigation Company over Columbia River. 34 feet in plan, resting on pile foundations, in which the piles were 60 feet long. These caissons were composed of i2X i2-inch timbers. They were sunk to a depth of from 10 to 20 feet below the original level of the bottom by loading stones on timbers placed across their tops and by pumping out the soft material with the sand and mud pump described in Art. 91. On reaching the final position a layer of 1-2-3 concrete, 5 to 250 BOX AND OPEN CAISSONS CHAP. VII 10 feet thick, was deposited around the piles by a steel-pipe tremie. This concrete was allowed to harden one week, after Section through Course 3 or 5 Top View Section A-A ( '(-'i; !y j.':[;i , '...'( ->'} Mfv;^::v^:;-;lv..; ; x.;...;.v :: ..; Va ..^.,v.::A< - L '"' >.-- L '] ' ' . ' JOE^^2 '( " '. "> ; :' ; - : -'.:'.-V.' :': &:.: ': ': : b///;-^ : ^^.'-{';V.v if-' Ll''.'.t_ |!'T''u ^ ''['i.Jb'<- '''''r'f-'i-V'.'-'-'.-'" ..''.'.: v'-'iiV. '' -' '.'-' j-'-'-'''''-' 1 1 It' 1 '. ' M-_li3i!i|i ." ' o^li'lKiii 1 1 .'j' :: : :: 'v.'-.'-.-'-.-'-^'-'--':-'- : '- '.- iSpB itjj 'll; ''Lll 1 ''".!;"'^:!' ' - '-' ''^'r-.-:-. : .'->-':v--:- ; ^.;:.'v sliilu ^! 'fjjij'.s j| ' JA. '. T ! ! ,'/Ji ^:.:;;J : ;-.!' : .%;:v:::i. : . :^iii A .ivd.v.v.'v.'-i-.vVP 1 1 i Cylindrical Hole r~ i5 ' j ' ^ ^- $&': Concrete"' -;-^vo i$jji > . 'Concrete H 1 pK .'-iw u i N T6 Bell Plates-* 12 'wide at top, 9f Vertical Section. FIG. 86a. Cutting Edge of Caisson, Penhorn Creek Viaduct, Jersey City, N. J. jointed sheathing, braced by i2Xi2-inch horizontal rangers. Four vertical i2Xi2-inch sticks were then placed, one at the middle of each waling piece, to serve as a guide for the caisson. The cast-iron cutting edge shown by the heavy lines in Fig. 860, was then placed in the bottom of the pit. Above this were placed outside and inside collapsible steel forms in 5-foot lengths. All caissons were cast in 20-foot units, the caisson being built to this height, allowed to set, sunk, and another section added. ART. 86. REINFORCED-CONCRETE CYLINDER CAISSONS 259 the whole operation being repeated until the desired depth was reached. Each section was allowed to harden six days be- fore it was sunk. Sinking through the mud and sand was effected for the most part by interior excavation with an orange-peel bucket. The water-jet was used to some extent and weighting was also resorted to at times. It was found advantageous to keep the jet pipes separate from the caisson and to work them by hand. The average rate of sinking through mud was 6| feet per day, while through the dense underlying sand only about ij feet per day could be accomplished. It was at first intended to found the caissons on rock, using an allowable bearing pressure of 10.8 tons per square foot, but later, owing to the greater depth of the rock, it was decided to found them on the dense sand above, which it was thought would safely bear a load of 7 tons per square foot. In order to reduce the unit pressure to this amount the bottom was belled out as shown in the illustration. The conical or belled section, which consisted of a number of TV-inch steel plates, was placed by a diver who, with the aid of a water-jet forced the dense sand from around the cutting edge and placed the plates. Each plate was forced into the sand a slight distance at the bottom and sprung behind the cutting edge at the top. Upon the com- pletion of this work the caisson was filled with 1-2^-5 concrete. Another interesting application of reinforced- concrete cylin- der caissons is that for the foundation of the lumber dock at Balboa, Canal Zone, the details of which are shown in Figs. S6b to e inclusive. la The bottom section forms a footing, and differs from the others in that the exterior surface is shaped like the frustum of a cone. The base of the footing rests on a shoe made up of steel plates, as shown in Fig. 86 b. The inside form (Fig. S6c) is wedged tightly against the upper edges of the diagonal plates of the shoe, and when the concrete is poured, the mixture fills only that portion of the shoe bounded by the outer vertical plate and the diagonals. In this way, a circular wedge-shaped cutting edge of steel is formed, entirely protecting the concrete." Engineering Record vol. 66, page 60, July 20, 1912. 260 BOX AND OPEN CAISSONS CHAP. VII r - ART. 86 REINFORCED-CONCRETE CYLINDER CAISSONS 261 3 Spaces /2t - J -<'';>." J- ,' . ./'i/-; r'flV' :?'''''' ' ;; r;- v >'.';' a-". '' isVi *] |%^; sps im. ~ Tk iv:'--. .':' ^^ *.V '' ''!.'&'(*'' i'- $!$$ * * '. s a.": i 'V'; ', '.* ; "'-; : * i .';'?" ' a::'o :. vV-.v ? fi '' 'y- ? i '; ,, 1* i i < - 7 'o"^- ---.:- /^v^-^ 5'0 < i '-jQ 'Q-~> ^ <---~~--' ^^^?^5? (f'jfV- 2 *! i-j'O"*' *$K 1 .!< so 10 - - * FIG. 906. Caisson for P. & L. E. R. R. Bridge, Beaver, Pa. The caissons, views of which are shown in Figs, gob and c, consisted of a concrete shell 7 feet thick, this thickness being maintained from the top to a point about 9 feet above the shoe, at which elevation it tapered to an 8-inch cutting edge. This cutting edge or shoe was formed by an 8X8 Xf -inch angle and a 2iX|-inch bent plate, the vertical leg of the angle extend- ing upward on the outer face of the caisson, while the bent plate had its inclined leg along the inner face of the wall. Rods | inch in diameter and 10 feet long, extending up into the concrete, held the shoe in place. There were two cross walls each 5 feet thick to stiffen the caisson, and these extended from the top of the caisson to about 3 feet above the shoe, a 276 BOX AND OPEN CAISSONS CHAP. VII trapezoidal portion at the bottom of each wall about 6 feet in height, being omitted. Rectangular cofferdams were first constructed around the site of each pier and these were unwatered to permit building the forms for the caissons. On completion of the forms a six- foot depth of concrete was deposited in the same and allowed to harden before more was added. Sinking was accomplished for the most part by dredging through the three wells with orange-peel buckets. When it was possible to keep the water down by pumping, the spoil under the shoe of the caisson was removed by hand to within reach of the buckets. Later, when boulders were encountered under the cutting edge they were removed by divers. When the caisson showed a tendency to stick, the water-jet was used. When within about 16 inches of the rock the pneumatic process was brought into use as explained in Art. 99. That the omission of reinforcement in a structure like the one just described may prove a costly mistake was shown in the cais- sons for the North Side Point bridge, across the Allegheny River, Pittsburgh, Pa. The caisson for the river pier had dimensions of 23 X 83! feet in plan, with four rectangular wells, 9X10 feet, and spaced 19 feet center to center. When the pier had been sunk to a depth of 17 feet below river bottom, a transverse crack developed at about mid-length and extended from the top to the river bottom as shown at the left in Fig. goe. The cracking was due to the unequal dredging in the different wells, causing the weight of the caisson to bear chiefly at mid-length. The cracked caisson was blasted to pieces and rernoved. The one placed afterward had smaller wells, and was reinforced with longitudinal rods. For an example of caissons for buildings which are sunk as open caissons and can be transformed into the pneumatic type see Engineering Record, vol. 63, page 185, Feb. 18, 1911. The first all-concrete open caisson used for bridge foundations in this country is probably the one for pier D of the Thebes Cantilever bridge. This caisson is 19X38 feet in plan and II ll rlf* FIG. god. Forms for Open Caisson of Concrete. See Fig. FIG. Qoe. Cracks in Caisson of Concrete without Reinforcement. ART. 91 SINKING OPEN CAISSONS 277 was placed in the winter of 1902-03. An open caisson (which was not constructed of either timber or metal) was first sunk in this country in 1898 by the Dravo Contracting Co., at Neville Island near Pittsburgh and was used for a pump well. ART. 91. SINKING OPEN CAISSONS There are five methods used in sinking open caissons: First, removing the material from within the caisson; second, weight- ing the structure; third, using the water-jet; fourth, driving down the caisson; and fifth, pulling down the caisson. The first method, which represents the fundamental idea of the open caisson, is always employed. For the small caisson, to be sunk but a few feet, as practised by the natives of countries in the Far East, excavating is done by baskets carried down, filled and brought up by divers. The modern method consists in pumping, or in dredging out the material with buckets. The mud and sand pump, the principle of which is described in Art. 107, is used where the material is largely silt, or other soft material. Fig. gia illustrates the pump used on the Fraser River bridge, at New Westminster, British Columbia. This pump, or ejector, which was operated by a hydraulic jet, at a pressure of 125 pounds per square inch, could handle anything with a diameter of less than 3 inches. The dimensions of the pump are shown in the illustrations. The top of the pressure pipe was fitted with a ball-and-socket joint and a 9o-degree bend with an enlarger to which were connected three lines of 2\- inch fire hose. A separate hydraulic jet, having a f-inch hole at the bottom and five f-inch holes in nearly vertical planes on the circumference of a circle and a few inches above the bottom, was used to agitate the material around the intake of the ejector. The most common method of removing material is by dredg- ing with an orange-peel or a clam-shell bucket. Where a layer of stiff clay is met it may be broken up by sending divers down to blast it to pieces, or it may sometimes be broken up by dropping down long steel rails vertically, which sink into the clay and tear it up in tipping over. A line is attached to the rails to withdraw them. 2 7 8 BOX AND OPEN CAISSONS CHAP. VII The most economical way to weight caissons is by making use of the permanent filling, and for this reason, where the size of the caisson makes it possible, a double wall should always be used. Temporary weighting, as with rails laid on top, etc., is always expensive on account of the time and labor involved, as well as on account of obstruction to the dredging operations. FIG. gia. Details of Hydraulic Ejector. FIG. 916. Tip of Water Jet. The rapid and successful sinking of the Hawkesbury bridge caissons (Art. 89) was largely due to their being designed to carry a large mass of concrete between the outer and inner shells, which was placed during sinking. The water-jet (Art. 17) is always a useful adjunct in caisson- sinking operations. By using the same freely around the cut- ART. 91 SINKING OPEN CAISSONS 279 ting edges and along the sides the frictional resistance is con- siderably decreased. Another advantage is that it tends to wash the material toward the interior of the caisson, where it can be picked up by the dredging buckets, which have previ- ously made a hole in the center. It is possible to drive caissons only when they are small and even then only light blows with the hammer may safely be given. Pulling the caisson down may sometimes be employed to advan- tage, if it is possible to drive piles around the outside and attach tackle to them and to the sides of the caisson. CHAPTER VIII PNEUMATIC CAISSONS FOR BRIDGES ART. 92. THE PNEUMATIC PROCESS The use of the plenum pneumatic process for founding deep piers is a good example of the application of scientific principles to foundation work. A pneumatic caisson may be defined as a structure, open at the bottom and closed at the top in other words, an inverted box in which compressed air is utilized to keep the water and mud from coming into the box, and which forms an integral part of the foundation. The caisson, which is usually not over 6 feet high in the work- ing chamber, issurmounted by a crib and cofferdam, the former, with the exception of one or more vertical wells, called shafts, being filled with concrete as the caisson sinks. This concreting, together with the excavating done in the working chamber, as the interior of the caisson is called, effects the sinking of the latter. The working chamber must be practically air- and water- tight, and yet there must be an opening for men to enter and leave the chamber, as well as an inlet and outlet for materials. These openings are provided by vertical shafts and air-locks. The shafts, wjiich extend from the roof of the caisson to a point well above the top of the crib and the level of the water outside, are usually of a circular or oval section and from i\ to 4 feet in maximum diameter. In the shafts, at the bottom, top, or between these two points, are placed the air-locks, they being air-tight chambers, often simply a part of the shaft itself, fitted with two doors, one of which leads to the working chamber and the other to the open air. The most pronounced advantage of the pneumatic caisson as compared with the open-caisson process lies in the fact that the 280 ART. 92 THE PNEUMATIC PROCESS 281 engineer has more control over the work, having a better oppor- tunity to sink the caisson vertically, to remove large boulders, sunken logs, etc., from under the cutting edge; the foundation bed can be properly prepared and personally inspected; and lastly, the concrete filling of the working chamber is deposited in air, thus giving a superior foundation" Another point, which is sometimes of great importance in placing foundations for build- ings, is that the soil about the caisson is not so liable to be dis- turbed when the pneumatic process is used. The one disadvan- tage of this process is that the men have to work under an air pressure which is sufficient to balance the pressure of the sur- rounding water in addition to atmospheric pressure, or practi- cally the full hydrostatic head from the cutting edge to the water surface. For depths from about 30 to no feet this type of caisson is extensively employed. For depths less than 30 feet the coffer- dam process is usually, but not always, a more economical method of placing the foundation while for depths greater than about no feet, corresponding to a pressure of over three atmospheres above the normal, the open-caisson method must be employed, since men cannot work advantageously under such high pressures. At the St. Louis Municipal bridge men worked at a maximum immersion of over 113 feet, the maximum gage pressure being 50 pounds, which is probably the world record for bridge caissons, with the possible exception of a bridge caisson in Denmark, where it is reported (Eng. News, vol. 26, page 467, Nov. 14, 1891) that a working depth of 115 feet was reached. Among other notable examples of deep immersions are the St. Louis arch bridge caissons, 109.7 feet; the Memphis bridge caissons, 106.4 feet; the Williamsburg bridge (New York) caissons, 107.5; an d the Broadway bridge (Portland, Ore.) caissons, 101 feet. The elevation of the bottom of the deepest caisson (No. 4) of the St. Louis Municipal bridge is 2.1 feet below the bottom of the east abutment caisson, or the deepest one of the St. Louis arch bridge. The caisson used in sinking a mine shaft near Deerwood, 282 PNUEMATIC CAISSONS FOR BRIDGES CHAP. VIII Minn., was sunk to a depth of 123 feet below ground- water level and 130 feet below the ground surface. The maximum pressure used was 52 pounds per square inch, a higher value than has probably ever been used in bridge or building caissons. As first applied the pneumatic 'caisson process was a very simple affair, the caisson Consisting of a cast-iron cylinder, called a pneumatic pile, which formed both the working chamber and a section of the pier. The first used in this country were sunk in 1852 in the Pedee River, North Carolina. The St. Louis arch bridge was the first in this country to be founded on large pneumatic caissons, its east abutment caisson, which had a maximum immersion of 109 feet 8| inches, being sunk in 1870. The second bridge in this country to be founded on large pneumatic caissons was the great Brooklyn suspension bridge, which, in its New York tower caisson, sunk in 1871, has the largest pneumatic caisson ever placed for a bridge foundation. It was 102 by 172 feet in plan and was sunk to a depth of 78 feet below high-water level. The pneumatic caisson process has been widely used in America and on the European continent. As a class, English engineers have apparently shown some aversion to it, and in many cases, where it seems to have been the preferable struc- ture on account of the presence of boulders and logs, the open- caisson process was used. American engineers have developed the wooden caisson to a high state of perfection, but at present (1914) owing to the high price of timber the tendency is toward the use of more .reinforced concrete and less timber. In Europe the metallic form of pneumatic caisson has been extensively used. To give some indication of the progress made in the science and art of foundation construction it is interesting to note that the cost per cubic yard of the substructure of the Municipal bridge at St. Louis is only 29.6 percent of the corresponding cost of that of the St. Louis arch bridge, which is located about a mile above it, and 50.8 percent of that of the Memphis bridge. The substructures of these three bridges were completed in 1911, 1871 and 1891 respectively. In this comparison the ART. 93 CAISSON ROOF CONSTRUCTION 283 approaches are excluded. As previously noted, the three bridges have deep foundations. The contract price for the caisson work of the Municipal bridge was $27.00 per cubic yard below the cutting edge, and $12.90 per cubic yard from the cutting edge to the top of the crib. ART. 93. CAISSON ROOF CONSTRUCTION TIMBER ROOFS. The design of the roof has always been largely a question of judgment as it is almost impossible to analyze the stresses. The tendency of roof construction has been constantly to decrease the thickness of the timber roof and consequently its cost. When concrete superseded stone masonry as a filling for the crib a considerable decrease in the thickness of the roof was made possible on account of the strength of the concrete. A more generous use of bulkheads and the arrangement of the bracing above and below the deck to act as trusses also aided in securing a thinner roof. At present many caissons do away with a permanent timber roof almost entirely by reinforcing the concrete filling of the crib. The roof is usually made with layers of i2Xi2-inch timbers, sheathed on the lower side with 2- or 3-inch planks. Sheathing may also be used between the courses of large timbers. The different courses run in different directions; if the roof is of a two-course thickness both courses may run transversely, while if it has three courses the lower and upper courses run transversely and the middle course longitudinally. All caulk- ing of the air chamber is done from the inside of the work- ing chamber, against the air blowing out, while the outside planking is caulked from the outside, to prevent the water from getting in. The roof of the io2Xi72-foot caisson for the New York tower of the Brooklyn bridge was composed of a solid mass of squared timbers, 22 feet thick, all timbers being 12X12 inches in section, and thoroughly drift-bolted together. This is the thickest roof that has ever been used. 284 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII The roof of the 31X79- foot rectangular caisson for the old piers of the Baltimore and Ohio Railroad bridge at Havre de Grace was composed of eight thicknesses of 1 2 X 1 2- inch timbers, the courses alternating in direction, some running longitudinally, others transversely, and still others diagonally. The lower sur- face was sheathed with 3X i2-inch planks. This form of roof is typical of a num- ber of caissons built under the direction of WILLIAM PATTON, who was an extrem- ist in respect to thick roofs. The roof of the east abut- ment caisson of the St. Louis arch bridge was only 4 feet 10 inches thick, the upper three layers being composed of i6Xi6-inch timbers. The shape of this caisson was an irregular hexagon, with ex- treme dimensions of 82 by 7 2^ feet. This comparatively thin roof was made possible by the use of two wooden bulkheads below the roof and two iron girders above, the latter running at right angles to the former, and all supporting the roof. The upper surface of this roof was covered with plate iron, ART, 93 CAISSON ROOF CONSTRUCTION 285 286 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII ART. 93 CAISSON ROOF CONSTRUCTION 287 while in the Brooklyn bridge caissons the under side was cov- ered with wr ought-iron plates; in both cases this was done to obtain an air-tight roof. It was a very expensive method, since oakum caulking is sufficient. But in the Brooklyn bridge caissons it was done for the added purpose of fire protection, for *fg VW.K- v_v *2 r o,www,#'is 288 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII in those early caissons torches were used for lighting purposes, and as there was always a considerable amount of air escaping between the timbers the danger of fire was very great. ection at Tbp of Caisson Supply 5 ha ft, v Note ; All Posts marked S3 enctat'Top of the Courses in whichtheyareshown Sectional Plqn. FIG. 93 So g o " I *C H _. ^-i Bsll B w 3 O gg S ^ >-i O ll a.*|j rt S? ART. 94 SIDES OF WORKING CHAMBER 293 example of a reinforced-concrete roof is that for the caissons of the Passyunk Ave. highway bridge piers, across the Schuylkill River, Philadelphia. The largest caisson was 22X60 feet in plan and its roof was reinforced with i-inch square, twisted horizontal rods running transversely and spaced 12 inches on centers. The thickness of the concrete slab first cast was 18 inches, the forms consisting of a temporary wooden ceiling of 3 X 1 2-inch planks. ART. 94. SIDES OF WORKING CHAMBER The sides of the caisson should be made strong and rigid enough, not only to take the direct vertical loads, but also to withstand safely sudden lateral thrusts, eccentric loads due to unequal sinking of opposite sides, etc. To prevent leakage of air outward and of water inward all joints should be thoroughly caulked. The necessary thickness of walls will depend some- what on the clear height of the working chamber, as well as on the kind of material through which the caisson is to be sunk. The clear height should not, however, vary much from 6 feet. The sides must be vertical. To batter the sides for the pur- pose of reducing the friction is to invite trouble. Such a design makes it more difficult to sink the caisson plumb, and is apt to increase instead of decrease the friction by allowing boulders to roll into the open space. Practically all working-chamber sides are constructed of two forms: namely, that in which the vertical section is V-shaped, and composed of two walls; or that in which the vertical section is essentially a rectangle and composed of a single wall. The former has the advantage of being more rigid and so requires less bracing, while the latter has the advantage of permitting excavation under the cutting edge to be more easily made. In the V-shaped form the space between the outer and inner walls may be built solid with timber, as was done in the east abutment caisson of the St. Louis arch bridge; or it may be made hollow and afterward filled with concrete, as was done 2Q4 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII in most of the caissons designed by G. S. M ORISON, a typical form of which is shown in Fig. 930. Here the outer wall was made of i2Xi2-inch timbers, sheathed on the outside with two layers of planking, the outer one running vertically and the inner one diagonally. The inner wall consisted of a single thickness of i7Xi7-inch timbers sheathed with 4-inch planks and tied to the outer wall with rods. The St. Louis Municipal bridge caissons, Fig. 93^, had out- side walls of i oX 1 2-inch timbers, sheathed with two courses of planking: one 3Xi2-inch, running diagonally, and the other, 2 X i2-inch, running vertically, the latter being on the outside to reduce friction in sinking. The inner wall was formed of 4X1 2-inch horizontal planks, stepped and supported at inter- vals of 10 feet on vertical struts. The small size of material used in this wall was made possible by reinforcing the concrete in the space between the walls. Stepping the wall made it possible to count on the horizontal projection of this inner wall as taking load when the caisson was filled with concrete and in its final position. This cannot be done when the wall is on a slope. A further advantage is that the projections gave better control of sinking, there being less danger of sudden drops than when the wall is sloped. The rectangular section of side wall is used more widely than the triangular, on account of the facility with which the spoil near the sides may be excavated. Figs. -930 and / illustrate a good example of this type. It is composed of a double thick- ness of horizontal i2Xi2-inch timbers, separated by a single thickness of vertical i2Xi2-inch timbers, some of which extend up beyond the caisson to form a part of the crib. Both the outside and inside faces of the wall are faced with 3Xi2-inch planks. Figs. 936, c and d also illustrate the same type. ART. 95. DETAILS OF CUTTING EDGE The cutting edge, as the part of the caisson which rests on the ground is called, must be designed to serve four functions: First, it must be sufficiently strong and tough to stand the ART. 95 DETAILS OF CUTTING EDGE 295 strains and abrasive action of sinking; second, it must be of a form which will allow the caisson to sink readily without excavating under the cutting edge; third, it must have bearing surface enough to prevent sudden sinking when a soft stratum is encountered; and fourth, it should be so designed that air cannot readily escape under the same. To fulfill the first requirement the cutting edge is usually made of some tough and strong wood, such as elm, or else is shod with a metal plate or piece of tough wood. The second and third are conflicting requirements; for the second true knife edge is the ideal form, while for the third a considerable breadth of bearing is desirable. As con- structed, the width will vary from about 4 inches to 18 inches. To meet the fourth requirement, a vertical plate extending about 6 inches below the cutting edge is often used. Where the soil is dense this plate may be dispensed with. Many engineers at present favor the blunt cutting edge in preference to the sharp one. T. K. THOMSON'S experience is, that where the knife edge is needed, i.e., in hard material, to allow getting close to the outside edge for excavating, it would cost too much to make the cutting edge strong enough, and where the material is soft a knife edge is not needed. Fig. 93 d illustrates the use of a timber wearing plank on the cutting edge. It was 6X12 inches in section, the main timber forming the cutting edge being 30X30 inches in section, while the upper inner corner of the latter was rebated 9 inches to form a seat for the feet of the vertical wall timbers. The advantage of a timber over a metal cutting edge lies in less time being required to obtain it, and in the greater ease with which it may be replaced when broken. The form of cutting edge used by G. S. MORISON, illustrated in Fig. 950, consisted of a horizontal and vertical plate, the latter being stiffened at intervals and fastened to the horizontal FIG. 950. Details of Cutting Edge. 296 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII plate by steel diaphragms, which are stiffened on the edges by three angles. The horizontal plate extended under, and was fastened to both the lower surf ace of the bottom timbers and the lower edge of the outside sheathing, while the vertical plate was fastened to the same outside sheathing. Near the bottom the vertical plate was reinforced with two others. Fig. 930 shows the appearance of this cutting edge in place. The bottom timber of the caisson shown in Fig. 93 / extended but beyond the timbers above to protect the lower edges of the out- side sheathing, while it in turn was protected by steel plates on all sides but the top. This form of construction, having a vertical plate on the outside and a hori- zontal angle with its vertical leg down and fastened by rivets to the vertical plate, and with its hori- zontal leg fastened to the lower sur- face of the lower timber, is widely used, but is not economical. The cutting edge of the caisson used in the Kinzie St. draw-bridge, Chicago, was formed with an 8- inch channel iron laid horizontally with flanges turned up as shown in Fig. 95^. The same general form was used on the Broadway bridge caissons (Fig. 93/0 > the only difference being that in the latter case the cutting-edge timber extended out to protect the bottom of the sheathing, while in the former case the channel iron served this purpose. This form of metal cutting edge is the most economical and was designed in 1901 by T. K. THOMSON. ART. 96. BRACING OF CAISSON Every caisson requires more or less bracing; the larger and higher it is the more bracing will it require. This bracing may Detail of Cu-tHnq Edqe. (Enlarged.) FIG. 956. ART. 96 BRACING OF CAISSON 297 be in the form of struts and tiers near the bottom, running horizontally the length and breadth of the caisson, or it may be in the form of bulkheads, or trusses. The latter two usually serve the added purpose of supporting the roof. The bracing in the 33X90- foot caisson of the St. Louis Municipal bridge, shown in Figs. 93^* and ;', consisted of eight transverse and two longitudinal lines of horizontal 12X1 2-inch struts spaced about 10 feet apart, with ij-inch adjustable rods on both sides of each strut. The struts at their inter- sections were braced with vertical i2Xi2-inch timbers and pairs of f -inch rods extending to the deck of the caisson. A similar form of bracing was employed in the Belief on taine bridge caissons, as illustrated in Fig. 930, as well as in the Broadway bridge caissons, Figs. 930 and/. The south main pier caisson of the New Quebec bridge, 55X180 feet in plan, was divided by timber bulkheads, as shown in Figs. 936 and c, into eighteen rectangular compart- ments approximately 19X25 feet in size. These longitudinal and transverse bulkheads were respectively 24 and 12 inches thick, except the lower course which was 12 inches thicker. All extended from the ceiling to about the top of the cutting edge. Each transverse bulkhead was trussed by a pair of adjustable diagonal rods, the ends of which took bearing in the end walls at roof level, through beveled washers; in the center they bore on steel plates, the latter in turn bearing on both longitudinal and transverse bulkheads. The end walls on each side of the longitudinal bulkhead, were braced by a solid- web knee brace 1 2 inches thick, reaching from the cutting edge to the top of the first transverse bulkhead. Between bulkheads the sides were knee-braced to the roof by single and double 12X1 2-inch struts inclined at an angle of 45 degrees. The bulkheads of the east abutment caisson of the St. Louis arch bridge were of very massive construction, being made of eight horizontal courses of timber, the upper course having eight timbers in it, making a width of 10 feet, while the bottom course had three timbers, making a width of 3^ feet. The numbers varied in the horizontal courses between these two 298 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII values in such a way as to give a V-shaped section of bulkhead. The height was 9 feet. A longitudinal wooden truss was used to brace the 31X79- foot caisson of the Havre de Grace bridge. It was 6 feet deep, the upper and lower chords being composed of two pieces of 12X1 2-inch timbers. The web members, both vertical and diagonal, were composed of timber struts and diagonal rods, the latter extending through the first deck course of the caisson. Cross braces were placed between the bottom chord of the truss and the side walls. ART. 97. CRIB CONSTRUCTION Some writers consider the crib as a part of the caisson, but since the crib may sometimes be dispensed with and the pier built directly on the caisson, it will avoid confusion by separat- ing the two. A certain height of crib is often built as an integral part of the caisson to facilitate floating the structure into place. The purpose of the crib is two-fold: First, it serves as a form for the concrete; and second, it serves temporarily as a coffer- dam to keep out the water. If the masonry or concrete work is kept sufficiently in advance of the sinking the crib may some- times be dispensed with, but this is sledom done because it brings too much weight on the caisson. The crib is a per- manent part of the foundation and usually its walls are a con- tinuation of the walls of the caisson, perhaps slightly modified. The crib is thoroughly braced with longitudinal and transverse timbers left permanently in place. Although it is customary to fill the crib with concrete, yet under some circumstances this may not be done. In the substructure for Pier 2 of the Memphis bridge, where the na- ture of the soil made it necessary that the load on the founda- tion bed be kept down to a minimum, the pockets near the walls in the crib were left empty, while for about 15 feet down from the top of the crib a solid timber grillage was used, thus decreasing the weight of the structure very considerably. The crib for the south main pier of the New Quebec bridge ART. 97 CRIB CONSTRUCTION 299 had a wall made of a single thickness of horizontal i2Xi2-inch timbers to a distance of 25 feet above the cutting edge of the caisson, braced by inside vertical 12X1 2-inch timbers, spaced as shown in Figs. 936 and c, the latter being extensions of certain of the vertical timbers forming the sides of the caisson. The outside was sheathed with the same material as used for the caisson. The walls were braced with horizontal longitudinal and transverse struts 24 inches apart vertically, up to a height of 25 feet above the cutting edge of the caisson, dividing the crib into ninety pockets approximately 10 feet square. A similar bracing course was placed 29 feet above the cutting edge of the caisson; above this point there was no bracing, it being replaced with a concrete retaining wall reaching to the top of the crib, built against the walls of the latter and battered on the interior face, increasing in thickness from the top down. This was placed early in order to allow it to harden before any stress was put upon it. The advantage of this retaining wall is that it made the upper part of the crib a solid monolithic mass of concrete. The crib shown in Fig. 930 had the bracing carried to the top and was notable on account of the manner in which the bracing was tied together with vertical rods. Here the lower courses of bracing helped to carry the roof loads; for this reason the part of the crib up to the top of the rods passing through the roof may be considered a part of the caisson. The walls of the cribs for the St. Louis Municipal bridge piers consisted for the most part of one thickness of loX 1 2-inch timbers, sheathed on the outside with one layer of 3-inch diag- onal and one layer of 3-inch vertical planks. The bracing consisted of vertical 12X1 2-inch timbers and of eight rows of horizontal transverse and two of horizontal longitudinal loX 12- inch timbers. As shown in Fig. 93^' a large amount of 3X10- inch diagonal bracing was also used, giving a truss-like action to the bracing and greatly strengthening it. The crib construction of the Broadway bridge is shown in Figs. 93<> and/; the detail are so simple that no explanation is necessary. 300 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII ART. 98. COFFERDAM CONSTRUCTION Both durability and appearance require that no part of the crib extend above low- water level; and moreover, to keep the obstruction to the current as small as possible, the crib is stopped and the pier commenced at a considerable distance below low water. In some cases, where the current has a high velocity, the pier is started at or below the river bed, or the upper part of the crib is built with pointed ends. For these reasons, unless conditions are such that the pier construction can be kept well above water-level, a cofferdam in which to build the pier becomes necessary. Ordinarily cofferdams may be dis- pensed with only when the construction is carried on at low water stages or when the friction and resistance to sinking is large. As a general rule it is desirable to keep the weight on the caisson *as small as possible as this affords better control of the sinking. Even when possible many engineers prefer not to start building the pier until the caisson is sunk to final position, for only at such a time can the masonry be started in the correct position. The walls of the cofferdam are usually made of lighter construction than those of the crib, but it is always thoroughly caulked, and braced by struts running the length and breadth of the structure. As the pier is built up these braces are removed and the walls are braced against the pier. On the completion of the latter the cofferdam is removed, if not the whole structure, at least that part above low water. Figs. 93 & and / illustrate the cofferdam used for one of the piers of the St. Louis Municipal bridge. The left dotted lines represent the top course of crib and the right dotted lines the top of struts. The cofferdam, which was 33 feet yj inches long, consisted of a frame of horizontal 6 X 8-inch and vertical 6X6- inch timbers, sheathed with 2Xi2-inch planks. It was braced with 6 X 8-inch struts, 4 feet apart vertically, and in rows about 10 feet apart horizontally. The cofferdam used for the Brooklyn pier of the Manhattan bridge, New York, N. Y., was one of the highest that has ever been used in pneumatic caisson work, being 44 feet high and ART. 99 PNEUMATIC CAISSONS OF CONCRETE 301 about 75X144 feet in plan. It was built in three sections, the sides of the first two sections being made of 10X1 2-inch horizontal timbers laid close and supported by i2Xi8-inch verticals, spaced 12 feet apart. On the outside two layers of 3 X i2-inch sheathing were placed, the inner planking being horizontal and the outer vertical. The upper section differed from the others only in having 8Xi2-inch instead of ioX 12- inch horizontals. ART. 99. PNEUMATIC CAISSONS or CONCRETE Pneumatic caissons built entirely of concrete have been'used to some extent in Europe, but in this country the nearest approach to the all- concrete pneumatic caisson are those for the Beaver bridge, described in Art. 90. As there explained most of the sinking was done by the open-well method. With the exception of a very few cases, like the one just noted, the tendency in this country has been to use wood, but at the same time to decrease the amount formerly used by reinforcing the lower part of the crib concrete, as was done in the St. Louis Municipal bridge caissons. A covering of timber offers three advantages: First, it avoids the necessity of waiting for the concrete to harden before commencing sinking operations; second, it offers less resistance to sinking because of the reduced friction on the sides; and third, it forms a protection in sinking for the concrete of the sides. The pneumatic process was used during the final part of the sinking of the Beaver bridge caissons in order that the bottom might be thoroughly cleaned, as well as to permit laying the concrete filling in air. The caisson was changed from the open to the pneumatic type in the following manner: It was first freed of water down to a level which permitted the placing of horizontal wooden frames in each of the 'wells at an elevation of about 9 feet above the cutting edge. Concrete was then placed on these forms, filling the wells, the first 7 feet being allowed to harden for a week before placing the rest. At the* center of each well a vertical shaft, 3 feet in diameter, was 302 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII placed to form a means of communication between the working chamber and the outside. ART. 100. PNEUMATIC CAISSONS or METAL The abundance of timber in America has limited the use of the metal type to relatively few cases, while in Europe it has been extensively used. The river piers of the St. Louis arch bridge, the first structure in this country founded on large pneumatic caissons, rest on metal caissons. Two reason may be given for this fact: First, there was considerable uncertainty as to the action of a timber roof when subjected to the horizontal thrust from the super- structure; and second, timber had not been used in caisson construction to serve as a precedent. The caisson for the east pier, which was hexagonal in plan, with over- all dimensions of 60X82 feet, had walls of wr ought- iron plates f inch thick, braced with iron brackets extending from the bottom to the top, and spaced i\ feet apart. The roof was formed of |-inch iron plates riveted to the lower flanges of thirteen parallel iron girders, spaced 5 feet 6 inches apart. It was also supported by two heavy bulkheads of oak timber, 7 feet high, in the air chamber. These strong supports for the roof were necessary because the latter had to take the entire weight of a loo-foot height of stone masonry. The walls of the caisson extended above the roof to form an enclosure, in which the masonry was laid. No monolithic con- crete was used in this structure. For some distance up the masonry covered the entire cross-section of the crib, but above this it was stepped off, the space between the iron envelope and the masonry being braced with timbers and filled with sand. For the west pier caisson the iron envelope was carried up but 20 feet, after which the masonry was laid in the open, care being taken to keep the top of the same above water-level. The metal pneumatic caissons for the Alexander III bridge, Paris, France, built in 1897, are among the largest of any type ever used. In plan one caisson had the shape of a parallelogram ART. 100 PNEUMATIC CAISSONS OF METAL 303 (the angle being 84 degrees), the length of the sides being approximately 145 and no feet, transversely and parallel, respectively, to the axis of the bridge. The working chamber had a clear height of 6.23 feet and through this extended four transverse girders, each 6.23 feet high, their bottoms forming cutting edges, and dividing the chamber into five subchambers. On their upper flanges these girders supported twenty-seven longitudinal girders, 5.2 feet deep, which carried the roof of the steel-plate platform that formed the deck of the caisson proper. The transverse girders had solid-plate webs for nearly one-third of their length at each end and open web members in the central part. The longitudinals were ordinary latticed girders. The working chamber had a roof of steel plates o. 2 inch thick which were fastened to the lower flanges of the longitudinal, and to the upper flanges of the transverse girders. These plates did not extend horizontally through to the vertical sides of the caisson, but at the sides followed down the inclined end posts of the transverse girders, and at the ends followed the knee braces down to the cutting edge to give sloping inside walls on all four sides. Between these inclined plates and the outer vertical walls was a triangular space filled with concrete. The outside wall plates and the transverse girders were all stiffened with knee braces extending from the cutting edge to the longi- tudinal girders. The outside wall plates were reinforced on the lower edges by an outside vertical plate and the vertical flange of an inner angle, while the transverse girders were reinforced for bearing and cutting strains by adding two angles riveted, with their hori- zontal flanges upward, to the lower edge of the vertical web plate of the lower chord. The cofferdam above was 19.7 feet high and was composed of riveted and caulked vertical plates, 0.118 inch thick, with a light angle-iron frame and light inclined angle-iron struts from near the upper edge and the middle of the top of the transverse girders. The total distance sunk was 27 feet below ordinary water-level. For further details the reader is referred to either Engineering News, vol 39, page 254, 304 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII April 21, 1898, or Engineering Record, vol. 37, page 275, Feb. 26, 1898. ART. 101. CYLINDER PIER CAISSONS The foundation for a cylinder pier is often placed by the pneumatic process, in which case, like the open-cylinder caisson, there is usually no particular point at which the caisson may be said to end and the pier begin. The pneumatic cylinder caisson is very similar to the open caisson in many cases, the only difference being that the former is fitted with horizontal dia- phragm doors to form the air-lock. Often a part of the sinking is done by the open-caisson method and the remainder by the pneumatic method. As noted in Art. 92 the cylinder caisson was the first type of foundation to which the pneumatic process of. sinking was applied in this country. Fig. loia illustrates the cylinder piers and pneumatic cylinder caissons used for the Columbia River bridge at Trail, B. C. The shells were of steel plates from rV to rV inch thick. The lower 6 1 feet were formed of a double shell, the diameter of the inner shell being 3 feet, and that of the outer one 9 feet at the bottom and 6 feet at the top. Beginning at a point 8 feet above the bottom of the caisson the inner shell was splayed out to meet the outer shell at the cutting edge, thus forming a working chamber 8 feet high. Near the bottom the two shells were braced together with diagonal lacing as shown in the diagram. The upper parts of the cylinders were connected and braced by two vertical transverse rVX6o-inch plates, 2 feet apart, braced together and the space between the two filled with concrete. The air-lock was formed by placing two diaphragm doors in the inner shaft, one about 13 feet above the cutting edge and the other at a point about 16 feet higher. As sinking proceeded, a third door, about 16 feet above the second door, was added, the upper two doors being used to form the lock, while the lower door was used for emergencies. These caissons were designed ART. 1 01 CYLINDER PIER CAISSONS 305 SecHon A- Horizontal Top Frame lite Bracing Frame BoHofn of Pier showing Web FIG. zoia. Pneumatic Cylinder Caissons, Trail, B. C. 306 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII by WADDELL & HARRINGTON, and may be considered to repre- sent current standard practice. In the repairs of the Atchafalaya River bridge, each pier consisted of a pair of 8-foot diameter steel cylinders, filled with concrete and braced together at the top by a stiffened web plate or diaphragm about 20 feet high, as shown in Fig. loib. Each cylinder had, in addition to the outer 8-foot diameter > "~T r ;-v 1 P i .-. -' r ; i vi FIG. 1016. Pneumatic Cylinder Caissons, Atchafalaya River Bridge. shell, an inner concentric shell 5 feet in diameter, with a conical section uniting it with the cutting edge and closing the lower end of the annular space between the two shells. The shells were connected by four stiff webs. The inside shell terminated about 22! feet below the top of the outer one, the latter having a total length of over 135^ feet and was made with ART. 102 COMBINATION CYLINDER CAISSONS 307 5-foot rings erected in lo-foot sections. The working chamber was 25 feet high, and had a roof consisting of a 2-foot oak diaphragm made of four thicknesses of timber, with a circular hole 2 feet in diameter closed by a cast-iron door. In the piers of the Glasgow bridge, which were sunk by the pneumatic process the diameter of the outer shell was 15 feet, the thickness of the shell at the base being ^ inch and at the top T 5 ^ inch. The shaft which was 3 feet 7 inches in diameter formed the inner cylinder, and this was removed before filling the working chamber and air-shaft. Almost no records exist of the use of the reinforced-concrete pneumatic cylinder caisson. In Art. 102 there is given an example of this type, in which the first part of the sinking was done by the open-caisson method and the latter part by the pneumatic process. ART. 102. COMBINATION CYLINDER CAISSONS With the cylinder caisson it is a simple matter to construct the cylinder to be used either as an open or a pneumatic caisson. This makes it possible to utilize the advantages of both methods of sinking, the open caisson being used for that part of the sinking in which the material can be dredged or pumped out, and the pneumatic process for that part where boulders or compact material is met with, and in finally prepar- ing the foundation bed and placing the concrete filling in the working chamber. The caissons for the Merrimac River bridge, between Salisbury and Newburyport, Mass., were of this type, Each caisson consisted of an 8-foot diameter cast-iron shell, the metal being i J inches thick and cast in 8-foot sections. These sections had inside flanges bolted together and a mixture of red lead and linseed oil was placed between the joints. The cylinders were sunk by inside dredging to a layer of boulders and gravel. They were then loaded with pig iron, air-locks placed on top, and air pressure applied. No attempt was made to sink the caissons through the boulders, but instead a novel method was used to transform this boulder and gravel 3 o8 PNEUMATIC CAISSONS FOR BRIDGES CHAP. VIII layer into a good foundation bed. The pressure in the cylinder was reduced a little allowing about a foot or more of water to rise. Portland cement was then mixed with the water to form a grout, which was kept well stirred while the air pressure was increased to force the grout into the gravel. On completion of the grouting a depth of from 10 to 20 feet of 1-2-4 concrete was laid under air pressure, and allowed to harden, after which the remainder was laid in the open. FIG. io2a. Pneumatic Caissons of Reinforced Concrete for Bronx Viaduct of New York Connecting Railway Fig. 1020 shows the main details of concrete cylinder caissons used for foundations of the Bronx viaduct of the New York Connecting Railway. The caissons varied from 10 to 18 feet in diameter and were sunk to a maximum depth of 55 feet. The cutting edge was formed of a steel angle and steel plate, and the concrete composing the caisson was well reinforced with vertical and horizontal rods. When sinking through clay the open dredging process was used, while in passing through quicksand air-locks were placed in the upper part of the shafts and the pneumatic process used. CHAPTER IX PNEUMATIC CAISSONS FOR BRIDGES ART. 103. SHAFTS AND AiR-Locxs The shafts, which form the means of communication between the working chamber and the outside, are circular in shape and in most cases are of steel plate f-inch thick; and in sections about 10 feet long, each section being flanged and bolted to the one above and below. Separate shafts are ordinarily used for men and materials, those for the men being about 3 feet in diameter, although if an elevator is used they are often as large as 6 feet in diameter. The shafts for the removal of spoil are about 2 feet in diameter. Where the depths are only moderate it is customary to have a ladder built in the shaft used by the men, but when the depth is considerable a power elevator should always be employed as it is extremely exhausting to climb a long distance after working under high pressure. The men often use the excavating bucket as an elevator. As explained in Art. 92 the air-lock is a chamber having two doors, one of which opens to the atmosphere and the other to the working chamber. These doors are so placed that the unequal air pressure will always force them against their seats, which have rubber gaskets to prevent the escape of air. The operation of the lock for men is as follows: The lower door being closed and the upper one open, a man enters; the upper door is then closed and compressed air slowly admitted to the lock, and as soon as the pressure in it becomes equal to that below, the lower door opens allowing the man to enter the working chamber. The air-lock may be of any shape and of any desired size, the latter depending on the number of men or the amount of material it is desired to lock through at a time. The material lock is often but a section of the shaft. 309 3 io PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX A Front Elevation, Section through Center. Section A-B. FIG. io3a. Material Lock used in Pneumatic Caissons of Memphis Bridge, 1891. ART. 103 SHAFTS AND AIR-LOCKS 3 11 In the early caissons the lock was placed at the bot- tom of the shaft and ex- tended down into the work- ing chamber, but at pres- ent the material lock is always placed at the top of the shaft, while the man lock is placed either at the top or some distance up from the bottom. Caisson sinking with the lock at the bottom is a risky un- dertaking because a 'blow- out/ that is, a sudden out- rush of air, will cause a like inrush of water ac- companied by a rapid sink- ing of the caisson, which is almost sure to damage the lock. With the lock out of commission the men in the working chamber have no chance to escape, while if the lock is at the top the men can climb up and take refuge in the shaft above the level of the water. About the only disadvantage in having the lock on top of the shaft lies in the necessity of remov- ing it each time a new sec- tion is added to the shaft; but with properly designed connections this can easily be done, and without dan- Vertical Section. rt Sectional Plan. FIG. 1036. Air Lock for Men, Memphis Bridge. 3 I2 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX ger, by having an auxiliary door fitted to the lower end of the shaft in the roof of the working chamber which is closed when the lock is taken off. Two forms of air-locks extensively employed for caissons used for the foundations of buildings are illustrated and ' 25'0" FIG. 103*:. Arrangement of Air Lock, Shahs, Pipes, etc. Bellefontaine Bridge- described in Art. 119. The particular advantage which these types possess is that the bucket may be lowered into the air chamber, filled and taken out without detaching from the hoisting rope. Another form of material lock which has been employed is illustrated in Fig. 1030, this particular one being used on the Memphis bridge caissons. The method of operation is de- scribed in Art. 107. The essential difference between this ART. 104 DESIGN OF CAISSONS 313 and the types described in Art. 119 lies in the fact that here the upper door, instead of being in a horizontal plane, lies in a vertical plane at B. This necessitates either dumping the material out on being brought to the top or else the bucket must be detached from the cable and taken out. The form of lock for men employed on the above mentioned bridge is illustated in Fig. 103^. It is shown in position in Fig. 103^. lu The upper shaft through which the elevator- cage runs is a cylinder 6 feet in diameter, the air-lock itself is a cylinder 6 feet in diameter, and the shaft leading to the caisson, a cylinder 4 feet in diameter; the three cylinders are tangent to each other, and the shells are connected by cast-iron door frames carrying doors, while a fourth door opening outward was placed at the bottom of the lower shaft; in working, the door between the two shafts was always kept closed, and the door at the bottom of the bottom shaft was always left open; it was possible, however, if an emergency had arisen to use the lower section of the shaft as an air-lock in itself; when the filling of the working chamber was completed the bottom door was per- manently closed." ART. 104. DESIGN OF CAISSONS It is impossible to compute even approximately the stresses in the various parts of a caisson and for this reason it is best largely to follow precedent. Engineers who are experts on caisson work, have built many caissons and by observing the weak points have developed strong structures with increasing economy. The examples given in the preceding articles are representative of the best forms in use, and are recommended to the careful consideration of engineers interested in this subject. For more extended information the reader is referred to the bibliography in Chap. XIX. T. K. ThoMSON, a consulting engineer who has specialized in pneumatic caissons, writes on their design as follows: 1 The Memphis Bridge, by GEO. S. MORISON. 314 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX J "It is necessary to use considerable common sense and experience in attempting to calculate the strains in a caisson. As regards the deck, for example, it is very easy to calculate the weight to be carried by the deck and the strains that would result therefrom, and we know that the air pressure acting up against the roof will counterbalance a great deal of this weight, making it, in fact, something like a pontoon floating in the water. But on the other hand, the air pressure is often slacked down to almost nothing in order to overcome the friction, and is raised again before much water has time to enter the working chamber; and sometimes an accident to the air plant will suddenly cut off the supply of air, throwing a tremendous strain on the roof. If the principal weight on the roof is concrete it will in many cases be self-sustaining unless too fresh. "The same with the sides. If the material were absolutely homogeneous all around and the caisson were sunk absolutely plumb, which almost never happens, and the air pressure were kept just equal to the outside pressure, then we would have practically no strain on the sides but all practical caisson men have seen the sides of caissons collapse, and some very strongly built ones at that. A very much more frequent cause of accident than loss of air pressure is to strike some obstruction on one side, deflecting the cutting edge, and thus throwing much of the weight of the caisson on the weakened side, making bad worse. . ...- "in building wooden caissons I very seldom halve the timbers or use dovetailed joints, preferring to use butt joints as much as possible with plenty of drift bolts. The trouble with butt joints, however, is that while a carpenter will make a dovetail or half-lap joint fit he will probably leave an inch or so play in a butt joint. "The deck timbers, as well as those in the sides, should be planed on one side and one edge, for the sizes would otherwise vary too much to get a good job, while the planking for the outside and inside of the air chamber should be either tongue and groove, or the sides should be planed for a caulking joint. 1 See " Construction," Nov., 1908. ART. 105 BUILDING AND PLACING THE CAISSON 315 The plank should, of course, have its faces also planed. " Since very many drift bolts are required in fastening together the heavy timbers in wooden caisson construction, it is iesirable to adopt the proper diameter of holes to be bored. For the results of experiments on the holding power of drift bolts and the best ratio of the diameter of hole to that of bolt, see Art. 10 in JACOB Y'S Structural Details. ART. 105. BUILDING AND PLACING THE CAISSON The caisson may be built on ways on the shore; on pontoons anchored near the shore, or over the site where it is to be sunk; or on a temporary platform supported by piles. Of the three methods, building on ways on the shore is the most widely used, but to make this method satisfactory the following conditions must obtain: First, there must be deep water near the shore; second, the soil must be sufficiently firm to hold the caisson, either with or without the use of bearing piles; third, there must be no danger of a high and rapid rise in the river; and fourth, the shore must not be at a great distance from the site of sinking. Where satisfactory shore conditions do not obtain and where the water is deep and subject to sudden rises the pontoon method is the best. Where the depth of water is not great and where the river is not subject to considerable changes of level the method of using a temporary platform on piling is con- venient. Caissons for abutments and buildings may usually be built directly on the ground near the site where they are to be sunk. When built on ways the caisson sometimes has a false bottom fitted to it to reduce the depth of immersion, and a sufficient height of crib is constructed, preliminary to launching, to insure the top being well above water-level. After launching and towing to the site more crib is added, the false bottom removed and the caisson sunk to the river bed by placing concrete in the crib. The launching ways used for the McKinley bridge over 316 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX the Mississippi River at St. Louis, Mo., consisted of a number of rows of piles capped with timbers running at right angles to the river and on a slope of if inches per foot. Each caisson was built on shoes extending the full width of the caisson, the long side of the caisson being parallel to the river, and each shoe rested on a cap timber on which it slid during launching. These shoes were spaced about 6 feet apart and were so made that they projected down over the sides of the caps. They were bolted to the latter on the land side of the caisson. The caisson was built with its bottom in a horizontal position by using wedges between the caisson and the shoes. The launch- ing was started by simultaneously sawing through the shoes below the bolts, which thus allowed the caisson to slide into the water. Fig. 1 05 a shows the caisson for one of the piers of the Van- couver bridge, Vancouver, Wash., as it was being built on the launching ways. The general scheme was about the same as for the McKinley bridge caissons. Where built on floats, either one or two pontoons may be used. Fig. 1056 shows one of the caissons of the Willamette River bridge of the Northern Pacific Railroad as it was being built between two barges or pontoons. The caisson was held be- tween the barges until a height of 20 feet had been built up, when long screws were attached and the caisson lowered into the water. Two heavy trusses, one at each end, tied the barges together to prevent any unequal motion of the latter by the waves. Another caisson for the same bridge was erected on two pontoons, and after building to a sufficient height the pontoons were scuttled by filling them with water, after which they were pulled out from under the caisson. The 78 X 144-foot caisson of the Manhattan bridge was built in a pontoon or float, 84 feet wide and 150 feet long, which had vertical sides 8 feet high. The float was built of 3-inch planks bolted to vertical and horizontal timbers. It was built in two halves separated by a longitudinal joint along the center line. Blocking was set up on the floor timbers and on this the caisson was built, thus making the latter accessible from below. On FIG. 105*3. Caisson on Launching Ways. Vancouver Bridge. FIG. 1056. Cassion Supported between Two Barges. Willamette River Bridge. (Facing p. 316.) ART. 1 06 SINKING THE CAISSON 317 completing the. caisson the joint between the two halves of the float was unlocked and sand dumped through the shafts of the caisson to the floor of the float to sink the halves of the latter, after which the same were pulled from beneath the caisson. Fig. io5c shows one part of the 4oXioo-foot pontoon of the St. Louis Municipal bridge caissons as it was being pulled from beneath the caisson. This pontoon, which was of the same type as that described above, was sunk by removing plugs from holes in the bottom of the pontoon. The caissons for the Passyiink Ave. bridge piers offer a good example of caissons built on a platform. Sixteen bearing piles were first driven in two longitudinal rows just clear of the caisson location. These were capped, and from these cap timbers four equidistant, transverse, i4Xi6-inch timbers were suspended by pairs of i^-inch rods, 16 feet long, threaded the entire length, and each provided with two nuts. Each trans- verse timber was held by means of a steel saddle on the under side, against which the lower nut of the rod bore and the other nut took bearing on a washer on top of the pile cap. The transverse timbers were first screwed up tightly against the under side of the cap timbers and on these the caisson was built. After building the cribs to a height of about 26 feet the caisson and transverse timbers were gradually lowered by unscrewing the nuts from the rods, which permitted the caisson to float in its exact position. ART. 1 06. SINKING THE CAISSON If mud covers the river bottom this should be dredged out before placing the caisson as it is cheaper to remove it in this manner than to excavate it within the working chamber. Great care must be exercised in grounding the caisson to place it in its correct position. If in tidal water, this may be done by placing concrete in the crib to an amount which will just ground the caisson at low tide. Then, by means of tackles attached to clusters of piles and to the caisson or crib, the structure is placed in its true position at high tide and grounded 318 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX as the water-level lowers. Concrete is then poured into the crib to an amount which will prevent floating when the tide rises. Often, where the caisson is slightly out of position, it may be floated by admitting a small amount of air into the working chamber. As soon as enough concrete has been placed to put on air pressure safely to expel the water from the working chamber, men enter to commence sinking operations. In clay the excavation may usually be kept some distance below the cutting edge, which offers the advantage of allowing more head-room for the men. This cannot be safely done in sand as the water is very sensitive to changes of pressure and so it is not possible to raise the pressure very much from that corresponding to the head on the cutting edge. In one of the caissons of the Rulo bridge a test well was sunk in clay 17 feet below the cutting edge without any increase in the air pressure, but when a 4-foot vein of gravel was struck the pressure had to be increased 8 to 10 pounds at once. In sinking caissons the load is at first usually carried on the cutting edge, but as the caisson gradually sinks more of the load is resisted by friction on the sides and less by bearing on the cutting edge. Contrary to the usual custom, in the case of the 55 X i8o-foot caisson of the New Quebec bridge, the details of which are shown in Figs. 936, c, and d, and which for the most part was sunk through sand, the load was not at any time supported on the cutting edge. x " Owing to the great size of the caisson, extraordinary pre- cautions were considered necessary to provide against any unequal settlement, or any twisting or other movement of the caisson, which might tend to open up the joints and seams and consequently allow air to escape. On this account it was decided that the ordinary method of sinking, where all the load is carred on the cutting edge, would not allow the movements of the caisson to be sufficiently controlled during the actual sinking. The rather unusual method was therefore employed of carrying the entire load on the bulkheads and the roof, and no load at all on the cutting edge. 1 Engineering News, vol. 68, page 854, Nov. 7, 1912. ART. 107 REMOVING SPOIL FROM WORKING CHAMBER 319 "The caisson was supported on 40 sand jacks, about 25 posts of i2X i2-inch yellow pine, and 54 sets of blocking. The jacks and posts bore directly against the roof, while the blocking was piled under the bulkheads. When ready for a drop the blocking and posts were first removed by washing the sand from under them with a water-jet; then the whole caisson was lowered by operating all the sand jacks simultaneously. The sand jacks were of simple construction, each one consisting of a 29-inch steel cylinder closed at the bottom, having near the bottom two 3-iXich holes with a sliding cover, and a plunger consisting of a single piece of timber fitting easily into the cylinder. The cylinder was filled two-thirds full of sand, the plunger inserted, and its upper end blocked against the roof. The operation of lowering consisted in opening the lower holes and inserting a water-jet, thus washing out the sand. "These jacks worked admirably, the result being that the caisson was sunk absolutely level and in its proper location. Before each drop a trench was excavated under the cutting edge to a depth of 2 or 3 feet, and filled with clay, which tended to prevent the escape of the air and also acted as a lubricant during sinking. This scheme was followed throughout the entire sinking and seemed to materially facilitate the operation." Sinking the caisson is accomplished by excavating the material in the working chamber and by placing concrete in the crib to weight the structure. The water-jet is sofrietimes employed to reduce friction on the sides. ART. 107. REMOVING SPOIL FROM WORKING CHAMBER Various devices have been developed for removing the spoil from the air chamber. Where the material is sand the blow-out process or mud-and-sand pump is ordinarily employed; where clay is encountered it is usually best to remove it with buckets, using some simple form of air-lock, or perhaps the clay may be mixed with water and the sand-and-mud-pump process used. Boulders must be removed through the air-locks. BLOW-OUT PROCESS. The blow-out process is a very simple 320 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX affair, the principle consisting of using the pressure in the air chamber to drive out sand or mud when it is piled around the inlet of a pipe which leads from the working chamber to the open air. The diameter of the pipe is usually about 4 or 5 inches, the top being fitted with an elbow to throw the sand in a horizontal direction, while the lower part has attached to it a flexible hose of large diameter with a valve. To blow out the sand and mud it is only necessary to heap it up around the mouth, open the valve, and the material is then carried out with a high velocity; in fact the velocity is so great that the pipe rapidly wears away. At the Havre de Grace bridge the elbow, which was of chilled iron, 4 inches thick, was worn through in two days. Considerable care must be exercised in placing the material against the inlet for if a considerable amount of air is not admitted with the sand and mud, it will clog, while if there is too much air admitted it is a waste. It has been found ad- vantageous to have small holes in the pipe above the inlet as this gives more uniform action, tending to draw the material up instead of merely driving it and thus lessening the amount of air entering with the sand and mud. Although the dry blow- out is a very rapid and satisfactory means of removing the spoil from the working chamber it has some disadvantages: First, a tendency to vary the pressure in the working chamber; and second, a tendency to cause rapid wear in the pipe elbow as noted above. The lowering of the pressure due to the air passing up through the pipe causes a very thick fog, making it difficult for the workmen to see. It is also apt to allow the water to enter from the outside. On the other hand, if the air compressors are supplying air at a rate sufficient to maintain a constant air pressure when the sand is being blown out, on stopping the latter operation the pressure may rise to a point sufficient to cause a blow-out under the cutting edge, which is usually followed by a flooding of the air chamber. Largely on account of the destructive action on the pipe, and for the added reasons just noted, the dry blow-out process is most satisfactory when the pressure in the working chamber is fairly low, although a head of at least 20 feet is necessary. This process is said to ART. 107 REMOVING SPOIL FROM WORKING CHAMBER 3 2I have been used first by WILLIAM SOOYSMITH in 1859 in building bridge piers over the Savannah River. SAND-AND-MUD PUMP. The principle involved in this form of excavator is that of the induced current, where a quantity of water with a high velocity causes a reduction of pressure which draws the mud and sand well mixed with water into the pipe. Fig. 107 a illustrates the form. used on the Memphis bridge. The water enters at the side under a high pressure and passes up through the small annular space, at which point, on account of the high velocity, the pressure is low. The lower part of the pump connects with a pipe or hose, the lower end of which rests in a pool of mud or sand and water. On account of the difference of pressure at the two ends of this pipe the mud is drawn into the pump and carried upward with the water, through a pipe which connects with the top of the pump. The essential difference between this form of excavator and the blow-out process is that in the former the water is the moving force doing the work while in the latter it is the air from the working chamber. The water pressure used is ordinarily about 80 pounds per square inch. This method was first used by JAMES B. EADS in the caissons of the St. Louis FIG. io7a. Sand-and- arch bridge. Fig. gia illustrates another Mud Pump. Memphis form of the sand-and-mud pump. In the Williamsburgh bridge, New York, the hose was extended to a sort of sump in the bottom of the excavation where its open end was placed below the surface of the water. Gravel, sand and mud were constantly fed into the nozzle by a laborer who raked it up and prevented clogging, and another man with a f-inch nozzle played a 5o-pound water-jet against the soil to wash it into the sump. For a description of this process as applied to open-caisson work the reader is referred to Art. 91. In some caisson work at Vertical Section. Horizontal Section. 322 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX Arran, Switzerland, instead of using a sump a horizontal hopper was employed, the discharge pipe leading from the lowest point in the hopper. A jet of water from a small pipe was con- stantly played on the material as it was fed into the hopper. REMOVING MATERIAL WITH BUCKETS. Clay is usually more cheaply removed with buckets than by any other method. Large rocks must be blasted to pieces and removed with buckets. As stated in Art. 103 where a form of lock similar to the Moran or O'Rourke lock is used, the bucket may be taken from the lock without removing it from the hoisting rope. In the form shown in Fig. 1030, instead of running the hoisting rope to an engine on the outside, the hoisting is done by compressed air from the working chamber working in the cylinder shown on the left. In this cylinder runs a piston, the two sets of sheaves being so arranged that one stroke of the piston lifts the bucket the whole distance. A novel device, called the water column, was used in the caissons of the Brooklyn bridge to remove the material. It consisted of an open shaft, the lower part extending into a sump which was kept full of water and the shaft itself was filled with water up to a point sufficient to balance the air pressure in the caisson. Workmen pushed the spoil under the shaft and from there it was removed by dredging with an orange-peel or clam-shell bucket. ART. 1 08. CONCRETING THE AIR CHAMBER When rock is reached, if the same is level, it is only necessary to clean off all loose material before depositing the concrete. On the other hand, if not level, some preliminary work must be done; if the rock has a uniform slope it should either be blasted down to a level surface or else stepped, unless very rough ; although if the rock surface is at practically the same elevation all around the cutting edge of the caisson, but irregular within, little more than a thorough cleaning will be necessary. For those caissons founded on clay or hard-pan a level surface is easily obtained. ART. 109 RATE OF SINKING 323 Caisson No. 10 of the Passyunk Ave. bridge landed on rock which bad a slope of about 5 feet in the length of the caisson. As soon as rock on the high side was reached, the cutting edge on the low side was blocked with 6Xi2-inch timbers, 6 feet apart, after which excavation under the cutting edge was carried to rock and extended i| feet out beyond the cutting edge. This excavation was then filled with concrete. In the caissons for the St. Louis Municipal bridge the rock surface was irregular but no attempt was made to level it off or to bring the caissons to bearing throughout. Where depressions occurred the sand was removed and sacks of concrete were deposited on the rock and tamped under the cutting edge, after which concrete was placed in the working chamber in the usual manner. The concrete for filling the working chamber may be carried in through; the material shafts and locks by means of buckets, or special arrangements may be made, by placing a cone-shaped frame above the lower door, by which a yard or more of concrete may be dumped into the lock through the upper door. The latter is then closed and air admitted to the lock allowing the lower door to open and the mass of concrete to fall through the shaft to the working chamber. The conical frame prevents the concrete from remaining in the lock when the lower door is opened. For a description of the method used in placing the concrete in the working chamber see Art. 186. ART. 109. RATE or SINKING The rate of caisson sinking varies greatly, the larger the caisson and the harder the material sunk through, the slower the rate. Sinking operations are usually carried on day and night, and the rate of sinking will vary from almost nothing where beds of boulders are encountered to as much as 3 feet a day where clean sand is met. Most engineers keep a chart of the progress of the work; Fig. ioga, which illustrates the progress in sinking one of the caissons of the Kinzie St. draw- bridge, Chicago, is a very satisfactory form of chart to use. The 3 2 4 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX caisson is shown in Figs. 1096 and c. Instead of carrying the whole caisson to bedrock the cutting edge was stopped about half way down and wells were then sunk the remainder of the distance. In sinking Pier D of the Memphis bridge, excluding long delays, an average rate of 1.5 feet per day of 24 hours FIG. ioga. Progress of Sinking Caissons. Kinzie St. Bridge, Chicago. was maintained through sand and only 0.31 foot through clay, while for Piers 2 and 5 of the Thebes bridge the average rates were 0.23 and 0.41 foot respectively; here hard gravel was encountered. ART. 109 RATE OF SINKING .325 326 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX The rate per day of sinking the St. Louis Municipal bridge caissons varied from an average of 0.68 foot for Pier 4 to 1.95 feet for Pier 3, with 1.28 feet as an average for all caissons. The best progress in one day was 5.17 feet, while the best seven-day run was 34 feet or 4.86 feet per day. For the caissons of the McKinley bridge, St. Louis, the average rate for all caissons was 2 feet per day, with a maximum of 7.7 feet in one day. .Plan.' FIG. lope. (See also Fig. 1096.) FRICTIONAL RESISTANCE Estimating the probable frictional resistance to be met with in sinking cais- sons is one of the most difficult features involved in the design. It depends upon numerous factors such as the kind of material pene- trated; the material composing the sides of caisson and crib ; depth to which sunk; whether the sides of the caisson are ver- tical or flared; whether or not the water-jet is used; and the amount of air leaking under the cutting edge. In general, the frictional resistance per square foot of exposed surface of caisson and crib will seldom be less than 250 nor more than 800 pounds, although in boulder-strewn material it may be as much as 1000 pounds. Next to mud and silt, sandy soils offer the least resistance, especially when carrying large amounts of water, while clay will offer less resistance than material con- taining boulders. With uniform soil conolitions the unit fric- tion will increase with the depth; for instance, at the McKinley bridge, which crosses the Mississippi River at St. Louis, the friction was found to be about 300 pounds per square foot of exposed surface at 40 feet, and 600 pounds at a penetration of 70 feet. Anything which tends to loosen the soil around the ART. no FRICTIONAL RESISTANCE 327 sides of the caisson and crib will decrease the friction, at least for a short time; escaping air has about the same effect as the water- jet in lubricating the material. Although flaring out the bottom of the caisson tends to reduce the side friction, yet, on account of possible wedging action by material falling into the open space above the bottom, and further, on account of the loss of guidance, pneumatic caissons are now practically all made with vertical outside walls. Table No. noa gives values for the skin friction when the caissons were well down for a number of notable structures. Table No. no b, taken from an article by H. L. WILEY in Trans- actions American Society of Civil Engineers, vol. 62, page 113, ^March, 1909, gives values of friction for both open and pneumatic caissons. TABLE NO. noa SKIN FRICTION FOR PNEUMATIC CAISSONS OF BRIDGES (Expressed in Pounds per Square Foot) Name of bridge Range for separate piers Aver- age No. of piers Materials penetrated in sinking caissons Belief ontaine 600700 648 4 Fine sand, sand, coarse sand, Blair Crossing Brooklyn 330-410 600 38l 4 boulders. Fine sand, coarse sand, clay. Cairo . . 6 2 2 3 2 7^O IO Sand. Havre de Grace McKinley 308-489 600 400 4 Silt, sand, mud. Memphis Miles Glacier. 365-837 62O 584 5 Sand, gravel, mud, clay, sedi- ment, very tough clay, quick- sand. Nebraska City New Omaha 409-590 472-673 525 617 3 5 Sand, gravel, some clay to bed- Rulo. 3<;i 044 614 4 rock. River sand, coarse sand, rubbish, Sioux City 314-535 463 4 clay, gravel. Fine sand, yellow sand, gravel, Williamsburg 7"?o clay, boulders. General average for nine bridges, 554 pounds per square inch. 328 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX TABLE NO. 1106 No. Type of caisson Method of sinking Material penetrated Skin fric- tion Depth below low water in feet Area of base in square feet i Cast iron Open excavation Gravel, clay 240 60 125 2 Cast iron Open excavation Sand clay 250 75 225 3 Cast iron Open excavation Sand 250 60 125 4 5 Wrought iron Cast iron Open excavation Open excavation Sand, clay Sand clay gravel. 285 300 140 100 IOOO 125 6 7 Cast iron. Cast iron Open excavation Open excavation Sand Silt 325 350 60 60 125 125 8 Steel construction. Open excavation Silt, sand clay 375 55 190 9 Cast iron Open excavation Silt mud clay. 39O 75 IOO 10 Timber construction Open excavation Sand 4SO 30 1300 II Steel construction. Open excavation Silt clay 450 60 700 12 Steel construction. Open excavation Silt clay sand 450 60 I2OO 13 14 Steel construction. . . Steel construction. Open excavation Open excavation Mud, sand Clay 450 450 65 75 1300 1500 IS 16 Iron construction. . . Cast iron Open excavation Open excavation Sand, gravel, clay Clay 480 50O 65 60 200 125 17 Steel construction. Open excavation Clay 700 65 I3OO 18 Masonry Pneumatic Sand mud 205 40 75 19 Timber construction Pneumatic Clay 250 35 800 20 Steel construction. Pneumatic Clay, sand 275 60 150 21 Timber construction Pneumatic Silt sand mud 310 75 2550 22 23 24 25 26 27 Timber construction Timber construction Timber construction Timber construction Steel construction. . . Timber Pneumatic Pneumatic Pneumatic Pneumatic Pneumatic Pneumatic Sand, clay, gravel.. . . Sand, clay, boulders. . Clay, sand, gravel. . . Sand, gravel, clay.. . . Sand, boulders Silt, clay, gravel 350 400 400 425 450 500 100 48 95 55 68 75 1200 1925 4500 1300 2700 1800 28 Iron cylinder Pneumatic Sand, shale 525 60 1 200 29 Timber construction Pneumatic Sand 540 75 1700 30 31 32 33 34 Timber construction Timber construction Timber construction Timber construction Timber construction Pneumatic Pneumatic Pneumatic Pneumatic Pneumatic Sand, clay Sand, gravel, clay. . . . Sand ' Sand, boulders Silt, sand, clay 600 650 650 660 900 75 8c 90 101 45 1400 2000 1200 2100 1700 In sinking the Commercial Cable Building caissons the fric- tional resistance varied from 250 to 300 pounds per square foot of exposed surface, while in the United Fire Insurance Co. caissons it was as high as 1000 pounds. The highest value of frictional resistance was observed in 1910 while sinking the concrete caisson for the pivot pier of the reconstructed swing bridge of the Grand Trunk Railway at Black Rock Harbor on the Niagara River. The material pene- trated was a very sticky red clay. The concrete open caisson weighed 8700 tons and 1084 tons of stone and pig iron were ART. in PHYSIOLOGICAL EFFECTS OF COMPRESSED AIR 329 piled on top of it. The area was 10235 square feet, thus giv- ing a frictional resistance of 1912 pounds per square foot. ART. in. PHYSIOLOGICAL EFFECTS OF COMPRESSED AIR The question of the physiological effects on the human system when working in compressed air is an important one from both the humanitarian and financial standpoints. In the past almost all the important works employing compressed air have levied a heavy toll of suffering and death on the 'sand-hogs/ as caisson workers are commonly called. For instance, on the caisson work of the St. Louis bridge there were 119 cases of so-called caisson disease, with 14 deaths from the same, while on the Brooklyn bridge there were no cases of illness, with 3 deaths. These, of course, were early examples; at the pres- ent time, owing to a better knowledge of the disease, the records are not so bad, but the disease still claims its victims in too many cases. No harmful effects are felt on entering the compressed air, or while remaining in it; only during decompression or after emerging are the workmen affected. The disease, which has been proven to be aeremia, may be divided into two classes: First, that in which the attack is light; and second, that in which it is severe. The first form is characterized by very severe pains, chiefly in the joints, and closely resembles rheumatism in its effects. From the tendency to cause its victim to double up in agony it is commonly known as the 'bends.' When the attack is very severe it usually paralyzes its victim and is commonly fatal. SENSATIONS FELT ON ENTERING THE AIR CHAMBER. On entering the air-lock and having the air pressure turned on, some of the sensations felt are heat, slight giddiness and head- ache, pain in the ears, breathlessness, inability to whisper caused by the resistance of the compressed air to the finer muscular movements of the tongue and a feeling of resistance to movement owing to the density of the air. A slight dis- comfort is usually felt in maintaining equilibrium between 330 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX the air pressure inside and outside the body, the most painful being in the ears, as noted above. This may be overcome by closing the mouth and holding the nose, and at the same time trying to expel the air from the lungs; such action makes the pressure in the tympanic cavity equal to the outside pressure by means of the Eustachian tubes which run from the back of the nasal passages to the cavity. This action should be repeated from time to time and as long as the pressure continues to in- crease. Relief may also be secured by the action of swallowing. A cold makes the feat more difficult since the Eustachian tubes are then somewhat blocked. Owing to breathing the denser air with its increased amount of oxygen, as soon as equilibrium obtains the general effect is some- what exhilarating and bracing. To quote one of the workmen in the Blackwall tunnel (England): l "I never felt happier than when I was in the compressed air. Always happy, and on the cheery side. Why, laddie, I would get up in the morning feeling very dour and queer, and just go into the workings and then whistle (?) and sing all day long." SENSATIONS FELT ON LEAVING AIR CHAMBER. On leaving the air pressure the caissonier feels cold, and this is felt most keenly during the passage through the air-lock, being due to the expansion of the air in the lock, as well as to the expansion and liberation of gases in the body. To counteract the effects of this cold the air-lock shoulcf be warmed and the men given strong hot coffee to drink on emerging, and should dress warmly. Another characteristic of decompression is a dense fog which occurs as the air becomes rarefied. Another sensation often manifested on emerging is an itching, pricking feeling under the skin on all parts of the body; this disappears in a few minutes. The foregoing are the sensations always felt; if the person is taken with caisson illness the symptoms may be manifold. l " Coming out again (from the working pressure) it was not so bad, but just chilly; bitter chilly, cold as charity. The pains would come on afterward, in an hour or so, or when you got into bed. Bends in the 1 Engineering News, vol. 51, page 437, May 5, 1904. ART. in PHYSIOLOGICAL EFFECTS OF COMPRESSED AIR 331 back, the wrists and the legs; just awful. Men would turn out in the middle of the night and come back to the works and get into the compressed air again in the medical locks. They had a full dose for a start, and let the pressure drop gradually. Then they went back home to bed. Do them any good? Eh, mon, its no for me to say. They thought so, but I thought it was only humbug, a faith dodge. When I had bends I just jumped about and took a drap of guid whuskey better than all your doctor's concoctions." The foregoing graphic description of the 'bends' and treatment for it indicates the attitude of the average 'ground-hog.' 114 The symptoms of caisson disease have been quite definitely estab- lished. First among these are neuralgic pains of an intermittent or paroxysmal character, and of varying severity. In the worst instances these pains, or cramps, as they are commonly called although they are rarely accompanied by muscular spasms are so intense as to completely unnerve strong men. This symptom is very seldom absent, and from it comes the popular name of 'bends' given to the disease. Another characteristic symptom which is always exhibited is a profuse cold per- spiration. Another symptom which is of frequent occurrence, but which is not always exhibited, is pain at the pit of the stomach, usually, but not always, attended by vomiting. In about 50 percent of the cases observed, paralysis has been a characteristic symptom. The degree of paralysis varies from slightly impaired sensation or numbness in the extremities to complete loss of sensation and motion in the affected parts, which are most frequently the legs and lower part of the body. Finally the sufferer usually exhibits a number of transient symptoms, which have their origin in the brain; these are headache, dizziness, double vision, incoherence of speech, and sometimes unconsciousness. The duration of these symptoms varies from a few hours to several weeks in case of paralysis. In fatal cases congestion of the brain or spinal cord always exists. A very notice- able fact is that the attack of the disease never takes place while the sub- ject is under air pressure, but always occurs while he is emerging from the compressed air chamber or after he has emerged." CAUSES OF CAISSON DISEASE. Various theories have been advanced from time to time relative to the cause of caisson disease. It is said that attention was first called to caisson disease at about the middle of the last century by TRIGER who applied the use of compressed air in sinking some coal shafts at Chalons on the banks of the Loire. 2 " HOPPE SEYLER (1857) and THOMAS SCHWANN (1858) in Germany, andBusQUOY (1861) 1 Engineering News, vol. 46, page 157, Sept. 5, 1901. 2 Engineering Record, vol. 63, page 362, April i, 1911. 332 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX in France, . . . gave the first correct suggestion as to the cause: viz., that it was due to the setting free of bubbles of gas in the blood. Nitrogen gas is dissolved, according to the law of partial pressures, during exposure to the compressed air, and this dissolved gas having no time to escape through the lungs, if the pressure be suddenly lowered, bubbles off just as carbonic acid escapes from aerated water when a bottle is uncorked." In 1871, DR. JAMINET, the physician in charge of the com- pressed air workers at the St. Louis bridge, became convinced from his studies that the disease was caused by too rapid a tissue change due to the absorption of an excess of oxygen. About two years later, DR. A. H. . SMITH, the surgeon in charge of the New York tower caisson of the Brooklyn bridge, arrived at the conclusion that the ill effects developed in work- ing under compressed air were-due to the pressure of the air forc- ing the blood from the surface of the body to the center and thereby causing internal congestion. But it was PAUL BERT, who, by his remarkable experiments, published in 1878, proved the true cause of caisson disease to be the effervescence of gas in the blood and tissue juices. Since then such authorities as PHILLOPON, VON SCHROTTER, HELLER, MAGER, HALDANE, HILL, SMITH, MACLEOD, GREENWOOD and others, have checked and extended BERT'S experiments. The gas which is present in the blood, and which comes out of solution if the pressure is too rapidly lowered, is mostly nitrogen, for if the chamber is properly ventilated there will be only a small amount of carbonic acid gas in the air, while the oxygen content dissolved by the blood is taken up chemically by the hemoglobin, as demonstrated by DR. HALDANE. As stated elsewhere the tissue fluids, chiefly the blood, dissolve the air according to D ALTON'S law of solution of gases in fluids; i.e., the amount of gas dissolved in a fluid is proportional to the pressure of the gas surrounding the fluid. Except for very high pressures, such as eight or ten atmospheres values which will never attain in caisson work these dissolved gases probably have no chemical effect on the system, and are quite harmless as long as they remain in solution. For high pressures the dis- ART. 112 PREVENTION OF CAISSON DISEASE 333 solved oxygen seems to have a toxic effect, causing a fatal inflammation of the lungs. Experiments have shown that with a pressure of ten atmospheres some animals will die in as short a time as 20 minutes. However, when the pressure of the surrounding air is lowered, the dissolved gases, mostly nitrogen, are thrown out of solution in the form of bubbles. If the lowering of the pressure is done slowly the gases are thrown out of the blood at the lungs without developing bubbles of any appreciable size. But if the pressure is rapidly lowered the gas bubbles stick, owing to their size, in the minute blood vessels and obstruct the flow of the blood, often causing the vessels to burst. The same condition ob- tains in the various tissues carrying juices saturated with gas; if these bubbles develop in the joints, we have the 'bends'; if in the spinal cord, paralysis; if in the heart, heart failure, etc. ART. 112. PREVENTION or CAISSON DISEASE If the cause of caisson illness is a mechanical action due to the development of bubbles in the blood and fluid tissues, which in turn is due to too rapid decompression, then manifestly the cure is decompression at a rate slow enough to avoid this phe- nomenon. The length of time will depend upon the amount of gas in the fluid tissues and upon the physical characteristics of the person being decompressed. The amount of gas in the fluid tissues will, in turn, depend upon (i) the degree of pressure in the working chamber and (2) the length of time under pressure. The length of time taken to saturate the body fluids at any particular pressure will vary greatly, depending upon the fat- ness of the subject, the amount of bodily work done, heat and moisture present, etc. From experiments DR. HALDANE con- cluded that in certain parts of the body where the circulation is rapid and the number of blood vessels high the tissue juices will become 50 percent saturated in 5 minutes, with complete saturation in 40 minutes; while other parts, lacking a copious supply of blood, will require 75 minutes for 50 percent saturation 334 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX and about 4 hours for 90 percent saturation. Experiments show that the fatty tissues absorb about five times as much gas as does the blood and the rate of absorption is much slower; the rate of desaturation will be correspondingly slow. For this reason men inclined toward fatness should never be employed for compressed-air work. The better the circulation of the blood the more quickly and easily will the gases be thrown out of the system; for this reason only men in good physical condi- tion should be employed. Old men, or those who have abused themselves by excessive drinking or other dissipation, should never be allowed in the working chamber. Authorities differ as to the time that should be allowed for decompression, but all agree that the usual time given is too short. Some urge a uniform rate of decompression, while others prefer stage decompression, that is, at first a rapid decom- pression to a certain pressure, followed by slower decompression. Seldom is more than 15 or 1 8 minutes given to decompression; the reason for this is that the air-lock is small and as a conse- quence the men must maintain cramped positions in the same. Moreover, the lock is usually cold and filled with fog, due to the decreasing pressure. Properly, the lock should be large enough to allow the men some freedom of motion and it should be ventilated with warm dry air. The French law, enacted in 1908, prescribes that for a head of water up to 65.6 feet not less than 21.2 cubic feet of air shall be provided for each man in the lock, and for depths above this not less than 24.7 cubic feet. During decompression the men should constantly move about and massage their various joints, as this has been found to assist materially in ridding the system of the gases. MACLEOD suggests the following time for decompression as being safe: Gage Pressure Length of Shift Decompression Period 15 to 30 4 hours | to i hour 45 to 60 4 hours i^ to 2 hours In Germany, VON SCHROTTER, HELLER and MAGER, in 1900, published a work in which they laid down the principle that a ART. 112 PREVENTION OF CAISSON DISEASE 335 uniform decompression at the rate of two minutes per o.i atmos- phere, or 20 minutes per atmosphere, was safe. The law of New York State (1913) governing the time of decompression for pneumatic caisson work for bridges and build- ings is as follows: Gage pressure in pounds 10 15 20 25 30 36 40 50 Time of decompression in minutes i 2 5 10 12 15 20 25 The time of work in caissons, given by this law, is as follows : Gage pressure- 0-21 22-30 31-35 36-40 4i-4S 45-so Time per day in 8 hrs. 6 hrs. 4 hrs. 3 hrs. 2 hrs. i* hrs. caisson. No. of shifts. 2 (minimum) 2 2 2 (min ) Length of shift. . . . 3 hrs 2 hrs ji hrs i hr hr (max.) (max.) Minimum time be- 30 consecutive i hr. 2 hrs. 3 hrs. 4 hrs. 5 hrs. tween shifts. minutes The theory upon which stage compression is based is that the gas in the blood will not effervesce until a marked diminution of pressure obtains, and as, to the point of effervescence, the gases are discharged at a rate varying with some function of the change of pressure, manifestly the more rapid the lowering of pressure the more quickly will the blood vessels be freed of the gases contained therein. Since almost no cases of aeremia are caused by rapid decompression from about 19 pounds gage pres- sure, it seems reasonable to assume that the pressure in the air- lock may be reduced that amount in about three minutes; from this point the pressure must be lowered quite slowly and should correspond to the natural rate of desaturation of the fluid tissues at that difference of pressure. When the gage pressure reaches about 19 pounds, the remainder of the decompression may be done quickly, for, as stated above, it appears that the average person can safely stand that difference of pressure. The fundamental idea upon which stage decompression is based is correct, but as there is but little experimental data and less precedent to guide one, it has not yet become general. Apart from the matter of slow decompression, other precau- 336 PNEUMATIC CAISSONS FOR BRIDGES CHAP. IX tions, if taken, will do much to lessen the occurrence of caisson disease. Anything which tends to lower the vital resistance of the human system tends to promote caisson illness. For this reason the physical conditions under which the men work should be as good as it 'is possible to make them: There should be furnished plenty of fresh air; electric lighting rather than gas or candle lighting should always be employed, as the latter tends to vitiate the air; the air should be kept at as reasonable a temperature as possible, which means that it should be cooled during the summer time, as compression raises its temperature. At present this is done in practically all work, either by spraying the compressed air as it enters the working chamber, or else by passing it through a coil of pipes externally cooled. J "It is well known that, in a confined atmosphere, man sooner or later suffers from the accumulation of poisonous gases. The criterion of this pollution of the atmosphere is the amount of carbonic acid (CO 2 ) found present. When the per- centage of CO2 in the air rises above o.i percent, evil effects are common. It should be clearly understood that these evil effects are not due to the carbonic acid itself, but to some other toxic property which the CC>2 content seems to run parallel with, and is, therefore, a measure of it. Now under pressure it is evident that such a gas will be still more dangerous. As a matter of fact, E. H. SNELL reports that an 'increase of CO 2 from 0.04 percent to o.i percent at 30 pounds pressure is the forerunner of much illness.' He found that by free ventilation of the caisson, so as to remove this CO 2 , the illness dropped from seven cases a day to one case in two days. . . . Ventilation is a matter which should be carefully provided for, since otherwise the COz and other poisonous constituents of polluted air will have their usual depressing effects on the workmen and render them more prone to suffer from decompression symptoms." Especially when sinking through foul material should care be exercised in keeping the air pure. T K. THOMSON reports that when sinking through the foul bottom of the Harlem River the 1 Cause, Treatment and Prevention of the Bends, by J. J. R. MACLEOD, Journ. Assoc. Eng. Soc., vol. 39, page 301, Nov., 1907. ART. ii2 PREVENTION OF CAISSON DISEASE 337 men suffered much from the bends, but when sinking through the clay below this, even though under a much greater pressure, very little trouble occurred. It is also noticed that a greater amount of sickness is apt to occur during concreting than at other times, this being due to the decrease in the leakage of the air, or inadequate ventilation. CURE FOR CAISSON DISEASE. The best and about the only cure for caisson disease is recompression with slow decompres- sion. If the patient can be put into the air before the gas bub- bles have had a chance to tear the blood vessels and fluid tissues a cure can usually be effected, but otherwise not. For this reason, a hospital air-lock, large and well ventilated, should always be maintained in readiness and the men should be housed near by, so that in case of delayed attacks they may be immediately recompressed. CHAPTER X PNEUMATIC CAISSONS FOR BUILDINGS ART. 113. GENERAL DEVELOPMENT The application of the pneumatic caisson to building founda- tions has been restricted very largely to the tall buildings or ' skyscrapers' of New York City. Two conditions occur there which require this form of foundation: First, the necessity for carrying the column loads to bedrock; and second, the presence of quicksand over the rock. Both the height of the buildings and the magnitude of the column loads make it imperative to found the piers on a very hard and unyielding stratum, prefer- ably bedrock, since any irregular settlement is exceedingly dangerous and difficult to remedy in tall buildings. The pres- ence of quicksand makes sinking to bedrock very difficult by other methods than that of the pneumatic caisson, due to the tendency of the material to flow into the excavation; while it is especially dangerous in the lower part of Manhattan Island, due to the liability of undermining adjacent building founda- tions, many of which rest on shallow foundations. The only disadvantage of the pneumatic method is its high cost, but this is fully justified where the security of very expensive buildings is at stake. In its details, the caisson for a building does not differ mate- rially, except in the matter of size, from the bridge caisson. It is customary in most cases to use separate piers for all the inte- rior columns, these being circular or square in plan; but special conditions, such as the close spacing of two or more columns, or lack of clearance, sometimes makes it necessary to use one pier for two or more columns. Where the grade of the cellar floor is below the ground-water line the wall piers often serve two functions: First, that of carrying the wall- column loads to rock; 338 ART. 113 GENERAL DEVELOPMENT 339 and second, that of acting as a dam or retaining wall to keep out the water. To accomplish the latter they must form a continu- ous wall and hence they are made rectangular in plan, as wide as is necessary to give the required stability as a dam or retain- ing wall usually between 6 and 8 feet and as long as can be conveniently handled, which is often as much as 30 feet. The ends of adjacent sections are then connected and made water-tight. For the circular form of caisson the diameter may vary from about 6 feet as a minimum to 15 feet or more. For a rectangu- lar section the largest that has ever been used for building foun- dations is in the New York Telephone Co. Building, where the largest caissons are 35 feet 3 inches by 38 feet 8 inches in plan. But more remarkable in many respects were some of the caissons used in the foundations of the Municipal Building, New York, one of which was 26 X 31 feet, and carried the load from five columns. In size this is not much larger than one used in the first building founded on pneumatic caissons; namely, the Manhattan Life Insurance Building, erected in 1893-94, where the caissons had dimensions of 21 feet 6 inches by 25 feet 6 inches. But in the magnitude of the single column loads and depth to which the caisson was sunk, a great development is apparent. The maximum column load in the Manhattan Life Building was about 400 ooo pounds, while in the Municipal Building it was about 5 475 ooo pounds; the depth of sinking below the street curb in the former was 54 feet, while in the lat- ter it was 140 feet; the maximum air pressures (gage) used were respectively 15 and 48 pounds per square inch, the latter being within 2 pounds of the maximum allowed by State law. The 140-foot depth below the curb corresponded to a depth of about 112 feet below the level of general excavation. For the most part the depth to which pneumatic caissons for buildings have been sunk have ranged somewhere between 30 and 90 feet below the curb, the true depth of sinking and the hydrostatic head worked against being less than this, depending on the amount of general excavating done before sinking the caissons and the position of the ground-water level, respectively. 340 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X In the development of pneumatic caissons for building foundations a tendency was manifested early to do away with permanent shafts and roofs of the working chambers by making them removable. When present as a permanent part of the pier they tend to divide the pier into two separate monoliths of concrete, one an inverted T-shaped mass formed by the filling in the working chamber and shaft well and the other a ring- shaped mass surrounding the shaft. Removing the shaft before filling the well with concrete has now become standard practice, while the use of a temporary roof is very general. The two common methods of accomplishing the latter are* First, to fill the crib with concrete only after the caisson is sunk and the roof removed; and second, to use a roof of reinforced concrete. Pneumatic caissons made of wood, steel, wood and steel combined, and of reinforced concrete have been used. They are all satisfactory and the choice in any particular case will depend on current prices and the time required to obtain the materials and to construct the caisson. As a rule in this country concrete is the most economical and steel the most expensive, and wood about half-way between. ART. 114. CAISSONS OF TIMBER Caissons made entirely of wood have been and are being extensively used, although not to the same extent that they are employed for bridge caissons. For square and rectangu- lar caissons the construction is simple and the time there- fore saved as compared with those of steel or concrete, may be considerable. Where the depth is not great nor the sinking difficult, the caisson and crib may be made of light construction. Such a form is exemplified in the caissons of the Rogers Building, New York, which varied in dimensions from 8 feet square to about 7X14 feet in plan, and were sunk to depths of from 28 L to 60 feet below the curb, corresponding to about 35 to 40 feet below the excavation level. The sides were made of 3-inch vertical plank fastened to two horizontal rectangular frames, one ART. 114 CAISSONS OF TIMBER 341 near the bottom and the other about 3 feet higher, and to the roof timbers, by two f-inch bolts at every intersection, the bolt heads being countersunk into the planks on the outside. All joints were caulked on the outside with oakum. The cutting K- ENO.NEWS. 24' 0" - Half Deck Plan. Half Plan of Working Chamber. FIG. 1140. Pneumatic Caisson of Timber Construction. edge was made by beveling the inside lower ends of the planking to a thickness of i inch. The lower horizontal which was of 4X1 2-inch material was but a few inches above the cutting edge and hence reinforced the same. The working chamber had a clear height of 6 feet and was covered with a roof made of two 342 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X solid courses of crossed 8 X 8-inch timber, the lower course rest- ing on 6 X 8-inch timbers bolted to the sheathing. The sheathing projected 6 feet above the lower side of the roof of the working chamber and formed one section of the crib The other sections were made in 1 4-foot lengths and were of the same general construction as the caisson sides. At the joints between the successive sections of the crib the ends of the sheathing were cut square and braced by an inside 6 X 1 2-inch frame, the latter being bolted to both sections to serve as a connecting flange. The cribs were braced at intermediate points by 6 X 8-inch horizontal timber frames. A much stronger form of wooden pneumatic caisson is illus- trated in Fig. 1 14 a, which is one of the 1 2 X 24-foot caissons used in the Gillender Building foundations. The sides of the work- ing chamber were composed of two thicknesses of 12X1 2-inch timbers sheathed on the outside and inside with 3! -inch mate- rial. The cutting-edge timber extended out beyond the walls, the outer part of the upper side abutting against the bottom of the outside sheathing, while the outside and bottom faces were protected by the cutting edge, which consisted of a steel angle and a vertical steel plate. The roof consisted of three thicknesses of 12X1 2-inch timbers, the upper and lower ones running transversely and the inter- mediate one longitudinally. The under side of the roof was- sheathed with 3! -inch material. The crib was composed of 31- inch sheathing, braced at intervals by horizontal frames of 8X i2-inch timbers. If less strength is desired the walls may be made of a single thickness of horizontal timbers laid closely and sheathed on the outside and inside. This was done in the caissons for the Mercantile Building, the timbers being 6X10 inches, the latter dimension horizontal, while the sheathing consisted of 3 X 12- inch planks. In this case the roof was composed of a double thickness of 1 2-inch timbers. The foregoing examples have permanent roof construction. The first wooden caissons doing away with this feature were those of the United States Express Co. Building. Here the wall ART. 114 CAISSONS OF TIMBER 343 caissons were built with a width of 5! feet, a height of 6 feet, and with lengths varying from 25 to 34 feet. The walls con- sisted of a single thickness of timber varying from 6X12 inches to 10X12 inches. Across the ioXio-inch top course were placed 3X3Xj-inch angles running transversely and spaced 3 feet apart, the vertical flanges being turned up. On these was placed a layer of if -inch tongue and groove boards which served as a form for concrete placed on top of the same. Instead of a crib, molds built of vertical tongue-and-grooved boards in sections 8 feet high, having the same length and breadth as the caisson, were built on top of the latter to receive the concrete. They were held together by outside horizontal. Type A. Steel Working Chamber for small circular Caissons ;(6'6"to8'6"Diam.) Type B. ' Type's C&D Timber Working Chamberfor Concrete Working Chamber for large Small rectangular Caissons , circular & rectangular Caissons. (5'6"to 7'6'wide.) (Circular 9'tol4'2";rectangular 8'wideandover.)l FIG. 1146. Types of Working Chambers, Municipal Building, New York. yokes, each made with 4X3X|-inch angles forming a rectangu- lar frame. Three yokes were used to a section, one at the top, one at the middle, and one at the bottom. On completion of the forms, a six-inch layer of concrete was placed on the roof forms; as soon as this had hardened somewhat 2 feet more of concrete was added, and this 2^-foot thickness of concrete served as the permanent roof, the temporary panels underneath being taken off. Fig. 1 146, type B, shows the type used in the Municipal Build- ing for rectangular caissons 5! to y| feet wide. It closely resem- bles those described in the two preceding paragraphs, the walls being made of a single thickness of i2Xi2-inch and 8X1 2-inch timbers, the bottom timbers being faced with 4X4- mcn steel angles to form the cutting edge. It was provided with a tempo- 344 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X rary deck of 2 -inch planks notched into the walls and this deck was removed after the first layer of roof concrete had hardened. The approximately square caissons used in the foundations of the Adams Express Building, New York, are illustrated in Fig. 1 14 c. The working chamber was 6 feet high and had sides com- posed of 4X1 2-inch timbers dressed on all sides and caulked. These sides were braced with vertical inside i2Xi2-inch \>9'6"Cassion */5 Side Elevation Elevation B~B FIG. ii4c. Caissons, Adams Express Bldg., New York. timbers at the four corners and at the mid-lengths, the latter extending beyond the caisson. The outside was sheathed with 2 X 8-inch vertical tongue-and-grooved planks, which extended up beyond the caisson to serve as a form for the concrete above the caisson. This sheathing took bearing against horizontal 12 X i2-inch timbers spaced 4 feet apart vertically, and arranged in pairs at right angles to each other, each pair being connected ART. 115 CAISSONS WITH METAL SHELLS 345 Q'O" - together with screw-ended rods. The sides were held apart by 3 X 8-inch struts which were removed when the concrete had been placed. The cutting-edge timber was 6X12 inches in section, beveled on the inner corner and projected beyond the horizontal timbers to cover the lower ends of the outside sheathing. The top of the working chamber was covered with 4X1 2-inch hori- zontal boards to serve as a form for the concrete above. A 3-foot layer of 1-2-4 con ~ crete was first placed on the deck, allowed to harden for 24 hours, after which a 6-foot layer was added every 24 hours. The deck sheathing was re- moved 48 hours after the first layer of concrete was placed. Plan. ART. 115. CAISSONS WITH METAL SHELLS / Connection for Cofferdam. Working 8)3 W"*&**lf Chamber. (^uwing Sectional Elevation. The use of steel shells for small circular pneumatic cais- sons has become standard prac- tice, but their use for caissons of a square or rectangular shape is rapidly decreasing. The ad- vantages of the steel shell may be summarized as follows: First, the thickness of the shell being small there is a maximum amount of working space in the air chamber, as well as a maximum amount of space to be filled with concrete; second, for the cylindrical form it compares favorably in ease of con- struction with wood and concrete; and third, it is easily made water-tight. FIG. 11501 Caisson for Inside Col- umn. Foundation, Mutual Life Bldg., New York. 346 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X The first pneumatic caissons used for a building, those of the Manhattan Life Building, were made of steel, and were both circular and rectangular in section. Figs. 115^ and b show the details of both forms of caissons used in the foundations of the Mutual Life Building. The caissons were sunk to solid rock, Connection for Air Shaft v Connection for Air Lock Sectional Cofferdam Connection Angle. \ Plan. Cofi&rdam 'Connection An fl | ._ 9 > ' > Half Longitudinal Sectional Elevation. Inoide. ^ Half End Elevotior Outside. Cuffing Edge. 8' " Half Transverse Sectional Elevation. FIG. 1156. Caisson for Wall Column. Mutual Life Bldg., New York. from 70 to 90 feet below the curb and from 50 to 70 feet below ground-water level. The roof of the cylindrical caisson was made of TV-inch steel plates riveted to the lower flanges of 15- inch I-beams, as well as to the shell of the caisson. The latter consisted of f -inch steel plates braced at intervals with circular 4X4Xj-inch steel angles. The lower part of the shell, rein- forced with an iSXf-inch plate, formed the cutting edge. In FIG. use. Sinking and Concreting Caissons, with Steel Forms. Municipal Building (Facing p. 346.) 348 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X those shapes of structural steel were used that could readily be obtained in the open market; the rest of the structure was made of wood, and the two materials combined in the simplest possible manner. For circular piers the caisson has a diam- eter varying from 6 to 12 feet; for diameters less than 6 feet it is a difficult matter to excavate the material in the working cham- ber, and on the other hand, few single column loads are large enough to require a caisson with a diameter of over 12 feet. The circular caisson is made of staves about 4X6 inches in section, usually dressed down to somewhat smaller dimensions, the outer and inner surfaces being cylindrical. The staves are fastened, at every intersec- tion, to inside 3 X 3-inch horizontal angle- iron rings, spaced from 3 to 5 feet apart, bolts of about f inch in diameter and coun- tersunk into the wood being used for this purpose. The staves are usually splined but in some cases they are only caulked. This type is illustrated in Fig. n6a. In the circular caissons of the Atlantic Mutual Building, which had an average diameter of about 7 feet, the cutting edges were made with a 28Xf-inch steel plate. To give bearing surface to the cutting edge, in order to better control the sinking and to protect the feet of the staves, a 3X3Xf- inch angle was riveted to the inside of the plate, parallel to its bottom edge, and J inch above it, the horizontal leg forming a shelf to receive the lower ends of the staves. FIG. ii 6a. Wooden The roof of the working chamber was formed Stave Caisson with De- , tachabie Roof and shaft by a removable steel dome | inch thick, ART. 117 CAISSONS OF REINFORCED CONCRETE 349 made in two sections and stiffened with radial steel angles. It was caulked with a hemp gasket and bolted to a 3 X 3-inch in- side steel angle ring about 6| feet above the cutting edge. The crib was of the same form of construction as the caisson, and was built as a continuation of the same to a height of 32 feet above the cutting edge. Where the 32 feet was not sufficient in height short lengths were added on top. These were made in two semi-cylindrical sections and were butt- jointed to the top of the crib already in place, and were caulked and bolted through the horizontal flanges of the angle-iron rings. For the wall piers of the New York Stock Exchange Building the caissons were made rectangular in form, 8 feet wide, from 24 to 30 feet long, and 8 feet high. They were sheathed with 4X1 2-inch vertical wooden staves with square caulked edges and without splines. These staves were fastened to successive courses of inside horizontal steel angles, the latter extending wholly around the caisson. The longitudinal walls were braced with horizontal transverse timbers resting on and bolted to the angle frames, as well as with tie rods, parallel and adjacent to the timber braces. The roof was formed with a removable steel plate dome, reinforced with transverse angles and fastened to frame angles about 6 feet above the cutting edge. The crib was exactly like the caisson, except that it was with- out roof or cutting edge. It was built in sections 15 feet high. The angle frames at the top of each section were set 3 inches below the top of the staves with the horizontal flange up. The angle at the bottom of the next upper section had its horizontal flange down and i inch below the lower end of the staves. This engaged the lower section and formed a tenon, thus binding the two sections together. A row of eye bolts, i foot apart, con- nected the horizontal flanges of the angle frames. ART. 117. CAISSONS OF REINFORCED CONCRETE Pneumatic caissons of reinforced concrete are now being widely used. The chief advantage of this type of caisson is that it gives a monolithic pier. A second advantage is that the caisson may be made at the site, thus avoiding the expense of 350 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X teaming the same. One disadvantage is that the required thick- ness of walls so reduces the working space that this type cannot be used for very small caissons. Another disadvantage is the time element involved in waiting for the concrete shell to harden. The foundation caissons of the Municipal Building were sunk in 1910 and were the first in which reinforced concrete was used throughout. Here both the circular and rectangular forms were employed; all circular caissons having diameters 9 feet or over and all rectangular ones having a width of 8 feet or over, were made of reinforced concrete. Types C and D, Fig. 114 b, show the outlines of the caissons; it will be noticed that the walls thicken from the cutting edge to the roof by stepping the concrete. As noted in Art. 94, this is a better arrangement than the tapered form because it gives a positive bearing between the chamber shell and the concrete filling, thus making the whole area of the bottom available for carrying the load, without relying on any bond stress. The thickness of the bot- tom of the wall was about 10 inches and the real cutting edge consisted of a steel channel and a 4 X 4-inch steel angle, the former laid horizontally with flanges up and the latter with its vertical leg down, thus giving the sharp cutting edge and broad bearing surface. The walls were well reinforced with both vertical and horizontal rods. No cribs were used, simple forms being employed in which to build a concrete shell, which was constructed before sinking was started. The caisson and the shell above the same were built directly on the spot where they were to be sunk. The forms for the interior of both circular and rectangular caissons were made of wood, while for the exterior faces and for the shell above the roof they were made of steel for the circular ones, and of wood for the rectangular ones. In the reinforced-concrete foundations for the Woolworth Building, New York, the inner forms were also of steel for the circular caissons. ART. 118. CRIB AND COFFERDAM The frame which is built on top of the caisson and which, together with the roof of the caisson, virtually forms an open ART. 118 CRIB AND COFFERDAM 351 box caisson, is generally called a cofferdam when applied to cais- son construction for buildings. In the preceding articles, it was designated as a crib, since it corresponds to the crib of the bridge substructure. This frame is usually built in sections, as noted in the preceding pages, and the top section sometimes forms a true cofferdam. As water seldom covers the ground for such caissons the cofferdam is not often employed, about the only time when it is used, is when the caisson is sunk before the general excavation for the cellar or sub-surface floors is made. In the latter case the cofferdam serves as a form just as the crib proper does, but after the general excavation is completed the cofferdam is removed. In the early deep foundations, such as those of the Manhattan Life Building, brick masonry was used for the pier material above the caisson, in which case the use of cribs was ordinarily dis- pensed with, the masonry being built up as the caisson sank. But this arrangement was not entirely satisfactory for it was found that in omitting the crib the friction on the sides was much increased, which was a disadvantage in itself, and especially dangerous in that it tended to tear apart the brick masonry. Another desirable feature of the crib is that it enables sinking to be carried on without regard to the progress of the masonry construction. When brick masonry was superseded by concrete, the latter being deposited on the deck of the caisson simultaneously with the sinking of the latter or after it had reached rock, the crib became a necessity. At the present time the tendency is toward the elimination of the crib. As noted in the preceding articles this is done by building a concrete shell virtually the pier, except for the hole left for the shafts before sinking op- erations are commenced. :.. If the caisson is not to be sunk over 30 feet the entire length of shell is cast previous to any sinking, beyond that of pitching the caisson, that is, sinking the cutting edge a foot or two to give stability; while if the depth is greater than (30 feet, the building and sinking are each done in two operations. This means that the pier is first built up part way, sunk till the top 352 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X reaches the surface of the ground, then the remainder built and the rest of the sinking done. ART. 119. SHAFTS AND AIR-LOCKS Steel shafts are always used in caissons for buildings, and owing to the limited space a single shaft usually serves for both men and materials. For this reason, and for the added one that it is usually made removable, it differs somewhat from the shafts commonly used in bridge caissons (Art. 103). As noted in Art. 1 13, in the development of pneumatic caisson work for buildings the tendency has been toward the elimination of such parts as FIGS, uga, b, c, and d. Collapsible and Removable Shaft. might weaken the finished pier. In eliminating the permanent steel shaft a considerable saving of money was effected in that it enabled using the same shafts many times. The first attempts were toward eliminating the steel shafts entirely, not even using the same during sinking operations, the idea being to employ a shaft lining of molded concrete, the latter to be made air-tight by painting. At present this is done to a considerable extent for the lower lengths. One form of collapsible or removable shaft is shown in Figs, iigfl-d, where a shows a sectional elevation of the caisson with the shaft lining in place; b shows a plan of the caisson, while c ART. 119 SHAFTS AND AIR-LOCKS 353 and d show details of one section of the lining. 1 " Each section was composed of two approximately semi-circular plates internally flanged for bolting to each other along one vertical edge, and a key interposed between the opposite edges of the plates. Internal flanges at the ends serve for bolting successive sections to each other. Ladder rungs were arranged conven- iently between the flanges of the key, and vertical guides were arranged just inside the line of the end flanges to guide the bucket past them." The shafts should be oiled or otherwise protected from adher- ing to the concrete. The bottom section of the shaft is usually not made removable, but is thoroughly bonded to the concrete in the crib (see Fig. 1146). This is done to prevent the air in the working chamber from leaking between the crib and the air shaft. It also adds resistance against the tendency of the air to blow out the shaft and air-lock. A somewhat better form of air-shaft than the one just described has an elliptical section in which there is sufficient clearance between the bucket and the ladder for a man to pass. This eliminates danger to the men in the working chamber from the lodging of the bucket in the shaft. Such a form of shaft is shown in the lower part of Fig. no/. The air-locks are always placed on the top of the shaft, and are made of steel. Two forms, called respectively, the Moran and the O'Rourke air-lock, have been used almost exclusively for work on building caissons. The feature most desired in air- locks for materials is high speed of operation. Figs. 1190 and/ 2 illustrate the Moran air-lock for the caissons of the Singer Building, New York. The upper and lower doors are not placed with their vertical axes in the same line. To begin operations the upper door is open and the lower one closed. The bucket is then let down into the air-lock, moved to one side, the upper door closed, the rope passing through a hole in the door 1 Recent Developments in Pneumatic Foundations for Buildings, by D. A. USINA, Trans. Am. Soc. C. E., vol. 61, page 219, Dec., 1908. 2 From Foundations for the New Singer Building, by T. K. THOMSON, Trans. Am. Soc. C. E., vol. 63, page n, June, 1909. 23 354 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X frame, and the valve in the pipe on the left is then placed in the position shown in the illustration; this permits the air from the shaft and working chamber below to enter the air-lock, and as soon as the pressure in the air-lock nearly equals that below, the lower door opens and the bucket is free to be let down. The lower door remains open as long as the bucket is below. FIGS. 1190 and /. Oval Shaft Arranged for Men to Pass Bucket. Moran Air-lock* On coming out the bucket is raised into the air-lock, the lower door closed, the valve turned to connect the air-lock with the outside air, which causes the pressure in the latter to drop to normal; this causes the upper door to open and the bucket is taken out. Both doors are circular gasketed steel plates operated by exterior counterweights. The upper door is some- ART. 119 SHAFTS AND AIR-LOCKS 355 times provided with a stuffing box to permit the passage of the hoisting rope when the door is closed. Elevation. Sectional Elevation. FIG. ii. Details of Construction of O'Rourke Air-Lock. The O'Rourke air-lock is illustrated in Fig. 119 g. l " Around the top opening is a circular ring, D, on the inside. This open- Engineering News, vol. 40, page 364, Dec. 8, 1898. 356 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X ing is closed by the pair of oppositely arranged convex swinging gates, E, the meeting edges of which are packed so as to make an air-tight closure. The opposite edges are provided with flanges F, adapted to close against the ring D, these flanges having flap gaskets, which protrude into the air-lock so that the air pressure striking them will make an air-tight seal by pressing them against the ring D. . . . "The gates E, are cut away at the center of the meeting edges, as shown at H, to receive and fix snugly upon the stuffing box J, banded with rubber, and having a hole through the cen- ter for the passage of the hoisting rope. The gates are hung by the arms K, to the common shafts G, one (M) being fixed to the shaft, and the other (N) running loose. This arrangement by means of the bevel gears and idler m, n, and o, allows the two doors to be moved in unison and in opposite directions .... It will be noticed that the levers have counterweights which balance the doors and thus enable one man to operate the lock. "The air-lock has its lower end closed by similar oppositely arranged swinging gates, P, which near their outer edges have seats Q, which fit against the ring R, with gaskets to secure a tight fit .... Unlike the upper gates E, the lower gates -P are swung by the arms T from separate centers or shafts, U and V. The gate arms are rigidly fixed to the shafts and turn with them. To secure opposite motion to the shafts, one is operated by a spur wheel from the other, as shown at / and v, the actuating force being obtained through the lever O. The admission and discharge of air to and from the locks is controlled by the three-way cock X, operated by a lever and bevel gear and connected with suitable piping to the air-shaft, there being no independent connections with the compressor." . . . ART. 120. SINKING THE CAISSON Steel caissons are fabricated at the bridge shops, assembled there or at the contractors' yards, brought to the site by teams, placed in position by derricks, and sunk. This refers to the ART. 120 SINKING THE CAISSON 357 practice in New York City. The same general scheme is usually employed with caissons of wood, the main difference being that the material is fabricated in a wood-working mill. The reason for the assembly work being done away from the site is the lim- ited space usually available at the site, and to the lack of vacant lots in the near vicinity. Some idea of the conditions obtaining at the site in most of the New York City foundation work may be obtained from Fig. 115^. As the average caisson with one section of crib seldom weighs over 10 tons it is not a difficult matter to team them. Before sinking the interior caissons the site is usually exca- vated down to ground-water level; at least this is true when the cellar floor is to be at or below that elevation. The caisson is then placed and one or more sections of the crib erected on the same, or a section of concrete shell cast if no crib is to be used. The first few feet of sinking is accomplished without the use of air pressure. The material is usually dug by hand and removed with buckets although the blow-out process is occasionally employed. The disadvantage of the latter process is due to the small volume of the working chamber making it difficult to maintain a constant pressure in the caisson. One of the gravest problems connected with sinking caissons for buildings is that of safeguarding adjacent buildings from undermining. When a caisson is sunk through quicksand within a few inches of a building, which perhaps is founded on a steel grillage, it is evident that great care must be taken not to disturb this quicksand under the grillage. This fact usually precludes the possibility of doing much 'blowing'; that, is, suddenly reducing the air pressure in the working chamber to let the caisson sink a few feet, or of using the water- jet on the outside to reduce friction. On account of the large friction developed in sinking building caissons much greater than with bridge caissons, where much of the crib is in water, and therefore not subjected to friction in addition to excavating the material from the caisson and filling the crib with concrete, special devices must be used to promote sinking. Greasing the sides of the caisson and crib 358 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X reduces the friction somewhat and it is usually advisable to do this. In some cases the caisson may be pulled down by attach- ing lines to caissons already sunk, or to driven piles, as well as to timbers across the top of the caisson to be pulled down. By far the most effective and customary way is to weight the caisson temporarily with pig iron. At present either heavy blocks, weighing as much as 4000 pounds each, or ballast boxes filled with pig iron, are employed. A good example of the use of large blocks may be seen in Fig. i i$c. Some of the ballast boxes hold as much as 12 ooo pounds of pig iron. The advantage of the blocks or boxes lies in the fact that they require no special plat- form or yokes on the crib, and are very quickly and easily placed and removed by the use of hoisting engines. Some of the largest caissons sunk to considerable depths have each required as much as 1000 tons of this weighting material, although the average caisson requires about 350 tons. From this it may be seen that for satisfactory cost a means of econom- ically handling this weighting iron had to be developed. In many of the earlier caissons, such as those of the Atlantic Mutual Building, described in Art. 116, an excessively large amount of temporary weighting was necessary, on account of the concrete not being placed until the caisson had reached its final position. This scheme was adopted in order that the roof of the caisson might be removed after sinking operations were over and the whole pier made a single monolith of concrete. But later caissons have preserved the latter feature without the expense of so much temporary weighting. As explained in Art. 114 this was brought about by using a thin temporary roof, only strong enough to hold a foot or two of concrete on top. At about the same time that concrete roofs came into use cribs were largely dispensed with. In their place forms were used, and as these forms were of light construction, the concrete was usually deposited in layers a few feet high, and allowed to harden before more was added. As soon as the concrete was sufficiently strong the forms were moved up and another layer of concrete placed. Where there are a considerable number of caissons to be sunk, it has become standard practice to build the concrete ART. 121 RATE OF SINKING . 359 as high as possible before starting to sink. The reasons for this are as follows: First, sinking can be done at a much more rapid rate than can the building of the concrete; second, it saves on the number of times that pig iron must be loaded and unloaded; and third, it makes less temporary weighting necessary. In the caissons for the City Investing Building the concreting was entirely finished before excavating in the working chamber was commenced, although in some cases caissons were sunk a few feet to give lateral stability to the tall shafts and to relieve the excessive weight on the walls of the working chamber. In the Singer Building, where bedrock was 70 feet below the surface, the concrete was built on the caissons to one-half the estimated total height before sinking was started, after which the cais- sons were sunk until the top of the concrete was down to the surface of the ground, after which sinking operations were stopped, the remainder of the concrete built and sinking re- sumed. In some of the piers of the Municipal Building three build-ups were necessary, the maximum height of any' one build being 60 feet. With these high piers great care is necessary in guiding them while sinking. For the caissons of the United States Express Building heavy horizontal frames, braced with inclined struts, enclosed them. These frames took bearing on greased vertical guide strips attached to the faces of the concrete after the forms were removed. ART. 121. RATE OF SINKING Although showing large variations the average rate of sinking caissons in New York City is high. This is largely on account of the fact that rush jobs are customary there, and on account of the high value of real estate, owners are willing to pay well for keeping the time required for placing the foundations down to a minimum. For this reason many of the records in sinking were not made under natural conditions, the cost being considerably higher than if more time had been taken. The caissons of the Manhattan Life Building, which were both 360 . PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X circular and rectangular in plan, the former shape averaging about 12 feet in diameter and the rectangular shape about 320 square feet in ground plan, were sunk a distance of 34 feet, mostly through fine sand. This sinking was done, the cribs filled with masonry and the working chamber and shafts filled with concrete, on an average of one caisson in eight days. This corresponds to a sinking rate of 4! feet per day. The caissons for the Atlantic Mutual Building (Art. 116) did not have their cribs filled with concrete until sinking was com- pleted. The material penetrated was largely quicksand. One caisson was sunk 24 feet in seven hours. Forty-two caissons were sunk and concreted in 36 days. In the caissons of the Trinity Building, the average rate of sinking through soft material such as quicksand was about i foot an hour, while through hard-pan it was only about one- third as much. These caissons were very similar to those of the U. S. Express Building (Art. 114), and were built up previously to sinking. The rate as 'here given refers only to the actual sinking and not to the time spent in building up the caisson filling the working chamber, etc. What is probably the best record ever made in caisson sinking was the placing of 87 caissons, all over 75 feet in depth, in 60 days. These were placed for the foundations of the Trinity Annex and U. S. Realty Buildings by the Foundation Co. of New York City. ART. 122. FILLING THE AIR CHAMBER Where the caisson is to rest on rock the surface should be thoroughly cleaned of loose and friable material before placing the concrete filling. If hard-pan, without any pockets of loose material in it, overlies the bedrock it is rarely advisable to carry the cutting edge of the caisson more than a few feet into the hard-pan. The best method is to stop sinking the caisson at hard-pan level and to carry the excavation below the cutting edge through the hard material down to rock. In this case, when the concrete is placed it will bond to the hard-pan and so ART. 123 WATER-TIGHT DAM OF WALL PIERS 361 reduce the load on the base, whereas if the caisson is sunk through the hard-pan to solid rock this bonding effect is lost. Another advantage of stopping the caisson at hard-pan lies in the ease with which the bottom section may be belled out to distribute the load over an area larger than the horizontal section of the caisson. For caissons in which the roofs are to be removed on the com- pletion of the sinking, the working chamber is filled with concrete, which is allowed to harden for about two days, after which the roof and shafts are removed, and the remaining space filled with concrete. ART. 123. WATER-TIGHT DAM OF WALL PIERS Many of the large buildings of New York City, built on piers founded by the pneumatic process, have their cellar floors a considerable distance below curb and ground- water levels which necessitates heavy dam construction around the sides. As explained in Art. 113 this dam construction is obtained by mak- ing the wall caissons rectangular in plan and sinking them with a small clearance between the ends of adjacent piers, and after- ward filling the space between the piers with concrete or clay to form a continuous and water-tight dam. Some clearance must be left in order to allow for slight deviations in sinking, the usual amount allowed being from 4 to 18 inches. The space between the piers may be made water-tight down to bedrock, in which case the use of the pneumatic-caisson process may sometimes be avoided for the interior column piers, or the space may be made water-tight to a level a little below the level of the cellar floor. The first building using this form of dam construction was the Commercial Cable Building. The clearance between the caissons varied from 4 to 10 inches. As soon as the cais- sons were sunk 3 -inch pipes were jetted down in the space be- tween the end walls, and clay pellets were forced through these pipes into the sand by means of a plunger operated by a pile-driver. As clay filled the space the pipes were gradually 362 PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X raised until the surface was reached, thus forming a water- tight dam of clay. As soon as this was completed, a section of the metal shell in the middle of the ends was removed and the open space filled with concrete. The caissons for the wall piers of the New York Stock Ex- change Building were sunk with a clearance of less than 2 inches, the average being i inch. That this is too small a clearance INSIDE ELEVATION CAISSON CONNECTIONS, BANK OF STATE OF NEW YORK FlG. 1230. CAISSON CONNECTION, STOCK EXCHANGE. FIGS. 1236 and c. was demonstrated in this work. Water- tightness was obtained in the following manner: As the crib and working chamber were filled with concrete semi-circular wells were left in the ends. On the completion of sinking the adjoining wooden walls were drawn together and bolted as shown in Fig. i2T The central part of the walls was then removed, thus combining the two wells into one, which was filled with concrete to bond the two piers together. The spaces between the caissons of the Bank of the State oi 1 From Recent Developments in Pneumatic Foundations for Buildings, by D. A. USINA, Trans. Am. Soc. C. E., vol. 61, Dec., 1908. ART. 123 WATER-TIGHT DAM OF WALL PIERS 363 New York Building were sealed by using two 2-inch vertical strips of timber on alternate caissons. These str *ps were re- cessed into the wall as shown in Fig. i2T > a. 1 On completion of sinking the strips were forced out against the adjacent caisson by the simple arrangement shown in the illustration. The method used for connecting the caissons for No. 42 Broadway is illustrated in Fig. I23&. 1 On completing the sink- ing the sand between the guide timbers was removed by jetting the same and the space was then filled with grout. The method used in the piers of the Trust Company of Amer- ica Building, where a 1 2-inch clearance was used, is illustrated in Fig. 123d. 1 As shown in section XX, semi-octagonal spaces in the center of the ends of the piers were left as wells when the concrete shells above the caissons were built, this building being done previously to the sinking. After sinking the caissons the earth in the 1 2-inch space between the cores was excavated to a depth of i foot and the upper boards A A were removed, cut and placed in the position A'. This alternate excavating and sheeting was carried down a few feet, after which the core planks were removed and a short section of a steel air-shaft cylinder set into it and concreted, after which the air-lock was placed on top. The slots S were filled with the shaft concrete and acted as keys to prevent the blowing out of the shafts. Air pressure was then put on and the remainder of the material excavated and boards placed down to the top of the caisson, after which the whole chamber was filled with concrete. A very neat arrangement was used in the caissons for the U. S. Express Building, where there were clearances of from 6 to 12 inches. 2 " Vertical grooves about 2 feet wide and 8 inches deep were made in ths ends of the wall piers and formed, with the clearances already noted for the caissons, wells, from 22 to 28 inches wide above the tops of the working chambers. Compound sheet piles were made with 3-inch planks wide enough to overlap the corners of adjacent piers at each joint Recent Developments in Pneumatic Foundations for Buildings, by . A. USINA, Trans. Am. Soc. C. E., vol. 61, Dec., 1908. 2 Engineering Record, vol. 53, page 316, March 3, 1906. PNEUMATIC CAISSONS FOR BUILDINGS CHAP. X and were driven close to the inner and outer faces of the piers so as to cover the joints between them .... " After the sheet piles were driven, 4-inch pipes were jetted down in the corners between their edges and the outer faces of JOINING CAISSONS IN TRUST COMPANY OF AMERICA BUILDING. FIG. i2^d. Method of Sinking Joint Well between Caissons. the piers, and as they were withdrawn grout was forced through them which effectually sealed the spaces between the piles and the piers. Men were then able to enter the well between the ART. 123 WATER-TIGHT DAM OF WALL PIERS 365 Street Surface. rn ^ _. Tern* ICot. Col. Foundcrf~ion Caisson ends of the piers and excavate the quicksand and hard-pan down to the tops of the caisson, caulking as they went any slight leaks between the sheet piles and the piers. Jet pipes from 2 to 6 inches in diameter were sunk in the narrow space between the caissons and removed or loosened the ma- terial down to the cut- ting edges. Grout was then introduced through them and with the sand and broken stone already there formed concrete thoroughly sealing the space between the working cham- bers. Afterward the well above the work- ing chamber was rammed full of ordi- nary concrete, thus making a solid key which united the wall v ^ piers and prevented v | leakage." ! Fig. 1230 shows a- line of wall column piers and the form of bracing usually em- ployed. The whole area of the building is first excavated to ground-water level and sheeted, after which the wall piers are sunk and keyed. The interior is then excavated to cellar floor level, the wall piers being temporarily braced as the excavation proceeds. The final bracing of these piers is done by means of the floor beams of the building. w^m^^ '/\*&// / /' / //'/// / //// m^/////v/. Wall Caisson -Concrete Hey r a . c fj ~ ENG.NEWS., FIG. 1230. Connection and Bracing of Wall Caissons. CHAPTER XI PIER FOUNDATIONS IN OPEN WELLS ART. 124. OPEN WELLS WITH SHEET-PILING A method much used for building foundations and occasion- ally for bridge substructures is that employing the open well. This method gives a type of foundation similar to the caisson but it is a simpler and more economical process under many conditions. Wells are sunk either by driving sheet-piling and then excavating, or by excavating first and sheeting afterward. The first method is used for quicksand or other material that will not stand up, while the second method is employed in clay, and forms the type known as the Chicago method because of its extensive use in that city. In either case as soon as the well is excavated to rock or hard-pan it is filled with concrete to form the pier. The application of the open-well method is limited to those cases in which a moderate amount of disturbance to the surrounding material will not damage adjacent foundations. The sheet-piling method has been used to depths of at least 60 feet and the Chicago method has been used for depths up to 120 feet or more. The open-well process with sheet-piling, which is used with marked success where rock may be found at moderate depths from 40 to 60 feet and where adjacent buildings are not in danger of being undermined, is virtually the cofferdam process applied to building foundations. This process differs from that used for bridge piers in that the sheet-piling usually acts as a form for the lower part of the pier concrete and oftentimes is left in to become more or less a permanent part of the pier. The wells are either circular, square or rectangular in plan; common sizes are about 6 feet in diameter or on a side, while for rectangular wells the greater dimension is rarely over 16 feet. 366 ART. 124 OPEN WELLS WITH SHEET-PILING 367 Wood, steel, or a com- bination of both may be used for the piling. If the well is not over 20 to 25 feet deep the sheet-piling is usually driven in a single sec- tion, but for greater depths two or more sections are used, the upper sections being large enough to per- mit offsetting and placing the lower sec- tions inside. The upper section of piling is driven first; this may be done by hand or ma- chine. If the driving is not difficult this is done before excavat- ing is commenced, since there is less like- lihood for the sur- rounding material to be disturbed through flowing into the well from underneath the piling. Great care should be taken to start the sheet-piling in its correct position as this will save much trouble later. On excavating the wells, which is commonly 4 Piece Drum 2"x6"x/o " Tongue and GrooveWood Lagging Plan Section FIG. i2 4 a. Open Well for Railway Exchange Building, St .Louis. 368 PIER FOUNDATIONS IN OPEN WELLS CHAP. XJ done by men with picks and shovels, throwing the spoil into buckets lowered into the wells, bracing should immediately be placed. As soon as the first section is driven and the material exca- vated the second section is started. On completion of the work to hard-pan or rock, the bottom is carefully cleaned and leveled and the lower section filled with concrete, a 1-2-4 r I ~3~5 mix- ture being used, and the sheet-piling serving as a form. The latter may be withdrawn after the concrete has set or it may be left permanently in place. If the sheet-piling is to be withdrawn the concrete should be protected in some manner from bonding to it. Above the lower section special forms are usually made for the pier and the whole, including the sheet-piling, with- drawn after the concrete has set. Fig. 1240 illustrates the cylindrical well sunk to rock for the twenty- two story Railway Exchange Building, St. Louis, Mo. The illustration indicates the character of the material sunk through as well as the distance sunk. For the upper section, 8 feet in diameter, 2 X 6-inch tongue-and-grooved wooden sheet- piling was used. It was driven by hand and braced by 3X1- inch two-piece rings. The lower section had a smaller diameter and was composed of g-inch Lackawanna steel sheet-piling, braced with four-piece wooden drums made of i2Xi4-inch material with cast-iron ball-and-socket joints at the ends. After the piling was driven the material, loosened and kept in sus- pension by a i J-inch jet under 100 pounds pressure, was removed with pumps. On completion of the excavation a 3-foot layer of 1-15-2 concrete was deposited to seal the bottom, no pump- ing being done in the meantime. After allowing the concrete to set for five or six hours the water was pumped out and the lower cylinder filled with concrete, the braces being removed at the same time. The sheet-piling was left in place. The square piers of the Bamberger Building, Newark, N. J., were built in two sections, with timber sheet-piling above and steel sheet-piling below. They present a good example of very careful guiding of the piling. Each cofferdam was 12 feet square on top and the upper section was lined with 3-inch ART. 124 OPEN WELLS WITH SHEET-PILING 369 tongue-and-grooved planks 20 feet long. The piling was assem- bled on horizontal skids to make panels 12 feet wide with trans- verse cleats on top and bottom. A pit was first excavated and in it was placed the bracing frame shown in the right-hand drawing of Fig. 1246. The three sets of horizontal ioX lo-inch frames were braced together with diagonal planks and the two upper frames rested on ioX 10- inch posts 4 feet long. The ends of the rangers were halved and were connected by short ioX-inch planks. '4 / * \ \ -(* y \ i <& z V 1 FIG. 1246. A Side Panel and Frame of Cofferdam. ' lu The side panels of vertical sheeting planks are lifted by a derrick, the tackle being attached to a bridle connected to the ends of a pair of horizontal planks tightly clamped to the upper end of the assembled panel (see left-hand illustration, Fig. 1246). After the four panels are set in place against the faces of the rangers forming the interior framework they are secured by light yokes of horizontal timbers and tension rods screwed up tight, after which the temporary cleats are removed and the sheeting is driven by light steam-hammers as the excavation progresses inside, the rangers being forced down as necessary." Fig. 1 240 shows the sinking of cylindrical wells for the foun- dations of the Kinney Building, Newark, N. J. After being assembled by stiff-leg derricks the steel-piling units were clamped together by outside wire cables holding them against inside ranger frames spaced from 2\ to 5 feet apart and made from two thicknesses of 3 X 5-inch scarfed planks with five to 1 Engineering Record, vol. 64, page 457, Oct. 14, 1911. 24 370 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI seven pieces in each course. The piling was driven to bottom before any excavating was done and was removed after the well was filled with, concrete. ART. 125. OPEN WELLS WITH SHEETING: THE CHICAGO METHOD The soil conditions in the downtown or business district of Chicago, where most of the heavy buildings are located, are peculiar and have led to a special type of foundation being used for many of the heavy structures. For a distance of about 14 feet below the street curb the soil consists of loam and made ground; below this there is a layer of clay having a thickness of from 70 to 80 feet, which overlies hard-pan or coarse gravel and solid rock. The upper 6 to 1 2 feet of this clay is hard and stiff and forms the bed on which rest many steel grillage founda- tions (Arts. 151, 152, 156) which, dating from 1878, were so extensively used in that city. Below this, the clay becomes softer and remains so down to the hard-pan, which has a thickness of from 10 to 20 feet. In general this softer clay differs from that above only in the larger amount of water contained in it. In places pockets of quicksand are present in the soft clay. The clay is sufficiently stiff to permit sinking wells by excavating the clay in sections about 4 feet deep, each section being sheeted with 2 X 6-inch or 3 X 6-inch planks in 4-foot lengths as soon as the section is excavated. In some cases the sheeting has been made of sheet metal. The wells vary from about 3 to 12 feet in diameter. Thus this method differs from the sheet-piling method essentially in that the excava- tion is made before the lining is placed, while in the sheet- piling method the lining is always placed in advance of the excavation. DIGGING THE WELL. The wells are excavated by hand to the required diameter, from one to four men working in a single well. As soon as a section is excavated tongue-and-grooved lagging, 2 or 3 inches thick and not over 6 inches wide and beveled to form a true circle, is placed. Two or perhaps three sr ART. 125 OPEN WELLS WITH SHEETING 371 iron hoops, f by 3 inches in section, or angle-iron hoops, are used to brace the sheeting of eacli section. These hoops are made in semi-circular form with their ends bent inward to form flanges which are bolted together as shown in Fig. 1 240. As soon as the bracing for one section is placed the next section is excavated and the lagging for that section, abutting against the lagging for the section above, is placed, and this cycle is repeated until the hard material is reached. Care must be exercised to have the lagging fit tightly against the clay in order to prevent any flow of the same. As this is somewhat difficult to accomplish with the above described type of hoops, another form has been invented by J. W. JACKSON. Each brace consists of four sections of steel tee bars bent to form a circular sectional rib bearing against the lagging, and of a hollow central hub to which are attached jack screws radiating from the hub like the spokes of a wheel. The heads of these jack screws are fitted to shoes on the horizontal web of the circular rib or rim. As many jacks as necessary may be used but not less than four, one for each section of the rib. The jacks may be set up to compress the surrounding material as much as desired. The spoil is removed from the wells by buckets operated by a windlass or other arrangement. For small jobs the windlass may be worked by hand but where a large number of piers are being sunk power is used. The Thomas Elevator Co. of Chicago build a multiple spool hoist which will operate a num- ber of wells by one motor, each one independently of all others (see Eng. News, vol. 65, page 133, Feb. 2, 1911). The lagging and bracing are sometimes removed as the con- crete is placed, but if the surrounding material is at all soft they are usually left in. A 1-3-5 mixture of concrete is com- monly used for the filling. Where the pier rests on hard-pan the lower part is ordinarily belled out to about twice the diameter of the pier, the belling being done at an angle of approximately 45 degrees. The unit bearing pressure allowed is about 7 tons per square foot for hard- pan and about 30 tons for rock. 37 2 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI APPLICATIONS. The first building in Chicago and the first in the United States, with the exception of the City Hall of Kansas City, to have this type of foundation was the Chicago Stock Exchange, built in 1892. This structure was founded on piles and on piers sunk by the Chicago method, the latter being used since it was feared that the jarring of pile driving would disturb the foundations of adjacent buildings. For the wells of the City Hall foundations in Kansas City a metal shell lining was used instead of wooden lagging and the piers were constructed of brick- work instead of concrete. The foundations for the new City Hall of Chicago were com- posed of circular concrete piers from 4 to 10 feet in diameter and seated on bedrock 96 to 120 feet below street grade. Three- inch tongue-and-grooved lagging in 4-foot lengths was used. The clay spoil was dug by hand, one to four men working in a well at one time. The buckets held 3 or 4 cubic feet and were raised and lowered by means of timber tripods set up over the wells. A drive wheel was placed on one side of each tripod and was connected to a shaft that carried a winding spool. A single endless cable on a hoisting engine connected with a number of the driving wheels the tripods being set up in straight rows and thus readily served seven or eight wells. In applying the Chicago method modifications may be made to suit local conditions; for instance, the sheet-piling and the sheeting method may be combined in the same well. This was done in the foundation work for the Hotel Brevoort, Chicago, where the presence of a high building nearby made necessary the use of steel sheet-piling for a depth of 30 feet, while below this the ordinary lagging was used. Fig. 125 a shows the details of the 65-foot wells used for the foundations of a double- track bascule bridge of the Baltimore & Ohio Railroad in South Chicago. The surface of the ground was at about water-level and for the upper 18 feet the material was quicksand, there being below this an impervious stratum of soft blue clay which extends to rock. A cofferdam made of 3Xi2-inch tongue-and-grooved sheet- piling in 2i-foot lengths was driven through the sand to the ART. 126 THE GROUTING PROCESS 373 stiff clay and braced with three tiers of 12 X 1 2-inch rangers, with 45-degree knee braces at the corners. The bracing was placed as the well was excavated. At the bottom a 1 2-foot diameter well was sunk and lined with lagging composed of courses of No. 20 corrugated iron in 2-foot widths and of lengths equal to the circumference of the well. Vertical 2 X 2-inch flange angles about 23 inches long were riveted to the rims of both ends of each section and through open holes in the outstanding legs were bolted together when placed in position to make complete rings. After placing the first section 12 inches of concrete was depos- ited between the same and the lower part of the cofferdam to seal the space between the cofferdam and well. As the material was excavated additional rings of lagging were placed, each one overlapping the one above it by a single corrugation. No bolt- ing of horizontal joints was done and no bracing was used. A 10- to i2-foot layer of quicksand with its surface 100 feet below the street curb was struck in sinking the wells of the Chi- cago Edison Go's, building. Below this there was a layer of boulders overlying the bedrock and these boulders varied from cobble-stone size to 5 feet in diameter. On reaching quicksand the usual method was abandoned and steel cylinders in three sections, with vertical joints flanged with angle-iron connections, were sunk. As the quicksand was removed from the interior these cylinders sank by their own weight until the boulders were reached. These had to be drilled and split open to permit the caissons, aided by jacks, to pass through. In the wells for the foundations of the Northwestern Railroad Terminal (see Eng. News, vol. 62, page 554, Nov. 18, 1909) the pneumatic caisson process was used when a heavy water- bearing stratum just above rock was struck. ART. 126. THE GROUTING PROCESS The general idea of the grouting process is to inject fluid cement between and among materials already in place and thus cement the mass into a solid concrete. The process may be used for 374 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI forming new foundations or for repairing old ones. For foun- dations on land two general methods may be used: The whole foundation bed, down to rock or other firm material, may be turned into concrete in situ and the piers built directly upon it; or a ring of concrete may be formed around the site, forming a sort of cofferdam, after which the interior may be excavated down to solid material and the substructure built within it. The latter method will give a more reliable foundation but a more expensive one. In using the former method it is a difficult matter to prevent pockets of uncemented material from being present. It seems that this process may be used satisfactorily for any material varying from the size of broken stone down to fine sand. Clayey material cannot be grouted. Two methods have been developed for the application of the grouting process; the first uses the cement in the form of a fluid, and the second in its dry state. The first may be subdivided into two methods, one being used where fine material is encount- ered and the other for coarse material. Where cement grout is used in fine material two pipes, a short distance apart, are first driven. Water is then pumped down one pipe and in taking a course of least resistance will come up the other pipe, thus cutting out a channel between the two pipes. By using a number of pipes as many channels as desired may be made. As soon as a well-developed* channel is formed cement grout is pumped through the pipe instead of the water. When the grout appears in the outlet pipe the latter is closed by a valve and the pumping continued, thus forcing the grout to permeate the sand around the channel. In this way a stratum of solid mortar or concrete is formed; by employing the same scheme at various depths the whole mass becomes solidified. Where medium-sized material is encountered it is often only necessary to drive a row of pipes and pour the grout into them, the head being sufficient to force the grout throughout the material. In coarse material the difficulty lies in keeping the grout within bounds and preventing it from spreading out in thin ART. 126 THE GROUTING PROCESS 375 layers and running into adjacent territory, or below the level at which it is desired to form the concrete. This difficulty may be overcome by using the principle of successive accretions. In using this method only a small amount of grout is poured into any one pipe at a time. After this has had time to set, more grout is poured in and the operation repeated until a solid floor of concrete is made. Walls may be made in the same manner, after which the interior may be filled with grout or excavated. The method which employs dry cement is as follows: The cement is blown through a if -inch pipe, drawn to a point at the lower end, in which there are three or more holes of about f inch diameter. The pipe is free to be raised or lowered, and is con- nected at its upper end with an air-pressure supply pipe. To this air-pressure pipe, suitable connections are made of suit- able branches, stop cocks, etc., and by means of an injector cement powder is fed into the air current. The cement powder, by means of an air current is forced through the small openings in the lower end of the pipe and is driven into the sand. In consequence of the boiling action caused by the air bubbles running through the water in the sand the cement is thoroughly mixed with the latter, and as soon as injecting is stopped the sand with the particles of cement clinging to it settles into place and forms concrete or mortar. The volume of cement used should be about one-fifth the volume of the sand. In fine material each sinking of the pipe will cover about i square foot of ground and the cement must be forced out at different elevations, the pipe being slowly drawn up as the cement is blown into the sand. The dry method is seldom used at present. For further details concerning this method the reader is referred to an article by FR. NEUKIRCH in Transactions Amer- ican Society of Civil Engineers, vol. 29, page 639, Sept., 1893, entitled Improved Method of Constructing Foundations under Water by Forcing Cement into Loose Sand or Gravel by Means of Air Pressure. 376 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI ART. 127. APPLICATIONS AND TESTS The exclusion of water from the site is one of the most expen- sive items connected with foundation work. The economy of the grouting process lies in the fact that the necessity for doing this may be avoided or else it may be done cheaply. Grouting has been used quite extensively for repairing dams, quay walls, etc., where the water has washed out the filling. In such cases it is customary to sink pipes and pour cement grout into them, the pressure head on the grout being sufficient to force it into place. It has been found that the pressure head of a column of grout is about double that of water. For an example of the use of the grouting process for the foundation of a cylinder caisson see Art. 102. The left abutment (on land) of a concrete arch bridge at Ehingen, Germany, was founded on a bed of concrete formed in place by the injection of grout. The material was water- bearing gravel. 1 " Twelve-foot lengths of ij-inch pipe, with an iron driving point loosely inserted in the lower end, were driven down to rock, and then, by raising a few inches, lifted clear of the driving point. Cement grout was then pumped in until a rapid rise in pressure indicated saturation; the pipe was then drawn up a small distance, grout pumped in again to saturation, and so on." Pipes were driven at intervals of 18 and 20 inches and test excavations made afterward showed a very good quality of concrete. 1 "To found the two river piers, cofferdams of sheet-piling were driven to rock and made water-tight by injection of cement through pipes driven around them. In the case of one of the piers, pipes were driven inside as well as outside, with the result that nearly the whole mass in the interior of the cofferdam was cemented into a block of concrete. On account of some layers of sand, however, about one-half of this mass was broken out again and the pier regularly built up of concrete above the re- maining conglomerate. At the other pier, the cementing was carried out only around the outside of the cofferdam, making 1 Engineering News, vol. 47, page 35, Jan. 9, 1902. ART. 127 APPLICATIONS AND TESTS 377 is perfectly tight. The interior was then excavated and the concrete of the pier built up directly on the rock." A good example of the successive accretion method of grout- ing is that of rebuilding one of the piers of a bridge on the New York Northern Railroad, across Croton Lake, N. Y. The pier was about 22 by 32 feet in plan and about 7 feet high. It resed on a crib 35 by 47 feet in plan, made of 4-inch planks laid cob fashion, and divided into nine compartments, filled with stone. The top of the crib was about 5 feet below water. The problem was to make a solid pier out of the one which, as originally built, was not filled with masonry but with rocks, sticks, dirt and all sorts of rubbish, there being merely a shell of masonry around the outside. As stated by the engineer, R. L. HARRIS: lt( We wanted a tight bottom at any level below the top of the crib and tight sides thence to the water surface. The idea was to use the materials that were in place, and make a caisson therein without disturbance, by cementing, for the floor of the caisson, a portion of the loose mass of irregular stone filling in the crib at any level below the top of the crib; and for walls, to cement from thence to the water surface, or as high as necessary to make a good connection with the shell; this could then be pumped out, the interior carefully excavated to the crib, and the space filled with concrete rammed in layers to the top of the old shell." Some of the interior masonry was removed from the top and then holes were worked among the stones extending a few feet below the top of the crib. " A long nozzle of if -inch iron pipe, connected to the discharge pipe of a No. 2 Douglas hand force pump, was inserted in one of these holes to its bottom, water was rapidly pumped through for a few minutes, then the suction hose was suddenly transferred to a reservoir of grout, composed of portland cement and fine sharp sand, in equal parts, mixed immediately before use ; a small quantity only of the grout was slowly forced through, and the nozzle was then withdrawn but the hole maintained, and the same operation was continued at *A cofferdam without Timber or Iron, by R. L. Harris, Trans. Am. Soc. C. E., vol. 24, page 234, March, 1891. 378 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI other holes, seldom returning to any hole the same day; the belief being, that in quiet water the cement would accrete on the surface of irregular stones at and below the level of the injection, and that by consecutive slight accretions at proper intervals of time the voids between them would be filled." The results were successful. TESTING THE GROUTING PROCESS. Although many exam- ples exist of the successful application of this method, yet there is always some uncertainty regarding the degree of success in any particular case. To test its reliability the Louisville & Nashville Railroad had some interesting experiments made, a complete description of which may be found in Engineering News, vol. 69, page 979, May 8, 1913. The most interesting experiment made was in gravel, where bedrock was 23 feet below the surface and the water-level 8 feet 24* Outside dfam. : 2' Inside diatn. **?* 7 Rows of 18 Holes ir-5 r^f ~^*fij 3 m ^^eT >l i -^ r* ? r< - \<-- - -. I.I - -2.0-- ,, i PerforaTions < 6 ->H in Point FIG. i27a. Well Point on End of Grouting Pipe. below. An analysis of the gravel gave the following percentage in its mechanical composition: Coarse gravel, 12, very fine gravel, 34, sand, 44, and silt, 10. Two-inch pipe in 5-foot sec- tions and with a well point, illustrated in Fig. 1270, were driven to rock on the circumference of a circle 15 feet in diameter and with a spacing of about 3 feet. An average unit pressure of 20 pounds was sufficient to force the grout into the gravel, although at times 60 pounds would not clear the pipe. The pipe was slowly withdrawn as the grout was forced in, the one operation follow- ing the other, enough grout being forced in to fill all voids for a distance of 2 feet out from the center of the pipe. On allowing the material to harden and then excavating the core, it was found that the wall was sufficiently good to allow the water to be pumped down within 2 feet of the rock. ART. 128 THE FREEZING PROCESS 379 Fig. 1276 shows the appearance of the concrete after removing the core. The grout followed the path of least resistance which was essentially upward. In coming up much of the silt in the gravel floated on the grout. In addition to the latter effect the grouting below tended to disturb the material at the top, causing the fine material there to separate from the coarse, thus leaving a very porous layer just above water-level, with a layer I5'(Diam.of Circle) Too of Concrete FIG. 1276, Typical Cross-section of Concrete Cylinder Formed by the Circle of Grouting Pipes. of silt at water-level. As a consequence, for 4 feet above the water surface the best concrete formed and this extended across the cylinder and had to be dug out with picks on excavating the core. On the other hand at the mud seam no concrete formed even at the pipe. Below the water-level the concrete was irregular and not especially good. ART. 128. THE FREEZING PROCESS The idea of freezing the soil, as an aid to excavation, has ex- isted for many years, and although it has attained a considerable degree of success in the sinking of mine shafts, particularly in 380 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI Germany and other foreign countries, it has seldom been applied to foundations. However, owing to the inherent possibilities of this process for foundations at great depths the principles are worthy of careful study. The presence of water causes the principal difficulties in foundation work, especially when water is present in very fine sand, forming what is known as quicksand. If the water can be frozen the work becomes easy. In the method invented in 1884 by F. H. POETSCH M. D., a Prussian, tubes are driven around the outside of, or into the soil, all over the site to be excavated, and a freezing mixture is made to circulate through these pipes, which gradually transforms the soil into a non- water-carrying solid mass, after which the excavation can easily be made. If the pipes are driven to a non-water-bearing stratum it is only necessary to freeze a wall around the site but if an impervious stratum is not reached the whole site, or a ring around the site and a layer of soil near the bottom must be frozen. Long water-tight tubes closed at the bottom, from 4 to 6 inches in diameter and spaced about 3 feet apart, are first driven through the mass to be frozen. Inside of these tubes are placed small pipes, from i to ij inches in diameter, which are open at the bottom or have openings in their sides near the bot- tom. A considerable number of the small circulating tubes are joined together by a larger pipe, and the larger or freezing tubes are capped and joined together by another pipe. A circuit is then formed and cold brine is drawn from a tank, pumped down the circulating tubes, up through the freezing tubes, and back to the freezing machine. For shaft sinking the pipes are usually placed around the circumference of a ring with perhaps a few inside which are so insulated that they freeze only the bottom of the shaft. What is said to be the first application of this process to building foundations is that for the substructure of a depart- ment store in Berlin. Fig. 1280 illustrates the conditions obtaining at the site as well as the general plan of the process. The subsoil was a quicksand with ground water-level about 13 feet below the curb. The foundations of adjoining buildings ART. 128 THE FREEZING PROCESS 381 were 10 feet below the curb, while the excavation for the new structure had to be carried to a depth of 36 feet below the curb. Sheet-piling was first used but as soon as the excavation reached below water-level the sand from under the adjoining buildings on one side of the lot commenced boiling up in the A ^ ooooooooooooo I '-The freezing pipes were placed about 6 sit from ihe sides of the adjoining building .--56'--. Y FIG. i28a. Building Foundation Constructed under the Freezing Process. excavation, causing several structures to settle and crack. The freezing process was then adopted. Freezing pipes 5 inches in diameter and about yV inch thick were sunk on 3 -foot cen- ters as shown in the illustration and extended 59 feet below curb level. The circulating pipes were i inch in diameter and were connected to a supply header at the top, while the 5-inch pipes 382 PIER FOUNDATIONS IN OPEN WELLS CHAP. XI were connected to a drain header. The liquor passed through the circulating pipes with a velocity of n^ feet per minute. About four weeks after the brine was started the ground was frozen a sufficient distance to begin excavating, after the com- pletion of which, the foundation was placed. The cost is said to have been lower than if the pneumatic caisson process had been employed. Only under special circumstances, or where no other process can be adopted, or where a refrigerating plant is located nearby, will the freezing process prove commercially practicable. It is an expensive, slow and uncertain process. ART. 129. HYDRAULIC CAISSONS This type of caisson has been used in a few cases for deep building foundations but it is ill-adapted to most soils. Where sand predominates and no boulders are present it may be used with success. The caisson consists of a riveted steel cylin- drical shell, say from 5 to 14 feet in diameter and as high as nec- essary. The lower edge is shod with a hollow cast-iron cutting edge of a triangular cross-section, which is perforated with many holes forming special nozzles. This cutting edge is composed of a number of sections, each section having an inside chamber independent of all other sections. By means of pipes and flex- ible tubing these chambers are connected with a force pump. The material is first excavated to ground-water level, after which the caisson is placed in this excavation; the caisson is then heavily weighted and water is forced into the cutting-edge chambers and thence out through the small nozzles to scour the material from under and around the cutting edge, thus causing the caisson to sink. When the stratum on which the caisson is to rest is reached the hydraulic pressure is discontinued and the spoil is excavated from the interior in the dry, after which the pier is built by filling with concrete. If the caisson is bedded in clay the excavating and pier-building are easily done in the dry, but if it rests on rock it is often a difficult matter to keep out the water. This feature and the risk of meeting boulders ART. 129 HYDRAULIC CAISSONS 383 in sinking makes this method of founding piers a very uncertain one. This type of caisson was used in placing the foundations of the Johnson and the Meyer- Jonassen Buildings, both located in New York City. Descriptions are given in Engineering Record, vol. 32, page 116; and vol. 33, page 315. It appears that the use of this method has been abandoned. CHAPTER XII ORDINARY BRIDGE PIERS ART. 130. GENERAL REQUIREMENTS In selecting the site of a bridge and arranging the piers, careful attention must be given to such matters as location of crossing, position and spacing of piers and abutments, height of bridge, required waterway, etc. Where the construction is in new country the location of the bridge can usually be made to suit the engineering requirements. These will be best satisfied where the width of the river is not great; however, it should not be located in the narrowest part for there the current is apt to be swift and the water deep at times of heavy rains, thus making the construction of the substructure both difficult and expensive. On the other hand, where the bridge is located in a built-up community it will have to be placed where it will best serve the needs of the people. If it is a highway structure it will connect main thoroughfares on the two sides of the river, while a railroad structure has to connect the rights-of-way. Building new streets or buying rights-of-way is very expensive in built-up vicinities and will usually be in excess of any pos- sible saving in the cost of the bridge by placing the latter in a more advantageous position from an engineering standpoint. In determining the number of piers and their spacing, due regard should be given to the financial considerations, the navi- gation interests, waterway requirements, and the Government rules and regulations. The financial requirements are best served by an arrangement which makes the total cost of the bridge, superstructure plus substructure, a minimum. As the cost of the superstructure varies approximately as the square of the length of a span and the cost of a pier with its foundation is approximately a constant 384 ART. 130 GENERAL REQUIREMENTS 385 for fairly wide ranges of span length, there is some length of span which, with its corresponding number of piers, will make the total cost of the bridge a minimum. For the deduction of such a formula see Art. 9 of MERRIMAN & JACOBY'S Roofs and Bridges, Part III. This formula shows that for minimum cost the cost of one river pier should equal the cost of the main and lateral trusses of one span. In deriving the for- mula it was assumed that the lengths of all spans are approximately equal. Navigation interests require that the piers shall be placed so as to cause as little danger and obstruction as possible to river traffic. Thus they should be kept out of the channel and should be spaced at considerable distances apart. The pier should rest on a stable, unyielding foundation, the base of which is well below the frost line and below the elevation of any possible scouring action. Where rock or other satis- factory bearing material lies at a depth not greater than from 20 to 30 feet below water level, the pier footing will usually be placed directly on the rock surface, a cofferdam being used if necessary. The material overlying the rock is first removed, after which the latter should be leveled or stepped off and cleared of all loose material before placing the footing for the pier. For depths varying from 20 to 40 feet or more a pile founda- tion will usually prove the cheapest. The correct principles of design for this type of foundation are discussed in preceding chapters. For depths greater than about 40 feet some type of caisson foundation is generally used. Shallow foundations, corresponding to the spread footings so much used for buildings, are seldom used for bridges. Up to about twnety years ago, a spread footing consisting of a timber grillage was a common type of foundation for bridges. The grillage consisted of a more or less open mass of timbers laid directly on the gravel bottom after dredging out a few feet, and extending to nearly low-water level. The grillage was built, with courses alternating in direction, to a height of a few feet on shore, after which it was launched, completed, towed to the site and sunk by filling the open spaces between the timbers 25 3 86 ORDINARY BRIDGE PIERS CHAP. XII '^i":i:r.T.vi::i"ii~T Cross -Section E- F ,r with stones, etc. The disadvantage of this type of foundation lies in the fact that it is practically impossible to land the grillage perfectly level owing to the great difficulty of preparing a level foundation bed. Another disadvantage lies in the danger from scour. Further details relating to this type of foundation may be found in an article by E. K. MORSE, in Proceedings Engineer's Society of Western Penn- sylvania, Feb., 1911, and in FOWLER'S Sub-aque- ous Foundations. Fig. 1300 illustrates an interesting type of shallow foundation which sup- ports the piers of the Kingshighway Viaduct, St. Louis, Mo. It con- sists of a reinforced-con- crete box open at the bottom and closed at the top. The top has a thickness of 4 feet, while the thickness of the sides and cross walls vary from i\ to 3 feet. It was originally intended to found the piers on concrete piles (shown in the diagram), but in testing some of the piles already driven the soil was found to be an incompressible but perfectly plastic clay, which would not take the arch thrust with a pile foundation. By using the concrete box the clay was confined to prevent flowing action, while the large area of the sides took care of the horizontal thrust. ART. 131. DEFINITIONS A bridge pier is a structure, usually composed of masonry, which is used to transmit the loads from the bridge superstruc- ture to the foundation. East 47-11'- - ->! EN&.NEWS FIG. i3oa. Reinforced-concrete Pier Footing, Viaduct, St. Louis, Mo. ART. 131 DEFINITIONS 387 Some of the common parts of a bridge pier are the following: BRIDGE SEAT. A block of stone or concrete resting on the top of a pier to support the pedestal or base plate. COPING. The top course of the pier, usually projecting beyond the other courses. BELTING COURSE. The course immediately below the coping course. FOOTING COURSES. Those courses at or near the bottom of the pier, which are wider than those in the main part of the pier. BODY. The main part of the pier. STARLING. That part of the pier below high water, the hori- zontal section of which lies outside of the largest rectangle that can be formed on the two sides of the pier. STARLING COPING. The offset course at about high water which forms the top course of the starling. BATTER. The slope of the sides and ends of the pier. The coping course serves to protect the pier from the weather. If made of stone masonry the stone is of the best quality and cut to make small joints; if of concrete a rich mixture is em- ployed. The top is usually made with a surface sloping from the middle downward to the sides and is often waterproofed with some waterproofing compound, especially when of con- crete. It is customary to give the coping course an offset of from 6 to 1 2 inches in order to prevent rain-water from dripping down the sides and ends of the pier, and also to improve the appearance of the pier. The chief function of the belting course is to strengthen the coping offset, but it also improves the appearance of the pier. In special cases two or three belting courses are used, while at other times none are employed. The function of the footing course is to distribute the load over a larger area than the base of the body of the pier. Unless reinforced the slope of the footing should not be over 30 degrees with the vertical; where reinforced the slope may be anything consistent with safe stresses in the steel and concrete as deter- mined when considering the projecting footing courses to act as a cantilever beam. As explained in Art. 132 the function of the starling is .to pass the water with the least possible disturbance, for then there will 388 ORDINARY BRIDGE PIERS CHAP. XII be the least pressure against the pier due to current, ice, and drift, less danger to navigation from eddies, and less danger from .under-scouring. ART. 132. FORM AND DIMENSIONS The two primary requirements of bridge piers are: First, to transmit the load from the superstructure to the foundation; and second, to disturb the natural movement of the water as little as possible. Naturally a minimum capitalized cost should also be sought. As the load from the superstructure is applied on the pier at two points, at a distance apart equal to the width of the trusses or girders center to center, the most economical way of satisfying the first requirement is the employment of two cylinders, one under each load, as described in Art. 138. On the other hand, the second requirement is best served with a form resembling a ship, modified to increase the stability of the pier against floating ice, debris, etc., and to make the con- struction cheaper. The shape generally used is that of a rec- tangle with triangles or segments of circles at both upstream and downstream ends, or at only the upstream end. The advan- tage of having starlings at both ends is that the foundation becomes symmetrical with the loads, thus avoiding an uneven distribution of pressure on the foundation bed; eddying on the downstream end of the pier is also reduced. Starlings are necessary only below high water. The triangular nose, usually made with a go-degree angle at the vertex, has the advantage over the curved nose in cheapness of construction, but experiments show that it offers more resist- ance to the passage of water. Experiments made by CRESY indicate the value of different shapes of piers in passing the water to be in the following order: First, elliptical horizontal sections; second, rectangular body with starlings formed by two circular arcs, tangent to the sides and described on the sides of an equilateral triangle; third, rectangular body with triangular starlings, the angle at the nose being 60 degrees; fourth, rec- tangular body with semicircular starlings; fifth, rectangular ART. 132 FORM AND DIMENSIONS 389 body with triangular starlings, the angle at the nose being 90 degrees; and sixth, rectangular body without starlings. Those forms which pass the current best lack strength and massiveness in their starlings. Where used in swift streams filled with ice in winter the starlings are heavily reinforced with old rails or structural shapes. For an example of such reinforcment the reader is referred to Art. 134. Where segments of circles are used the curves are tangent to the sides of the pier and have radii somewhat greater than half the thickness of the pier to give a pointed end. A value used on many piers and recommended by G. S. MORISON is three-quar- ters the width of the pier. Above high water the ends of the pier may be made square but a much better appearance is secured when a semicircular form is used. A combination of the straight and circular nose is sometimes adopted and is illus- trated in Art. 135. Where the pier extends a considerable dis- tance above high water it is customary to reduce the section somewhat above that elevation. More complete details of this are given in Art. 134. DIMENSIONS OF BRIDGE PIERS. The dimensions of ordi- nary bridge piers depend upon the load to be supported, class of superstructure, height of pier, type of foundation, and magni- tude of lateral forces to be resisted. The dimensions of the top of the pier depend on the distance between trusses or girders, plus a certain amount necessary to prevent the load from the pedestals approaching too closely the edges of the pier, under the coping. GREINER specifies 1 that the width shall not be less than 4 feet, nor less than that required for the bearings of the superstructure plus i foot, nor less than that required to give the required stability. The ques- tion of stability is discussed in Art. 136. He also specifies that the length under the coping shall not be less than the dis- tance out to out of superstructure bearings plus one and one- quarter times the width of the pier. For electric railway bridges C. C. SCHNEIDER, in an article in the Street Railway Journal, Sept. 15, 1906, specifies that the 1 General Specifications for Bridges, Part III, by J. E. GREINER. 390 ORDINARY BRIDGE PIERS CHAP. XII thickness of the pier under the coping should not be less than 4 feet. "The usual practice is to have the masonry on top (under coping) project 3 inches in the direction of the thickness FIG. 1320. Outline of Standard Concrete Pier. of the pier and at least 6 inches in the direction of the length of the pier beyond the edges of the base plate.'' For piers support- ing two spans of approximately the same length, Table No. 13 20, To obtain volume -Follow horizon/a/ line height to an intersecfion with curved line indicating w/dtn, /hen vertically up or down to intersect. tic-ally up or down to intersection with curved line indicating length, thence horizontally across toscale indicating vo/ume 1200 FIG. 1326. Diagram for Cubature of Concrete Piers. taken from the article just noted, gives the approximate mini- mum dimensions for electric railway bridge piers. Fig. 13 20 shows the standard form of pier for the Harriman ART. 132 FORM AND DIMENSIONS 391 Lines, while Tables Nos. 13 ib and c respectively give the lengths and widths under copings for various types of superstructures. Fig. 13 ib gives the volume of masonry in this type of pier for various heights, lengths and widths. The coping course usually has a thickness varying from i to 2\ feet, and an offset depending on the thickness. When concrete is used GREINER specifies that " copings shall not have a less depth than i foot nor less than one- sixth of the thickness of the stem measured under coping. They shall project over the faces of the stem to an extent equal to about one-third their depth. This projection shall be neatly moulded on the bottom and champ fered on the top and have all corners rounded." COOPER specifies that la the coping shall extend at least 3 inches all around, but not more than one-third of its thickness." This specification is for highway and electric railway bridges. The specifications for the Harriman Lines call for a 4-inch projection of coping for concrete piers and for ma- sonry piers 10 feet and under in height, and a 6-inch projection for masonry piers over 10 feet high. In the Thebes bridge piers, Fig. 134^, the thickness of the stone masonry coping is 27 inches and the projection 24 inches. The belting course not only improves the appearance of the pier but helps to secure a greater projection of the coping course. Its dimensions and form vary. As noted in a previous article a single or double belting may be employed or the same may be dispensed with altogether. When used it is usually made of about the same or somewhat less thickness as the coping course and its projection beyond the stem of the pier is closely equal to the projection of the coping course beyond the belting course. As to whether a double belting course is preferable to a single one in any given case will depend on*the desired total off-set of the coping course with reference to the stem of the pier. In the following articles a number of examples of piers are illustrated which show clearly their belting courses. 1 General Specifications for Foundations and Substructures of Highway and Electric Railway Bridges, by THEODORE COOPER. 392 ORDINARY BRIDGE PIERS CHAP. XII TABLE NO. 1320 APPROXIMATE MINIMUM DIMENSIONS or ELECTRIC RAILWAY BRIDGE PIERS Thickness of pier under coping Span Class A Class B Class C S. T. D. T. S. T | D. T. S. T. D. T. 25 4-0 4-0 4-0 4-0 4- 4-0 50 4-0 5-3 4-0 4-0 4- o 4-0 75 4-6 6-0 4-0 4-6 4- o 4-0 100 5-o 6-6 4-0 5-o 4- o 4-0 125 5-4 7-0 4-0 5-4 4- o 4-4 150 5-8 7-6 4-3 5-8 4- o 4-8 175 6-0 8-0 4-6 6-0 4- o 5-o 200 6-4 8-6 4-9 6-4 4- o 5-4 250 7-0 9-6 5-3 7-0 4- 6 6-0 300 7-8 10-6 5-9 7-8 4-10 6-6 350 8-4 1 1-4 6-2 8-4 5- 2 7-0 400 9-0 I2-O 6-6 9-0 5- 6 7-6 Length of pier under coping = distance center to center of trusses + figures below Class A Class B Class C S. T. | D. T. S. T. | D. T. S. T. D. T. So 3-6 4-0 3-6 3-6 3-6 3-6 IOO 4-0 5-o 3-6 4-0 3-6 3-6 ISO 4-6 5-6 4-0 4-6 3-6 4-0 200 5-o 6-0 4-0 5-o 3-6 4-6 250 5-o 6-6 4-6 5-o 4- o 4-6 300 5-6 7-0 4-6 5-6 4- o 5-o 350 6-0 7-6 4-6 6-0 4- 6 5-o 400 6-0 7-6 5-o 6-0 4- 6 5-6 Note: All values are expressed in feet and inches. S. T. = single track; D. T. = double track. Class A, heavy traffic; Class B, medium traffic; Class C, light traffic. TABLE NO. 13 2b LENGTH UNDER COPING OF CONCRETE BRIDGE PIERS HARRIMAN LINES' STANDARD, 1906 Deck plate girders Through riveted trusses Span... 20 30 40 50 60 70 80 90 IOO iooi IIOJ 125 140 j 150 Length . 8-4 9-2 9-0 9-2 10-0 II-O I I-O 1 2-2 12-2 20-0 1 20-0 20-0 20-820-8 Through pin trusses || Through plate girders Span . . . 150 1 60 1 80 2OO 30 40 50 60 I 70 80 90 IOO Length. 21-2 21-2 21-421-4 16-8 17-10 1 8-2 19-0 19-10 19-6 19-8 19-10 Note: Length of pier to correspond to length given in table for the longer span All dimensions are expressed in feet and inches. ART. 132 FORM AND DIMENSIONS 393 S 3 co PL, H . w | H PO H T 1O 8 I 5 o 1 1 ! 1 Through pin . I M 1 1 00 1 M M o j, i i M 1 I 1 to a -t 1 M I CO i co i CO I 1 4, Jo 00 CO T co 1 M 1 cs 1 1 1 CS 1 00 1 to V 00 8 01 O CO O to vg R 00 ON 8 8 10 10 to jjj 5 8 II " sassnj^ p9^9 -AU qSnoJijx S9SSIU} 394 ORDINARY BRIDGE PIERS CHAP. XII The sides of the body or stem of the pier are invariably given a batter of either i in 24 or i in 12. Above high water the ends are also given this batter. The former value is more com- monly used for high piers and the latter for low piers. Either gives a pier of good appearance and will usually furnish ade- quate stability and a base of sufficient size. The footing courses serve to transfer the load from the body of the pier to the foundation and for this reason they are given a larger horizontal section than the base of the body of the pier. GREINER specifies the following in regard to their dimen- sions: "The upper surface of the upper footing course shall not project more than i foot beyond any face of the stem. . . . The depth of any footing course shall not be less than 2 feet and the courses may be stepped off at an angle of about 30 degrees with the vertical or have a uniform batter of the same amount. When constructed on pile foundations the footings shall encase the piles to a depth of at least 6 inches, and the distance from the center of any pile to the outside face of the footing shall not be less than i| feet." ART. 133. MATERIALS AND CONSTRUCTION Previous to about 1880 it was the universal rule to build piers entirely of stone masonry, while at the present time most piers are built either entirely of concrete or of a concrete hearting and stone facing. Three conditions have brought about this change : First, the decrease in the cost of cement; second, the increase in the strength and the greater reliability of cement and con- crete; and third, the increased cost of cut stone, due to the labor factor. Among the earliest of the all-concrete piers in this country were those used for a bridge across the Medina River, i8| miles west of San Antonio, Texas, built in 1881. In Nova Scotia they were first used in 1883. In both of these instances concrete was used because of the absence of good stone in the vicinity and the high cost of transportation. In Europe the all-concrete ART. 133 MATERIALS AND CONSTRUCTION 395 pier was used somewhat earlier than the above dates. For some years after its introduction 'the development of the all-concrete pier was slow. In an address delivered in 1899, G. S. MORISON said: *" Prejudices have been raised against it (concrete) through inferior work done in this country when it was first introduced, but it is within the limits of possibilities that an artificial stone can be made in this way which will be as good and as durable as the natural stones which are commonly used; when this is accomplished the advantages of a truly monolithic construction will make concrete the best building material, and, except for the facings of monumental works, where nothing can take the place of the finest stone from nature's laboratory, it may be universally used." Considering the stone-masonry pier as exemplified in many large bridges built by G. S. MORISON, the facing courses are mostly limestone ashlar, with granite ashlar for the upstream nose stones for all courses between high and low water. The backing is composed of limestone rubble, in some cases with, and in other cases without, coursed joints. For the Belle- fontaine bridge, built in 1892, it was specified that the backing stones should have the same thickness as the face stones and that the spaces between the large stones of the backing should not occupy more than one-fifth of the volume of the pier inside the face stones, and that these spaces should be filled with good rubble masonry. The piers for the Merchants bridge across the Mississippi River at St. Louis, built in 1889, were among the early large piers to have concrete backing. Here the coping course, the three courses below this, and the starling coping course were all of stone masonry, the remainder of the backing being concrete. Fig. 1330 shows the details of the stone masonry for the starling coping for piers I and IV. For complete and up-to-date specifications for stone masonry the reader is referred to the Manual of the American Railway Engineering Association. The advantage of concrete over stone masonry lies in its Engineering Record, vol. 39, page 497, April 29, 1899. 396 ORDINARY BRIDGE PIERS CHAP. XII lesser cost. Although its compressive strength is somewhat less than that of first-class stone masonry, yet on account of its monolithic character, most engineers agree that it is the more suitable material, except possibly for the facing of the pier. Mixtures of 1-2^-5 or 1-3-6 proportions are usually adopted for the hearting, and a richer mixture for the coping course. There are some advantages, however, in using a facing of stone masonry, among these being the saving in the expense of t I Downstream End Section at A. Section atB. SectionatC. Section at D. FIG. i33a. Starling Coping Course for Pier IV, Merchant's Bridge, St. Louis. Isometric View of Stone 12. forms, the more rapid rate of construction possible, the more attractive appearance of the pier, and the elimination of sur- face cracks. These surface cracks, almost always present in plain concrete piers, are due to the expansion and contrac- tion, caused by temperature changes, of the outer layer of concrete. Where a stone-masonry facing and concrete backing are used for piers bearing very heavy loads the facing stones should be ART. 133 MATERIAL AND CONSTRUCTION 397 tied in with rods, as shown in Fig. 134^. Where the all- concrete pier is used it is advisable to place reinforcing rods near the surface. This reinforcement will prevent the occur- rence of, or at least decrease the size of, the cracks noted above, and will also add an element of safety by taking any tensile stresses in the concrete. Reinforcement in horizontal planes under the coping and above the bottom of the footing serves to carry the loads more uniformly into the pier and foundation. GREINER'S Specifications state : " All faces of the stems above the -footing courses, unless otherwise specified, shall have surface reinforcement for bonding the concrete composed of a network of round or deformed bars with meshes of about i foot vertical by 2 feet horizontal, the weight of metal being not less than 2\ pounds for railway and i| pounds for other bridges for each square foot of surface reinforced. This network shall be embedded in the concrete to a depth of 2 inches, the horizontal rods being on the outside of the vertical rods and wired thereto. The vertical rods shall extend into the footings to an extent necessary for proper bond. The faces of copings shall have continuous surface reinforcement, of the same weight per square foot of surface, as provided for stems. . . . "The lower footing course when on pile foundations shall have horizontal reinforcement for bonding the concrete composed of a layer of rods forming a network placed about 6 inches above the bed or placed around and between the embedded part of the piles, the weight of metal per square foot of network being not less than 3 pounds for railway and 2 pounds for other bridges. The stem shall have similar layers of horizontal reinforcement of the same weight per square foot as provided for surface reinforcement, embedded i foot below the coping, i foot above the footing course and at intermediate points at intervals not exceeding 20 feet. A similar network shall be embedded in the coping about 2 inches below its upper surface. The meshes in the horizontal layers of network shall be preferably square." ORDINARY BRIDGE PIERS CHAP. XII ART. 134. EXAMPLES OF SOLID PIERS Fig. 1340 illustrates a simple form of the solid all-concrete pier used by the Western Maryland Railroad. The dimensions are given in the diagram. lu The upstream end of the pier is -.^ Boise of Rail. Cross- Section. Side Elevation. FIG. 1340. Concrete Bridge Pier, Fourth Crossing of Potomac River, Western Maryland Railroad. built with its sides at a 45 -degree angle with its transverse axis to form a cutwater end, the nose of which extends 3 feet 3 inches beyond the corner of the pier at the lower edge of the cop- ing. This nose was molded to a circle by inserting within the forms a strip of No. 16 iron, 9 inches wide, bent to a 6-inch 1 Engineering Record, vol. 51, page 304, March n, 1905. ART. 134 EXAMPLES OF SOLID PIERS 399 radius. It is held in place by i-inch bolts, 9 inches long, ex- tending into the concrete. They have a welded head on the end outside the plate, and a head and a 2-inch washer on. the end in the concrete." A good example of the all-concrete pier with reinforcement near the outer surface is shown in Fig. 1346, which illustrates one of the piers for the Gilbertsville bridge. The bottom of the footing and top of the coping are also reinforced. El. 109. 3' -IQ'O l ; 3 : 6 Concrete. End Elevation Cross- Section S Boise Cbrsting Half Ran. Half Pile P/an. FIG. 1346. General Dimensions of Piers of Illinois Central Railroad Bridge over Tennessee River, Gilbertsville, Ky. Fig. i34<; shows the sectional elevation and plans of various courses of the part above high water of Pier 3 of the Beaver bridge of the Pittsburgh & Lake Erie Railroad. The facing is of ashlar sandstone with 1-3-5 concrete backing. As shown in the illustrations the facing was securely tied to the backing by ij-inch rods running both lengthwise and crosswise. Extra rods were used to reinforce the hearting. Contrary to the usual practice in large stone-faced piers a stone coping course was not 400 ORDINARY BRIDGE PIERS CHAP. XII used, a ring around the outside being of stone and the rest concrete. The shoe grillage of I-beams which takes the load from the superstructure and distributes it over an area of 240 square feet on the pier rests on and is supported by a 1-2-4 mixture of concrete (the darker portion in the illustration). To waterproof the top of the pier a granolithic roof about 3 FIG. 134^. Cross-section and Plans of Pier 3, Pittsburgh & Lake Erie Railway Bridge over Ohio River, Beaver, Pa. inches thick was placed over the entire top. The total load from the superstructure is 12 ooo tons and the pressure on the masonry under the grillage is about 25 tons per square foot. Fig. 1346? shows a common type where the pier is offset all around at the high-water line and has a starling coping course projecting on both sides and ends. Pier 2 of the Thebes bridge of the Illinois Central Railroad is a type of pier used in many large structures across the Miss- f FIG. 1340. Pier 2 of Cantilever Bridge over the Mississippi River at Thebes, 111. Designed by Noble and Modjeski. April i, 1905. FIG. i34/. Pier 3 of McKinley Bridge over the Mississippi River at St. Louis, Mo., Showing Starling with Conical Top. May 16, 1909. (Facing Fig. 134*.) FIG. 134*'. A Pier of the Victoria, or Grand Trunk Railroad Bridge over the St. Lawrence River at Montreal, Ont. Built in 1858. The nose of the ice-breaker has an inclination of about 43 degrees, and is protected by iron plates. See Engineering Record, vol. 38, page 444 and 466, Oct. 22 and 29, 1898. ART. 134 EXAMPLES OF SOLID PIERS 401 issippi and Missouri Rivers. As shown in Fig. 1340, it is a very simple form of pier and in its simplicity lies its beauty. The sides are parallel and the ends are formed by two circular arcs meeting. Above high water the ends are semicircular. The coping projects 2 feet beyond the pier and the projection is M/Hflqr I 'J 49' .-- t"* 1 This Surface fine \ Pointed on both \ Ends of Pier-.. I n a* - 1 62 '/Ok" End Elevation, Side Elevation on Up nd *i Caisson Plan. FIG. i34g. General Dimensions of Pier 3 of the McKinley Bridge. divided between the coping and the belting course below. The starling coping covers the starling only. The pier has a batter of i in 24. Another bridge having piers of about the same form as that just described is the McKinley bridge at St. Louis. The most 26 402 ORDINARY BRIDGE PIERS CHAP. XII notable difference between the piers of the McKinley and Thebes bridges is in the treatment of the top of the starling. As shown in Fig. i34/ and g, the starling coping in the former bridge is dispensed with and the top of the starling finished with a conical surface. For the McKinley bridge piers the facing is of limestone, with the exception of the bridge seats and the upstream nose stones above the river bed, which are of granite. The hearting is of concrete with the exception of the three courses below the coping, which are backed with limestone masonry. lu The Side Elevation^j R- / s i s fe'-.-yl End Elevation Section Plan FIG. i34/z. Pier with Ice-breaking Cutwater. Flag Point Bridge of Copper River & Northwestern Railway, Alaska. curved surfaces of the upstream starlings are close pointed to J-inch projection. The exposed surfaces of the main copings and the projecting bottom beds of the belting courses are planed. A 4-inch draft line is cut along the lower edges of the belting courses and on each side of the vertical angles of the down- stream starlings. All other stones are quarry faced, with pro- jections not exceeding 3 inches." The piers of the McKinley bridge were designed by RALPH 1 Engineering News, vol. 63, page 9, Jan. 6, 1910. ART. 135 EXAMPLES OF HOLLOW PIERS 403 MODJESKI, and those of the Thebes bridge by ALFRED NOBLE and RALPH MODJESKI. The piers for both of these bridges resemble closely the standard type designed by GEORGE S. MORISON. Fi^. 134/5 illustrates the pier of a bridge across Copper River, Alaska, built to withstand very heavy ice pressure. The cut water has a heavy slope to lift as well as to cut and divert the ice, and is heavily reinforced with old track rails. The sides are also reinforced with rails. Fig. 1347 illustrates the steel plate protection for the nose of a pier of the Spokane bridge of the Inland Empire System. '^Strap Anchors, 18 "lonq; 2 "wide ( Nut End of at I Bo Irs 1vbe inside.) FIG. 134;. Section of Steel Nose of Pier. The steel plates were \ inch thick and 5 feet 8| inches wide on each side of the vertex and extended from the river bottom to above high water. They were anchored to the pier byj-inch Z-shaped straps 18 inches long and spaced 18 inches apart, staggered on the nose. At the vertex the plates were reinforced with a 4X4X|-inch angle. ART. 135.' EXAMPLES OF HOLLOW PIERS In the solid bridge pier a considerable part of the hearting near the top of the pier and between the pedestal bearings takes but little load. In other words, the pier acts more or less like a double- cylinder pier, the part directly under the bearings acting somewhat as independent legs to carry the load, the remainder 404 ORDINARY BRIDGE PIERS CHAP. XII acting chiefly as a bracing system. For this reason a consider- able amount of concrete may be saved with but small loss of strength by making the pier more or less hollow. However, when this is done the remaining concrete should be well rein- FIG i35#- Channel Piers of the Municipal Bridge over the Mississippi River, St. Louis, Mo. forced. It is not advisable in all cases to dispense with any of the filling, for massiveness or weight tends to reduce vibration. The hollow pier is a compromise between the solid and the cylinder pier; it is less expensive than the former but has FIG. 1456. Northern Pacific Railway Bridge over Heart River at the Fourth Crossing, 4 miles west of Mandan, North Dakota, Showing Abutments and Paved Protection of Embankments. Completed in 1905. tf I d ART. 135 EXAMPLES OF HOLLOW PIERS 405 somewhat less stability and rigidity; it is more expensive than the latter but is far more stable and makes a more attractive substructure. The river piers of the Municipal bridge across the Mississippi River at ' St. Louis, Mo., illustrate the hollow type of pier. As shown in Figs. 13 50 and b, the part above high water consists of a tall bat- tered shaft with a large hol- low interior space, virtually forming two independent shafts braced together with a well reinforced arch at the top and walls of masonry on the sides, the latter also ser- ving to give it the appear- ance of a solid pier. There is a hollow space of less size below high water. This pier is also of interest on account of the shape of cutwater which, as shown in the plan view, Fig. 13 50, is a combi- nation of the straight and curved types for the upstream end and semicircular for the downstream end. The con- tract price for these piers was $9.50 per cubic yard from the top of the crib to the coping, and $1.90 per cubic foot for coping and bridge seats. A hollow pier resting on a pile foundation and supporting reinforced-concrete slabs is illustrated in Fig. 13 5^. The con- crete for the footings was a 1-2-4 mixture while that for the pier 406 ORDINARY BRIDGE PIERS CHAP. XII shaft was a 1-25-5 mixture. In all, 186 piers of this type were used on two bridges of the Pennsylvania Railroad. The piers of the Sparkman Street bridge, Nashville, Tenn., are shown in Fig. 135 d. l "They consist of two concrete towers extending from bridge seat to footing course, and battered on all sides J inch to i foot, being braced together by a reinforced- holes for Dowels *' I^^^W^il _ A n o n n n n r " ! n n ": r ! ri n n n si n FIG. 135^. Piers for Bush and Gunpowder River Bridges concrete arch and corbeled coping course at the top, and by reinforced side curtain walls from the footing course up to the high-water line. The curtain walls are 2 feet thick at the top, carried down plumb on the inside, and battering with the towers on the outside. The walls are reinforced with a heavy meshed fabric placed near both inside and outside faces, this fabric extending also entirely around the towers up to the top of the curtain walls." 1 Engineering News, vol. 26, page 576, Nov. 25, 1909. ART. 135 EXAMPLES OF HOLLOW PIERS 407 Probably the boldest example of the hollow bridge pier is that for a bridge across the Willamette River near Portland, Ore., which is illustrated in Fig. 13 50. The bottom 10 feet of the pier is of solid concrete, while above this it consists of a reinforced- *H *>r r r< - 1 - -40CfoC. " >~-----*-~:"*----------** HUH r^ I'Diam. ! ; ^" ; 1 i j^i, < 5J'2'~- -> Y\2'*.4' Opening !< 72^ J Elevation . eft* I c Y- / *g % j t ! "*k\4 ..; s 1 i) ^1 i *A 7 -r-i ' *// i 4rrTT Detail of Coping and Belt, Enlarged. - 20 Section A-B 72' LHfc MEW&. Plan. FIG 135 d. Typical Channel Pier, Sparkman Street Bridge; Nashville, Tenn. Arched above and hollow below starling coping course. concrete shell and reinforced-concrete columns, the latter carry- ing directly the loads from the superstructure. The hollow >art is braced by horizontal reinforced-concrete diaphragms. 408 ORDINARY BRIDGE PIERS c/ffe Seerf CHAP. XII Longitudinal and Transverse sections. 2" Bars c foe top art of Jbotfotn Plan of Diaphragm No. i. FIG. 1350. ^Upper Part of Tall Reinforced-concrete Pier, Oregon- Washington Railroad & Navigation Co. Bridge over Willamette River, Portland, Oregon. ART. 136 STABILITY OF PIERS 409 From the bottom to the top the sides are battered i inch to the foot. The side walls are 18 inches thick and *"are ^reinforced as vertical slabs spanning horizontally between the columns and vertically between the horizontal diaphragms. . . . "Between the outside walls of the hollow superstructure are seven reinforced-concrete horizontal diaphragms each 2 feet thick, which are designed as flat plates that may be loaded from above or below. ... At the center of each diaphragm is a 3-foot circular hole which permits the free passage of water between the eight stories. ... In one side of the lowest story is an opening 12 inches wide and the full height of that story so water may rise and fall inside the pier with variations in the stage of the river. The reinforced-concrete walls, . . . therefore, are not normally subject to a head of water, but the design provides for any emergency that may occur by including in them reinforcement placed so that a head may be brought against the walls and diaphragms from any direction." ART. 136. STABILITY OF PIERS LOADS. The vertical forces to be sustained on any horizontal plane of a bridge pier are the live load, impact load, weight of superstructure, and weight of pier above the plane in question. Impact loads are usually ignored, but more generally on high- way than on railroad bridge piers. For the latter some con- sideration should be given to impact forces for low piers and for the upper part of high piers. The lateral forces to be resisted by a railroad pier are tractive forces, wind on train, wind on trusses, wind on pier, river cur- rent, and ice pressure. It is customary to specify a tractive force equal to 0.2 of the live load; where the bridge is a double- track structure some authorities specify a full live load on both tracks and others on one track, the latter being more gen- eral. For highway bridge piers tractive forces may usually be neglected. 1 Engineering Record, vol. 62, page 160, Aug. 6, 1910. 410 ORDINARY BRIDGE PIERS CHAP. XII The wind load on train and trusses should be the same as those used in designing the superstructure, which is customarily taken at 30 pounds per square foot of exposed vertical surface of both trusses and train, or 150 pounds per linear foot of bridge for each lateral system, applied at the panel points, and 300 pounds per linear foot of train applied at a point 7 feet above the base of rail. Wind on the end of the pier may be taken at 30 pounds per square foot where the ends are without starlings and 20 pounds per square foot of vertical projection where starlings are present. The law governing the pressure on bridge piers due to a river current is not definitely known. The formula P=(Kwv 2 )/2g is frequently used, in which P is the pressure in pounds per square foot of vertical projection, K a constant, v the velocity of current in feet per second, w the weight of a cubic foot of water, and g the acceleration due to gravity (approximately 32.2 feet per second per second). GREINER in his General Specifications for Bridges, Part III, Substructures and Concrete Bridges, gives a value for (Kw)/2g of 1.5 for flat surfaces and one-half of this for rounded surfaces, with a minimum of 150 pounds per square foot for flat surfaces subjected to freshets and 50 pounds in tidal streams, with one-half of these values for rounded ends. Experiments show that the velocity varies with the depth approximately as the ordinates of an ellipse, the maximum being somewhat below the surface. The center of pressure is com- monly assumed at one-third the distance from the water surface to the river bed. This assumption is on the safe side. Ice exerts its greatest pressure when in the form of a field of moving ice forcing its way past the pier. In this condition the ice is more or less soft. In the specifications noted above a value of 50 ooo pounds per foot of pier width for a zo-inch thick- ness of ice (417 pounds per square inch) is given for flat surfaces, and one-half of this value for rounded surfaces. Other thick- nesses will have proportionate values. For the North Side Point Bridge, Pittsburgh, Pa., the river piers, which had rounded ends, were designed to resist a horizontal ice pressure of 48 ooo ART. 137 EXAMPLE OF PIER DESIGN 411 pounds per linear foot of width. A value used in the design of a number of large dams in this country is 47 ooo pounds per linear foot of width. METHODS OF FAILURE OF BRIDGE PIERS. To be stable a pier must be safe against sliding on any horizontal section, crushing at the toe of any horizontal section, and free from tension at the heel of any horizontal section; this also applies to the base of the pier. For a rectangular or nearly rectangular sec- tion the last condition will obtain if the resultant of all the forces above the plane in question cuts the section within the middle third. The forces resisting sliding are friction of masonry on masonry for stone masonry piers, the shearing strength of the concrete for concrete piers, and a combination of both for combination piers. For a table giving friction values for various kinds of stone masonry and for the shearing strength of concrete see American Civil Engineers' Pocket Book, page 577. If the pier dimensions at the top accord with standard practice as outlined in Art. 132, and if the pier has the conventional batter of i in 12 or i in 24, all sections will be amply safe against sliding. DOUGLAS 1 recommends the following allowable compressive unit-stresses in pounds per square inch: Stone masonry with 1-2 portland cement mortar and joints not over \ inch thick, granite, 700; hard limestone, 650; medium limestone and mar- ble, 600; soft limestone and sandstone, 500; where joints are over \ inch thick, 450 pounds for all kinds of sound building stones; for 1-2-4 concrete, 450; 1-3-6 concrete, 350; and 1-4-8 concrete, 250. ART. 137. EXAMPLE OF PIER DESIGN The following example which analyzes the pressures on the foundation of Pier 5 (Fig. 1370) of the Tennessee River bridge of the Illinois Central Railroad, is taken for the most part from an article by W. M. TORRANCE in Engineering News, vol. 53, page 548, May 25, 1905. Wind on pier, current and ice were ' See American Civil Engineers' Pocket Book, page 576. 412 ORDINARY BRIDGE PIERS CHAP. XII nol considered in the original article. The bed of the river is slightly exposed at low water. 11 Yardage of concrete: Upper 2 ft. of coping, 1-2-4 concrete; area in plan, 609 sq. ft.; volume 45 cu. yds. Lower 2 ft. of coping, 1-25-6 concrete; area in plan, 556 sq. ft. ; volume 41 cu. yds. Shaft of pier, 1-2^-6 concrete; top area, 490.5 sq. ft.; bottom area, 786.6 sq. ft.; medium area, 631.1 sq. ft.; volume by prismoidal formula (for height 56.86 ft.) .... i 335 cu. yds. Footing course, 1-3-6 concrete; top area, 926.5 sq. ft.; bottom area, i 801.8 sq. ft.; medium area, i 321.9 sq. ft. ; volume by prismoidal formula (for height of 6 ft) ... 298 cu. yds. Foundation course, 1-3-6 concrete; volume, 4Xy2Xf f . 352 cu. yds. Summary: 1-2-4 concrete in coping 45 cu. yds. 1-2^-6 concrete in coping and shaft. . . i 376 cu. yds. 1-3-6 concrete in footing and founda- tion ' 650 cu. yds. Total 2 071 cu. yds. Weightof pier, at 155 Ibs. per cu. ft., 2 071X27X155. ... 8667000 Ibs. Dead load, three trusses with ballast floor, 9 126X300. . . 2 738 ooo Ibs. Live load from 300 ft. of double-track train loads, 5000 X 2X300 3000000 Ibs. Total gravity load on foundation 14 405 ooo Ibs. "The tractive force on the bridge is taken at two-tenths of the live load, as already stated; for each pier in question, that is Tractive force = 3 000000X0.2 = 600 ooo Ibs. "Considering that this force acts in line of the lower chord pins (the trusses and floor system take care of it down to that level), 1 there results Maximum tractive moment about foundation bed, in direction of tracks is 600000X72.35 = 43410000 ft. -Ibs. It will be noticed that the tractive force is calculated on the full double- track load, which provides for its being called into play from both tracks in the same direction simultaneously." To get the moments transverse to the bridge, there is a wind load on the upper lateral system of 300X150 = 45000 Ibs., wind load on the" lower system of the same amount, and wind 1 An assumption on the safe side and involving an error less than 2 percent in this case. ART. 137 EXAMPLE OF PIER DESIGN 413 load on train of 300X300=90000 Ibs. acting at a point 7 feet above the base of rail. Multiplying each of these forces by their respective distances from the base of footing the overturning moment for wind on trusses is 8 100 ooo ft. -Ibs., and for wind on ^ Base of Ran. EI.IIO.O for Ballaitrct Floor \ BasToTRairtliO^O^ with Timber Ties High Water El. 95.0 Low Water. El. 46.0 J v> I El.31.0 \ I Side Eieva-t-ion . looooooooo oTooooooooooo ooooooooooo o ooboooooooo oooooooooooo )OOOOOOOOOOO oooooooooooo ,|"- .'"h OOOOOOOOOOO \Base Castinji'tO ooooooooooo OOOOOOOG- e-o 33 'c?*~ -------- *1 End Elevation. FIG. 1370. River Pier 5, Illinois Central Railroad Bridge over Tennessee River, Gilbertsville, Ky. NOTE. Top of coping to base of rail is 7 feet 5.375 inches instead of 10 feet. Ele- vation of base of rail is 109.31 instead of 109.0 feet. Half Top Plan. | Half Pile Plan ain is 7 740 ooo ft. -Ibs., making a total of 15 840 ooo ft.-lbs. for ind on superstructure. The projection, on a vertical plane transverse to the pier, )f the part subject to wind is 675 square feet. The moment 414 ORDINARY BRIDGE PIERS CHAP. XII about the foundation bed due to wind on pier =20X675X3 1.5 is 425 200 ft.-lbs. The moment about the foundation bed due to river current, assuming a maximum velocity of 10 feet per second, is 0.75 X io 2 X6o2X22.5 = i 01 6 ooo ft.-lbs. The moment about the foundation bed due to the pressure of a lo-inch thickness of ice at 50 ooo Ibs. per foot of width of pier is 25000X10.35X53.6 = 13 869000 ft.-lbs. The following computations of unit loads at base are made: First, by considering the earth to take all the load; and second, considering the piles to take all the load: Direct load on base due to, Weight of Superstructure Per sq. ft .............. 2 738 0007(72X33)= 1 152 Ibs. = 0.58 tons. Per pile ............... 2 738 000/306 = 8 950 Ibs. = 4.47 tons. Weight of Substructure Per sq. ft .............. 8 667 0007(72X33)= 3 650 Ibs. = 1.82 tons. Per pile ............... 8 667 000/306 = 28 330 Ibs. = 14.17 tons. Live Load Per sq. ft. ............ 3 ooo 0007(72X33)= i 264 Ibs. = 0.63 tons. Per pile ............... 3 ooo 000/306 = 9 800 Ibs. = 4.90 tons. Reduction of pressure due to uplift at high water: Per sq. ft .............. 3 260 000/^2X33) = i 372 Ibs. = 0.69 tons. Per pile ............... 3 260 000/306 = 10 660 Ibs. = 5.33 tons. Reduction of pressure due to uplift at low water: Per sq. ft .............. i 340 000/^2X33) = 564 Ibs. = 0.29 tons. Per pile ............... i 340 000/306 = 4 380 Ibs. = 2.19 tons. The moment of inertia of the base in bi-quadratic feet about an axis through the center of gravity and parallel with the long axis of the pier is The maximum and minimum pressures on the base due to tractive forces are (43410000X16.5)7215 600= 3 320 Ibs. per sq. ft. = =*= 1.66 tons per sq. ft. The moment of inertia of the pile tops about an axis through the center of gravity and parallel with the long axis of the pier, and in units of the area of one pile top times quadratic feet (neglecting moment of inertia about the gravity axis of the in- ART. 137 EXAMPLE OF PIER DESIGN 415 dividual pile tops) is 2[24( = 26860. The maximum and minimum loads per pile due to tractive force are (43410000X15)726860= 24 250 Ibs. = ="=12.12 tons. The moment of inertia of the base in bi-quadratic feet about an axis through the center^ of gravity and parallel with the short axis of the pier is (33X72 3 )/i2 = i 026000. The maximum and minimum pressures per square foot on the base due to the following: For wind on trusses, (8 100000X36)71 02600= ='=0284284 Ibs. = =*=o. 14 tons. For wind on train, (7 740 000X36)71 026 000= =*= 272 Ibs. = == 0.14 tons. For wind on pier, (425 200X36)71 026000= === 14.9 Ibs. =0.007 tons. For river current and ice, (14 880 000X36)71 026 000= 522 Ibs. = ="=0.26 tons. The moment of inertia of the pile tops about an axis through the center of gravity and parallel with the short axis of the pier, and in units of the area of one pile top times quadratic feet (neglecting moment of inertia about the gravity axis of the indi- vidual pile tops) is 2[ 7 (^ 2 +4^ 2 +. .34^5 2 H6( 3 2 +6 2 +. . . The maximum and minimum loads per pile are as follows: For wind on trusses, . (8 100000X34.5)7127 100= 2 200 Ibs. == fc i.io tons. For wind on train, (7 740000X34.5)7127 100= ="= 2 100 Ibs. ==*=i. 05 tons. For wind on pier, (425 200X34.5)7127 100= 115 Ibs. = ='=0.057 tons, and For river current and ice, (14880000X34.5)7127 100= 4040^3 = = 1 =2.o2 tons. It will be seen that the maximum pressure, assuming no up- lift, is 5.23 tons per square foot or 39.83 tons per pile, while with uplift the values are respectively 4.69 and 35.68. The minimum values show that compression always exists, although at some points it is very slight. 416 ORDINARY BRIDGE PIERS CHAP. XII Summary of unit-loading on foundation: Tons per sq. ft. Tons per pile Weight of superstructure o. 58 4-47 Weight of pier 1.82 14 . 17 Live load o . 63 4 . 90 Uplift at high water 0.69 5.33 Uplift at low water o. 29 2 . 19 Tractive force 1.66 12.12 Wind on trusses : 0.14 i . 10 Wind on train o. 14 i .05 Wind on pier o . 01 p . 06 River current and ice o . 26 2 . 02 f Max.. . ^.23 39.83 Assuming no uplift \ . _. ^ 6 I Mm 0.83 7.25 . , ,.,, [Max 4.69 35-68 Assuming full uplift { A ... \ Mm 0.14 1.92 Regarding the effect of uplift, in a case like this, where water is more or less free to get under the pier there is no question of its action. On the other hand it cannot act with full hydro- static pressure on account of the presence of gravel and of the pile tops bearing against the pier. A few words of explanation regarding the method of getting the maximum and minimum values in the above table may be advisable. In this pier, where the top is but a slight distance above high water, wind on pier cannot act simultaneously with ice and current, or at least, that which acts may be neglected. In computing the minimum pressure the live load is included as the negative values due to tractive force and wind on train overbalanced the positive value due to direct pressure. In finding the maximum pressure by considering uplift, the condi- tions obtaining at low water were used, since these give a greater value than for high water. In getting the minimum values with uplift, high water was used. In studying the horizontal section of the pier the same method is to be followed as in obtaining the pressure on the base, ex- cept that uplift will be omitted. CHAPTER XIII CYLINDER AND PIVOT PIERS ART. 138. GENERAL ARRANGEMENT For light bridges the massive piers and foundations described in the preceding articles may furnish strength and stability far in excess of the requirements. This is due largely to the fact that the dimensions of the pier are governed not alone by the magnitude of the loads and the required bearing area on the foundations, but also by the distance between superstructure pedestals or base plates, size of pedestals, and necessary edge distances. For this reason in many cases it may prove econom- FIG. 1386. Oxford Mill Pond Bridge, Chicago & Northwestern Railway. ical to use cylinder piers. This type of pier consists of a number of long slender cylinders composed in most cases of steel shells filled with concrete. When used to support fixed spans the pier consists of two or more cylinders in a line perpendicular, or nearly so, to the direction of the bridge, as illustrated in Fig. 1380; when used to support a trestle four cylinders are used, as illustrated in Fig. 1386; while for a pivot pier one cylinder at the center and a number of others on the circumference of a circle are frequently used. Pivot piers are also formed of one large cylinder; this type is described in Art. 142. 27 417 41 8 CYLINDER AND PIVOT PIERS CHAP. XIII The cylinders may be composed of concrete, brick, or stone masonry. They usually have a metal shell of cast iron, wrought iron, or steel. Wrought iron is not used at the present time. Cylinders piers may be founded on bedrock or hard-pan, on piles, open cylinder caissons, or pneumatic cylinder caissons. When founded on caissons the pier is simply a continuation of the caisson, and as such is described in Arts. 85, 101 and 102. The following articles deal chiefly with the cylinder pier founded on bedrock or on piles, taking up only those features of the other two types which have not already been described. ART. 139. METAL SHELL CYLINDER PIERS ON PILES. Where the cylinders are of small diameter, piles are driven and the cylinder shells set over the same and filled with concrete. With the larger cylinders the shells are often placed before driving the piles. If the top stratum is composed of silt or other soft material this should be excavated to a fairly solid material in order that the piles may have lateral support; care should also be taken to have the excavation carried below low- water level as well as to a depth free from any danger of scour. After excavating, the piles are driven and their tops cut off at some elevation above the surface of the ground. The cyl- inder shells rest on the river bottom or are sunk a few feet into the same. If clay is penetrated it is sometimes possible to pump out the water and place the concrete filling in the dry; otherwise a few feet of concrete are placed in the bottom, and allowed to harden a few days; after which the cylinder is pumped out and the remainder of the filling placed in the dry. The concrete placed through the water should have about 20 percent more cement in it than that placed in the dry to allow for the washing- out action of the water. The cylinder pier with pile foundations was first used in 1868 for the substructure of a bridge in Rhode Island as stated in BAKER'S Masonry Construction. The Tensas River bridge in Alabama, built in 1870, was one of the early large structures using this type of foundation. ART. 139 METAL SHELL CYLINDER PIERS 419 The shells, of cast iron i^ inches thick, had exterior diameters of 4 and 6 feet, and were in sections 10 feet long, the sections being united by bolts through interior flanges 2 inches thick and riTTTi MM/ FIG. 1390. Cylinder Piers of Victoria Bridge over Bear River, Nova Scotia. 3 inches wide. For the fixed spans of the bridge each pier was composed of two 6-foot diameter cylinders 16 feet apart, while the pivot pier had a central cylinder 6 feet in diameter and six 42O CYLINDER AND PIVOT PIERS CHAP. XIII 4-foot cylinders arranged hexagonally on the circumference of a circle 25 feet in diameter. Squared piles arranged closely together, with 12 in each of the 6-foot cylinders and 5 in the 4-foot ones, were driven to a depth of not less than 20 feet into the sandy bed of the river. Their tops were then tied together with bolts and sawed off at low- water level, 15 feet above the bed of the river. The cylinders were then sunk 10 feet into the bed of the river and enveloping the pile clusters, pumped out and filled with concrete. The shells for the piers of the Victoria bridge in Nova Scotia, constructed in 1888, were made of wrought iron. The rim of the shells rested on piles cut off at the surface of the ground; other piles extended up into the cylinder as shown in Fig. 139 a. 1 The piers were protected against scour and braced by cribs filled with stone and concrete, as well as by outside rip-rap. Much larger cylinders than those above described were used in the Norfolk and Western Railroad bridge No. 5 across Eliza- beth River at Norfolk, Va. The lower part of the cylinder for Pier 2 consisted of a f-inch steel shell 20 feet in diameter and 15 feet 9 inches long, stiffened by ^X^-inch angles spaced 5 feet apart vertically. A temporary upper section of the same diam- eter and high enough to reach to above water-level was attached to act as a cofferdam. The shell was then let down through the water, 23 feet deep at low tide, and sunk about 18 feet into the 1 Bridge Foundations in Nova Scotia, by MARTIN MURPHY, Trans. Am. Soc. C. E., vol. 29, page 629, Sept., 1893. Rail Grillage, S Layers ecrch of 6, 85 Ib. Rails p ; FIG. 1396. Typical Cylinder Pier. River Bridge, N. & W. R.R. Elizabeth ART. 139 METAL SHELL CYLINDER PIERS 421 mud by dropping it a few times from a considerable height. The material was then excavated to the bottom edge of the shell after which 80 piles were driven, and cut off by a diver at an elevation 7 feet above the cylinder bottom. Concrete of a 1-2-4 mixture was then deposited through the water to within 6 inches of the tops of the piles. After allowing this to set 4 or 5 days the cylinder was pumped out and a 2-foot layer of con- crete, enclosing a grillage of rails, was placed over the tops of the piles to more uniformly distribute the load over them. As shown in Fig. 1396 a cast-iron cylinder 10 feet in diameter was then placed in the larger cylinder. This shell was made in four lengths of 8 feet 9 inches each and each length was composed of four segments, the whole being bolted together through inside flanges. The metal was i inch thick. In the diagram the upper horizontal line represents the base of rail. Round iron bars i| inches in diameter and i\ feet long were run through the cast-iron shell near the bottom, and the outside cylinder was then filled with 1-2-4 concrete, which was crowned up on a 3o-degree slope. Concrete was placed in the ro-foot cylinder to within 2 feet of the top and a heavy beam grillage was set on this, crowned, and grouted with concrete. The outside cofferdam was then removed. Cast iron was used for the upper part of the pier because of its better lasting qualities when only periodically immersed. In the foregoing examples, in all cases some of the piles were extended well up into the cylinder. The advantage of this is the added stability against sliding and overturning. If the cylinders are not subjected to horizontal forces of any consider- able magnitude the piling may be cut at the base of the cylin- der or lower. If this is done the piles are surmounted with a concrete capping or timber grillage and the cylinders placed on it. The piers for the approach spans of the Cairo bridge of the Illinois Central Railroad were each formed of two 8-foot cyl- inders. Since no water covered the site, a circular pit 8 feet deep was dug for each cylinder and 12 oak piles driven in it. The pits were then filled with concrete to the proper elevation, 422 CYLINDER AND PIVOT PIERS CHAP. XIII FIG. I3QC. Cylinder Piers of Avon River Bridge, Windsor, Nova Scotia ART. 140 DESIGN AND CONSTRUCTION 423 after which the cylinders were placed and concrete filled in around them to a depth of 6 inches. The cylinders were then filled with concrete. ON ROCK OR HARD-PAN. Where the bottom is rock or hard- pan it is only necessary to clean and level off the site, place the cylinder, and fill it with concrete. Where horizontal forces occur the piers must be fastened to the foundation bed in some manner. This may be done by drilling holes in the latter and grouting rails or steel bars into the same, as was done for the piers of the Avon River bridge, Nova Scotia, illustrated in Fig. i$gc. ART. 140. DESIGN AND CONSTRUCTION The size of the cylinder will depend on the load to be sup- ported and the character of the foundation. The area of the base, with the pile founda- tion, is governed by the number of piles and their spacing, while if the pier rests on rock or hard-pan the area is governed by the allowable bearing pressure on the same. The area of the upper part of the pier will depend upon the size of the pedestals or base plates of the bridge. In general it is advantageous to have the diameter of the cylinder as small as possible, to avoid re- stricting the water way and offering resistance to the current, ice, and drift ma- terial. Where much ice and drift are present it may be ad- visable to use a pointed nose, as illustrated in Fig. 1400. Where the required diameters at the top and bottom differ materially, a shell having a smaller diameter at the top than at Sectional Plan L,4x4-. Plate \ \ V Plate * Elevation Flatten all rivets on out- side fo^ FIG. 1400;. Cylinder Pier with Pointed End. 424 CYLINDER AND PIVOT PIERS CHAP. XIII the bottom should be used. This may be done by using two separate shells as indicated in Fig. 1396 or by a connection similar to Fig. 1400, or by using a shell in the form of a frustum of a cone, as illustrated in Fig. ioia. The thickness of the shell is usually made just sufficient to take care of the stresses developed in handling and placing. Experience has demonstrated that it is inadvisable to use less then a f-inch thickness, although a yV-inch thickness is often specified for highway bridge cylinders. A thickness of more than | inch will seldom be required even for large cylinders. Complete specifications and tables giving diameters and thick- ness of shells for highway bridge piers are given in COOPER'S General Specifications for Foundations and Substructures of Highway and Electric Railway bridges. STABILITY OF PIERS. The four possible methods of failure are undermining; settling, due to excessive pressure on the foundation; sliding; and overturning. Undermining is placed first because of the many failures of highway bridge piers in this country due to this cause. Where founded on caissons there is no danger from this source, but where founded on piles care should be taken to have the whole length of the piles well below any possible scouring action, otherwise the founda- tion may collapse through lack of lateral stability. If it is impracticable to get the piles down to such an elevation cribs should be built around the tops as shown in Fig. 1390. The same protection should be given the foundation, where the material composing it is clay or hard-pan or even the softer kinds of rock, if the piers are located in a scouring current. To prevent settlement the foundation, if composed of piles, should be designed in accordance with the rules given in Chapter III with regard to safe loads on piles; or if hard-pan or rock, in accordance with safe unit-loads as given in Art. 179. The vertical load may usually be assumed as uniformly distributed over the base of the cylinder, for the transverse loads are resisted by a truss-like action of the cylinders and bracing. Thus, with a two-cylinder pier, in addition to the vertical loads due to the live load, weight of superstructure ART. 140 DESIGN AND CONSTRUCTION 425 and pier, there will be a downward vertical load on one cylin- der equal to the moment of the transverse loads about the bottom of the pier divided by the distance between cylinders center to center. Base of Rail Sectional Side Elevation Ground Line Section on Center Line of Pier ENG. NEWS Plan FIG. 1406. Cylinder Piers Braced by a Truss Encased in Reinforced Concrete Where forces exist tending to slide the pier, if a pile founda- tion is used some of the piles should extend well up into the cylinder; while if the cylinders rest on bedrock they should be anchored to the rock surface. A rockfilled crib placed 426 CYLINDER AND PIVOT PIERS CHAP. XIII around the cylinders, as illustrated in Figs. 139^ and c will add resistance to sliding. To resist overturning, strong and rigid bracing should con- nect the cylinders. Many forms of bracing are illustrated in the accompanying figures; these include simple ties and struts ofmetal and wood, as in Figs. 1390 and c\ latticed girders, as in Fig. 1380; plate girders, as in Fig. ioi&; double plate girders filled with concrete, as in Fig. 101 a\ and deep trusses embedded in concrete, Fig. 1406. ART. 141. REINFORCED- CONCRETE CYLINDER PIERS One of the disadvantages of the metal- shell type of pier is the necessity of keeping it painted. Although with steel shells it is not customary to design the shell to take any of the load yet it is advisable to prevent the same from rusting for two reasons: First, the shell takes any tensile stresses that may develop in the pier due to eccentric loading, ice pressure, etc. ; and second, the appearance of the pier during the rusting of the shell, as well as the stained appearance of the concrete afterward is unsightly. The metal shell may be avoided by building the pier in forms in a cofferdam or by using a pre-molded shell of reinforced concrete. In either case the pier should be well reinforced with steel rods. Each pier of a bridge at Buffalo, N. Y., on the Lake Shore & Michigan Southern Railroad was formed of two shafts, 30 feet 6 inches apart on centers, braced together with a steel girder encased in reinforced concrete. This girder served to transfer the load from the superstructure to the shafts. Each shaft, 13 feet 6 inches in diameter and about 51 feet high, rested on solid rock 36 feet below water-level. The shafts were constructed in cofferdams 18 feet in diameter, made of Lackawanna steel sheet-piling in 45-foot lengths. To within 21 feet of the top each shaft of the pier was octagonal in section and above this circular. The reinforcement consisted of 80 vertical ij-inch corrugated bars extending from the top to a point 30 feet ART. 141 REINFORCED-CONCRETE CYLINDER PIERS 427 below and lying on the circumference of a circle 6 inches inside of the surface. The strut, composed of a reinforced-concrete girder 4 feet 6 inches deep and about 5 feet wide, was reinforced with 48 corrugated bars ij inches square and 30 feet long, spaced about 6 inches center to center all around the strut, 6 inches from side Top_Qf_Roadwgy_ Pier 6 Section A-A FIG. i4ia. Reinforced-concrete Double-cylinder Pier. and bottom faces and 12 inches below the top face. As stated above it was further reinforced with a steel plate girder. Fig. 14 1 a illustrates the reinforced-concrete cylinder piers of a highway bridge over the St. Croix River at Hudson, Wis. Each pier consists of two reinforced-concrete shafts from 4 to 5 feet in diameter and braced together with reinforced-concrete 428 CYLINDER AND PIVOT PIERS CHAP. XIII The webs. These shafts had separate pile foundations, shafts were cast in wooden forms in i4-foot sections. In constructing the piers for a bridge across the River Wan- beck, Stakeford, England, the cylinders were formed of sections of reinforced-concrete shells 48 inches in diameter placed over i4-inch pre-molded concrete piles driven into the river. The FIG. 1416. Braced Bent of Reinforced-concrete Cylinder Piers. cylinders rested on the river bottom. After placing the shells, reinforcing rods were lowered into the same and the cylinders filled with concrete. The bracing was also of reinforced con- crete. The structure is illustrated in Fig. 14 ib. ART. 142. LARGE CYLINDER OR PIVOT PIERS This type of pier, used almost exclusively for the center support of swing spans, resembles the cylinder pier in shape and the ordinary masonry pier in massiveness. The same types of foundations, kinds of material, and methods of construction are used as for ordinary piers. Where protection against ice and drift is necessary it is furnished by means of an independent pier, often constructed of long piles. ART. 142 LARGE CYLINDER OR PIVOT PIERS 429 Fig. 1420 illustrates the all-concrete solid pivot pier on piles used for the St. Louis River bridge near New Duluth, Minn. The depth of water being about 28 feet, the pier was constructed in wooden forms inside of a circular steel sheet-pile cofferdam 36 feet in diameter. After driving the piles and cutting them off about 4 feet above the dredged bottom, a 6-foot layer of concrete was placed to form the 36-foot diameter footing course, the sheet- piling serving as a form for the sides. Above this footing course the form for the pier & consisted of a wooden-stave I run n rr \m u u u li y iJ U T li u u u lj u Section A-A Elevation of Center Pier FIG. 1420. Concrete Pivot Pier, St. Louis River Bridge, Duluth, Minn. water tank 16 feet high having a side batter of i inch to the Foot (Fig. 142 b). The second lift was made by raising the tank and planing a few of the staves to fit the new dimensions. For the coping course galvanized iron of the section shown in the illustration was used. A grillage of 24-inch I-beams distributed :he load over the pier. The pivot pier construction of the Dumbarton bridge of the 43 CYLINDER AND PIVOT PIERS CHAP. XIII Central California Railroad, merits particular attention because of .its simple solution of a difficult problem. At the site the depth of water at low tide was 51 feet and at high tide 58 feet, with a maximum velocity of current of 4^ miles an hour. The bottom consisted of soft mud overlying stiffer material. On account of the great depth of water and velocity of current the --3F-"-- Use these hoops for { upper forms at same elevat'ipn. Staves 2'x6*xl6'O* S I. S and beveled to t.i ^ 32'0" - * Forms for Concrete Center Pier FIG. 1426. Form for Constructing Concrete Pivot Pier. cofferdam process was not practicable and caisson foundations would have been expensive. Hence it was decided to employ a metal shell with a pile foundation. The cylinder had a diameter of 40 feet and was 72 feet 5 inches high in five vertical sections, After dredging out about 10 feet of the soft material on the bottom the first section of the cylinder was lowered. This was effected by first lowering a guide frame of structural shapes and ART. 142 LARGE CYLINDER OR PIVOT PIERS 431 driving its feet into the bottom, after which the section of the cylinder was placed around this frame and lowered. Inside this section 141 piles were driven to a penetration of about 30 feet Part Side Elevation. Base of Rail, El. I < n'n" s High Water 1.95.0 ' ~'~~ K 59 Half Elevation. Half Section. Half Top Plan. Half Pile Plan FIG. 142^. Reinforced-Concrete Pivot Pier, Illinois Central Railroad Bridge, Gilbertsville, Ky. and cut off below low- water level; some only about 3 feet below low water and others near the bottom. On completion of the pile driving more sections of the shell were added, each section 432 CYLINDER AND PIVOT PIERS CHAP. XIII being filled with concrete placed through the water to within 7 feet of the top before another section was added. This was the highest level at which the top of the concrete would not be disturbed by the tidal current passing over the top. Further details of this interesting work may be found in an article by E. J. SCHNEIDER in Transactions of the American Society of Civil Engineers, vol. 76, page 1572, Dec., 1913, entitled Con- struction Problems, Dumbarton bridge, Central California Railway; or in Engineering Record, vol. 62, page 172, Aug. 13, 1910. Where the lateral forces on the piers are small it is not necessary to extend the piles into the cylinders. In the con- struction of a pivot pier in the Willamette River, Portland, Ore., where the depth of water was 60 feet, piles were driven and cut off near the bottom. A timber grillage extending to within 3 feet of low-water mark was placed on the piles. On this grillage was placed a steel shell 46 feet in diameter about 30 feet high, which was filled with concrete to form the pivot pier. Fig. 83^ shows the pivot pier of the Chelsea Bridge North, Boston, which was faced with stone masonry. The foundation for this pier is described in Art. 83. As in the case of ordinary bridge piers the tendency at present is to make the pivot pier of hollow construction, leaving out masonry from that part of the pier that is but slightly stressed. Fig. 14 2C shows the reinforced concrete hollow pivot pier of the Tenriessee River bridge of the Illinois Central Railroad. The hollow space is domed at the top and bottom. The entire load from the superstructure comes on the pier through a cast- iron track 38 feet in diameter. The circular center line of the 8-foot wall has the same diameter, thus avoiding eccentric stresses in the pier. CHAPTER XIV BRIDGE ABUTMENTS ART. 143. FORM AND DIMENSIONS A bridge abutment is a masonry structure at one end of a bridge used for the double purpose of transferring the loads from the bridge superstructure to the foundation and to give such lateral support to the adjacent embankment as is required to maintain it in position. The abutment serves both as a pier and as a retaining wall. Because of the latter function, involving as it does the question of earth pressure, any possible mathe- matical treatment on the design of abutments has not yet been developed in a satisfactory manner. Fig. 1436! shows a typical section of an abutment through its center and parallel with the directon of the bridge. A is the bridge seat, which consists of a horizontal surface on which rest the end bearings of the superstructure; B is the back or parapet wall, which supports the upper part of the embankment and prevents the same from spilling down on the bridge seat; C is the main body or stem of the abutment; and D is the footing. The forces acting upon the abutment are as shown in the illus- tration: First, the loads on the bridge seat, which consist of a vertical force from the live and dead loads from the superstruc- ture and a horizontal force due to traction and in some cases to expansion and contraction of the bridge spans; second, the 28 433 FIG. 1430. Section of Abut- ment Indicating the External Forces Acting upon It. 434 BRIDGE ABUTMENTS CHAP. XIV earth pressure from the embankment against the back of the wall, due both to the weight of embankment and weight of live load; third, the weight of the abutment; and fourth, the reac- tions from the foundation. Abutments are classified according to their form. The three original types are the wing-wall abutment, the U-abutment, and the T-abutment. At present there are many modifications of these fundamental types. In the wing-wall abutment the wings, which may be parallel with the face of the wall or at any angle with the same, serve merely to keep* the embankment material from slipping into the stream or moving out into the roadway, as shown in Figs. 145^ and b. In the U-abutment the wings are made parallel with the roadway. The front wall is usually located at a point such that the side embankment mate- rial, having a slope of ij on i or i on i, will not extend out beyond the face of the abutment (Fig. 1436). The T-abutment has the same form of bridge seat as the wing-wall and U-abut- ment, but instead of wings it has a solid stem which supports the track or roadway back to a point at which the embank- ment is sufficiently high to support it. This type is illustrated in Figs. 1467 and g. DIMENSIONS OF ABUTMENTS. Like the bridge pier the dimen- sions of the bridge abutment will vary with many conditions, such as class of superstructure, height of abutment, type of foundation, and kind of embankment. However, owing to the uncertainties involved in the design, certain dimensions are being standardized to a large extent. The dimensions of the top of an abutment will depend on the same factors as the top of a bridge pier, except that where in the latter case bearing must be furnished for two trusses or girders, in the former case there must be a width sufficient for one truss or girder bearing plus a distance e (Fig. 1430) which is neces- sary to furnish the required stability to the parapet wall. The value of e is usually taken as 0.40^ or 0.45^ unless the parapet wall is reinforced. lu The width of bridge seats, exclusive of the projection of 1 General Specifications for Bridges, Part III, by J. E. GREINER. ART. 143 FORM AND DIMENSIONS 435 the coping, shall be at least 12 inches greater than required for the bed plates of steel superstructures, and the length of bridge seats shall not be less than the total width of bridge out to out of bearings plus 4 feet. The upper surfaces of the back and slope walls shall not have a less width than 2 feet for rail- way and if feet for other bridges. The thickness of coping shall not be less than 18 inches for railway, and 12 inches for other bridges." Table 143 a gives the approximate minimum dimensions of thickness and length under coping for electric railway bridges. TABLE No. Span Thickness of abutment under coping given = thickness of back wall + figures below Class A Class B Class C S. T. D. T. S. T. D. T. S. T. D. T. 25 2- o 2- 2 2- O 2-0 2-0 2-0 50 2- 2 2- 9 2- 2-2 2-0 2- O 75 2- 6 3- 3 2- O 2-6 2- O 2- 100 2- 8 3- 6 2- O 2-8 2- O 2- 2 125 2-10 3- 9 2- 2 2-IO 2- O 2- 4 150 3- o 4- o 2- 4 3-0 2-0 2- 6 175 3~ 2 4- 3 2- 6 3-2 2-0 2- 8 200 3- 4 4- 6 2- 8 3-4 2-2 2-IO 250 3- 8 300 4- o 5- 2-1 I 5-6 3-1 3-8 2-5 4-0 2-7 3- 2 3-6 350 4- 4 400 4- 8 5-10 6- 2 3~ 3 3- 5 4-4 2-9 4- 8 2-1 i 3-10 4- o Span Length of abutment under coping = distance center to center of trusses + figures below Class A Class B Class C S. T. D. T. S. T. D. T. S. T. D. T. SO 3-6 4-0 3-6 3-6 3-6 3-6 IOO 4-0 5-o 3-6 4-0 3-6 3-6 150 4-6 5-6 4-0 4-6 3-6 4-0 2OO S-o 6-0 4-0 5-o 3-6 4-6 250 S-o 6-6 4-6 5-o 4-0 4-6 300 5-6 7-0 4-6 5-6 4-0 5-o 350 6-0 7-6 4-6 6-0 4-6 S-o 4OO 6-0 7-6 5-o 6-0 4-6 5-6 Note: All dimensions are expressed in feet and inches. S. T. = single track; D. T. = double track. Class A, heavy traffic; Class B, medium traffic; Class C, light traffic. l From article by C. C. SCHNEIDER in Street Railway Journal, Sept. 15, 1906. 43 6 BRIDGE ABUTMENTS CHAP. XIV The thickness of the stem may be designed in accordance with the methods outlined in Art. 144. However, owing to the uncertainties involved in estimating the earth pressure, as well as to the possible large forces resulting from the freezing of water in the embankment, the thickness at any point should not be made less than 0.4 the height at that point. Some experi- enced engineers specify a coefficient of 0.5 where the abutment rests directly on soil. GREINER states that J "the thickness of the stem or back wall at any elevation shall not be less than 0.45 of the height of the masonry above that elevation for steam railway bridges, and 0.4 for other bridges." ART. 144. DESIGN AND CONSTRUCTION Abutments may be built of stone masonry, concrete, or rein- forced concrete. For the reasons given in Art. 133 stone masonry is but little used at present. A facing of stone is some- times used, but not to the extent that it is used for piers, since abutments are usually not subjected to the action of the current, with its accompanying ice and drift material. Where built of concrete it is advisable to use a small amount of surface reinforcement for the same reasons as those given for piers in Art. 133. According to GREINER, "The surface bonding rein- forcement shall be the same as provided for piers, but no hori- zontal layers of network will be required." Solid massive abutments may be made with 1-2^-5 to 1-3-6 concrete below the coping, with a 1-2-4 mixture for copings and parts above the same. For reinforced-concrete abutments all concrete should be a 1-2-4 mixture; or better, one part of cement to six parts of aggregate (before combining the sand and stone), the sand and stone being in such proportions as will give the densest concrete as determined by trial mixtures. DESIGN OF ABUTMENTS. The vertical loads to be sustained on any horizontal plane are the live load, impact load, weight of superstructure and weight of abutment above the plane in question. Impact may usually be neglected. 1 General Specifications for Bridges, Part III, by J. E. GREINER. ART. 144 DESIGN AND CONSTRUCTION 437 The lateral forces parallel to the axis of the bridge are the tractive force and the pressure from the embankment due to both the weight of the embankment material and the live load. At right angles to the axis of the bridge are the wind loads from the superstructure and on the abutment. The latter two are usually neglected, their effect being slight compared with the other forces. Of all the forces coming on the abutment the earth pressure from the embankment is the most uncertain in its effect and the most difficult to analyze. For descriptions of various methods of computing earth pressure, the reader is referred to HOWE'S Retaining Walls for Earth; CHURCH'S Mechanics of Engineering; and TURNEAURE and MAURER'S Principles of Reinforced-Concrete Construction. The other forces, with the exception of the weight of the pier, will be the same as those used in designing the superstructure. For stability the solid gravity abutment must satisfy the same conditions as those given for piers in Art. 136. For rein- forced-concrete abutments the base must satisfy these same con- ditions while the constituent parts of abutments are designed as beams and columns. Unless the abutment rests on rock or some other unyielding material it is not entirely satisfactory to have the resultant cut the base just within the middle third; it should be close to the center in order to give an approximately uniform pressure over the whole base. This is true for the reason that a slight unequal settlement causes a considerable lateral movement at the top, giving a condition illustrated in Fig. 1440. If the back face of the abutment is vertical and at the same time the dimen- sion e (Fig. 1430) is diminished by reinforcing the parapet wall with vertical rods near the rear surface, and the footing is extended and reinforced near the bottom as shown by the dotted lines in Fig. 143^, the pressure may be made to strike the base near the center. Fig. 144 b shows the design of abutment 5 of the Beaver bridge of the Pittsburgh and Lake Erie Railroad. The unit-pressures due to the different resultants are given in the following table. 438 BRIDGE ABUTMENTS CHAP. XIV _ Subgrade farft 7,>00'7bl. LL 12,00/0 21 f ,000 x.643 ^ of Abutment. Jo find Point of Application of rr P "take Moments ><3 s 'about anv Point A. - 2,052.000x19.6 + 117,000x43.1 20.9' Weight of Earth* I36.000lb$. _ t Total* 178,000 Ibs. 178.000*. 643 / ~lf4,454Ibs.onl. Loads on Abutment Foundation- Masonr 5006 tons. Forces Shown in Diagram on tment. are those acting on one-half of Abu Earth inside 1070 Fill at Ends 732 Total I 1,200 tons. II, ZOO -.- 3/5 = 35. 5 tons -Averaqe Load per Pi/e.asiuminq that Entire Weight rests on Piles. FIG. 1446. Diagram of Forces Acting on North Abutment and its Foundation. Pittsburgh & Lake Erie Railroad Bridge over Ohio River at Beaver, Pa., 1908-10. ART. 145 WING- WALL ABUTMENTS 439 TABLE 1440. UNIT-PRESSURES (Fig. 1446) No. Loading Max. Min. Mean I Masonry unloaded, no fills. 2 . 3 o.o 1.6 2 Masonry and fill at back 2 3 I C I 3 Masonry, dead load, and fill at back 2-5 2.1 2-3 4 Masonry, dead load, live load, and fill at back. 2.7 2-5 2.6 S Masonry, dead load, live load, and fill at 3-2 3-o 3.1 back and front. 6 Masonry, dead load, live load, fills back and 3-6 3-2 3-4 front, earth inside. ART. 145. WING- WALL ABUTMENTS This type of abutment usually has its wings parallel to, and in the line of, the face or front wall of the abutment when used for street crossings, as shown in /Fig. 1450; while for river cross- ings the wings are usually at an angle with the front face. The advantage of deflecting the wings in the latter case is that the abutment is thus better protected from water getting in behind the same, and it also allows the current to pass with less dis- turbance. It is not customary to extend the wings to the toe of the embankment, they being stopped some distance back of this point and the material allowed to spill out in front of the ends. Where the stream is liable to scour away this material it should be riprapped as shown in Fig. 1456. According to 1 BAKER, the proper angle of deflection for the wings, for a minimum amount of masonry, will be between 25 and 35 degrees from a line through the front face of the abut- ment, if the earth flowing around the toe is to be kept 3 or 4 feet back of this line. The wing walls are designed as retaining walls. The thickness at any point should not be less than 0.3 the height at that point. For low abutments a solid section is employed. Fig. 145^ illustrates this type. The exposed faces have steel reinforce- ment as a protection against cracking through expansion and contraction of the concrete near the outside. Reinforcement is also placed just above the pile foundation to distribute the load more uniformly over the same. The design of this abut- 1 Masonry Construction, tenth edition, page 526. 440 BRIDGE ABUTMENTS CHAP. XIV ment would have been improved if the bridge seat had been moved a short distance to the right by narrowing and re- inforcing the parapet wall, and the footing had been moved a short distance to the left. The only added expense in so do- ing would have been, in the slightly increased cost of the superstructure. Section 0-B FIG. 145^. Abutment of Peoria & Pekin Union Railway over Illinois River at Peoria, 111. For high abutments the reinforced-concrete buttressed abutment will show some economy over the solid type. The first structure of this type was designed by A. 0. CUNNINGHAM, in 1903, for a bridge on the Wabash Railroad at Monticello, 111. Figs. 145 d and 145 e show views of this abutment from the front and rear respectively, while Fig. i45/ shows a section of the ART. 146 U-ABUTMENTS AND T-ABUTMENTS 441 same. As is seen in these illustrations the abutment consists of a floor, face wall, bridge seat, parapet wall and buttresses. For stability this type requires a wider base than the solid sec- tion abutment, for here earth filling instead of concrete con- tributes to a large part of the stability. The design of the buttressed abutment is similar to that of the buttressed retaining wall, the main difference being that in the former the buttresses under the bridge seat serve to carry, as columns, the weight of the superstructure, as well as acting as beams to resist the earth pressure. For the outline of, as well as an ex- ample of, the design of but- tressed .retaining walls, see TAYLOR and THOMPSON'S Concrete, Plain and Rein- forced. .*. 15' O" ........... -*i FIG. i45/. Section of Reinforced- concrete Abutment. ART. 146. U-ABUTMENTS AND T-ABUTMENTS The U-abutment is a special form of the wing- wall abutment in which the wings are parallel with the roadway or track. The one disadvantage of this type is that a part of the embankment, that outside of the wings, does not receive any protection. This lack of protection may preclude the possibility of using this type where the water rises to a level above the foot of the abut- ment. On account of the wings being partially buried they do not receive as much pressure as those of the wing-wall abut- ment, although experience shows that the wedging action caused by the live load ' hammering' the fill between the walls exerts 442 BRIDGE ABUTMENTS CHAP. XIV _j L _. A/?" n" i's-i" 1 , , :, r'-'l fy -XJ f. SK'l/Jv- .''* Of O\ - fJvf T* 1 1 \ A j CM i j 4 1 ^ \ $ x x> ...^ ! / "K x x / i Y ? ^ \i i ~^ - ^^ >/ ?1 ^ X \ s5?' 5l rnco X x ^l ^.l >^ Y I \ i^l x xl I y v Y/$///Wfl^f//'^ ^ V v I / \ 1 ^^ L Side Elevation. Plan. 7 [W IVJO II I / 1 y he- 9' II -'--->( Half Section '^-. io'5"~->\ | Ha)f - "A- I Front Elevation FIG. 1460. Typical Plain Concrete U-abutment Chicago, Milwaukee and St. Paul Railway. ART. 146 U-ABUTMENTS AND T-ABUTMENTS 443 a very considerable pressure. If the side walls are well tied to the face wall with steel reinforcing rods, the thickness of the face wall may be somewhat decreased. Fig. 1460 shows a typical U-abutment. Fig. 1466 indicates a type in which the side walls are con- nected by transverse walls. In this way the side walls are made to act as beams of spans equal to the distances between trans- verse walls, thus reducing the necessary thickness of the same. The floor distributes the loads over a considerable area of soil Half Sec tion A A . Half Rear Elevation.. 49-9' - Section on o 10 O O 1.8 8.8. v , - .-, ON 1 8 Q < P ^ i uuinpQ 6z co ^ to O O vO CO CN tovo II II II II II 'S'Sg O cu > cu cu > & a & cJ O ! IS s ^ ^H O cu cu p p CU CO ^ 2 d cu 3 J3 C C +j -^ CX S 'S 8 'So ^ ^ -S3 ^1 2 5 ^ cu -5 d d * o C^ ^Q rj jo c 73 462 SPREAD FOUNDATIONS CHAP. XV The weak ' element of the McCullough formula is that although it gives under dead load the same unit-pressure for all foundations, yet for column No. 24 it gives a pressure of 8580 pounds per square foot for dead plus one-half live load and 10 740 pounds per square foot for dead plus live load, both of which are dangerously high when compared to a safe value of 7000 pounds per square foot. The Schneider for- mula, which also gives under dead load the same unit-pressure for all found- ations, and a maximum dead plus live-load pres- sure of 7000 pounds per square foot, is very con- servative. Neither of these two formulas gives any consideration to the live load in causing settle- -r A i 4 i Q n 1 - -L_ , J i ! ! j I sl r &5 1 ! ! i i ; M-S> L ' 1 ! i * ' 7f ^ *p \ 1 --J' 6"- >k 3' 0" - lO'O- ment. MORAN'S formula ==t ""I seems better in this respect since it recognizes the in- FIG. 1530. Steel I-Beam Grillage for a Single Column. fluence of the probable live load and gives to it one- half the weight that is given the dead load. In it the unit- pressure for dead plus one-half probable live load is so chosen that the maximum pressure under dead plus live load equals the safe bearing power of the foundation bed. The dead- plus-live-load formula gives entirely too much weight to live load, as is seen from the large variation in the dead-load stresses. For a further discussion on this subject see Engineering News, vol. 69, page 463, March 6, 1913, and page 687, April 3, 1913. the maximum probable live load. As a further illustration, in many school- houses there is an assembly room which is only used when the class rooms are vacant and consequently if class-room loads are used assembly-room loads should be omitted or vice versa; the greater one of these loadings to be used for the prob- able load." A full explanation of his method may also be found in the revised edition of KIDDER'S Architects' and Builders' Pocket Book. ART. 153 DESIGN OF I-BEAM GRILLAGES 463 In designing steel grillage foundations the following assump- tions are made : First, the pressure from the footing is uniformly distributed over the bed; second, the pressure of one tier of beams on another is uniformly distributed over the latter; third, each tier acts independently of all other tiers; and fourth, the concrete filling and covering carries no stress, acting merely as a protection against corrosion. For the single-column grillage the square base. is the most economical shape. Where the possible width is restricted, as in the case of wall-column footings, the grillage should be made as nearly square as possible. Economy also results in using a minimum number of tiers. EXAMPLE OF DESIGN OF SINGLE-COLUMN FOOTING. Load=6oo ooo Ibs. Allowable pressure on foundation bed = 6000 Ibs. per sq. ft. Size of column base = 3 X4 ft. Required area of base = 600 000/6000= 100 sq. ft. A base 10 ft. square is adopted. Assume two tiers of beams. For the top tier, the maximum bending moment M = (600 000/4) (5 2)12 = 5 400 ooo Ib. -in. Using 16000 Ibs. per sq. in. as the safe unit-stress in the outer fiber, the total section modulus required = I/e = 5 400 000/16 ooo = 337 in 3 . Trying various combinations of beams, the following results are obtained: No. Number of beams I/e re- quired Size of beam I/e fur- nished Width of flange Clear- ance i 3 112.3 2o"-65 Ib. 117.0 6.25 in. 8.6 in. 2 4 84.2 i8"-55 Ib. 88.4 6.00 in. 4 . o in. 3 5 67.4 i5"-55 Ib. 68.1 5-75 in. i . 8 in. The choice lies between Nos. i and 2, since No. 3 does not give sufficient clearance. The weight favors No. i, being 250 pounds lighter, while No. 2 gives a more satisfactory clearance and has less depth, thus saving on concrete rilling and also on excavation work. Cost of 250 Ibs. of steel at 2\ cents .................... $6.25 Cost of a 2-in. thickness of concrete .................. $i .65 Amount saved by using design No. i ". $4.60 For the lower tier: Max. M = (600 000/4) (5 1.5)12 = 6300000 lb.- in. Total required I/e = 6 300 000/16 000 = 394 in 3 . The following results are obtained by trying various combinations of beams: 464 SPREAD FOUNDATIONS X:HAP. XV No. Number of beams 1 fe re- quired Size of beam I/e fur- nished Width of flange Clear- ance 1 10 39.4 i2"-4o Ib. 41.0 5. 21 in. 7.5 in. 2 12 32.9 i2"-3i| Ib. 36.0 5. oo in. 5. 5 in. 3 14 28.2 i2"-3i| Ib. 36.0 5. oo in. 3. 8 in. 4 16 24.6 io"-25 Ib. 24.4 4. 66 in. 3.0 in. The choice lies between Nos. 2 and 4; the latter has 220 pounds more steel but the clearance is better and a 2-inch depth of concrete is saved^ Cost of 220 Ibs. of steel at 2\ cents $5 - 50 Cost of a 2-inch thickness of concrete. $4 . 50 Amount saved by using design No. 2 $i . oo ART. 154. DESIGN or DOUBLE- COLUMN FOOTINGS Where the two-column loads are equal the base of the footing should be rectangular in shape and symmetrical about a line ... -- - t - - "- -- ^ w. ;-;- 1 '- " J :: - ^-, 2~ J / f^ 1 - _ :: .. __ - f J ^ T-T- 1 --. - -n y /- ... .. ... ::: ... ... ^fe--&-^-_-_-~-_-_<%-- :_-_^_-j::^ 4^--J -X- FIG. 1540. Double-Column Footing of Steel I- Beams. midway between the columns. The total area of the base hav- ing been determined and the distance between columns fixed, the proportion of length to breath for the base of footing should be such that the moment in the lower tier of beams under the column centers equals that at a point midway between the col- ART. 154 DESIGN OF DOUBLE-COLUMN FOOTINGS 465 umns. This makes the three maximum moments approxi- mately equal, and gives the greatest economy of material. EXAMPLE OF DESIGN OF DOUBLE-COLUMN FOOTING, EQUAL LOADS. Column loads =500 ooo Ibs. Column spacing=i2 ft. Allowable pressure on ground =4000 Ibs. per sq. ft. Size of column bases = 3^X3 ft. Allowable unit-stress in beams = 16 ooo Ibs. per sq. in. To get the value x that will make the three moments equal, 500 000(6 x)/2 = $ooooox 2 /2(6+x) 500 ooo(yV), whence 2 = 4.77 ft- Required bearing area of base = i ooo 000/4000= 250 sq. ft. Using a value of x of 4.75 ft., 6 = 2507(12+2X4. 7s) = n. 63 ft.; say 11.75. Let two tiers of beams be assumed. Computing for top tier: Max. M= 500 000(11.75 3)12/8 = 6 560 ooo Ib.-in. Total required I/e = 6 560 000/16 000 = 410 in 3 . After trying various combinations of beams, the results are: No. Number of beams I/e re- quired Size of beam I/e fur- nished Width of flange Clear- ance 3 136.7 24 "-8o Ib. 173-9 7.0 in. 10.5 in. 4 102.5 2o"-65 Ib. 117.0 6.25 in. 5-3 in. 5 82.0 i8"-55 lb- 88.4 6.0 in. 3 . o in. No. 2 will be adopted. For lower tier the three positions of maximum bending moment are at the center and 4.45 ft. from each end. M at center = 500 ooo (6 5.375)12 = 3 750000 Ib.-in. M &t, 4.45 ft. from the end= [500 ooo 4.452 500 ooo i.45 2 l . - . - - 12 = 3 750 ooo Ib.-m. iQ-75 2 3.5 2 J Total required 7/e = 3 750 000/16000=234. Upon trying various combinations of beams, the results are found to be: No. Number of beams I/e re- quired Size of beam I/e fur- nished Width of flange Clear- ance i 12 iQ-5 9 "-2i lb. 18.9 4-33 in. 8 . i in. 2 14 16.7 9 "-2I lb. 18.9 4-33 in. 6.1 in. 3 16 14.6 8"-i8 lb. 14.2 4.0 in. 5 . i in. 4 18 13-0 8"-i8 lb. 14.2 4.0 in. 4.1 in. No. 3 will be adopted. When the column loads are not equal the center of gravity of the base of the grillage is usually made to coincide with the line of action of the resultant of the two column loads by making the base a trapezoid; or, if the loads are nearly equal, it may be done 30 4 66 SPREAD FOUNDATIONS CHAP. XV by using a rectangular shape and making the cantilever end at the heavy load longer than the other cantilever end. The trapezoidal shape may be obtained either by using a larger number of beams at the heavy load end, or by using the same number of beams and spacing them more closely at one end than at the other. A combination of the two methods is sometimes used. -y^*O/-/"-^L* I S\ <: i -3H FIG. 1546. Steel I-beam Grillage for Two Columns Supporting Unequal Loads. The load on Column No. i is 500 ooo Ibs; that on No. 2 is 400 ooo Ibs. If the proportions of the base are so fixed that the bending moment under the center of each column equals that at the center of gravity of the base, the three maximum moments in the lower tier of grillage will be closely equal; this condition gives approximately the minimum amount of material. The most satisfactory method of determining the dimensions to secure this result is by trial. ART. 154 DESIGN OF DOUBLE-COLUMN FOOTINGS 467 EXAMPLE or DESIGN OF DOUBLE-COLUMN FOOTING, UNEQUAL LOADS. Column loads and spacing as shown in Fig. 154 b. Allowable pressure on foundation bed = 4000 Ibs. per sq. ft. Size of column bases as shown in Fig. I54&. Allowable unit-stress in beams= 16000 Ibs. per sq. in. Re- quired bearing area of base =900 000/4000 =2 25 sq. ft. Distance from Column No. i to resultant of both column loads = 400 000X10/900 000 = 4-45 ft- After a few trials it was found that the moments under the centers of the two columns and under the center of gravity of base line of action of resultant of two column loads were approximately equal when ^ = 3.625 ft., and 6 = 4.625 ft. To get b and c: (5+^)18.25/2 = 225 and (18.25/3) (&+2c)/(&+c) = 3.625+4.45 = 8.075. Solving these two equations simultaneously we find that approximately b= 16.6 ft. and c = 8.o ft. Using two tiers of beams, the computations for the upper tier under Column No. i give: Max. If =(500000/8) (14.88 3)12 = 8 910000 Ib.-in. Total required l/e 557 in 3 . After trying various combinations of beams, the results are as follows, and No. i is adopted: No. Number of beams I/e re- quired Size of beam I/e fur- nished Width of flange Clear- ance i 2 3 4 186.0 139-5 24 "-9o Ib. 24 "-8o Ib. 186.5 173-9 7-13 in. 7.0 in. 7.3 in. 2.7 in. For the upper tier under Column No. 2 : Max/ M= (400 000/8) (10.18-2.75)12 = 4458000 Ib.-in. Total re- quired 7/6=279 in 3 . Trying various combinations of beams gives the following results, No. i being adopted: I/e fur- nished No. Number of beams Clear- ance 7/6 re- . -i I/e fur- Width quired Slze of beams nished of flange 1 3 93.0 i8"-6olb. 93-5 6.10 in. 7.3 in. 2 4 69.7 i8"-55 Ib. 88.4 6.00 in. 3.0 in. In designing the lower tier and running all beams full length, let # = the distance from the left end of grillage to section in question, the expression for bending moments under Column No. i, between the two columns, and under Column No. 2, are respectively as follows: 468 SPREAD FOUNDATIONS CHAP. XV Jf(col. No.i) 4000 x (49.80.471*) O 500000 (% 2.125) : M (between cols.) = 4000 x' (49.8 o . 47 ix) 500 000(2 3.625) If (col. No. 2) = 4000 x -'(49.8-0.471*)- O 500000(^-3.625)- 4OOOOO (X 12. 25) 2 2.75 2 To get the values of x for the maximum value of M in each of the above equations equate dM/dx equal to zero, which gives 3.42, 8.58 and 13.91 ft., respectively. Substituting these three values of x in the preceding equations, the corresponding values of M are, 236000 lb.-in., 231000 lb.-in., and 232000 Ib.-in. The maximum maximorum is therefore 236 ooo lb.-in. Total required I/e = 177 in. 3 Trying various combinations of beams, there is obtained: No. Num- ber of beams /Are- quired Size of beam I/e fur- nished Width of flange Clearance i 10 17.7 9"-2i Ib. 18.9 4- 33 in. 5. 9 to 17. 3 in. 2 12 14.7 8"-2oilb. 15.0 4 . 08 in. 4.3 to 13. 6 in. 3 14 12.7 8"-i8 Ib. 14.2 4 . oo in. 3.1 to 10.9 in. U 16 II. 7"-i7l lb- II. 2 3.66 in. 2. 5 to 9. 3 in. No. 4 will be adopted. Reinforcing bars should be placed in the concrete near the upper surface for the wider half of the footing. ART. 155. DISTRIBUTION or PRESSURE ON BASE There is some question regarding the error involved in the assumption that the pressure from the footing is uniformly distributed on the ground. Taking the case of the single- column square footing it is evident that the base of the footing will assume a saucer-like shape, and as a consequence the pres- sure will be a maximum at the center and a minimum at the outside. The law governing the variation of pressure will ART. 156 STEEL GRILLAGE FOUNDATIONS 469 depend on the relative deflections of different points on the base of the footing, as well as on the modulus of compressibility of the soil and the thickness of the compressible stratum. Where the modulus is low and the thickness considerable, the slight difference in total deformation at different points will cause but a slight difference in pressure. Where the soil is compressible but inelastic, or soft and subject to lateral flow, a fairly uniform distribution of pressure quickly obtains. Where the material has a high modulus of compressibility, as in shale or rock, the footing should be designed for stiff- ness as well as for strength or else the surface of the material should be shaped to fit the curve taken by the base of the foot- ing when fully loaded, otherwise the pressure will be very un- evenly distributed. For example, by using a stress-strain diagram of the values obtained in the foundation tests of the St. Paul Building, New York City (see Engineering Record, vol. 33, page 388, May 2, 1896), a theoretical solution shows that for the typical steel-grillage footing the pressure varies from a maximum at the center to approximately zero at the outside. The material on which the above foundation tests were made consisted of very compact sand, while the whole area of the lot was covered with a layer of concrete and steel beams buried in concrete, the tests being made through a hole. ART. 156. STEEL GRILLAGE FOUNDATIONS Most of the grillages used in the foundations for the Phelan Building, San Francisco, were 15 feet square, and made with two cross tiers of I-beams from 1 8 to 24 inches in depth, or with an upper tier of built-up girders and a lower tier of I-beams, as shown in Fig. 1560. The complete grillage plan is shown in Fig. 1565. 1 "All footings are made with a bed of concrete 12 inches thick and 12 inches wider and longer than the dimensions of the first tier of grillage beams. In the upper part of the con- crete there are two full-length rectangular grooves transverse 1 Engineering Record, vol. 57, page 366, March 28, 1908. 470 SPREAD FOUNDATIONS CHAP. XV to the lower tier of grillage beams. In each groove a T V-inch angle was carefully leveled with the upper edge of its vertical flange truly horizontal and f inch above the surface Boiler Room FT *!Wr?W*fSH '' SubBaseme^ $& FIG. 1560. Footings with Plate Girders and I-beams in Double Tiers. of the concrete. These serve as leveling bars to receive the lower flanges of the grillage beams and insure their exact height. The spaces between the beams and the concrete footings were grouted, the second tier of beams was shimmed f inch above the top flanges of the lower tier and grouted, the cast- iron pedestals were set f inch above the top flan- ges of the distributing beams and grouted, and ^ a solid mass of concrete was FIG. 1566. Grillage Plan of Phelan Building, San Francisco, Cal. filled in 6 inches around the outer edges of the beams and pedestals and up to the cellar floor, completely enclosing and protecting all the substructure steel work." ART. 156 STEEL GRILLAGE FOUNDATIONS 471 Fig. 156^ illustrates a very heavy grillage foundation for four columns of the Curtis Building, Philadelphia. It was necessary to use a single grillage for the four columns because of the short distances between the latter. The distributing girders for Columns Nos. 254 and 255 have 48XlHnch webs t -IO -4- Q'2'i....jf _ -- FIG. 1 5 6c. Special Footing for Four Columns, Curtis Building, Philadelphia. reinforced by 5X3X|-inch vertical stifltener angles and two 13 X 1-inch vertical side plates, and the top flanges of the girders are connected by transverse tie plates. The column loads are transmitted to the triple distributing girders by bolsters made of solid slabs of plain square steel billets 472 SPREAD FOUNDATIONS CHAP. XV which are bolted to the upper flanges of the girders. The concrete footing is reinforced with rods for part of the base, due to the fact that the I-beams are there a con- siderable distance apart, thus developing beam action in the concrete. BarctaL St 9 10 Pbrk Place FIG. i$6d. Plan of Piers and Grillages for the Woolworth Building. The Woolworth Building, New York City, is founded on solid rock 115 feet below the curb level. The loads are car- ried from the columns to bedrock through grillage footings resting on reinforced-concrete piers. Fig. 156^ shows the general lay out for the foundation, while 1560 shows some of the details. ART. 156 STEEL GRILLAGE FOUNDATIONS 473 474 SPREAD FOUNDATIONS CHAP. XV ART. 157. DESIGN OF REINFORCED-CONCRETE SPREAD FOUNDATIONS Instead of serving merely as a protection for the steel, con- crete may be made to take a part of the load by using a rein- forced-concrete footing in place of the I-beam grillage, thus lessening the cost of the foundation. Another advantage pos- sessed by a reinforcednconcrete foundation is that it can be cast in any shape or form desired. It may be in the form of a flat slab or of the slab-and-beam type (Fig. 1590). The former i uses more concrete, while in *- - ^-3' 0"- ->H 2' 6"*, the latter the form work is more expensive. For some interesting modifications of the elementary type the reader is referred to Art. 159. DESIGN OF A REINFORCED- CONCRETE WALL FOOTING. Assuming the load to be 64 ooo pounds per linear foot of wall and the allowable bearing on the soil 4000 pounds per square foot, the width of footing will be 64000/4000=16 feet. The thick- ness of the wall is 2 feet (Fig. 1570). The footing will be designed at three sections, at a, 5^ feet from the center of the wall, at b, 3 feet from the center, and at c, i foot from the center. Taking a i-foot length of footing the vertical shears and bending moments will be as follows: ,,. 4000X2.52X12 Va = 4000X2^ = 10 ooo Ib. M a =~ -- - =150 ooo Ib.-m. FIG. 1570. Reinforced-concrete Wall Footing. V b =4000X5 =20ooolb. M b = = 600000 Ib. -in. V c = 4000X7 = 28 ooo Ib. M e 000 ART. 157 REINFORCED-CONCRETE SPREAD FOUNDATIONS 475 A 1-2-4 concrete will be used, with an allowable compressive unit-stress 1 in the concrete of f c = 600 Ibs. per sq. in. and an allowable tensile unit-stress in the steel of f s =i6 ooo Ibs. per sq. in. The ratio of the modulus of elasticity of steel to that of concrete will be assumed as ^=15. The depth to center of steel rods necessary to give a compressive stress in the concrete of 600 Ibs. per sq. in. is given by the formula, d= ^M/(Rb), in which R = f c kj/2. In the latter formula 2 k= ^2pn-\-(pn) 2 pn and j = i - k/3 ; p = |/y( ~r + i Y The work involved in get- jc \nj c / ting the value of R will be greatly reduced by using the dia- grams found in TURNEAURE and MAURER'S Reinforced-Con- crete Construction. For the problem at hand the value of R is 95. Solving iord, d a = V 150 0007(95X1 2) = n.$m.',d b = V 6000007(95X12) =23.oin.;and v d c = V z 176000/95X12) = 32.1 in. (32^ in. being adopted). As it is inadvisable to use a depth at any section less than about 6 inches the form shown in Fig. 157 a will be adopted. The steel in the bottom will be given a 2 -in. insulation. The area of steel required at each section is given by the formula, A=M/(f s jd). Using the values of d obtained above, so that the footing be equally strong in tension and compression: A a 150 ooo/(i6 000X0.88X11. 5) = 0.92 square inch, A b = 600 ooo/(i6 000X0.88X23 ) = 1.85 square inches, A c =i 176 ooo/(i6 000X0.88X32. i) = 2. 60 square inches. Using a rod spacing of 3 inches center to center there will be 4 rods in one foot of length of the footing. The required area of each rod will be 2.60/4 = 0.650 sq. in. A lo-inch square 1 In a wedge-shaped beam the greater principal stress at the outer fibers acts parallel to the upper surface of the beam and with an intensity equal to the maxi- mum normal stress on a vertical plane divided by cos 2 **, in which a is the angle of inclination of the upper surface of the beam; hence, the allowable bending unit stress should be taken equal to the safe compressive stress in the concrete multi- plied by cos 2 a. 2 Based upon the assumption that the normal stress in the concrete on any vertical section varies as a straight line and that the stress in the steel equals n times the stress in the concrete. For formulas based on a different assumption see Proc. Am. Soc. C. E., vol. 39, page 2067, Nov. 1913. 476 SPREAD FOUNDATIONS CHAP. XV twisted rod, giving an area of 0.660 sq. in. will be adopted. Three rods will furnish the required area at b, while two rods will furnish that required at a; hence certain of the rods may be bent up or cut off as shown in Fig. 157^. Using an allowable bond unit-stress of 140 Ibs. per sq. in. of rod surface the necessary length of rod to develop full strength is (16 000X0.66)7(140X3. 25) = 23. 2 in. Computing the bond stress in the rods by the formula l u(Sd M tan a)/(jd 2 2o) in which tan a is the slope of the upper surface of the footing and S0 the perimeter of the rods at the section in question, the values are as follows: MO = (10000X15.4 !5ooooXo.3i2)/(o.88Xi5.4 2 X6.5o) = 7glb./sq. in. u b =(20000X24.75 6oooooXo.3i2)/(o.88X24.75 2 X9.75) = 59lb./sq. in. u c =(28000X32.25 1 176 000X0.312)7(0.88X32. 25 2 X 13) =45 lb./sq. in. All of these values are well below the safe limit of 140 Ibs. per sq. in. Assuming that the concrete takes no longitudinal tension the maximum intensity of diagonal tension is given by the formula t=(SdM tan a )/(jd 2 ). A shorter method of com- puting the maximum diagonal tension is by taking the bond stress values and multiplying them by the perimeter of the rods. Thus, t a =(79X6.50)712 = 43 Ibs. per sq. in. tb =(59X9-75)712 = 48 Ibs. per sq. in. *c =(45X13.0 )/i2 = 49 Ibs. per sq. in. Although conservative specifications limit the allowable diagonal tension to 40 pounds per square inch, the above can be safely carried by the concrete without reinforcement, but to illustrate the method stirrups will be designed to carry all of this tension. Placing the stirrups on a 45-degree slope and using f-inch square twisted rods with two prongs in a 1 2-inch length, as shown in Fig. 1570, the strength of one line of stirrups in a i2-inch length will be 16 oooX(|-) 2 X2 = 45 oc pounds. Denoting the horizontal distance between rows of 1 Only approximately true when p is not constant. ART. 158 REINFORCED-CONCRETE COLUMN FOOTINGS 477 stirrups by s the formula is, s = 45007(1 2 X/X cos 45), giving S a =4500/12X43X0.707 = 12 inches. S b =4500/12X48X0.707 = 11 inches. S c =4500/12X49X0.707 = 10 inches. A uniform spacing of 10 inches will be adopted. In this type of beam the maximum intensity of vertical shear occurs at the top and equals fc tan a, where a is the in- clination of the upper surface of the slab. The shearing stress is therefore 600X0.312 = 187 pounds per square inch. ART. 158. DESIGN OF REINFORCED-CONCRETE COLUMN FOOTINGS The stresses in a reinforced-concrete footing for a column are due more to flat-slab action than to beam action and hence are much less determinate than in the wall footing. However, the stresses may be approximately analyzed by either flat-slab or beam formulas. The former method is not entirely satisfactory, due partly to the neces- sary approximations of any formulas based on the theory of the* flat plate, and partly to the tedious com- putations involved unless specially prepared tables or diagrams are used. . r . , . - FIG. 1580. Column Footing of For an example of the design ot a Reinforced Concrete, footing based on the flat-slab prin- ciple see page 644 of the second edition of TAYLOR and THOMP- SON'S Concrete, Plain and Reinforced. Where beam formulas are used it is generally assumed that the section of maximum bending moment and shear is at the outer face of the column. If the footing has a two-way rein- forcement the stress cannot be uniformly distributed over this section. For instance, looking at Fig. 158 a, the load from the soil at point c will evidently go to the column through dc 478 SPREAD FOUNDATIONS CHAP. XV acting as a cantilever beam. On the other hand a part of the load at a will first go to some point as c through ac acting as a beam, and the balance to some point as b through ab acting as a beam. The part which goes to c will then go to d through cd acting as a beam, while the part which goes to b will go to e through be acting as a beam. Thus it is evident that the stress along the plane A- A will vary from a maximum at the column face to a minimum near the sides of the footing. From experiments made in the testing laboratory at the University of Illinois, A. N. TALBOT summarizes the proper method of design as follows: x "For footings having projec- tions of ordinary dimensions, the critical section for the bending moment for one direction (which in two-way reinforced con- crete footings is to be resisted by one set of bars) may be taken to be at a vertical section passing through the face of the pier. In calculating this moment, all the upward load on the rectangle lying between a face of the pier and the edge of the footing is considered to act at a center of pressure located at a point halfway out from the pier, and half of the upward load on the two corner squares is considered to act at a center of pressure located at a point six- tenths of the width of the projection from the given section. . . . "With two-way reinforcement evenly spaced over the foot- ing, it seems that the tensile stress is approximately the same in bars lying within a space somewhat greater than the width of the pier and that there is also considerable stress in the bars which lie near the edges of the footing. For intermediate bars stresses intermediate in amount will be developed. For footings having two-way reinforcement spaced uniformly over the footing, the method proposed, for determining the maxi- mum tensile stress in the reinforcing bars, is to use in the cal- culation of resisting moment at a section at the face of the pier the area of all the bars which lie within a width of footing equal to the width of pier plus twice the thickness of footing, plus half the remaining distance on each side to the edge of the footing. This method gives results in keeping with the results 1 Bulletin No. 67, Engineering Experiment Station, University of Illinois. ART. 158 REINFORCED-CONCRETE COLUMN FOOTINGS 479 of tests. When the spacing through the middle of the width of the footing is closer, or even when the bars are concentrated in the middle portion, the same method may be applied without serious error. Enough reinforcement should be placed in the outer portion to prevent the concentration of tension cracks in the concrete and to provide for other distribution stresses. "The method proposed for calculating maximum bond stress in column footings having two-way reinforcement evenly spaced, or spaced as noted in the pre- ceding paragraph, is to use the ordinary bond-stress formula, and to consider the circumfer- ences of all the bars which were used in the calculation of tensile stress, and to take for the exter- nal shear that amount of upward pressure or load which was used in the calculation of the bending moment at the given section." In the preceding discussion the slab is assumed to have a hori- zontal upper surface. DESIGN OF A FOUR- WAY RE- INFORCED FOOTING. A footing with four-way reinforcement (Fig. 1586) is more susceptible of a rational analysis than the two-way reinforced foot- ing. Tests by A. N. TALBOT (see previous reference) show that this type gives a somewhat stronger footing than the two-way type. Assuming the load to be 210000 pounds and the allowable bearing on the soil 3000 Ibs. per sq. ft., the area of the footing will be 210 000/3000 = 70 sq. ft. A baseS feet 6 inches square will be used. The column base will be assumed as 20 inches square. In this design the part ABCD in Fig. 158 & will be assumed to act as a free cantilever about CD, as will also ABEF, ABGH FIG. 1586. Reinforcement for Column Footing. 480 SPREAD FOUNDATIONS CHAP. XV and ABKL about EF, GH and KL respectively; in other words, it will be assumed that there is no stress on the planes AD and BC. Dividing the horizontal distance between AB and DC into four equal parts by the lines bi, b 2 and 6 3 , the lengths of the lines 6 , &i, &2, 63 and 5 4 are respectively 8.50, 6.79, 5.08, 3.37 and 1.67 ft. Let AI, A z , A 3 and A represent respectively the areas of the base of the footing to the right of the b lines of the corresponding subscripts, then their values will be^4i= 6.54, ,4 2 = ii. 6, ^3 = 15.2 and ^4 = 17.35, all expressed in square feet. The upward pressure from the soil is 2ioooo/(8.5) 2 =29io Ibs. per sq. ft. The shears on the sections &i, b 2 , b s and & 4 are respectively 19 ooo, 33 ooo, 44 200 and 50 500 pounds. The moment of the upward pressure to the right of and about bi is 19 oooX 2 >< 8 -5+ 6 -79 x oJ54 X i 2 = ioiooo Ib.-in. The 8.5+6-79 3 moments of the forces to the right of and about b%, bs and b are respectively 376000, 775000, and i 267000 Ib.-in. Using an allowable unit stress for the rods of 16 ooo Ibs. per sq. in. and for the concrete of 650 cos 2 01 = 500 (approximately) Ibs. per sq. in., in which a is the angle made by the upper surface with the horizontal, the values of d as given in the [formula d = M/(Rb) are ^1 = 4. 2, J 2 = 9-3, ^3 = 16.4 and ^4=29.8 in. Using the formula A=M/(f s jd) to get the required area of cross-section of steel at bi, 6 2 , 3 and 6 4 , the respective values are 1.69, 2.83, 3.30 and 2.97 sq. in. Assuming 12 square twisted rods, the required area of each one is 3.30/12 = 0.275 sq. in. A iVinch rod furnishes an area of 0.316 sq. in. The rods will be placed as shown in Fig. 1586, each layer being ij in. above the one below it. The ordinates to the curved line in Fig. 1586 represent the required depths, but, as shown in the same illustration, the depths adopted will be greater than these. The bond stresses as given by the formula u=(Sd M tan a)/ o) are 48, 50, 44 and 36 Ibs. per sq. in. for the sections b z , bz, and b respectively. The maximum unit shear is f c tan 01 = 500X0.586 = 293 Ibs. ART. 159 CONCRETE SPREAD FOUNDATIONS 481 per sq. in. This is a rather high value but as it occurs at the point of maximum compression and so does not develop a heavy diagonal tension, it may be considered safe. Assuming that the concrete takes no direct tension the maximum diagonal tension for each section, as given by the formula t=(Sd M tan a)/(bjd 2 ), is /i=i6, 2 = 22, 3 = 29 and / 4 = 48 Ibs. per sq. in. Hence stirrups are required for only a short distance from the face of the column. The method of design of the same is treated in Art. 157 and will not be repeated here. The design of the slab-and-beam type of footing follows closely the method of design of slabs and beams in building construction. The slab serves as a beam to carry the load from the soil to the beam, the span being taken as the distance center to center of beams; and the latter, acting as cantilevers, carry it to the column. Where the beams have constant cross- sections the formulas for stresses as derived in any standard treatise on reinforced concrete are applicable, and where tapered, the formulas given in Art. 157 may be used.' Where one footing serves for two columns, the method of obtaining the shape of footing, as well as the shears and bending moments, is similar to that for the I-beam grillage (Art. 154), while the standard formulas are applicable in finding the stresses. On page 647 of the second edition of TAYLOR and THOMPSON'S Concrete, Plain and Reinforced, an example of this type of foot- ing is worked out. ART. 159. CONCRETE SPREAD FOUNDATIONS Two standard forms of the reinforced-concrete spread foot- ings used for the column foundations of a railway terminal sta- tion at Atlanta, Ga., are shown in Fig. 1590. The one illus- trated on the left was used for 20 X 24-inch columns and was in the form of a truncated pyramidal slab reinforced with bars and stirrups. The one shown on the right was of the beam-and-slab type. The details are sufficiently shown to require no explanation. 31 482 SPREAD FOUNDATIONS CHAP. XV The 125-foot concrete block chimney for the St. Joseph's Home, Chicago, was founded on a blue clay, the base of the foundation extending about 5 feet below the surface of the ground. The footing, shown in Figs. 159^ and c, consists of a circular slab 24 feet in diameter and 10 inches thick, on which is built a box with a square outer surface 8 feet 3 inches on a side, and with an octagonal inner surface about 6 feet 7 {"Diagonal Rod ^'Diagonal Rod FIG. 1590. Pyramidal and Ribbed Slab Footings of Reinforced Concrete, Atlanta Terminal Station, Southern Railway. inches between opposite faces. The box is about 4 feet high. la From either corner of this box extends a series of eight cantilever ribs reaching approximately to the outer edge of the slab as shown in the accompanying view. These cantilever ribs are each 14 inches wide, 4 feet deep at the box and slope off uniformly to a width of 8 inches at the top of the slab. Engineering Record, vol. 65, page 636, June 8, 1912. ART. 159 CONCRETE SPREAD FOUNDATIONS 483 Round Bars {/"Round Ba | FIG. 1596. Slab and Box Footing of Reinforced Concrete for a 1 25-foot Chimney in Chicago. FIG. i59c. View of the same Footing as shown in Fig. 1596. 4 8 4 SPREAD FOUNDATIONS CHAP. XV Their effective depth is virtually 4 feet plus the effective depth of the slab, as they are built integral with it; and their rein- forcement, which consists of i-inch round bars and J-inch ver- tical stirrups, extends up from the lower surface of the slab, as shown in the accompanying drawing. The base is thus made up of a series of slabs, each supported by the adjacent canti- lever ribs and reinforced with f-inch round bars spaced according to the position of the slab in the base. That portion of the base enclosed at the center is reinforced with a double system of J-inch round bars, spaced 6j inches on centers." Fig. 159^ illustrates a reinf orced-concrete footing on a pile foundation, Fig. 1590 represents a novel type of foundation used for a loft building in New York City. There were three lines of columns, two lines of wall columns and one line through the cen- .io'-8- ****+* ter. The foundation pre- tf'Bar Rmqs s Welded J \ V .'Fastened X- 1 /, '^""Rmq.Welded $' 4 n-~n r~ feas ! i i^ r *LLU LLU L UJ ' FIG. 159^. Column Footing of Reinforced Concrete Supported by Pre-molded Concrete Piles. sented something of a problem because the ad- joining structure rested on a pile foundation, which the architect feared was in a poor condition. On account of the desire not to be forced to the expense of underpinning this adjoining building, a deep founda- tion was out of the question. The simple spread footing could not be used for the wall columns because of lack of space. As finally constructed, the foundation consisted of a solid frame- work of reinforced-concrete beams. ART. 159 CONCRETE SPREAD FOUNDATIONS 485 1 "The special feature of the cantilever construction is that the one cross-beam and a portion of each longitudinal beam form a T-section, the center of gravity of which is the same as the center of gravity of the column loads plus the weight of the side wall. Thus, looking at Fig. 1590, it will be seen that half of the load coming on the column in the center of the build- ing and the whole load coming on a wall column and the wall - 10-7* >k-5-8*>K -K>'-9"^5 L 8"^ B j * '-5* >!<: 74-5* >k M--5" > ^ k- - /4-5-*-~- EN&.NEWS FIG. ; pi an o f Reinforced-Concrete cantilever Footings of 1 2-story Loft Building, 25-29 West 3ist Street, New York City. load adjacent to that column is carried on that portion of the side concrete beam and the cross-beam there shown, and that the center of gravity of these loads is the same as the center of gravity of the T-beam formed by the side beam with the transverse beam going at right angles from it. The .variation in the loads and, consequently, in the centers of gravity, re- sulted in different shapes and sizes of the supporting beams." 1 Engineering News, vol. 68, page 995, Nov. 28, 1912. 486 SPREAD FOUNDATIONS CHAP. XV Reinforced-concrete spread foundations covering the whole area of the basement were used for the factories of Herman Behr f & Co., and W. H. Sweeney Mfg. Co., Brooklyn, N. Y. Fig. I59/ shows the details for the first-named factory. This raft foundation, which was of the beam-and-slab type, had a slab thickness of i foot and a beam thickness of 3" feet. The beams formed continuous lines under the outer wall and along the cen- ter line of the columns lengthwise of the building, the column spac- ing being 16 feet 10 inches longitudinally and approximately 79! feet transversely. These beams were 5 feet wide under the sS-lM'Sq. Straight Bars f '_. ! ^Boxment Floor ^ . .... J-'.-.-i-.-j 'ft , -l"5q.BarJ, /7'3"hng. ^:^^^ 6 ' c - K>c - Center Line* f - ' uT-L f t~ l~!"t r -jTl" [it '-i T . ffll-^^^^Rrj-tttl-^^ FIG. iS9/. Spread Foundation. FIG. i59g. Spread Foundation. walls and 6 feet wide under the columns. The intervening space between beams was brought up nearly to surface level by a dirt fill, and a finished concrete floor was laid over the whole area. As shown in the illustration the reinforcement for the 1 2 -inch slab consisted of transverse bars i inch square, spaced 5 inches on centers and 3 inches from the top of the slab. The beams under the columns were reinforced with eleven i J-inch square bars near the upper surface, the five center bars being carried through straight and the six outside bars bent down under the column. The foundation of the W. H. Sweeney Mfg. Company's factory consisted of a slab over the whole area surmounted by truncated pyramidal slabs under all the columns and a trape- ART. 159 CONCRETE SPREAD FOUNDATIONS ss 487 Wariest Section A- B. Section Section E-F. C-D. Section 6~H. (Detail of Footing) FIG. i59/*. Reinforced- concrete Arch Foun- dation of Warehouse at 418-426 West Street, New York City. 488 SPREAD FOUNDATIONS CHAP. XV zoidal-shaped slab under the wall, as shown in Fig. 159^. The columns were spaced approximately 16 feet on centers in both directions. The column footings were raised 2 feet 6 inches above the top of the raft slab and the latter was reinforced with six lines of rods about i^ feet on centers, and laid in both directions along the center lines of the columns. Further rein- forcement was used in the bottom of the slab under the columns and walls, as shown in the illustration. The inverted arch foundation of reinforced concrete as used for a building in New York City presents an unusual type of spread foundation. Its adoption was due to the necessity of having a very shallow foundation. The limit of depth fixed >K td'O'. .rmi , ~ Col.3 Sub Basement Floor ^hSLm . ........ J. ................. 2&0 / -------- - ......... 4 Co/p Fin SubBosement Floor CoAg ^-Waterproofing SECTION Y-Y ' ~ >!< 26^ -J Cokl4 s Wate'-proofinoj FIG. 159*. Cellar Floor Sections Showing Grillage Beams and Reinforced-Concrete Girders, Pope Building, Cleveland, O. by the architect was not sufficient for isolated reinforced-con- crete footings, and as steel I-beam grillages would have cost about 25 percent more, the inverted arch form was used. The arches ran in both directions between columns as shown in Fig. 159^. They were 12 inches deep at the crown and 42 inches deep under the cast-iron column bases, and varied from 4 to 5 feet in width. The reinforcement consisted of |- inch round, straight, corrugated bars in the bottom, spaced 6 inches on centers, and i|-inch bent bars in the top, spaced the same distance. All end spans were made of rectangular or T-shaped concrete beams, to provide for the thrust in the adjoining arches. For further details see Engineering News, vol. 66, page 763, Dec. 28, 1911. In the foundation for the Pope Building, Cleveland, Ohio, a ART. 159 CONCRETE SPREAD FOUNDATIONS 489 combination of a steel grillage and a reinforced-concrete raft foundation was used. The material upon which the founda- tion was placed consisted of a few feet of quicksand overlying clay. As the sides of the lot were enclosed by a permanent steel cofferdam extending well down into the clay, the quick- sand was not subject to outside disturbance, and hence made a satisfactory cushion. A 6-inch layer of concrete was first spread over the bottom and covered with tar and felt water- proofing, after which a 1 6-inch layer of concrete was placed on the waterproofing. On this were located the I-beam gril- lages, as shown in Fig. 1592', section A- A being taken at right angles to the street and section Y-Y parallel with the street. The grillages were made of two tiers of 24-inch I-beams, each supporting a single column. In all the intermediate spaces the concrete floor slab was reinforced with rods, thus providing for the distribution of the column loads over the entire bottom. CHAPTER XVI UNDERPINNING BUILDINGS ART. 1 60. NEEDLE-BEAM UNDERPINNING The technical term underpinning is used to denote the placing of new foundations or supports under existing structures. As an engineering art and science this work has been developed almost entirely in a few large cities, notably New York, Chicago and Boston. In New York the subways and the modern 'sky-scraper,' with its foundations carried far below those of surrounding structures, have compelled the placing of new and deeper foundations for many buildings. Some of these under- pinned buildings have wall loads as high as 45 tons per linear foot and column loads of 300 tons or more. The underpinning of such heavy buildings requires great skill and care, for it must be done in such a manner that no settlement occurs; with the mechanical equipment of the modern office building, such as elevators, motors, engines, etc., a very slight differentia) settlement often causes trouble. Moreover, the work must often be done hastily and in a limited space. The two general methods of underpinning are : First, the use of needle-beams to support the structure temporarily, after which the old foundations are removed and new ones placed; and second, the use of vertical cylinders (without temporarily supporting the structure) in the plane of and under the walls, carried down to solid bearing. The needle-beam method of underpinning may be called the indirect method since the function of the needle-beams is merely to take the loads temporarily from the old foundation to permit removing the latter and the building of new founda- tions. This method is the older and more widely used, being universally applied where the new foundation is of a simple type and not carried to a great depth. 490 ART. 1 60 NEEDLE-BEAM UNDERPINNING 49 1 The fundamental principle of the needle-beam method con- sists in cutting holes through the walls of the building at inter- vals of from 3 to 10 feet or more, depending somewhat on the strength of the walls, and placing wooden or steel beams through these openings. The ends of the beams are held on temporary J ^ k W^-^:V^- "W-W--W-:! UUiJ FIG. i6oa. First Step. FIG. 1606. Second Step. supports placed at a sufficient distance from the wall to permit excavation and reconstruction work to be carried on under the wall. The needles are raised by placing jacks under the ends of the beams until they take bearing on the wall and thus lift the latter from its old foundation. FIG. i6oc. Third Step. FIG. i6od. Fourth Step. Figs. i6oa-d illustrates the general method used in under- pinning the Cross Building, New York City. 1 "The first step was to cut through the old brick wall, which was 56 inches thick, Engineering News, vol. 68, page 1134, Dec. 19, 1912. 49 2 . UNDERPINNING BUILDINGS CHAP. XVI an opening large enough to allow the entering of the needle- beams, made up of four 24-inch I-beams. . . . The needles, which were spaced about 6 feet apart along the wall, were supported on the inside of the old building by blocks placed on the concrete cellar floor, and on the outside by blocks supported on the earth immediately alongside the wall. Sheathing was then driven outside of the blocks, and an excavation made to solid rock. On this rock a rough concrete footing was placed and 12X1 2-inch posts erected to carry the outside end of the needle-beams, the needle-beams then being supported on the inside by blocking on the concrete pavement and on the out- side by heavy posts on a solid concrete footing. Shims were driven in under the brick wall for support and sheathing driven on the inside of the old building, as shown in Fig. i6oc. Excavation was then made under the brick walls to rock bottom, and the entire old footing removed. A new con- crete footing was placed on this rock bottom." . . . Oftentimes conditions make it impossible to occupy the space on both sides of the wall, the space on the inside being perhaps occupied by a store or storage room; or the space on the out- side is taken up with other construction work. In either case the method just described must be modified. One way of avoiding interior work is to use the figure-4 needle-beam as described in Art. 164. A number of arrangements may be em- ployed to avoid occupying space outside the wall, among which the most widely used is the cantilever needling plan described in Art. 163; another scheme uses needle-beams of the regular type at considerable distances apart, the intermediate needles having their outside ends bearing on a truss or girder, parallel and close to the wall on the outside, the ends of the truss or girder bearing on the regular needles. This method materially reduces the space used on the outside. DESIGN OF NEEDLE-BEAMS. Probably the most difficult feature in the design of a needle-beam system lies in estimating the load on any particular member. The rest of the design is a matter of elementary mechanics and needs no discussion here. The total weight of the structure to be supported can usually ART. 161 EXAMPLES WITH NEEDLE-BEAMS 493 be approximated with sufficient accuracy; if the needle-beams are spaced at equal distances apart, it will ordinarily be assumed that all take the same load. To make this a fact, care should be exercised to have all jackscrews raised the same amount. A good scheme is to have one or two men do all this work, giv- ing each jackscrew perhaps half a turn at a time. ART. 161. EXAMPLES WITH NEEDLE -BEAMS Needle-beams are usually supported in one of the following ways: First, by struts resting on concrete bases; second, on piles; or third, on cribbing built on the surface of the ground. The first method is satisfactory where the loads are not unduly large and where good bearing can be obtained; it also takes up the least space. Where the ground is soft a pile foundation Bearin 2Afi IOO*30'o'Long Present WoilFy/ -:^:;---v"^- r ^WV We? New Wall- FIG. i6ia. Underpinning with Needle Beams and Pile Bents. is the only satisfactory method of insuring absolute stability. The crib form may be used where the loads are large and must be distributed over a considerable area of the ground. Fig. i6od illustrates the strut method of support, the details of which are described in Art. 160. Fig. i6ia shows the details of the method used for under- pinning buildings adjacent to the Adams Express Building, New York City. Here the inside ends of the needles were supported on blocking resting on the cellar floor, while the 494 UNDERPINNING BUILDINGS CHAP. XVI outside ends rested on 12X1 2-inch timbers running parallel to the wall, under which were the 5o-ton jacks used in raising and supporting the wall. These in turn rested on small blocks which took bearing on longitudinal 12X1 2-inch timbers, the latter resting on pile bents. J-e'St-eo/ Pipes FIG. i6ib. Underpinning a 3oo-ton Column on Quicksand, Sargent Building, New York City. Fig. i6ib illustrates the form of needling which uses only cribwork for its support. The needle-beams, of which there are four, support a 300- ton column. lu The first-floor beams were blocked and wedged up on the girders close to the columns, 1 Engineering Record, vol. 61, page 649, May 14, 1910. ART. 162 SUPPORTING WALL BELOW BEAMS 495 and sills were laid across them on the first floor adjacent to the column to receive two pairs of posts wedged to bearing on the under side of the box girder close to the column. The wedges were driven and the jacks operated to take the floor and wall loads from the column to the cribbing and to compen- sate for any settlement of the latter." Fig. 1620 shows the method of underpinning the Benedict Building, New York City. The needle-beams rested on struts on the outside and cribbing on the inside. Holes about 5 feet apart were first cut in the wall and into these holes were inserted needle-beams composed of 1 5-inch I-beams in groups of three, each group being tied together with iron yokes at both ends. On the outer end of the needle-beams two 2o-ton jack- screws rested on two i2Xi2-inch vertical posts and took bearing against horizontal steel plates on the lower flanges of the I-beams. The posts took bearing at their lower ends on 5 X 5-foot grillages of i2Xi2-inch timbers resting on the concrete footing. ART. 162. SUPPORTING WALL BELOW BEAMS With the needle-beam method of underpinning it is usually impracticable to support the wall from below the old founda- tion. For this reason, if the new foundation is to be con- structed only up to the old, it becomes necessary to use some special method of supporting the wall and old foundation below the needling. In the case of the Benedict Building, Fig. 1620, this was done as follows: 1 " Narrow excavations were made between the old wall and the sheeted pits, and the latter were braced against the face of the masonry as the excavation proceeded. When it reached the bottom of the old footing, small drifts were extended under it and in them 'springing needles', each consisting of a pair of i2Xi2-inch horizontal timbers bolted to the verti- cal shores, were inserted with their ends bearing against the bottom of the old footing. Vertical chains with turnbuckle 'Engineering Record, vol. 55, page 267, March 2, 1907. 496 UNDERPINNING BUILDINGS CHAP. XVI adjustments were attached to the I-beam needles above, close to the face of the wall, and engaged the springing needles, formed fulcrums for the latter which acted as cantilevers sup- porting the footing below the main needle-beams. A vertical CITY INVESTING CO. BUILDING BENEDICT BUILDING FIG. 1620. Underpinning Methods for Benedict Building, New York. strut was inserted between the ends of the springing beams and the I-beam needles to relieve the connection to the vertical shores and take the upward cantilever reaction." Fig. 1626 illustrates another method for a suspended sup- ART. 163 THE CANTILEVER METHOD 497 port for the footing. l " A steel bearing plate was seated across the top flanges of each pair of I-beams and gave bearing for the nuts on the upper ends of two 2-inch vertical rods about 7 feet long. The nuts on the lower ends of these rods engaged a cross plate or saddle, forming a fulcrum for an 8-inch hori- zontal cantilever I-beam 10 feet long. The long arms of the cantilever reacted upward against some of the I-beam stringers supporting the outer ends of the needle-beams. The short FIG. 1626. -Suspended Support for Footing, Silversmith' s Building, New York. arms took bearings about 2 feet long on the under side of the old concrete footing, supporting it across the thickness of the wall, so that when undermined by the excavation for the new foundation the old footing looked in cross-sections like a cantilever projecting about 2 feet beyond the inner face of the wall and proved strong enough to resist the bending moment thus developed. " ART. 163. THE CANTILEVER METHOD Where, for some reason, the work cannot be carried on from both sides of the wall, the cantilever method may be employed. The possible modifications of this method are many, but two examples are illustrated to show the fundamental principles. In the construction of the present building at No. 42 Broad- 1 Engineering Record, vol. 56, page 348, Sept. 28, 1907. 32 UNDERPINNING BUILDINGS CHAP. XVI way, New York City, it was necessary to sink caissons close to the seven-story building then occupying the site of No. 44 Broadway. In order not to delay the sinking of the caissons it became necessary to avoid supporting some of the needle- beams on the site of No. 42. For this reason the scheme shown in Fig. 1 63 a was adopted. lu Two groups of five 20-inch I-beams, 30 feet long and 21 feet apart in the clear, were put through the foot of the wall Crib. Fulcrum Beams suspended from Needle Girders FIG. 163(1. Counter- weighted Needle Beams and Girders, for Building at 44 Brtfadway, New York City. at right angles and supported on crib work and jackscrews at both ends. In building No. 44 there were suspended from both groups close to the wall, four 24-inch I-beams 30 feet long carried on yokes screwed up close to the under side of the needle girders. These beams served as a fulcrum to sup- port three sets of four 20-inch cantilever I-beams each. These Engineering Record, vol. 48, page 698, Dec. 5, 1903. ART. 163 THE CANTILEVER METHOD 499 Pig Iror Brick Pier- Recess ii il \ Section Y-Y ji I*PM KK* ; ^^BL^^ i ^^>^><^^r i *^'" f /////// '//// //Y T^M ax 7/7 Sectional Elevation X'X K-- -^ - About 10' 0" h/4^/ JLtafcLMLU Secnonal Elevat,on V-V Secfl n W ' W FIG. 1636. Arrangement of Underpinning, 92-94 Maiden Lane, New York City. 5OO UNDERPINNING BUILDINGS CHAP. XVI cantilevers were located in the center and at both ends of the section of the wall included between the needle girders so as to leave about equal space between them. They converged in No. 44 where a platform was built on their extremities and loaded with pig iron to form a counterweight against the upward reaction. The wall was supported on the needle girders and on the ends of the cantilevers by double rows of special 20- ton jackscrews." An example of underpinning in which all the supporting was done from the inside, in order not to interfere with con- struction work carried on outside, is shown in Fig. 163 b. The needle-beams, with their ends inserted in holes in the wall, were fulcrumed on jackscrews 5 feet from the inside face of the wall. The beams took bearing on blocks of wood which were bored at each end for a 4-inch jackscrew and which rested on cast-steel nuts engaging the screws. The lower ends of the screws took bearing on cast-steel base plates seated on sills which transmitted the load to a timber grillage. Auxiliary supports were wedged up against the needles to take the load in case of failure of the jacks. The wall loads were transferred to the needles through timber blocks with a few inches of cement on top to develop more uniform bearing. The sets of needles were spaced 9 or 10 feet apart, but, as shown in Section W-W, Fig. 163^, inter- mediate bearing was obtained through blocking and wedges resting on an 8 X 8-inch horizontal beam. Supporting tim- bers were jacked up under the lower flanges of the needles in the plane of the wall as a precautionary measure, until the new foundation was ready to be constructed. The long arms of the cantilevers reacted against the main floor girders in the first floor through blocking and wedges, and were further held down by cast-iron ballast and by anchor- ing to the piers through pairs of horizontal I-beams. The latter engaged recesses in the piers and had transverse pieces across their bottom flanges. To these transverse pieces were attached lengths of wire rope passing up over the blocks on top of the needles. ART. 164 FIGURE-FOUR NEEDLES 501 ART. 164. FIGURE-FOUR NEEDLES The methods explained in the last article are used where it is necessary to avoid using space on the outside of the building. Where there is no available space on the inside, the figure-4 method is generally employed. Fig. 1640 shows the details of this method as used in the Bene- dict Building, New York City. Pits 5 feet square and about 6 feet on centers were first excavated and sheeted to about 30 feet below the curb, and on the bottom a 3-foot layer of concrete was placed. On this concrete a timber grillage was erected to dis- tribute the load from a i2Xi2-inch shore to the concrete foot- ing. The lower ends of the shores, which were about 30 feet long, took bearing against short horizontal timbers, the latter in turn bearing against either one or two jackscrews reacting against foot blocks. The upper end of each shore was sur- mounted with a saddle plate and wedges and was notched into the wall. The saddle plate gave bearing to i-inch vertical rod suspenders, to the lower ends of which were fastened turnbuckles and chains, engaging the 12X1 2-inch needle-beams. The springing needles, which by a cantilever action took the load from the wall, were placed by first excavating the space between the sheeted pits and the wall. The outer ends were bolted to the inclined shores and took bearing against reaction cleats above them. To take the weight of the wall from the old footing the jack- screws were first operated to bring the shore to a tight bearing to take some of the weight of the wall above, after which the turnbuckles were screwed up until the remainder of the weight of the wall was transferred to the system of needles. With this type of underpinning a very stable footing must be provided for the lower end of the shore, for, whereas with the ordinary form of needle underpinning a part of the weight of the wall is transferred to one side and a part to the other, here the entire weight is carried to one side. Another condition to guard against is the tendency of the shore to push in the wall on account of the horizontal component of its thrust^ This hori- 502 UNDERPINNING BUILDINGS CHAP. XVI CITY INVESTING CO. BUILDING Wed Saddle plat BENEDICT BUILDING FIG. 1640 Underpinning with Figure-Four Needle Method, Benedict Building, New York City. FIG. 1646. Use of Long Shores in Underpinning Cross Building, New York. (Facing p. 502.) ART. 165 PLACING THE NEW FOUNDATION 503 zontal force is ordinarily not large and almost any building has sufficient strength to withstand it if the shore be inserted at a floor level, thus permitting the floor system to transmit it to all parts of the building. SHORES OR PUSHERS. As an auxiliary to other methods shores are often used in underpinning work. Fundamentally they are the figure 4 needle-beams without the vertical rod FIG. 164(7. Showing Ashlar Face Wall of the Fanner's Loan & Trust Company's Building in New York City. and horizontal needles, and as a result they can take only the weight of the wall above the points at which the struts are notched into them. For this reason the use of shores must be combined with some other type of underpinning. Fig. 164^ shows several long shores inserted, while Fig. 164^ illustrates the use of shorter shores. ART. 165. PLACING THE NEW FOUNDATION As the object of underpinning is the protection of foundations from being undermined through the excavation of adjacent 504 UNDERPINNING BUILDINGS CHAP. XVI material at a lower level, it follows that in general only those structures having shallow foundations will require underpinning. The two types of new foundations are the shallow and the deep foundations. The former consists of a simple masonry or con- crete footing, or of a spread footing, and is the type which uses the needle-beam method of underpinning. The new foundation is placed as deep as the new excavation is to be made. The deep foundation includes the cylinder, the caisson and the tubular pile piers. Masonry and concrete footings, as well as spread footings, are described in Chap. XV. Curb Level El. -t-is-i. CELLAR Ce/lar Floor El +6^} -Brick Pier* Brick Restored Curb LeveH VAULT Cel/ar Floor-? FIG. i65<2. Method of Underpinning Centre Street Buildings, New York, due to Subway Excavations. Where pier systems are used, it is customary to give the wall no temporary support as the sinking operations deprive the wall of but a small section of bearing at a time. Conditions sometimes are such that it is advisable to temporarily sup- port the wall on needle-beams before sinking the piers. Such is the case where the wall is weak or is too light to take the cylinder reactions. Fig. 1650 illustrates a case in which steel cylinders were use:l. ART. 165 PLACING THE NEW FOUNDATION 505 It closely resembles the Breuchaud method described in the following articles, the essential difference being that here needle- beams were used temporarily to take the load. Horizontal I-beams recessed into the face of the wall carried its weight to the transverse 24-inch I-beams, which served the double purpose of carrying the weight of the wall thus allow- ing deep trenches to be dug under the same and of furnishing FIG. 1656. Method of Sinking Open Cribs for Underpinning, Merchant's and Trader's Bank Building, New York. reactions for sinking the sectional steel pipe by hydraulic jacks. The cylinders were sunk to solid bearing, filled with concrete and capped with a footing wall on which was built the new brick wall to connect to the old wall. The left-hand illustration shows a single cylinder, and the right-hand illustration two cylinders being used. Fig. 1656 indicates the use of a caisson for the new founda- tion of a column. 1 " A heavy bracket made of a steel plate 26 inches long and ii inches thick, bent at right angles, was Engineering Record, vol. 49, page 135, Jan. 30, 1904. 506 UNDERPINNING BUILDINGS CHAP. XVI secured to the street face of the column by five f-inch stud- bolts. Its longitudinal face took bearing on the upper flange of a 24-inch I-beam needle parallel to the street line which was supported on a sill in the sidewalk vault and on cribbing in the excavation for the new building. The granite pedestal was removed, the concrete footing torn out and the excavation carried down a little lower to receive ther bottom course of a timber crib or caisson 36 inches wide and 42 inches long inside. This course consisted of four 4X1 2-inch oak planks set edge- wise, and having their lower sides beveled to a cutting edge. They were connected at the corners by short vertical angles and had i-inch tie-rods with countersunk heads in the direc- tion transverse to the lot line. The two sides parallel with the lot line had mortised joints with the other two sides, and the frame thus formed was provided with vertical oak dowels i inch in diameter which projected from the upper edge to lock it to the succeeding course. "Timbers were set on the upper edges of the planks, and two 30-ton jacks seated in the middle of them reacted against the granite pedestal which was inserted between their tops and the base plate. A laborer with a shovel and scoop exca- vated the sand from the interior of this caisson as it was forced down by two other men operating the hydraulic jacks. When the jacks had made a full stroke, the pedestal was sup- ported by cross pieces temporarily inserted under it and bear- ing on needle beams and sills. The jacks were then released, another course added to the caisson, the jacks replaced, the caisson forced down and excavation continued and so on," . . . When the caisson was sunk to place the bottom of the excavation was carefully leveled and the excavation filled with concrete rammed in 6-inch layers. ART. 166. JOINING TO THE OLD WALL After needling the wall and placing the new concrete founda- tion, brick piers are built upon the new foundation between the needles to within a few feet of the bottom of the old wall. On ART. 167 THE BREUCHAUD PROCESS 507 these piers are placed pairs of cut stones of the same length and thickness as the piers, and about 14 inches high. One stone sets loosely on the other, with pairs of steel wedges between. The brick pier is then continued on the upper stones until the under side of the old wall is reached, to which it is carefully joined. The wedges are then driven together until the load is lifted from the needles, after which the latter are removed and the brickwork of the wall completed, the final appearance being that shown in Fig. i6$a. The wedges are then sawed off flush with the faces of the wall and the space between the cut stones filled with grout. Theoretically, the entire load is carried through the wedges but actually some settlement doubtless occurs to distribute the load throughout the length of the wall. The caisson foundation shown in Fig. 1656 was joined to the column as follows: ia The top of the caisson was covered by heavy flagstones set so as not to bear on the timber walls, and on them a brick pier was built up nearly to the height of the granite pedestal and capped with a cut granite block, be- tween which and the pedestal, pairs of steel wedges were driven until the weight of the column was transferred from the needle beam to the new footing." ART. 167. THE BREUCHAUD PROCESS The Breuchaud process of underpinning consists of sinking a series of cylinders in the plane of the wall and spaced a few feet apart. They are sunk to hard-pan or rock and form the support for the wall. The work is carried out in the following order: First, horizontal and vertical recesses are cut in the wall near its foot; second, horizontal bearing beams and verti- cal steel cylinders are placed in these recesses; third, the cylin- ders are forced down to solid bearing by jacking against the under side of the horizontal beams and by excavating the material from the interior of the cylinder; and fourth, the cylinders are then filled with concrete and wedged against the 1 Engineering Record, vol. 49, page 135, Jan. 30, 1904. 508 UNDERPINNING BUILDINGS CHAP. XVI horizontal beams, thus transferring the weight of the wall from the original supports to rock or hard-pan. This method possesses the following advantages over the needle-beam method: First, it occupies less space; second, it makes it unnecessary to enter the basement of the building, the cutting being done from the outside and usually not en- tirely through the wall; and third, it is cheaper if the founda- tion is to be carried down a considerable distance. In general it may be said that for shallow underpinning the needle-beam method is preferable; while for deep work the Breuchaud method, or a modification of the same, is better. The Breuchaud process may be divided into two systems, the pipe and the cylinder. The essential difference in the opera- tion of the two systems lies in the fact that workmen can enter the cylinders but not the pipes. DESCRIPTION OF SHELLS. The shells are usually made with a cutting-edge section of steel, and with other sections of steel or cast iron. The sections are from 4 to 8 feet in length, and when of cast iron are flange-bolted on the inside; when of steel they may be flange-bolted or fastened with a screw joint. The load to be carried or the necessity for workmen to enter the cylinder determines their diameter. The magnitude of the load to be taken by a cylinder depends upon the weight of the wall per linear foot and the spacing of the cylinders. The shells are usually designed to take all the load, no reliance being placed on the concrete filling to assist in carrying it, the reason for this being that the load is placed on the cylinders before the concrete hardens. The spacing of the cylinders cannot vary between wide limits, for on the one hand there must be a clear- ance between cylinders sufficient to furnish proper bearing area on the soil while the piers are being sunk, while on the other hand the maximum spacing is limited, owing to the local concentrated stresses involved in carrying the load from the wall to the cylinder. The usual spacing of cylinders is from 5 to 12 feet. The cylinders may vary in diameter from about 6 inches, carrying a load of from 30 to 40 tons each, to 3 or 4 feet, carrying a load as high as 400 tons. A double-shell ART. 167 THE BREUCHAUD PROCESS 509 cylinder is sometimes used, in which case added strength is developed by breaking horizontal joints. If workmen are to enter the cylinder the latter should have a diameter of at least 30 inches. This will be desirable where boulders are encountered, where sinking must be done through hard-pan, or where it is desired to carefully prepare the bottom on completion of sinking. The work in the cylinder must usually be done under air pressure and hence they are made so as to be easily transformed into pneumatic caissons. In Fig. 1670 is shown the lower riveted steel section of the cylinders and the air-lock used in underpinning the Stokes Building, an eleven-story structure having a wall load of 45 tons per linear foot. The top of this section was .faced to receive the bottom of the lowest of the cast-iron sections, which were made in 6-foot lengths ordinarily, with special 2- and 4-foot lengths to finish out with. The flange connections were made with twenty-eight i-inch steel bolts, and were machine faced to give a clearance in order to prevent bearing of flanges, so that the pressure would be transmitted directly through the shells of the cylinder. The cylinders were built up to the required height and on the upper sections were placed the steel- plate bearing rings to receive the girders on which rested the jacks. The 5-inch pipe carried away the material washed out. On reaching hard-pan the bearing ring was removed and there was inserted between the flanges of the last two sections a heavy cast diaphragm. A similar one was also placed on top of the upper section. The top section was then made to serve as an air-lock by fitting steel doors with rubber gaskets, to the under sides of the diaphragms. The cylinders used in underpinning the Trust Company of America Building, New York City, were made entirely of steel and were 3 feet in diameter, with two longitudinal lock- bar joints. The metal was f inch thick. Each section had horizontal circular angles riveted to it at both ends to provide flanges for connecting the successive sections. In some underpinning at No. 73-75 East 54th Street, New York, cylinders of f-inch steel and 12 inches in diameter were UNDERPINNING BUILDINGS CHAP. XVI 7. C V c a a bj| j i" s \ / 5 * ART. 1 68 METHOD OF SINKING CYLINDERS used. They were first set up in 20-foot lengths. x "As these were jacked down the upper sections, 4 feet long, were coupled to them by inside cast-iron sleeves about f inch thick and 9 inches long, slightly tapered at the ends to enter the pipe and having a horizontal exterior rib, about i inch wide, and of the same thickness as the pipe, on the center line. The edges of the rib were slightly beveled so that the ends of the pipe would draw up against it and make a solid contact undef heavy pres- sure, thus insuring a perfect fit and very rapid assembling of the pipe sections as the work progressed." ART. 1 68. METHOD OF SINKING CYLINDERS The cylinders are sunk: First, by means of hydraulic or screw jacks bearing against the wall above and forcing them down; second, by using a water-jet on the inside of the cylinder to loosen the material around the cutting edge; and third, by excavating the material from the inside. A horizontal recess of a size sufficient to receive I-beams is first made in the wall about 12 feet above its base. I-beams are then placed in it and wedged up tightly against the top, after which a vertical recess, extending from the horizontal recess to the foot of the wall, is cut out. The horizontal beams serve the double function of carrying the weight of the wall above the vertical recess and acting as a reaction for the jacks used in sinking the cylinders. On completion of the vertical recess the lower section of the cylinder is placed in position in the recess. A screw or hydraulic jack is then placed on the section and forces the cylinder down by reacting against the horizon- tal I-beams through blocking. As soon as the cylinder has been forced down a distance equal to the full stroke of the jack more blocking is placed between the latter and the bear- ing beams, and the operation repeated. On completion of the sinking of one section of the cylinder another section is added and the operation repeated until the cutting edge has reached the desired position. 1 Engineering Record, vol. 64, page 276, Sept. 2, 1911. 512 UNDERPINNING BUILDINGS CHAP. XVI In the case of the larger cylinders fitted for pneumatic pres- sure, they are sunk as far as possible by washing out the material, assisted perhaps by a sand pump; the doors are then put on and the remainder of the sinking is done by the pneumatic process. At the same time jacks are operated to force the cylinder down. In the case of the smaller pipes the material is sometimes bored out with an auger, a g-inch auger being used fbr a lo-inch pipe. The following description, together with that given in Art. 167, shows the method used in placing the cylinders for the Stokes Building, this being the first large structure in which the Brick Wall of Stokes Building Concrete Elevation. Isometric View. FIG. i68a. Recesses Cut in the Wall for Underpinning. Breuchaud method of underpinning was applied, the work being done in 1896. Recesses of the form shown in Fig. i6Sa were cut in the wall to a depth of 3 feet, the material in the upper horizontal rectangle being first removed. Five i5~inch I- beams were then placed in this opening and wedged tightly against the upper surface of the recess. The vertical rec- tangular recess was then cut out. A section of the cylinder was then placed in the vertical recess and on it were placed two I-beams 34 inches long. On these I-beams rested a large hydraulic jack which took bearing on the 1 5-inch I-beams above through timber blocking. As the cylinder was jacked down the material inside was washed out with a jet pipe. ART. 169 CONCRETING THE CYLINDERS 513 ART. 169. CONCRETING THE CYLINDERS Curb Ef.0.0 '.'}'.- ';*- v- 1 ; ili -OricrJnat Footing-Mills Building Wafer hi FIG. 1690. Typical Underpinning Cylin- der for Mills Building, New York. 33 Where pipes are used little can be done in preparing the bottom further than to inspect it; to pump out the water if possible; and to see by means of an electric light if the de- sired bearing has been reached and that all loose material has been removed. On the other hand, with the larger cylinders the bottom can be cleaned and leveled off, and the foundation bearing extended if desired. This was done in the Old Mills Building of New York, by spread- ing out the opening through the hard-pan to a maximum diameter of 5 feet 6 inches. Radial steel grillage beams, Fig. 1690, resting on a concrete footing, took the load from the cylin- der through steel wedges. A 1-2-4 concrete is ordinarily used for the cylinder filling. For pipe cylinders the con- crete must very often be placed through water. To insure a rich mixture at the bottom it is advisable first to pump in some grout or to drop in some dry cement, and on this to place the concrete. After placing a few feet of the concrete and allowing it to harden, the pipe may be pumped out and the remainder of the concrete laid in the dry. Where deposited through water a cylindrical bucket of a diameter somewhat smaller than that of the pipe and about 3 feet long is often used. The bucket has a flap bottom, and two lines, one Top of H&rd Pprn ftac/ic*/ Steel frrillage Beams Pock, El. -65.0 ' -$>-6"---?>\ ' EN&.N! UNDERPINNING BUILDINGS CHAP. XVI attached to the bail of the bucket and the other to the flap. In lowering the bucket the weight is carried by the flap line but after the bucket is seated on the bottom it is pulled up by the bail line, which causes the concrete to be deposited through the bottom. This avoids any possibility of the water washing the concrete and separating the constituent materials. For pneumatic cylinders the working chamber is first filled with concrete, with perhaps a layer of grout or mortar on the bottom, after which the air pressure is left on for about 48 hours. The remainder of the cylinder is then filled with concrete. ART. 170. TRANSFERRING LOAD TO CYLINDER Fig. 170^ illustrates the method used in transferring the loads to the cylinders in the Empire Building, New York. The underpinning cylinders were first capped and the recess _ , , . , , , above them filled with brick work to a certain height. On this brickwork two granite blocks were placed, one resting loosely on the other, after which the remainder of the brickwork was placed. Pairs of steel wedges were then inserted between the granite bearing blocks and driven together, thus separating the two blocks and bringing the wall loads to the cylinders. The FIG. 1700. Underpinning the Empire , nflrp Kptwppn tViP hlorti wac Building, New York. " l WC( |OCKS WaS then filled with cement grout. After the cylinders of the Stokes Building had been filled with concrete the top of each cylinder was capped with a top bearing plate (Fig. 1670.) Five I-beams were then placed on the top of each cylinder as shown in Fig. 1706. Steel posts were placed in the vertical recess and rested on steel plates which in turn rested on the lower tier of I-beams, the posts extending to within 2 inches of the under side of the upper tier ART. 171 OTHER MODERN METHODS 515 of I-beams previously placed (Art. 168). Steel plates were placed on these posts and pairs of forged steel wedges then driven together between these plates and the lower stokes Bui/ding surface of the upper tier of I-beams to bring the wall load to the cylinder. After this the recess was solidly bricked up. The lower tier of I- beams serves a triple pur- pose: First, it reduces the amount of load com- ing through the upper tier, thus lessening the stress in the brickwork at that point; second, it car- ries the weight of the wall below the upper tier of beams to the pier, where it must otherwise remain on the old foot- ing; and third, it elimi- nates stress in the new brickwork in the vertical recess. 5-' 'Bea ' / j 'S/ '?->,'',ncirdpa Part Elevation. im#^/ m$& fyffiffi'. Cross Section. FIG. 1706. Underpinning the Stokes Build- ing, New York City. ART. 171. OTHER MODERN METHODS' Another method of underpinning, developed to cheapen the cost and reduce the risk in many cases, especially where the building to be underpinned is light or poorly constructed, is to sink shafts with plates, as was done in underpinning the Cambridge B uilding, New York City. ia The cylinders (Fig. 1710) were 4 feet in diameter, and had Underpinning the Cambridge Building, New York City, by T. K. THOMSON Trans. Am. Soc. C. E., vol. 67, page 553. UNDERPINNING BUILDINGS CHAP. XVI very thin shells. The method of placing them constitutes a new system of underpinning; for, instead of placing the bottom section first and jacking it into the ground, and then plac- ing another section on top and repeating the operation, 40 Sectional Plan, Enlarqed. All Plates to have square Edges flush with Heel of Angle. /Ill Angles 2% "*2i "x %'. All Rivets "Diam., Heads Flattened Outside. All ' open Holes ~"Diam, Each Shaft ft be put down as a Vertical Tunnel, Using Poling Boards if necessary, and Compressed Air if Water is encountered. Spaces behind 5hells to be filled with 6 rout. j Top i s 'i $ection i s ,?i'*ttW ^ 41 \ j --.. - 1 T^PIates S^ 4 FIG. lyia. Elevation. Underpinning by THOMSON'S Method of Vertical Tunneling. a space was excavated for the top section, which was made 4 feet deep, and the space outside of this top section was back- filled, generally with concrete, and remained permanently in that position. ART. 171 OTHER MODERN METHODS 517 "A laborer then entered the top section and, with a short- handled shovel, excavated the material under the cutting edge sufficiently to insert one segment of the next ring. All the rings below the top section were 2 feet deep and in four segments, one of which was small, to act as a key, as in tunnel lining. In this key segment the connection angles were bent 13^ degrees from the radial, to permit putting the key in place. The joints of the other segments, of course, were on the radial lines. All the plates were f\ inch thick, and all the angles, both horizontal and vertical, were 2^X2|Xi inches. When the first segment under the top section had been bolted in place, the excavation was made for the second segment, then the third, and then the fourth or key. Where the ground was good, the excavation was made for all four segments at once." No water was encountered in the above operation, thus elimi- nating the necessity for using air pressure. Where the latter is used all joints must be caulked. Another method patented by OGDEN MERRILL, makes use of a nest of telescoped cylinders or caissons. The upper section is first jacked down and then the other sections are jacked inside of this, after removing the material from the inside. The pneu- matic process has been applied also to this form of construction. CHAPTER XVII EXPLORATIONS AND UNIT LOADS ART. 172. TEST PITS AND SOUNDING RODS A simple method of examining a foundation site is to sink test pits by open excavation somewhat deeper than the exca- vation otherwise required for the substructure. Sometimes it may be necessary to line the pit with sheeting and to use a hand pump to keep down the water, but instead of increasing the cost materially on this account, other methods may be adopted. The principal advantage of the open pit consists in the possibility of examining not only the variation in character of the earth encountered but in observing the degree of its natural compactness when in place. This method is practi- cally confined to shallow foundations. A sounding rod consists of an iron rod or pipe, i or i^ inches in diameter, which is driven into the ground with a maul, and turned after each blow. It serves merely to determine whether the resistance is increasing or decreasing, variable or constant. A sunken log, boulder, or some other obstruction can stop the driving. The information thus secured is so unsatisfactory and inadequate that it is frequently misleading. The rod may find a stratum of gravel but fail to reach the soft stratum underneath it, because the resistance is so large that it cannot be driven farther. In one instance, eight men on the handle bar were unable to push the sounding rod over 7 feet into stiff mud or clay, but on driving test piles at the same spot no difficulty was found in driving down 70- foot piles. The following quotation indicates the manner in which sound- ing rods are sometimes used in practice: "Adjacent to the wooden test piles, and in other places, the soil was tested and explored by driving standard steel test rods i inch in diameter ART. 173 BORINGS WITH AUGERS 519 made up of 4-foot sections connected by screwed sleeve couplings. They were driven by a 1 2-pound sledge to a refusal of from i to \ inch for the last blow, at which their penetration was assumed to afford a reliable indica- tion of the penetration of a standard tapered concrete pile driven to the required refusal." ART. 173. BORINGS WITH AUGERS A simple and effective tool to use in exploring the site under proposed structures consists of an ordinary wood-auger 2 inches in diameter welded to a black pipe about 18 inches long, and which is connected by ordinary couplings to 1 2-foot sections of pipe. The handle used in turning is 2 feet long and is made of two pieces of f-inch round iron welded to a strong ring that will pass freely over the coupling, and is secured to the pipe by a f X2|-inch set-screw. In starting the boring great care is necessary to keep the auger vertical. Five turns fill the bit, which is then with- drawn to the surface, and cleaned after examining the material. When the hole is too deep to raise the auger by hand, it is lifted by a block and fall suspended from a wooden folding tripod, a 3-foot chain being used to grip the pipe. Before lowering the chain for a new grip, the handle is attached, so that there is no chance of the auger dropping when any sec- tions of the pipe have been removed. Another auger I inch in diameter connected to 6-foot sections of |-inch pipe is required when the hole becomes clogged so that the larger auger can no longer be used. With dry sand it is necessary to pour enough water into the hole to make the grains stick together that they may be lifted. When sand and gravel become troublesome and the hole will not retain its shape, a 3-inch casing is driven, being handled in 4- or 5- foot lengths. A 2-inch drill with chisel point attached to sections of pipe like the auger, may also be needed to cut through some obstructions. Borings with augers have been used for depths up to 100 feet. The borings are regularly inspected as the ground is pene- trated and a record kept of the depths and variations of mate- 520 EXPLORATIONS AND UNIT LOADS CHAP. XVII rials encountered. Even with the aid of the casing this method of boring is not applicable in fine-running gravel or in quick- sand unless it is a thin stratum. The loose material may then be removed by a sand pump which consists of a narrow cylin- drical bucket with a cutting edge at the bottom and above this a flap valve opening upward. It is partly filled by rapidly raising and dropping it alternately. One form of earth or clay auger has two cylindrical cutters pointed and bent at the bottom, so as to draw the auger into the earth, and after rotation, to support a lot of excavated material during its withdrawal to the surface. This tool is designed to penetrate compact material like hard-pan and frozen earth. Sometimes the hole will retain its shape better if the di- ameter is larger. It is claimed that a diameter of 8 inches is frequently advantageous for ordinary depths unless the pro- portion of sand is too large. A post-hole digger may be used up to about 1 6 feet. ART. 174. WASH BORINGS When considerable work is to be done a standard outfit for wash-drill borings is employed which consists of a small der- rick or tripod, the casing, hollow drill rods, and a hand force pump, together with their accessories and necessary tools. A convenient size of tripod has timber legs 3X4 inches in section and 18 feet long. The rope for raising and lowering the casing and drill rods is manipulated either directly by hand or with the aid of a drum. The casing is composed of extra heavy pipe in about 5-foot lengths, with flush joints so as to form a smooth exterior surface. The usual size has a nominal inside diameter of 2\ inches. The hollow drill rods are made of heavy seamless steel tubing usually in 5-foot lengths, but sometimes as long as 16 feet, connected by special coupling pieces about 6 inches long. The usual size of drill rod has an outside diameter of ij inches for a 2! -inch casing. To the bottom drill rod is attached a chopping bit with an X-shaped ART. 174 WASH BORINGS chisel point, and with four openings for the water-jet. The hand pump consists of. a double-acting force pump with a single hand lever and i|-inch suction. The upper drill rod is connected to the hose from the pump by means of a hoisting water swivel, so that it may be raised or lowered and rotated during operation without twisting the hose. During operation water is forced down through the hollow drill rod, and, escaping through the jet at the bit, carries upward the loose material in the annular space between the rods and casing. In suitable material the drill rod is worked down by rotating it. In harder material it must be lowered by 'churn- ing.' This is accomplished by raising it up a short distance and letting it drop. Meanwhile the casing is also worked down by rotating it. If this will not answer the purpose, the casing must be driven down. If the tripod has only a single pulley the drill rods have to be withdrawn when the casing is to be driven deeper. By using a double block and a jar weight the operation of driving the casing may go on simultaneously with the drilling and jetting. In this manner the casing is kept loose. To protect the casing a drive head is screwed into the top section and into that a hollow guide which guides the cylindrical jar weight in its movements. The upper section of the casing has slots in the side for the escape of the water and sediment or other loosened material. After the overflow which is caught in a bucket has settled, samples are taken and put in glass bottles for preservation. They are properly labelled to correspond with other records. This operation is continued until the required depth is reached or until obstacles like boulders are encountered. If a boulder is not too large a small charge of dynamite may be used by an experienced operator, care being taken to raise the casing high enough to avoid any damage from the explosion. With this equipment borings _can be made in sand, gravel, clay, in varying degrees of hardness, including indurated clay and hard-pan. For borings into rock, shot drills or diamond drills are required. When only a small amount of work is to be done and in light 522 EXPLORATIONS AND UNIT LOADS CHAP. XVII or sandy material, a less expensive outfit may be employed. Ordinary pipe can be used for the casing, a good size being 2 inches in diameter. Gas or water pipe f inch in diameter may be substituted for the hollow drill rods, with a water swivel made of ordinary bends and nipples. Lighter chopping bits may be used. Sometimes the bit has only a single chisel point with an opening on each side for the jet, or the bit may be re- placed by a plain jet pipe. In silt and some mixtures of clay and sand, it may not be necessary always to have the casing follow the inner pipe to its full depth as the material will retain the shape of the hole. In sand and gravel both pipes must be sunk together, pains being taken to keep them turning and occa- sionally to lift the inner pipe a little to prevent it from binding. In some instances the casing has teeth cut into the end of its lower section which is also flared out slightly. This will facilitate sinking by rotation, but little, if any, hammering being required. Since only the finer material may be washed up while the coarser material is pushed aside in the hole which is scoured out by the jet, it is possible to misinterpret the indications of wash borings. In order to obtain samples of the material pene- trated in its natural relation, the bit or jet may be re- placed temporarily by a short piece of brass pipe which is then pressed into the softened ground at the bottom and lifted out for examination. It is not always possible to distinguish between a large boulder and bedrock. By making a number of borings on different parts of a foundation site and comparing the eleva- tions of the supposed rock surface it may be assumed that unless these are nearly at the same level, the higher erratic elevations may indicate boulders. Additional borings should be" made near these locations to see whether greater penetra- tions can be obtained. Since the action of the jet and of the chopping bit often radically change the natural condition of some material pene- trated, it is desirable to take out dry samples or cores whenever feasible. This can be done in the hardest clay or the softer ART. 174 WASH BORINGS 523 shales by using a saw-tooth bit working dry. and thus obtain a perfect knowledge of the material. Unless this is done a hard clay which is suitable in every way for a foundation bed may be passed by, and thus incur unnecessary extra expense to carry the foundation to a lower level. Although in some cases the results obtained by wash borings alone may be only negative their use in conjunction with core borings for the balance of the depth required may save expense by materially reducing the number of core borings. The records of test borings should show the kinds of material, the thickness of various strata, the elevation of ground water, etc. By comparing these data for various parts of the site it can be seen whether any given stratum is fairly uniform in thickness or runs out between two borings; and which stratum should be selected to bear the given load, or to receive some further test by loading if necessary. As an illustration of the information furnished by borings and what its effect was upon the construction of the founda- tion, reference is made to Eng. News, vol. 68, page 914, Nov. 14, 1912. The site of the Brooklyn anchorage pier of the Man- hattan bridge was explored by nine preliminary test borings which indicated sand, gravel, boulders and clay in irregular strata down to rock at a depth of 70 to 75 feet below mean high water. Tests of the ground were made by loading it and by driving piles, and from a study of all these results and the surrounding conditions it was decided to drive bearing piles to carry the foundation load. An analysis of cost for wash-drill borings made in Resi- dency No. 5 of the New York State Barge Canal may be found- in a valuable article by EMILE Low in Eng. News, vol. 57, page 54, Jan. 17, 1907. The analysis includes 14 items of cost, and the total cost per linear foot of boring for 17 monthly ac- counts and several field parties, ranges from 17.55 to 5 2 -^3 cents, the average being 36.97 cents. The average depth of hole is 27.7 feet. The cost given does not include that of the plant nor that of extraordinary repairs, for which an addition should be made estimated at 2 cents. The cost of the outfit 524 EXPLORATIONS AND UNIT LOADS CHAP. XVII and tools required for each party was $277.98. The article gives a full description of the equipment, copies of the forms used for records and reports, and the character of the material penetrated for each account. The costs for similar borings made on the Deep Waterways Surveys in the same state during 1897 to 1900, are 11.2, 13.0, 25.1, 54.1, 68.4, 70.6 and 85.2 cents per foot for different routes or divisions. The borings varied in depth from a few feet to 190 feet. ART. 175. CORE DRILLING WITH DIAMONDS Rock strata are tested by using core drills to remove specimens of the rock in the form of cores which can be examined. In some of these drills the cutting is done by black diamonds, in others by chilled shot or crushed steel, and in still others by toothed cutters. In the operation of a diamond drill a hollow bit is rotated rapidly, in which two rows of diamonds are set around the edge in such a manner that all the cutting is done by them and with a small clearance both inside and outside. Water is forced down through the hollow drill rods and bit to keep the latter cool, and in passing up outside of them carries the cuttings to the surface. The bit is screwed to the core barrel and that in turn to the drill rods. The bit cuts an annular channel and the core formed within it is protected by the descending core barrel. At intervals the core is broken off by a special device and lifted out along with the barrel. Two kinds of black diamonds are used for this work, carbons being set for cutting hard rock, and bortz for soft rock. The bort is as hard as the carbon but not so tough. For medium rock half carbon and half bortz may be used. In practice it is customary to let diamond drill work for foundations by contract as operators of skill and experience are required. Drilling machines are manufactured of different designs and in a number of sizes, operated in most cases by power. The diameter of core varies from i to 2 inches for foundation ART. 175 CORE DRILLING WITH DIAMONDS 525 purposes, larger sizes of core being removed in wells, tunnels, and deep mine prospecting. If surface material overlies the rock it must first be pene- trated by the method of wash borings as described in the preceding article and the casing driven into the surface of the rock, making a tight joint to exclude the entrance of sand or clay. The diamond drill may then be set up over the casing and operations continued. The following statement is quoted from an article by Resi- dent Engineer F. H. BAINBRIDGE in Mine and Quarry for Oct., 1908, regarding the borings made for the Chicago and Northwestern Railway bridge over the Mississippi River at Clinton, la. The equipment was mounted on a scow. The diamond drill operated 2-inch core bits. Both standpipe and casing had flush joints, their diameters being 4! and 3 inches respectively. "The materials encountered were in order as follows: Recent alluvial sands, glacial drift of gravel, sand and boulders, a shale consisting of sand with a clay matrix, and finally limestone bedrock. The upper stratum of bedrock was identified by fossils and general appearance as belonging to the Gower stage of the Niagara series of Silurian rocks. This overlaid conformably rock of the Delaware stage of the same series. In the middle of the river the Gower rock and nearly 50 feet of the Delaware rock had been entirely eroded. Great care was taken to ascertain the possible ex- istence of subterranean pockets or overhanging cliffs in the rock. Only two of these pockets were found, however, both in the same boring, and these were only i and 6 inches in depth. Both were filled with sand, con- sisting of about equal parts of quartz and dolomite sand. Some of the borings were carried down 30 to 40 feet into the bedrock to determine the possible existence of these subterranean pockets. " All the boulders encountered were such.as could be easily broken with the chopping bit and no dynamite was found necessary. To determine the consistency of the shale, cores were taken out with saw-tooth bits working dry, showing perfectly the consistency of the material. The saw-tooth bit or the chopping bit working with the pump gave no idea of what this material was, and without the expedient of the dry core an excellent foundation would have been overlooked, and a foundation sought 30 feet lower. "Borings in the limestone were made with a bortz bit when the water was still, and with the chopping bit, taking occasional cores with the saw- 526 EXPLORATIONS AND UNIT LOADS CHAP. XVII tooth bits. Fully 95 percent of the borings in the limestone were made with the bortz bit. The aggregate length of casing put down was 692 feet, and that of casing driven through hard material was 406.5 feet. The aggregate length of borings in shale was 86 feet, and in limestone, 226 feet. The cost was as follows: Labor, $456.16; coal, $124.41; deprecia- tion of bortz, estimated, $200.00; scow, $287.24; and depreciation in tools, pipe, etc., $200.00; total, $1267.81. The scow still has value which is somewhat uncertain. Omitting this credit, the cost of the work amounted to $1.83 per foot." In exploring for the tower foundations of the Williams- burgh bridge, wash borings were first made, the pipe being driven to what appeared to be rock, and then a dynamite car- tridge was exploded. If the pipe could not be driven farther after the explosion it was at first assumed that bedrock was reached. Upon making diamond drill borings it was found that instead of 50 feet to bedrock on the New York side, the true depth varied from 46.1 to 68.3 feet; and on the Brooklyn side, instead of 75 to 80 feet, it varied from 80 to 104 feet. In nearly every case the wash borings had met a large boulder, and the charge of dynamite was not sufficient to break it. The diamond drilling was extended from 10 to 20 feet into the rock. A. summary of Experience in Diamond Drill Work on the Deep Waterways Survey with Statistics of Cost is published in Engineering News, vol. 50, page 83, July 23, 1903. The data relate to 25 holes of an average depth of 98.5 feet. The conditions under which the work was done are described and the special difficulties noted. The total carbon loss is 25^ carats in drilling 1688 feet of rock, making the cost for diamonds 47.7 cents per foot, at $36.50 per carat. The rate for drilling in different kinds of rock, in feet per hour, is: quartzite 1.7; limestone, 2.5; sandstone, 3.0; and shale, 5.0. The distribution of time is as follows: Sinking casing 325 hours 17 percent Drilling rock 753 hours 41 percent Delays 386 hours 20 percent Moving (38 times) 356 hours 19 percent Holidays and storms 60 hours 3 percent Total. . 1880 hours 100 percent ART. 176 CORE DRILLING WITHOUT DIAMONDS 527 The delays due to moving were unusually high on account of frequent and long moves, as well as bad weather and delays in getting cars. The total length of casing sunk was 552 feet, and of holes drilled in rock, 1910 feet. The general average depth sunk per day of 10 hours is therefore 13.1 feet when moving and other delays are included, and 16.2 feet when the time for moving is excluded. While actually working, the rate of sinking the cas- ing through sand, gravel, etc., was 17.0 feet, and of drilling in rock, 25.3 feet per zo-hour day. The analysis of cost is given including 13 items, the total cost per foot averaging $3.137. ART. 176. CORE DRILLING WITHOUT DIAMONDS The increasing demand for black diamonds for diamond drilling in mine prospecting and for other purposes led to such a rise in price as to exceed tenfold the cost when the core drill was first practically developed. This naturally led to the in- vention of core drills without the use of diamonds. In one type of such drills, chilled steel shot are made to travel under a hollow soft steel bit which rotates and exerts a pressure on the shot at the same time, thereby causing them to mill away the rock. The bit is screwed to the core barrel and that is screwed to the hollow drill rods as in diamond drills. One side of the bit has a V-shaped or diagonal slot in it to aid the shot in work- ing freely under the bit and to permit some of. the water from the jet to escape without passing under the edge of the bit. Another special feature of one make of shot drill is the calyx or sludge receiver. It is formed by a tube surrounding the drill rods above the core barrel, in which are deposited the chips or sludge on account of the sudden decrease in velocity of the upward current of water. The cuttings thus received form a duplicate record of the strata penetrated. If sufficient water is used to bring the cuttings to the surface, its velocity is so great as to wash the shot away from under the bit. The sizes of cores cut by shot drills are generally larger than those of diamond drills and range from i| to 20 inches. 528 EXPLORATIONS AND UNIT LOADS CHAP. XVII The largest cores are required for other purposes than founda- tion explorations. Cores 4 to 5 inches in diameter can be extracted as cheaply as those of 2 inches or less while the rate of progress is as good or better than for the smaller cores. Except for the very hardest rocks the shot drill is found to be more economical than the diamond drill. The successful operation of the drill requires the proper regulation of the amount of shot necessary to remove the cut- tings without displacing the shot; and of the pressure to exert upon the bit to obtain the most effective cutting. The most serious difficulty is due to crevices in the rock in which the shot may be lost, requiring either some means of artificially sealing the openings, feeding the shot slowly but continuously by an expert operator, or substituting a toothed bit to drill past the crevice. Some machines are arranged to imbed the shot in the bit by churning instead of direct pressure. In another type of drill without the use of diamonds, steel bits are used with different forms of teeth, and also operated by rotation. One of these known as the Davis cutter has long, tempered steel teeth with angles from 30 to 35 degrees, while between them are vertical grooves on the outer surface of the bit. Instead of grinding with a uniform motion the long teeth chip away the rock by an action closely resembling that of a hammer and chisel. This cutter is used for the softer rocks, as well as for other material overlying the rock, instead of a chopping bit. An excellent article by ROBERT RIDGEWAY on boring methods and machines, difficulties encountered and results of explora- tions in various mixtures of glacial materials as well as rock, is entitled Sub-surface Investigation on the Catskill Aqueduct, Board of Water Supply, in Engineering Record, vol. 57, pages 522 and 557, April 18 and 25, 1908. See also Chap. IV on Borings and Sub-surface Investigations in a volume on The Catskill Water Supply of New York City by LAZARUS WHITE, New York, 1913. ART. 177 NEED OF SUB-SURFACE EXPLORATION 529 ART. 177. NEED OF SUB -SURFACE EXPLORATIONS It is as essential to the proper design of foundations to determine accurately the local conditions under the surface of the ground or below the bed of a stream as to observe the con- trolling conditions of the stream itself, or to know the character of the superstructure and the magnitude and direction of all the external forces acting upon the substructure. To discover the character of the underlying strata and to find their respect- ive depths below high and low water in the case of a bridge, or below the surface or the level of ground water in the case of a building, it is necessary to make excavations, or borings, and in some instances to drive test piles. In many locations con- ditions vary greatly within short distances. Adequate exploration is often omitted because of the labor, time and cost. The cost of exploration, however, is frequently less than that otherwise required merely to revise the plans of the structures involved, without considering the unnecessary cost of the structures due to lack of information. There are abundant examples to prove that where adequate exploration is omitted, it may result in the loss of the structure, or in greatly increased cost. In one instance a bridge pier was built upon a surface of hard-pan in the river bottom. No examina- tion was made on account of the swift current which had a ve- locity of 5 miles per hour. Without warning the pier sank out of sight causing the loss of the two adjacent spans of the bridge, and of a number of human lives. Upon making an investiga- tion afterward it was found that the hard-pan was only a thin stratum overlying a deep layer of soft clay. In another ex- ample a bridge abutment which was founded on 6o-foot timber piles settled slowly until it reached a maximum of 3 feet, after an attempt to stop it by means of additional piles around the outside. Exploration proved the settlement to be due to a lo-foot layer of peat 35 feet below the surface, which was flow- ing apparently under the superimposed load. This experi- ence emphasizes the statement made in Art. 36 that test piles alone may be insufficient. Experience has also shown that the 34 530 EXPLORATIONS AND UNIT LOADS CHAP. XVII cost of exploration may frequently save much larger sums in the annual cost of maintenance of structures like pile trestle bridges. In a certain project the chief engineer estimated that $100000 was saved in the cost of construction by a thorough preliminary exploration of the ground. Another important reason why adequate explorations should be made is that the owner ought to assume full responsibility for the local conditions and that the contractor should not be obliged to gamble on uncertainties relating thereto. The con- tractor should be asked to bid on guaranteed local conditions, with an increase or reduction in price for variations from these that may be discovered later. Occasionally inadequate explora- tions may be made which are equally unfair to the contractor. For example, only four borings were made on a city block to be covered by an important building, dne at each corner; but it was distinctly stated that these borings were furnished as general and not as specific information to the contractor and that he must assume all chances as to the sub-surface formations. The contract price for the foundations alone was $208453.00. An engineer of large experience made the following statement in 1910, based upon his own practice and his observations of ordinary conditions: "I consider it very important and the expenditure well warranted to first determine definitely by test borings or drilling what the actual depth and character of the foundation is before any detailed plans are prepared. Such determinations enable the designer to design the structure as it should be built to meet the conditions, assuming that the test borings or drillings have been properly made, and such an order of procedure saves much time in the designing room by eliminating numerous changes in plans where unexpected conditions arise when the foundations are being excavated, and which is frequently the case. In nearly all cases there is a hurry to start the foundation masonry and frequently plans cannot be, or are not, properly modified to suit the conditions and meet the require- ments of economy. Furthermore, with a proper knowledge of the founda- tions the contractor is placed in possession of definite information, and with the plans properly designed once and for all, with possibly some minor modifications, the result is a large economy to the company paying for the work, and which also eliminates questions of extra prices and frequently some arguments over changed conditions affecting unit prices." ART. 178 TEST FOR BEARING CAPACITY 531 In general, two sets of borings should be made for an impor- tant bridge crossing. In the first set a number of borings are located on the center line of the proposed location, to determine whether the site furnishes favorable conditions; and if so to make an approximate estimate of the most economical location of the piers and the length of spans. Sometimes government regulations for navigable streams or the influence of ice or flood conditions must also be considered. After the piers are located tentatively additional borings should be made at the site of each pier. At least four borings, or one at each corner, are necessary, and several intermediate ones may be required unless the adjacent indications are nearly the same. ART. 178. TESTS FOR BEARING CAPACITY After an exploration has been made of the different strata a test should be made at the surface on which the foundation is to rest to determine the bearing capacity of the ground. Fig. 1780 shows the appliances often used for this purpose, the hard-pan being tested at the base of a pier to be built in an open well. The surface is scraped to a level plane by means of a straight- edge. The platform is loaded with blocks of cast iron or other weights, and is transferred to the bearing plate at the foot of the post. The platform is held in proper position by wedges loosely placed against the sheeting, and the settlement is meas- ured by taking readings on the steel tape at the top of the shaft. In one example of such a test, a load of 24200 pounds per square foot produced a settlement of f\ inch in 44 hours. The working load adopted was 13 300 pounds per square foot. When the platform is placed above the natural surface it may be braced conveniently by extending the post above the height to be occupied by the loading, and into a loosely fitting collar which is held in position by four inclined shores; or four vertical timbers supported by shores may be placed so as to correspond to the four sheeting planks which take bearing from the wedges in Fig. 1780. To determine the bearing power of the sand on which some 532 EXPLORATIONS AND UNIT LOADS CHAP. XVII of the pneumatic caissons under the Municipal Building in New York City were to be founded, a 1 6-inch casing was driven, and cleaned out by means of a sand pump. Inside of the casing was placed a lo-inch pipe having a bearing disk 14 inches in diameter at- tached at the bottom and a balanced platform at the top to receive the load. Three tests were made at different depths. At a depth of 77 feet below the curb loads of 15, 22.5 and 28 tons per square foot produced settle- ments of |J, i If and 2 If inches respectively. Later one of the circular caissons was tested. Its base had an area of 90.8 square feet and was 72 feet below the curb. The load was applied by in- crements of i ton per square foot every 24 hours. A load of 6 tons per square foot, which was that used in de- signing the caissons, caused a settlement of J inch with- out further increase during a rest of six days. After the load was increased to 10 tons Hardpan FIG. i;8a. per square foot the total settlement was if inch with- out further increase. The following extract is made from the regulations (1912) of the Building Department of the Borough of_Manhattan: ART. 178 TESTS FOR BEARING CAPACITY 533 "The soil shall be tested in one or more places as the conditions may determine or warrant, at the level at which it is proposed to place the bottom of the foundations of the structure. Each test shall be made so as to load the soil over an area of not less than 4 square feet in any one place. The accepted safe load shall not exceed two-thirds of the final test load. The loading of the soil shall proceed as follows: (a) The load per square foot which it is proper to impose upon the soil shall be first applied and allowed to remain for at least 48 hours undisturbed, measurements or readings being taken once each 24 hours or oftener to determine the settle- ment, if any. (b) After the expiration of the 48 hours the additional 50 percent excess load shall be applied and the total load allowed to remain undisturbed for a period of at least six days, careful measurements and readings being taken once in 24 hours, or oftener, in order to determine the settlement. The test shall not be considered satisfactory or the result acceptable unless the proposed safe load shows no appreciable settlement for at least two days and the total test load shows no settlement for at least four days." The loaded area has most frequently been taken at i square foot, but it is better to take a larger area like that specified in the preceding paragraph and to subject it to a load not exceeding twice that of the proposed working load than to overload a much smaller area. To get the best results it is important to make the test on a surface as near the elevation of the proposed base of the foundation as possible, not at the surface of the ground, and with as little clearance as possible between the bearing disk or plate and the sides of the excavation or casing. It is also desirable to know whether any elasticity exists in the ground, and for this purpose the reduction in settlement should be measured as the load is taken off in parts with short intervals of rest between. The unloading may be done more rapidly than the loading. Tests on beds of clay should extend over longer time intervals depending upon their character. An excellent graphic representation of the phenomena of tests for bearing power consists in laying off the time intervals as abscissas, the loads per square foot as positive ordinates, and the settlements as negative ordinates. The curve of settlement below the axis can thus be compared directly with the stepped load line above the axis, showing the effect of both 534 EXPLORATIONS AND UNIT LOADS CHAP. XVII increase in load and of intervals of rest after the successive increments of load. ART. 179. VALUES OF BEARING CAPACITY No definite values can be given in general to the safe loads on foundation beds since it is impossible to classify accurately the various kinds of earth. Unless the bearing capacity of the material at a given site is already known it should be determined by direct experiment. Too little attention has been given to this subject and but small additions have been made in recent years to any real knowledge of the material on which the foundations of structures rest. For preliminary estimates and some other purposes, limiting values of bearing capacity may be employed for several classes of material. In his General Specifications for Structural Work of Buildings, C. C. SCHNEIDER recommends that the pressures on foundations are not to exceed the following values in tons per square foot: Soft clay, i; ordinary clay and dry sand mixed with clay, 2; dry sand and dry clay, 3; hard clay and firm, coarse sand, 4; firm, coarse sand and gravel, 6. Other experienced engineers have characterized these values as needlessly conservative, but it was claimed in reply that conservative values were adopted because the effect of settlement in the foundation of a building is more injurious than in a bridge pier. The same specifications also contain a table giving the bearing capacity for different kinds of ground as prescribed in the building codes of a number of American cities. The Building Code recommended by the National Board of Fire Underwriters gives the following limiting values, also expressed in tons per square foot: Soft clay, i; clay and sand together, wet and springy, 2; loam, clay and fine sand, firm and dry, 3 ; very firm, coarse sand, stiff gravel or hard clay, 4. In H. B. SEAMAN'S Specifications for Bridges and Subways the allowable static pressures are given as follows, in tons per square foot: Silt, i; moist clay, 2; clean sand or dry clay, 4; coarse sand or gravel, 6; hard-pan or compacted gravel, 10; ART. 179 VALUES OF BEARING CAPACITY 535 sound ledge rock, 60. It is stated, however, that these pres- sures are for the most favorable conditions, and that for ques- tionable material they should be reduced 50 percent. In deep foundations, friction and buoyancy may be allowed for in computation. The following paragraph is quoted from J. E. GREINER'S General Specifications for Bridges, Part III: "85. When foundations are subjected to the loads and forces specified in paragraph 84, the maximum permissible pressure per square foot on any part of the surface of the supporting strata, when in thick beds, shall be as follows, but it is advisable to use a considerably less pressure unless absolutely certain as to the character of the bottom. Firm rock, 30; dry coarse gravel and sand, well cemented, 5; hard dry compact sand, 4; hard dry clay, 3 tons." The following allowable loads, expressed in tons per square foot, were adopted Oct. n, 1905, by the Harriman Lines: Alluvial, adobe, soil, 0.5; clean, dry sand, 2; compact sand, cemented, 4; gravel and sand, cemented, 8; moist, soft clay, i; dry clay in thick beds, 4; soft bedrock, 5; hard bedrock, 20; hardest bedrock with no seams, 200. The most elaborate collection of data on unit pressures adopted for stable structures on the material upon which they are founded is contained in a volume entitled Allowable Pres- sures on Deep Foundations, by ELMER L. CORTHELL. The data relate to 178 works, and an analysis of some of them gives the following results: Examples Material Range of pressure, Ibs. Average, Ibs. 10 Fine sand 4 500-11 600 9 ooo 33 Coarse sand and gravel 4 800-15 500 10 200 10 Sand and clay 5 000-17 ooo 9 800 7 Alluvium and silt 3 000-12 400 5 800 - 16 Hard clay 4 000-16 ooo 10 160 5 Hard-pan 6000-24000 17400 " These cases show no settlement. The range is considerable and no doubt in the case of the minimum pressure a much larger weight could have been imposed on the material without pro- ducing settlement. For a safe rule, therefore, the average is EXPLORATIONS AND UNIT LOADS CHAP. XVII low and a safe pressure upon the material would lie somewhere between the average and the maximum pressure." The same volume contains the pressure for instances in which notable settlement took place, as well as values of frictional resistance for cylinder and masonry piers. The bearing capacity of the ground depends not only upon its character or composition but also on the amount of water which it contains or is liable to receive, and the degree to which it is confined to its location. Sand can sustain very heavy loads with but slight or negligible compression. When it directly overlays rock or some other thick stratum of hard material and is securely confined, or is artificially protected against the possibility of lateral displacement, it forms a satis- factory foundation bed and will safely carry heavy loads. The supporting power of clay is very variable and depends in a large measure upon its variety and upon its degree of satu- ration with moisture. The clays vary considerably in their chemical constituents, which in turn affect the amount of mois- ture which they can absorb. Certain deposits are known to be compact and hard and have a high supporting power, while others are plastic and easily compressed. The chief character- istic which renders clay more or less unstable as a foundation material is its property of retaining water which is once ad- mitted, and its tendency to soften gradually as the amount of water increases. In plastic clay and other soft material the depth of foundation should enter as a factor in determining the allowable pressure. In other words, the so-called buoyancy of the foundation material is a function of the depth of 'displace- ment' of the building or other structure. The point of bearing must be carried below the possibility of upward reaction along- side. This principle has sometimes found expression in a practical rule that "in compressible ground the depth of a foundation ought not to be less than one-fourth of the intended height of the building above ground; that is, for a shaft of 200 feet, the foundation should be made secure to a depth of 50 feet by piling, or by well-sinking and concrete. Masses of concrete, brick, or stone, placed upon a compressible substratum, how- ART. 179 VALUES OF BEARING CAPACITY 537 ever cramped or bound, may prove unsafe. Solidity for a considerable depth alone can be relied upon. Mere enlarge- ment of a base may not in itself be sufficient." It must also be remembered that large areas of compressible ground will not continuously support as large a unit load as a smaller area for a short time. When clay is mixed with other materials, like coarse sand and gravel, its supporting power is considerably increased, being greater in proportion as the other materials are in excess up to the point of forming a cemented mass, in which the clay is just sufficient in quantity to act as a cement in binding the other materials together. In this condition the clay is often found in an indurated state, and the hardness of the mixture, commonly 'called hard-pan, is proverbial. CHAPTER XVIII PNEUMATIC CAISSON PRACTICE 1 ART. 180. HISTORICAL NOTES In 1852 an attempt was made in the Pedee River in North Carolina to use the ingenious vacuum method, invented by POTTS, to place the foundations for a bridge. His plan con- sisted in exhausting the air from cylinders 6 feet in diameter, thereby causing the atmosphere to exert a pressure of 14.7 pounds per square inch, or a total pressure of about 30 tons which it was thought would force each cylinder through a depth of 25 feet of sand. Unfortunately, the attempt proved unsuccessful, since no allowance had been made for the presence of logs which were encountered under the cutting edge. Accordingly, the opposite method was tried, or that of pump- ing additional air into the cylinders, thus introducing in America what was designated as the plenum pneumatic method. By this method the air is compressed sufficiently to balance the water pressure, thus keeping the water out of the working chamber. As a cubic foot of fresh water weighs about 62^ pounds, the pressure per square inch at a depth of i foot is 0.434 pounds and at a depth of 100 feet, 43.4 pounds. The second set of caissons to be sunk in America were those of the Third Avenue bridge over Harlem River, New York, about 1860, the third being those for the famous steel arch bridge at St. Louis begun in 1868. The earliest patent for a compressed-air shaft was granted to THOMAS COCHRANE in 1830, while the first application was made in the river Seine, at Loire, by M. TRIGER in 1839. Compressed air had been used in diving bells, however, for many centuries, although the first 1 By T. KENNARD THOMSON, C. E., D. Sc., Consulting Engineer, 50 Church St., New York City. 538 ART. 181 RESULTS OF EVOLUTION 539 record of using a pump to compress the air in a diving bell is in 1778 by SMEATON, a noted English engineer, for repairing the foundations of a bridge over the river Tyne, at Hexham. ART. 181. RESULTS OF EVOLUTION The first and second sets of caissons referred to in Art. 180 were iron cylinders only 4 to 6 feet in diameter. The first large caissons were built for the deep foundations of the Eads bridge at St. Louis and the Brooklyn bridge in New York. They were of very massive timber construction on account of the stone masonry being placed directly upon the deck. The heavy roof or deck was also used in the early days of concrete by some engineers, but in the decade following 1880, the thickness was reduced to less than 3 feet for bridge piers in some of the large rivers. In the Hartford stone arch bridge, the largest caisson was 46 by 131 feet in size and had a timber deck only 4 feet thick. As this caisson had no bulkheads or diaphragms, it contained the largest undivided air-chamber ever used. Mass- ive framed timber cribs with solid walls and heavy bracing were also used above the caisson deck, but the walls were reduced in time to 3-inch planking with sufficient timber bracing to resist the water pressure and possible bumps from boats, etc. The first building ever founded on pneumatic caissons was the Manhattan Life building at 66 Broadway, New York, in 1893. The caissons were of heavy steel construction, about 9 feet high with a 7-foot working chamber. It was intended to build the brick piers directly on the caissons as they sank, but the friction of the ground against the brick wall was too great for the green mortar and forced open the joints between the brick. This method was then replaced by building steel cofferdams above the caisson and filling them with concrete. The steel in turn was supplanted by wood. Caissons and cofferdams built of steel with rectangular horizontal sections were used for many years, but have been abandoned in America while those with circular sections are restricted to small diameters. Except for the small sizes, it is . 540 PNEUMATIC CAISSON PRACTICE CHAP. XVIII always cheaper to use wood and concrete; and in many cases it is cheaper to use wood only for forms when all the concrete can be placed before sinking starts, and which has often been done successfully up to heights a little over 30 feet above the cutting edge. This method is not economical, however, when the depth of sinking is so large as to require two or three 'build-ups' of concrete during which the sinking must be interrupted. To stop sinking temporarily is bad since it requires continual pumping of air during the interval, thus increasing the overhead charges, and also allows the ground to cake against the sides, thus greatly increasing the friction. In one example, the mov- able derrick was shifted to another caisson instead of waiting several days for the 'build-up,' as the adding of concrete is called, and it was 60 days before sinking was resumed on this caisson. During this period compressed air was pumped into the working chamber to keep the ground from caving in, although it would have been cheaper to flood the caisson for that purpose. It is much cheaper in such cases to use a cofferdam of 2-inch plank and to work continuously until the penetra- tion is completed. To sum up the results of evolution, it is found to be the best practice to use steel for small circular caissons, say from 30 inches to 6 feet in diameter; in larger sizes to use mass concrete with 2-inch timber sides, with reinforcement around the shafts, working chamber and sides, where it is necessary to keep joints from opening. It is believed to be better to leave on the thin timber sides, since it avoids unnecessary delays in sinking, reduces the skin friction as well as the liability of rupturing the concrete due to the friction, and makes it easier to keep the caissons plumb and in position. Caissons with a timber roof and sides for the working chamber and with timber cofferdam on top are economical for only deep sinking in harbors or rivers, where buoyancy is an advantage. The writer has sunk caissons in water 60 feet deep where the cutting edge had to penetrate 30 feet below the bottom. The top of the concrete had to be kept about 25 feet below the water surface in the river, requiring great care with the bracing of the ART. 182 CONSTRUCTION OF CAISSONS 541 timber cofferdam and to guard against concrete buckets knock- ing out braces, as well as injury from passing barges, derrick boats, etc. If no timber had been used in constructing the caisson, the distance from the water surface to the concrete being deposited would have been much greater. ART. 182. CONSTRUCTION OF CAISSONS For constructing caissons from 30 to 36 inches in diameter, such as are used chiefly for underpinning purposes, cast iron is preferable, with a thickness of ij to ^ inches. The sections should be about 5 feet long with substantial flanges to bolt them together, shorter sections being ordered to make up the requisite total length, which varies in each case. See illustra- tions in an article on Foundations of the New Mutual Life Insurance Building, New York City, in Engineering News, vol. 45, page 221, March 28, 1901. Steel plates f inch thick have been used but in some cases were badly twisted or warped while being jacked down, thus greatly reducing if not destroying the value of the cylinders as columns. Cast iron is much less liable to rust than steel. When caissons are sunk in the open for new buildings, it rarely pays to use a smaller diameter than 6 feet; the working chamber then consists of a steel shell about f inc hthick, with a steel-angle ring above the cutting edge and one or two more rings of say 3|X3JX^-inch angles between the cutting edge and the deck. If the steel cofferdam above a caisson of this diameter is omitted and removable forms used, the ring of con- crete between the inside shaft and outside surface is only from i to ij feet in thickness, and unless the concrete is heavily reinforced, both vertically and horizontally, the concrete is sure to crack as has often been proved by experience. The size arid spacing of the reinforcing bars depends on the depth of penetration, and in these circular caissons, 6 feet or over in di- ameter, it is often more economical to use wooden sides from the cutting edge to the top. In the larger caissons, whether of wood or concrete, the first 542 PNEUMATIC CAISSON PRACTICE CHAP. XVIII detail of construction, and on which there is still the widest difference of opinion, is the cutting edge. Naturally, every one wants the bottom of the caisson to be as thin as possible, so that the sand hogs can remove the material under the cutting edge with the least difficulty. Most superintendents demand a 'knife cutting edge/ which is a mistaken policy, for in fine sand where such a knife edge works like a charm, it is not needed, whereas in other material where it seems to be needed it cannot be made strong enough to stand the terrific pressure. It is sure to be buckled and then becomes worse than no cut- ting edge at all, often causing considerable delay, while it is being removed. The best form of cutting edge for either timber or concrete caissons consists of an 8-inch channel laid flat with its back down, or a 1 2-inch oak block sized down to 8 inches on the bottom. The 8-inch channel cutting edge was first designed by the writer for Arthur McMullen & Co., in 1901, and it has been used by them frequently. It is the most economical form. The side walls of the working chamber require great care and judgment in their design. Theoretically, if the caisson is plumb, and the air pressure just balances the outside pressure there is no pressure on the sides except that due to the load on the top, including the weight of concrete placed. But cais- sons are very rarely absolutely plumb, and they often get badly warped as well as inclined, due to more obstruction on one side than on the other, causing the sides frequently to buckle, sometimes to collapse, or to break away from the roof. In one instance, where the last kind of accident occurred, the cutting edge was in sand about 20 feet above rock, and had to be left there, the balance of the excavation being made by a vertical tunnel method. In another example, the side walls of the working chamber made of f - and ^-inch steel plates, braced firmly every i\ feet, have been observed to buckle at least 2 inches under the outside pressure. Timber side walls are most readily braced and repaired, but must be firmly attached to the structure above to prevent ART. 182 CONSTRUCTION OF CAISSONS 543 breaking away. In another instance, a reinforced-concrete caisson landed hard on one side, and in consequence the steel rods from the cutting edge up were badly buckled, forcing the concrete side walls into the working chamber, leaving the out- side timber bare, which fortunately had been left in place. Curiously, the thick reinforced-concrete wall was destroyed, while the 3 -inch plank remained. In small caissons the cutting edge and sides should be made strong enough to withstand the pressure without cross bracing, but in large caissons it is customary to use substantial struts every 10 or 15 feet, and most designers use solid timber bulk- heads in long or wide caissons, making an air chamber about 20 feet wide. However, as every bulkhead makes two more cutting edges to work under, and since this part of the ex- cavation is the most expensive, the writer has preferred to omit the bulkheads and has done so successfully up to a width of 46 feet and a length of 131 feet, at Hartford, Conn. The size and spacing of this bracing must be governed by experience. The caissons at Hartford are typical of others used successfully at Pittsburgh, Mingo Junction, Havre de Grace, and Pierre. The earliest wooden caissons had much heavier wooden decks than were needed to act as supports for the stone ma- sonry. Steel caissons also had heavy beam deck construction even when concrete was supported. It was long thought neces- sary to have a timber or steel deck to secure an air-tight job, but experience has shown that by first placing a layer of mortar, it is easier to secure air- tightness with concrete than with wood or steel. Upon reflection, it was seen that under concrete a deck of timber or steel was needed only as a temporary form, except when the concrete was shallow and then it could be reinforced. There are three good reasons for omitting the permanent wooden deck : First, it is more compressible than concrete and is liable to loads sufficient to compress it; second, concrete is cheaper than wood; and third, danger of injury from the teredo wherever it exists. The old theory that the teredo will only 544 PNEUMATIC CAISSON PRACTICE CHAP. XVIII start work near the water surface is erroneous according to the observations of the writer who examined piles driven two years previously for a bridge at Fall River, Mass., and which were cut off 40 or 50 feet below the surface, and carried a timber grillage 4 feet thick on which the granite masonry pier was built. The piles were eaten through allowing one end of the pier to drop 2 feet. When several pile heads were cut off, brought to the surface and cut open, live teredo and limnoria were discovered, although the location was within 200 feet of the mouth of a sewer. Whether the teredo, due to its objec- tion to crossing joints, entering beyond a certain distance, etc., would destroy the deck of a large wooden caisson, is an open question, but the danger is great enough to rule out timber in the future whenever possible. There are some accidents or errors of judgment against which the designer is powerless. For instance, one of the best super- intendents in the country put too large a charge of dynamite outside of the cutting edge to break up the rock and blew out the end of the caisson. Besides making it a total wreck, the jar combined with an extra high tide broke the bond between the concrete and bedrock in an adjoining caisson, about 200 feet away, and lifted the caisson enough to require its removal and rebuilding. Numerous cases have occurred where the deck has been badly warped by allowing one corner to land on a harder substance than the rest of the cutting edge, or by not having the bed dredged to a uniform depth before placing the caisson. One of the Quebec bridge caissons was thus injured. ART. 183. CAULKING, SHAFTS AND LIGHTING One of the advantages of concrete caissons is the absence of joints to be caulked. In steel caissons the joints must be caulked with a regular caulking tool, while in wooden caissons, every joint must be tightly packed with oakum and often with a^coat of pitch also, in spite of which there is a considerable loss of air. ART. 183 CAULKING, SHAFTS AND LIGHTING 545 In caulking with oakum, one man can cover about 180 feet of joint in a day, going over the work twice but using only a single line of oakum. In wooden or steel caissons, it is very hard to get a water- and air-tight job, even with the best caulk- ing and flushing the deck with mortar before placing the con- crete. No one likes to see the air bubbling up through the green concrete, much less to see it form a water-spout several feet above the top of the concrete. In New York, the escape of air from below the cutting edge or elsewhere has been observed in buildings from 100 to 200 feet away. The preceding statements about caulking the side walls and deck of the working chamber apply even in a higher degree to the cofferdam above the caisson, especially as the top of the concrete may be many feet below the water surface. A small leak requires pumping and this is the greatest enemy of concrete. Small caissons under 4 or 5 feet in diameter are practically all shaft, but in larger sizes, one or more inner shafts are used to take men and material in and out of the caisson. For sizes up to 12 or 15 feet in length, it is customary to have only one shaft for both men and material. Sometimes this is simply a material shaft, 3 feet in diameter, with a ladder set in the side, while at other times, a combined shaft is used, an oblong affair divided into two compartments, one with a ladder for men and the otjier for taking material in and out. Whenever the size of the caisson permits, there should be two or more shafts to avoid unnecessary danger to the men, and also to facilitate filling the air chamber. Temporary failure of the lock to work, or the jamming of a bucket in the shaft, has often held the men as prisoners for hours, sometimes more than twelve, and sometimes with serious loss of life. On the other hand, two shafts are more expensive than one, even al- lowing for the extra handling of material, and contractors do not like to incur the extra expenditure of time and money. But several shafts do not always insure safety. Some years ago, in the Passaic River, one of the best foremen failed fasten the bucket properly to the hoisting rope, and 35 546 PNEUMATIC CAISSON PRACTICE CHAP. XVIII the bucket dropped in the lock, forced the bottom door open while the top was also open, thus allowing all the compressed air to escape and drowning nearly all the men in the working chamber, including the foreman himself. If the shaft is made of steel and not buried in concrete, it should be f inch thick, and properly fastened so that neither shaft nor lock can be blown off, as has sometimes occurred. If the steel shaft is buried in the concrete, it may be built of j-inch metal, provided it is designed so that it cannot be blown off. At first, it was customary to use heavy steel shafts which were left in the concrete, but this proved so expensive that the plan was modified to leave only the bottom section buried in the shaft, its length not exceeding 8 to 10 feet and sometimes only 18 inches. The rest of the shaft was protected from the concrete by a timber box surrounding it. But as the concrete often leaked through the box and set around the shaft, prevent- ing its removal, and causing considerable loss to the con- tractor, two other methods were adopted later. In the first plan, a heavy cast-iron collapsible shaft is used which is removed after the air chamber is filled. In the second plan, timber forms with rungs for a ladder are used in the shaft except for the upper section near the lock, especial care being taken to provide an adequate connection of the steel shaft to the con- crete. A number of fatal accidents have occurred in which the lock was blown off from the caisson. When candles were employed for lighting, there was con- stant danger of fire. A fire started in the joints of a timber deck and fanned by compressed air is very difficult to put out, even by flooding the working chamber. More recently, upon hoisting a bale of oakum from the 4-foot joint well between two caissons, a candle in the lock was knocked over, the rope set on fire and the blazing oakum dropped on the men below. Two men were burned to death and several others seriously injured. All caissons should be lighted by electricity whenever pos- sible, even the small joint caissons between the main ones, as the accident just cited indicates. Apart from the danger of ART. 184 METHODS OF LAUNCHING 547 fire, the old tallow candle was never satisfactory, for as the rate of combustion is greater in compressed air, the lungs of the workmen are so filled with soot that many days are required to get rid of it. Electric-light wires are generally carried down the shaft and occasionally a bare wire will charge the iron ladder giving an unwelcome shock to the men using it. The pipes, 3 or 4 inches in diameter, which convey the compressed air to the working chamber, as well as the gas pipe for whistling or signalling to the men outside, were formerly left in the concrete, but in later practice, they are sometimes placed in a pocket next to the shaft, so that they can be removed and used again. The same arrangement is applied to the pipes, about 5 inches in diameter, which are used to blow out material when that method is suitable. These details and many others cannot be designed by any one who has not worked in a caisson and is not familiar with methods of operation, without making serious blunders. ART. 184. METHODS OF LAUNCHING There are practically four methods of getting a caisson into the water: First, when built on shore, it is skidded into the water on launching ways; second, when built in a pontoon, the pontoon is taken away underneath; third, when built on a boat or wharf, the caisson is lifted by derricks and placed in the water; and fourth, when the cutting edge is supported from a temporary platform on piles or boats, and is then lowered by long screw rods, or block and tackle, etc., to a firm bottom. When built on shore and skidded into the water, no more work is done before launching than is necessary; the bottom of all shafts should be closed temporarily and a small amount of grout or concrete placed on the deck to make it water-tight. A caisson of ordinary size and timber construction will draw about 8 to 10 feet of water when floated and must have enough cofferdam to prevent flooding. A failure to provide skids or runways of ample strength has resulted in several breakdowns 548 PNEUMATIC CAISSON PRACTICE CHAP. XVIII before launching, with a loss of thousands of dollars and consider- able valuable time. The method of building on a pontoon is very satisfactory, especially when a number of caissons can be built on the same pontoon. A pontoon is a flat-bottomed boat with vertical sides, leaving a clear space of about 5 feet in which to' work all around the caisson. The bottom is constructed of 12X12 -inch timbers spaced 2 to 3 feet apart, to which 4-inch planks are spiked underneath. The sides are 6 or 7 feet high or sufficient to prevent any danger of flooding during con- struction. Both the bottom and sides are thoroughly caulked with oakum. These pontoons are made of two or more parts bolted to- gether in the middle and so arranged that after the caisson has been built to a height of 14 to 20 feet above the cutting edge, caulked, with shafts, etc., in place and properly connected to the deck, the bolts connecting the two halves can be removed. Stone or gravel is then placed on the center of the pontoon, and when everything is ready the valves are opened, allowing the pontoon to fill with water until the caisson floats. Sometimes the arrangement is so perfect that the minute the caisson floats the two halves of the pontoon shoot from under and the launch- ing is completed. It is often necessary, however, to attach tugs to pull the sections apart; or, by means of struts attached to the caisson and by block and tackle, the pontoon sections are pushed apart. At one time a superintendent forgot to sink the pontoon first in order to relieve it of the weight of the caisson, and upon trying to pull away the pontoon sections, he succeeded merely in letting in water enough to freeze the caisson to the pontoon; accordingly, it took two weeks instead of about three minutes to launch it. At Hartford, where seven caissons were 23 feet wide and two were 46 feet wide, the pon- toon was built for the smaller size and additional sections were added for the larger size. Building on boats or shore and lifting the caissons bodily into the water, depends upon local conditions, and applies to the smaller caissons. The fourth method is in some cases the only ART. 185 PLACING AND SINKING 549 one which can be adopted economically. For example, at Pierre, S. D., the bed of the Missouri River consisted of very fine silt and the water was too shallow to float a caisson; if a channel 10 feet deep were dredged out, it would fill up before the caisson could be towed into place. Piles were therefore driven to form the supports for a platform around the site of each caisson and about 32 rods were suspended from these platforms in such a way that the cutting edge could be built upon their hooks at the bottom. After the caisson was built up about 14 feet above the cutting edge, it was lowered by si- multaneously turning the nuts on the 32 rods until the cutting edge came to rest on the bottom. The rods were then discon- nected for use on the next caisson while building up the coffer- dam and concreting were continued. It took from 10 to 12 hours to lower a caisson. ART. 185. PLACING AND SINKING Before launching a caisson and lowering it to position, the site must be prepared by excavating the higher spots to a level surface. If the low spots are filled, they are not as firm as the other material and thus cause trouble. Leveling the site properly is especially important in a swift current. When possible, guide piles are driven on each side and sometimes clusters of piles are driven up- and downstream to which lines are attached to hold the caisson in position until it is sunk deep enough to be safe. These guide frames support working plat- forms, form parts of supports for derricks unless they are mounted on boats, act as wharves for boats of stone, sand or cement, and for the sand hogs' boat. In some cases, it is advantageous to build a temporary island of gravel, sand, etc., on which to build the caissons in position, looking out for the danger of floods, since some rivers rise enough in 24 hours to wash away such an island. After the caisson has reached the proper position, the shafts are built up and concreting started until the cutting edge has penetrated far enough into the ground to make it safe to put 550 PNEUMATIC CAISSON PRACTICE CHAP. XVIII on air and send down the sand hogs. In the Mohawk river, caissons were started on artificial islands, while in the Susque- hanna river, at Havre de Grace, they had to be sunk through 60 feet of water. At the former locality, the concrete was well above the water surface from the start of sinking, while at the latter, the concrete had to be kept 25 to 30 feet below the surface until the bottom was reached. The ideal condition during sinking is to have just weight enough to keep the caisson moving gradually and continuously, with the cutting edge a few inches below the excavation in the working chamber, until the final position is reached, but it is difficult to secure this condition. If a caisson is too heavy, it is liable to break the side friction and fill the air chamber with sand, and if it is not heavy enough, as frequently happens, it is necessary to lower the air pressure to start the movement, thus giving jerky sinking. In caissons for city buildings, it is a common occurrence to see the excavation carried from i to 2 feet below the cutting edge, and then to have the air pressure lowered for a few seconds, the friction being suddenly overcome, and the caisson sunk 2 feet or more. Sometimes, however, hundreds of tons of pig-iron or cast-iron blocks are piled on top to assist the opera- tion of sinking. The caissons for the Zinn Building in New York (see Canadian Engineer, Feb. 22, 1912) first penetrated made ground and the Hudson River silt. On lowering the air pressure the friction was suddenly overcome and the caisson sank until sand and mud filled the air chamber, resulting in the loss of a shift of eight hours. This accident occurred fifteen times at that site, sometimes without lowering the pressure; a record of misfortune which has never been equalled. Fortunately the men were in the shaft when it happened the first time and were On the watch afterward. In sinking the first caisson for the Municipal Building in New York, when the penetration was nearly 100 feet below ground water-level, the air pipe broke and within 15 minutes sand filled the working chamber and extended 16 feet up into the shaft, while the water had risen 42 feet above the cutting ART. 185 PLACING AND SINKING 551 edge. The men were on the way up the shaft when the connec- tion broke and the water followed the feet of the last man nearly as fast as he could climb. If plenty of weight in the form of iron blocks can be obtained without too much cost, it is better to use it in sinking, for reducing the air pressure or using a water- jet is almost sure to increase the friction for the next drop, with exasperating results. It is essential to have sufficient outside bracing to keep the caisson in line until the penetration reaches 25 to 30 feet. If it gets far out of line before that, it is almost impossible to plumb it again, and is likely to get out of line still more as it sinks. If it is nearly plumb at that depth, there is rarely much trouble at greater depths. The more it is out of plumb, the more is the caisson apt to be warped, greatly increasing the frictional resistance. Very few caissons, however, are less than 6 inches out of plumb, or out of line, and a greater allowance than this should always be made in designing foundations. It is useless to specify that no caisson will be accepted, if it is more than 6 inches out of plumb or position, if sunk to any considerable depth. It would be a radical remedy to remove a caisson sunk from 40 to 90 feet and start over again, for generally the loss of time to the owner would be sufficient to prevent enforcing such a provision against the contractor. Pneumatic caissons are used only where water is encountered, and where the volume of water is too great to permit pump- ing in an open cofferdam, or where such an operation would endanger adjoining structures by drawing the water and sand from under them and thus allowing settlement. The air pressure must be just sufficient to keep the water from flowing in and bringing the sand with it. Even when much care is employed with compressed air, trouble on this account occurs frequently and sometimes at a considerable distance away. For instance, while sinking the foundations for Liberty Tower in New York City, a certain quantity of water and sand must have escaped from under the Chamber of Commerce Building on the opposite side of the street, causing the interior columns 55 2 PNEUMATIC CAISSON PRACTICE CHAP. XVIII to settle considerably while the outside walls were apparently not disturbed. ART. 186. EXCAVATION AND SEALING Two methods are in use for removing material from the work- ing chamber: First, by buckets and derricks; and second, by blowing it out. In the first method, the sand hogs shovel or lift the material into buckets which hold about a third of a cubic yard. The bucket is attached to a cable and hoisted into the lock at the top of the shaft, the bottom door is closed and the top door opened, thus allowing the bucket to be swung clear of the lock, emptied and returned to the caisson for another load without having been disconnected from the cable. Oc- casionally the lock has no top door but one at the side, in which case the bucket is dumped while still in the lock. Such a lock works better with sandy ground than with sticky clay. The makers claim that it is more economical than other locks, especially for small sizes. When conditions permit the use of the blow method, this is the cheapest. It requires a 4- or 5-inch cast-iron pipe from the surface to the deck, from which is extended a flexible hose with a valve near the lower end. Above the surface the pipe must have a bend or elbow to direct the material away from the caisson. In operation, the material is shoveled or washed into a pile at the end of the hose, and the valve opened to let the compressed air carry it out. The material can be removed much faster than it can be shoveled into a pile, or than the con- creting can be continued at the top. A large volume of air escapes, while gravel and even fair-sized stones go out with such terrific velocity that a cast-iron elbow 2 inches thick is worn through in an hour. In one instance, the windows of a tug 200 feet away were broken. Accordingly, the hardest manganese steel is used for these elbows. While waiting for a new one the expedient has been adopted of fastening a ' i2-inch block of wood to the old elbow. The most important part of pneumatic caisson work is in ART. 1 86 EXCAVATION AND SEALING 553 sealing the air chamber, or filling the space betwee'n the bottom of the excavation and the deck of the caisson with concrete. By the old method, the concrete was spread on the botton> until it extended a foot or two above the cutting edge, and then it was benched up around the sides, using boards for bulkheads if necessary, until the concrete was 3 or 4 inches below the deck. The remaining space was filled by ramming into it a fairly dry mortar. This method was very expensive and unsatisfactory, for the concrete had to be fairly dry to stand benching. Dry concrete should never be used in compressed air, since the moisture is absorbed so rapidly. The writer has examined old work and found the concrete, which had been placed in this manner, in a very poor condition. He has also taken out concrete, which was mixed very wet, from the bottom of a caisson and found it to be exceptionally good. In another method, the filling was continued either by bucket or concrete chutes until the wet concrete reached the roof. Actual measurements have shown a space of \ to f inch between the concrete and the deck due to the shrinking of the concrete while setting. The writer's present practice is as follows: The roof is sloped as much as possible and air vents I or 2 inches in diameter are placed as far as possible from the shaft used for the concrete. The air chamber is filled with very wet concrete to within 10 or 12 inches of the roof. Meanwhile, the air pressure was gradu- ally reduced according to the change in head from the cutting edges upward. Work is then suspended for at least 24 hours under air pressure, by which time the 5 feet of concrete will attain its permanent shrinkage. The air-lock is then taken off and concrete is dumped down the shaft to fill the space in the air chamber and some distance up the shaft. This concrete is made as wet as possible, while grout is used in some cases. If properly done, it will be found that the air has all been forced up the vents and the grout from the concrete stand 6 to 20 feet up the vent pipes, thus indicating that the chamber is entirely filled. 554 PNEUMATIC CAISSON PRACTICE CHAP. XVIII ART. 187. JOINTS BETWEEN CAISSONS There are several methods of making a joint between two caissons to prevent the flow of water between them. One method is by stock ramming, as applied on the Mutual Life Building foundations in 1900. The caissons were 18 feet wide, made of steel and filled with concrete. They were kept from getting too close together "by two 6 X 6-inch oak strips, spaced about 4 feet apart and held in place by 6 X 4-inch steel angles. Between the two caissons and these strips a 4-inch pipe was forced to rock, and pellets of clay were rammed down the pipe by an iron rod under the weight of a pile-hammer. This method exerts a high pressure and is capable of doing much damage if not carefully watched. For example, in trying to stop a leak in a dam, 500 cubic yards of concrete were cracked and lifted by the force of the clay driven through one pipe. The oak strips referred to above kept the clay from spreading and it was thus thoroughly compacted to hold back the water while the cellar was dug, and while 2 feet of brick from the inside face was placed between the ends of the caissons for a permanent water- tight wall. Forcing down grout instead of clay has also been tried, but did not prove as successful. On the Commercial Cable Building, in 1896, the so-called half-moon joint was used for the first time. The steel caissons were 6 feet wide and so arranged that 4 feet of the end walls of each caisson could be removed after sinking. Behind these plates timber form!? had kept the concrete back, leaving a semi- circular opening, so that the two adjoining openings formed a shaft about 4 feet in diameter from the top to the bottom. Before removing the end sections, however, stock ramming was applied on each side, with the result that the clay filled not only the space between the caissons, but spread into the lot as far as 20 feet in extreme cases. After the sections were removed, the vertical shaft was cleaned out and filled with concrete, making for the first time a continuous concrete wall all around the build- ing to exclude the water. In many cases, no stock ramming was used, but a lock at- ART. 1 88 PLANT AND EQUIPMENT 555 tached to a small shaft was concreted or bolted in place over the 3~or 4-foot circular shaft, and after the application of com- pressed air, the sand hogs closed the two openings in the shaft, working downward from the top and removing the material at the same time. This is often done by nailing short boards against upright timbers placed in the ends of the caissons before sinking. In one instance, these boards, not being strong enough or properly fastened, were blown out allowing the ground to flow in and kill two men in the shaft or key-way. To close the opening between the caissons, by driving sheet-piling on each side before applying air, is quicker and cheaper than stock ramming but not nearly so effective. See Art. 123 for illustrations. ART. 1 88. PLANT AND EQUIPMENT The pipes to supply compressed air are generally 4 inches in diameter, and there should be two from the caisson deck to the top to facilitate changing the connection as the cofferdam is built up. One 4-inch pipe is sufficient from the caisson to the compressors, with smaller pipes for high pressure to operate the locks. In winter these pipes should be placed in a box filled with manure to prevent freezing. The compressors, electric-lighting and pumping plants are sometimes compactly arranged on a big float, although it often pays to locate them on shore alongside of a railroad track on account of coaling facilities. Where an old bridge is located next to the one under construction, it affords a good support for the pipe lines; or a light trestle may be built on piles to carry them; or the pipes may be laid on the river bottom, although this is not so desirable. It is impossible to lay down any rigid rule for the size of plant required. It depends both on the number of caissons and on the season of the year or climatic conditions. It always pays to have plenty of boiler capacity. For a bridge of fair size there should be two boilers of 150 and four of 80 horse- power capacity each. There should always be one more air 556 PNEUMATIC CAISSON PRACTICE CHAP. XVIII compressor than is needed for constant service, to allow for repairs that will certainly be required. Nothing is so expensive on contract work as delay. A work of this magnitude probably requires three or four compressors with an aggregate capacity of 2500 to 4000 cubic feet of free air per minute. In illustration of the effect of weather and location on the cost of work, two examples are given, in both of which the work extended over a year including winter and summer. The first work was in the east where about 20 caissons of medium size required 5000 tons of coal at a cost of $15 ooo. The second was in the west, where 5000 tons of coal were also required, but at a cost of $40000. Although the number of caissons and the total yardage of caisson work were only about one-half as large as for the eastern location, yet on account of severe weather and higher price, the coal cost over five times as much per cubic yard of caisson work. Both jobs were handled by the same contractor, and with the same staff and plant. This fact indi- cates why it is so difficult to compute the cost of pneumatic work in advance. One of the best money-saving devices for a contractor who has a number of caissons to build is a saw arbor run by com- pressed air or electricity. The time saved in cutting the large timbers to the right length, and in securing small timbers of the proper dimensions, pays for the machine in a short time. A good pipe-cutting machine with dies, etc., is also indispensable, as well as augers to bore holes for bolts and drift bolts and a hammer to drive them, both run by compressed air. An ample supply of the best stiff-leg and guy derricks, and necessary side tracks, wharves, cement and other storage buildings, will well repay the large outlay required. Cable- ways up to 1600 fee tin span have been used to advantage in some cases, while in others they proved a source of loss. ART. 189. AIR-LOCKS AND CONCRETE One of the most important contrivances on a pneumatic caisson job is an air-lock, without which the work cannot be carried on. It consists of an air chamber with one door opening ART. 189 AIR-LOCKS AND CONCRETE 557 to the atmosphere and another into the shaft or working chamber. In the early caissons, the lock was placed below the shaft in the working chamber. This is an inconvenient and unsafe position for the lock, for if the caisson becomes too heavy, there is danger of crushing the lock, and then the lock has to be taken apart and removed before the shaft can be filled with concrete. The lock was probably put at the bottom to permit adding new sections to the shaft without removing the lock, and before the idea occurred to any one of placing an additional door at the bottom of the shaft. This door is now used to prevent the escape of air when the lock is lifted off temporarily to add shafting. It is also useful in case of emergency. Although it did not take long for the advantages of placing the lock at the top of the shaft to become apparent, the hoisting mechanism was placed inside of the lock. Accordingly, the bucket was lifted from the working chamber into the lock, the lower door closed, and the material dumped through a side door or again lifted through a top door, thus requiring the material to be handled twice. This cumbersome and slow method is still used in Europe and occasionally in this country. This arrangement was superseded by means of the modern locks which permit the bucket to be lowered into the working chamber, filled, hoisted out, emptied, and returned to the work- ing chamber without detaching it from the cable. The first lock to accomplish this saving of time and money had its top door in two horizontal halves, meeting over the center of the shaft and leaving a hole for a stuffing box 3 or 4 inches in diame- ter at the center of the joint. The stuffing box was so packed that the steel cable could pass through freely without allowing much air to escape. When the bucket was hoisted out of the lock, the stuffing box remained on the cable near the bale of the bucket. Later it was found by experiment that by making the hole in the doors only large enough for the cable to pass through, the loss of air was not sufficient to warrant the use of a patent stuffing box. Since there is no necessity for the cable to pass through the lower door of the lock when closed, the best 558 PNEUMATIC CAISSON PRACTICE CHAP. XVIII form is a single round door slightly larger than the opening and hinged on one side. It is known as a flap door since it swings up against its seat where it is held by air pressure. A rubber gasket about | inch thick and 3 to 4 inches wide is usually at- tached to the door to prevent the escape of air between the door and its seat. According to present practice, then, the derrick lowers the bucket into the lock, the upper doors close against the cable, after the lock is filled with air the lower door drops open by its own weight and the passage is clear for the bucket to be lowered into the working chamber. The bucket is filled and hoisted again into the lock, the lower door is swung up by levers on the outside, the air in the lock is allowed to escape, permitting the upper doors to be opened and the bucket hoisted out and emp- tied. The entire cycle of operation for a half-yard bucket can be repeated 20 times an hour, a vast improvement over the older system. Numerous patents have been taken out to get around the original one. One lock has a circular flap door at the top as well as at the bottom, the upper one having a slot extending from the center to the edge to permit the door to shut while the bucket is suspended in the lock. An additional contrivance covers the slot afterward. Another lock, more extensively used, has a circular top door so placed that the edge of the door is directly over the center of the shaft, permitting the hole for the cable to be located at the edge of the door instead of the center. This arrangement requires the lock tender to give the bucket or cable a slight push as it enters or leaves the lock. In a still later design, the cable passes through the door frame instead of the door. Apparently every practicable form of lock has been patented. All those described above have doors open- ing inward, so that when they are closed the air pressure holds them shut. This is the only safe method, for the greater the pressure, the tighter the door is held. However, locks have been built with upper doors closing from the outside and held shut by means of screws, etc. When the bucket is taken out of the lock, the door and stuffing box remain on the cable. ART. 190 ALLOWABLE BEARING UNDER CAISSONS 559 But few of the locks were manufactured as the patent was promptly bought by the owner of other patents. Bucket locks are used extensively in concreting the working chamber as well as in excavating small caissons, but for large caissons having two shafts, a special concrete lock is used. It usually consists of an ordinary 3-foot shaft with a door in the bottom, and a cone above the lower door. The lock is placed on top of the shaft and has a hopper located above it. As soon as a yard or so of concrete has been dumped into the lock, the upper door is closed and the bottom one opened, allowing the mass to fall down the shaft into the working chamber. In this manner, concrete can be taken in about as fast as the men below signal for it. All concrete for caisson work should be as non-porous as possible. The principal means toward this end consists in making the mixture of sand and cement in the proportion of one part, by volume, of cement to two parts of clean, sharp and coarse sand. Four, five, or even more parts of stone or gravel to one of cement can be used for this mixture, provided it is made wet enough. A poorer mixture than one to two of cement and sand will not have the voids of the sand filled, while a wet 1-2-4 mixture will not usually have as much stone as can be safely covered. When dry concrete used to be employed, it was hard to get a 1-2-4 mixture properly rammed, but with wet concrete, the stone immediately disappears in the cement and sand, insuring good concrete without voids. ART. 190. ALLOWABLE BEARING UNDER .CAISSONS The maximum pressure allowed on bedrock or good hard- pan should be based on the strength of concrete, and should never exceed 15 tons per square foot. Good concrete, as indi- cated by careful tests, will resist very much higher pressures, and so will bedrock and many kinds of hard-pan; but in order to allow a reasonable factor of safety to cover imperfect work or material, even if such lapses occur only occasionally in the night, this pressure should not be exceeded. 560 PNEUMATIC CAISSON PRACTICE CHAP. XVIII Good sand on the surface, and not under a caisson, should not be loaded over 2 or 3 tons per square foot; but if it is under a caisson and 30 feet or more below the surface where it cannot be disturbed, it can safely be loaded to a maximum limit of 6 tons. In New York City, the hard-pan varies from 2 to 30 feet in thickness, with 30 to 60 feet of quicksand above it, and sometimes from 2 to 40 feet of sand, boulders, etc., below it. It also varies in quality from a material resembling good con- crete to that of loose sand. For clay and other materials, the variations are so great that no definite load should be specified until the local conditions of each case have been carefully ex- amined and considered. In one example, open concrete cylinders were sunk from 30 to 90 feet to beds of various grades of fine and coarse sand. The one which was apparently the most unfavorable was sub- jected to a test load of 10 tons per square foot, causing a settle- ment of about I inch, one-half of which was recovered upon removing the load. After a concrete viaduct to carry a railroad was built upon these cylinders, several of them began to settle, and continued until at the end of about a year the maximum was reached, some cases amounting to 6 inches. After that no further trouble occurred. ART. 191. REMARKS ON UNDERPINNING Since Chap. XVI on underpinning is so complete, but little remains to be added except to present conclusions. It is generally found to be more economical to use inclined shores, needles, or both, on light buildings; that is, on ordinary buildings up to six or seven stories high. For higher buildings, or where bedrock is easily accessible, the system patented by BREUCHAUD in 1896 can be depended upon to give good results, but it is not recommended to use smaller diameters than 30 inches, which permit sending men down to the bottom. The more recent patented systems, namely, MERRILL'S telescopic method and THOMSON'S vertical tunnel method, are fully described in Chap. XVI. ART. 191 REMARKS ON UNDERPINNING 561 In the writer's experience, 1 6-inch cylinders have been jacked down under a six-story building until the weight of the old building was taken off the old foundations, and then after the shoring was completed, these cylinders settled when an adjoining caisson was sunk, thus requiring the use of inclined shores after all. Later, when the Gillender Building was removed to give place to the Bankers' Trust Building, he wit^ nessed the removal (in 1911) of 14-inch cylinders which had been sunk in 1877 under an adjoining building, and they were found to be filled with excellent concrete except within a few feet at the bottom, which was filled with sand. This observa- tion probably accounts for the settlement just mentioned. CHAPTER XIX REFERENCES TO ENGINEERING LITERATURE ART. 192. LITERATURE ON FOUNDATIONS Very few books have been published in this country which are devoted exclusively to the subject of foundations. In most cases the subject is treated in one or two chapters of a book, as indicated in the following list. The list is not complete but contains the most important works which should be ac- cessible in college libraries. With a few exceptions, only American works are included. The dates of publication given are those of the first editions of the respective works. American School of Correspondence. Cyclopedia of Architecture, Carpentry and Building. Chicago, 1907. Vol. 3 contains 22 pages on foundations. ARTHUR, WILLIAM. Contractors' and Builders' Handbook. New York, 1911. Contains one chapter (18 pages) on foundations, j/ BAKER, I. O. Treatise on Masonry Construction. New York, 1889. The tenth edition contains four chapters on foundations, the titles of which are: Introductory; ordinary foundations; pile foundations; and foundations under water; covering about 18 percent of the volume. Bridge abutments and piers are treated in two additional chapters. BUEL, A. W., and HILL, C. S. Reinforced Concrete. New York, 1904. The second edition contains 28 pages on reinforced- concrete footings and on concrete piles. BYRNE, A. T. Inspector's Pocket-Book. Materials and Workman- ship in Construction. New York, 1892. The third edition contains 29 pages on foundations. ^CORTHELL, E. L. Allowable Pressures on Deep Foundations. New York, 1907. The entire book, containing 98 pages and 8 folding tables, is devoted to a record of pressures on deep foundations for 178 structures of different kinds located in different countries, as well as of the condi- tions in the respective cases. FIEBEGER, G. J. Civil Engineering. New York, 1905. One chapter is devoted to foundations. FOSTER, W. C. Treatise on Wooden Trestle Bridges. New York, 562 ART. 192 LITERATURE ON FOUNDATIONS 563 1891. The fourth edition contains three chapters on pile-bents, pile- drivers, and concrete [pile] trestles. That on pile-bents includes some notes on pile driving. ** FOWLER, C. E. Subaqueous Foundations. New York, 1914. This work supersedes Fowler's Cofferdam Process for Piers, first published in 1898, and his Ordinary Foundations, under which title the second edition was published in 1905. FREITAG, J. K. Architectural Engineering. New York, 1895. Con- tains one chapter on the foundations of buildings, relating principally to steel-grillage and reinforced-concrete footings, with some data on founda- tion loads. FRYE, A. L. Civil Engineers' Pocket-Book. New York, 1913. Con- tains one section, 29 pages, on foundations. GILBERT, G. H., WIGHTMAN, L. J., and SAUNDERS, W. L. Subways and Tunnels of New York. Methods and Costs. New York, 1912. In one appendix 12 pages are devoted to the sinking of pneumatic caissons for tall buildings in New York. Several other appendices give informa- tion on the use of compressed air for tunnel work, shaft sinking, etc., and on the equipment required. GILLETTE, H. P., and HILL, C. S. Concrete Construction, Methods and Cost. New York and Chicago, 1908. Contains one chapter on methods and cost of concrete and pier construction. GILLETTE, H. P. Handbook of Cost Data for Contractors and Engi- neers. New York, 1906. Includes data on the cost of piles, drivers, mak- ing piles, driving piles, sawing-off piles, pulling piles, blasting piles, puddle, a bridge foundation and cofferdam. HARCOURT, L. F. VERNON. Civil Engineering as Applied to Construc- tion. London, 1902. Contains one chapter on foundations and piers of bridges, and another one on excavations, dredging, pile driving, and cofferdams. HILL, LEONARD. Caisson Sickness and the Physiology of Work in Compressed Air. London, 1912. HOOL, G. A. Reinforced-Concrete Construction. Vol. 2. Retaining Walls and Buildings. New York, 1913. One chapter (49 pages) is devoted to foundations, including the bearing capacity of soils, shallow footings, and concrete piles. Another chapter on retaining walls includes designs of their footings. International Library of Technology. Scranton, 1905. Volume 52 contains section 18 (189 pages) on the simple types of footings and but- tresses, and section 20 (70 pages) on shallow foundations and cantilever foundation girders. KIDDER, F. E. Architect's and Builder's Pocket-Book. New York, 1884. The fifteenth edition contains one chapter (about 65 pages) on foundations and spread footings. 564 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX KIDDER, F. E. Building Construction and Superintendence. Part I. Masons' Work. New York, 1896. Contains three chapters, respec- tively, on foundations on firm soils; on foundations on compressible soils; and on masonry footings and foundation walls, shoring and underpinning. MAHAN, D. H. Treatise on Civil Engineering. New York, 1873. Contains two chapters on foundations of structures on land, and in water, respectively. This work is out of print. MERRIMAN, M., Editor in Chief. American Civil Engineer's Pocket- Book. New York, 1911. Contains 35 pages on foundations on land and under water; and some other articles on foundations of reinforced concrete, on shafts and borings, etc. MITCHELL, C. F. Building Construction. London, 1913. (Seventh edition.) Contains one chapter on foundations, including piles, wall and column footings, drainage, and shaft sinking and trenching. ^ PATTON, W. M. Practical Treatise on Foundations. New York, 1893. In the second edition about 50 percent of the book is devoted to the subject of foundations proper. In the first edition, the corresponding percentage was only 27. PATTON, W. M. Treatise on Civil Engineering. New York, 1895. Contains one chapter on foundations and foundation beds. POWELL, G. T. Foundations and Foundation Walls. New York, 1884. An elementary treatise on the foundations of ordinary buildings. REID, H. A. Concrete and Reinforced-Concrete Construction. New York, 1907. Contains one chapter on foundations, devoted practically to shallow footings and reinforced-concrete piles. RICKEY, H. G. Building Foreman's Pocket-Book and Ready Reference. New York, 1909. Contains 8 pages on piles for foundations. RICKEY, H. G. Handbook for Superintendents of Construction, Architects, Builders and Building Inspectors. New York, 1905. Con- tains 25 pages on pile foundations and shallow footings. TAYLOR, F. W., and THOMPSON, S. E. Treatise on Concrete, Plain and Reinforced. New York, 1905. The second edition contains one chapter (20 pages) on foundations and piers, treating particularly of single and combined footings of reinforced concrete and of concrete piles. TAYLOR, F. N. Manual of Civil Engineering Practice. London, 1911. Contains one chapter on foundations and pile driving. TRAUTWINE, J. C., J. C. JR., and J. C. 3rd. Civil Engineers' Pocket- Book. New York, 1872. The nineteenth edition contains one section of 1 8 pages on foundations. WHEELER, J. B. Elementary Course of Civil Engineering. New York, 1876. Contains two chapters on foundations on land and in water, respectively. Out of print. " WHITE, LAZARUS. The Catskill Water Supply of New York City. New York, 1913. One chapter gives descriptions of borings and sub- ART. 192 LITERATURE ON FOUNDATIONS 565 surface investigations, and another one of exploration for the Hudson River crossing, including 49 pages in all. The following valuable monographs on important bridges and their foundations have been published in book form. They deserve study by engineers with reference to the historical development of American foundation practice. CLARKE, T. C The Quincy Bridge. New York, 1869. Three chap- ters and an appendix are devoted to the physical characteristics of the Mississippi River, a description of the substructure and foundations, specifications and classified cost. The foundations and equipment for construction are illustrated by 12 plates. The open caissons, and coffer- dams with removable sides on grillage, were used for pile foundations, protected from scour by loaded timber cribs. CHANUTE, OCTAVE, and MORISON, GEORGE. The Kansas City Bridge. New York, 1870. Four chapters give the regimen of the Missouri River, the foundations, masonry, and classified cost of the work; an appendix gives tables showing the progress of sinking a pier, with soundings, weights, etc.; while 6 plates illustrate foundation works, piers, and equip- ment. Four piers were founded on bed-rock with open timber caissons having dredging wells, while two piers were founded on piles. WOODWARD, C. M. History of the St. Louis Bridge. St. Louis, 1881. Six chapters are devoted to the deep pneumatic foundations for the two river piers and east abutment, the physiological effects of compressed air, computations on the stability of the piers, and on classified costs. Two other chapters relate to the west abutment which required a cofferdam to be built under extraordinary difficulties, to financial and engineering considerations relating to preliminary and final foundation plans, and to sinking by the pneumatic process. The substructure and foundations are illustrated by 15 plates of plans and views. MORISON, GEORGE S. Plattsmouth Bridge, 1882; Bismarck Bridge, 1884; Blair Crossing Bridge, 1886; New Omaha Bridge, 1889; Rulo Bridge, 1890; Sioux City Bridge, 1891; Nebraska City Bridge, 1892; Cairo Bridge, 1892; Bellefontaine Bridge, 1894; Memphis Bridge, 1894. These reports give the most complete information about pneumatic foundations of any that have been published. The kinds of data given are indicated by the report on the Bellefontaine Bridge. The general description includes the trestle approach on piles, the classified cost of each pneumatic foundation in detail, and the cost and quantity of masonry in the piers. In ap- pendices are given a record of sinking the caissons with elevations, im- mersion, weights, air pressure, and skin friction; the time, costs, and materials used in foundations; and the specifications for masonry. The 566 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX plates show elevations and plans of the piers; detail drawings of the caissons; a diagram giving the rate of progress in sinking caissons; and a water-gage record. In most cases a record of the preliminary borings is also given. In the first two reports, however, the weights and skin friction for the caissons, computed daily while sinking, are not given. HUTTON, W. R. The Washington Bridge. New York, 1889. In 20 pages the text gives a brief description of the substructure, the specifica- tions for the masonry, a table of diamond drill borings, and a record of sinking the pneumatic caisson. The illustrations include 4 plates on foundations besides 20 on masonry. BOLLER, A. P. The Thames River Bridge. New York, 1890. The text gives a record of soundings and borings, a description of foundations, weights and settlement of piers. Three plates have illustrations on foundations. Four of the piers are supported by pile foundations, the upper parts of the piles being protected by timber cribs sunk into holes previously dredged. The masonry was built in cofferdams with re- movable sides on grillage, and sunk to bearing on the piles. After removing the cofferdams, a filling of sand and gravel was placed around the piers and in the cribs. NOBLE, ALFRED, and MODJESKI, RALPH. The Thebes Bridge. Chi- cago, 1907. The description of the substructure is supplemented by 14 plates and several half-tone views. The river piers were founded by the pneumatic process, and one of the shore piers by means of an open caisson of reinforced concrete. The specifications for the substructure are given in an appendix. Cambridge Bridge Commission. Report of the Commission and ot the Chief Engieeer (WILLIAM JACKSON) upon the Construction of the Cam- bridge Bridge. Boston, 1909. The description of the substructure and the analysis of its cost are supplemented by 12 views, n folding plates and 6 folding schedules of expenditures. The piers and abutments are all supported on pile foundations. MODJESKI, RALPH. The Vancouver- Portland Bridges. Chicago, 1910. The description of the substructure is illustrated by 23 plates. The specifications are given in an appendix. This report includes the Washington Channel bridge over the Columbia River, Shaw's (or Hay- den's) Island viaduct, the Oregon Slough bridge, and the Willamette River bridge. The piers of the bridges over the two rivers were founded by the pneumatic process while the abutments and the remaining piers have pile foundations. A large number of selected references to engineering periodi- cals and the proceedings or transactions of engineering societies are given in the following articles. They are intended for the ART. 193 TIMBER PILES AND PILE DRIVING 567 benefit of those who desire to study any topic more extensively or in greater detail than the limits of this volume allow for the descriptions and illustrations given in the text. No attempt is made to refer to all the engineering periodicals published in this country, nor to include every reference that may be found in the periodicals selected. It will be observed that the titles of the following articles in this chapter correspond to those of preceding chapters. The authors will appreciate information regarding errors discovered in the references. It is a valuable exercise for the student to compare the general arrangement and details of construction for any given type of structure relating to foundations, as designed by different engineers, and to note which features constitute the essential elements of that type, and which ones are dependent merely upon local conditions and therefore subject to more or less variation. To make the results of such studies readily available for future reference, they should be placed upon separate sheets of paper and filed in accordance with a suitable classification of subjects. ART 193. TIMBER PILES AND PILE DRIVING TIMBER PILES. Tough Pine Piles from Nova Scotia. Eng. News, v. 22, p. 368, Oct. 19, 1889. Life of Different Kinds of Timber Piles. Report of Committee and Discussion. Proc. Assoc. Ry. Supts. B. & B., 1899, v. 9, p. 50. Calculating the Cubical Contents of Piling. Eng. News, v. 54, p. 170, Aug. 17,1905. Table prepared by E. O. Faulkner of A. T. & S. F. Ry. See Richey's Building Foreman's Pocket-Book, PP- 474, 475- ORDINARY PILE-DRIVERS. Pile-Hammer Ropes. Including tests. Proc. Assoc. Ry. Supts. B. & B., 1897, v. 7, p. 250. Repairing a leaking cofferdam; and pile driving methods at Leech Lake, Eng. News, v. 46, p. 189, Sept. 19, 1901. Driving Difficult Piles for Bridge Renewal. Eng. Rec., v. 43, p. 54, January 19, 1901. Electric Pile-Driver and Derrick. Eng. News, v. 47, p. 513, June 26, 1902 Sectional Elevation of Apparatus for Subaqueous Pile Driving. Chas. Sooysmith. Eng. News, v. 48, p. 472, December 4, 1902. An Excellent Type of Land Pile-Driver. Eng. News, v. 50, p. 66, July 16, 1903. A Novel Tilting Pile-Driver. J. H. Baer. Eng. News, v. 50, p. 205, Sept. 3, 1903. A Chute for Driving Batter Piles. Eng. Rec., v. 50, p. 56, July 9, 1904. Derricks 568 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX and Sheet-Pile Drivers for Foundation Work. Eng. Rec., v. 50, p. 254, Aug. 27, 1904. Steel Sheet-Piling for a Boiler Room Excavation. Eng. Rec., v. 52, p. 472, Oct. 21, 1905. Steam Pile and Sheet-Pile Drivers on the New York Barge Canal. Emile Low. Eng. Rec., v. 55, p. 298, Mar. 2, 1907. A Pile Trestle Erected with a Pivotal Pile-Driver. R. Balfour. Eng. News, v. 58, p. 160, Aug. 15, 1907. Highest Pile-Driver. I. H. Frederickson. Eng. News, v. 58, p. 173, ug. 15, 1907. Non- Patented Pivotal Pile-Driver. Charles Hansel. Eng. News, v. 58. p. 201, Aug. 22, 1907. Telescoping Leads for Pile-Drivers. H. P, Shoemaker. Eng. News, v. 48, p. 524, Nov. 14, 1907. Revolving Pile- Driver. Eng. News, v. 59, p. 368, April 2, 1908. Driving Long Piles with Short Leads. Frank B. McLean. Eng. News, v. 60, p. 41, July 9, 1908. Steel Pile-Driver Leads. Eng. Rec., v. 63, p. 250, Mar. 4, 1911. Roller Case Pile-Driver used in the construction of permanent Trestle Extension on the Ogden-Lucin Cut-off. C. M. Kurtz. Eng. News, v. 66, p. 338, Sept. 21, 1911. TRACK PILE-DRIVERS. Best and most Economical Railway Track Pile-Driver. Proc. Assoc. Ry. Supts. B. & B., 1896, v. 6, p. 197. Rail- way Pile-Driver. G. W. Smith. Jour. W. Soc. Engrs., v. 4, p. 251, June, 1899; Eng. News, v. 42, p. 314, Nov. 16, 1899; Eng. Rec., v. 41, p. 154, Feb. 17, 1900. Best Design and Recent Practice in Building Railroad Track Pile-Drivers. Proc. Assoc. Ry. Supt. B. & B., v. 12, p. 163, Oct., 1902; Eng. News, v. 48, p. 363, Oct. 30, 1902. Improved and Combination Collapsible Pile-Drivers for Railroad work. Eng. Rec., v. 49, p. 358, Mar. 19, 1904. Interstate Ry. Pile-Drivers. Ry. Age Gaz., v. 46, p. 677, Mar. 19, 1909. High Powered Locomotive Pile-Driver Carrying its own Turntable. Walter Ferris. Eng. News, v. 62, 538, Nov. 18, 1909; Ry. Age Gaz.,v. 47, p. 998, Nov. 19, 1909. Reprinted from Jour. Am. Soc. M. E., Jan., 1909. Pile-Driver Leads on a Loco- motive Crane. Eng. Rec., v. 64, p. 608, Nov. 18, 1911. Driving Trestle Piles with a Locomotive Crane. Eng. News, v. 66, p. 625, Nov. 23, 191 1. Desirable Features of a Track Pile-Driver. Proc. Am. Ry. Eng. Assoc., 1911, v. 12, p. 286, Parti. Convertible Railway Pile-Driver and Locomotive Crane. Eng. News, v. 71, p. 374, Feb. 12, 1914. EQUIPMENT. Crane's Steam Pile-Hammer. Eng. Rec., v. 15, p. 372, Mar. 12, 1887. Why the Nasmyth Steam- Hammer has not displaced the Friction- Clutch Pile-Driver. Eng. News, v. 50, p. 13, July 2, 1903. Direct-Acting Steam Pile-Hammer. Eng. News, v. 36, p. 38, July 16, 1896. New Design of Steam Pile-Driver. Comparison of Several Types of Drivers. A. A. Goubert. Eng. News, v. 63, p. 79, Jan. 20, 1910. Goubert Pile-Driving Hammer. R. R. Age Gaz., v. 48, p. 216, Jan. 28, 1910. Advantages and Disadvantages of a Steam Pile-Driving Hammer. Eugene Lentilhon. Eng. News, v. 36, p. 58, June 23, 1906. Observations on Driving Piles with a Steam-Hammer. J. J. Welsh. ARI. 193 TIMBER PILES AND PILE DRIVING 569 Jour. Assoc. Eng. Soc., v. 33, p. 193, Sept., 1904. S team-Hammers vs. Drop Hammers for Pile-Drivers. Report of Committee. Proc. Assoc. Ry. Supts. B. & B., v. 14, p. 200, Oct., 1904; R. R. Gaz. v. 37, p. 501, Oct. 28,1904; Eng. News, v. 52, p. 378, Oct. 27, 1904. Pile-Driving Notes. J. E. Crawford. Eng. News, v. 61, p. 622, June 10, 1909. Pile Rings and Method of Protecting Pile Heads in Driving. Report of Committee and Discussion. Proc. Assoc. Ry. Supts. B. & B., 1898, v. 8, p. 60. Protecting Pile Heads. Report of Committee. Proc. Assoc. Ry. Supt. B. & B., v. 8, p. 60, Oct., 1898; Eng. Rec., v. 38, p. 450, Oct. 22, 1898. Is the use of an Iron Follower or Cap on Piles to be Recommended? Sam'l Young. Eng. News, v. 50, p. 247, Sept. 17, 1903. Pile Driving. Eugene Lentilhon. Eng. News, v. 29, p. 14, Jan. 5, 1893. Cast-Iron Shoes with Chilled Points. Eng. News, v. 32, p. 224, Sept. 20, 1894. Pile Shoes. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. n, p. 194, Part I. Pile Splices. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. u, p. 192, Part I. PILE DRIVING. Principles of Practice. Manual Am. Ry. Eng. Assoc. Pile Driving. S. E. Thompson. Eng. News, v. 46, p. 282, Oct. 17, 1901; Eng. Rec., v. 44, p. 8, July 6, 1901. Pile Driving. E. H. Bedsler. Eng. News, v. 16, p. 83, August 7, 1886. Notes on Pile Foundations in Chicago. Eng. News, v. 30, p. 228, Sept. 21, 1893. Some Instances of Piles and Pile Driving, New and Old. Horace J. Howe. Jour. Assoc. Eng. Soc., v. 20, p. 257, 294, Apr., 1898. Notes on Pile Driving. Jas. C. Hough. Jour. Assoc. Eng. Soc., v. 25, p. 135, Sept., 1900. Driving Piles in Dry Ground. P. F. Barr. Eng. News, v. 52, p. 545, Dec. 15, 1904. Novel Method of Facilitating Pile Driving. I. O. Baker. Eng. News, v. 57, 576, May 23, 1907. Some Pile-Driving Experiments in Connection with the Construction of the Charles River Dam. J. A. Holmes. Engr.-Contr., v. 29, p. 115, Feb. 19, 1908. Pile- Driving Notes. J. E. Crawford. Eng. News, v. 61, p. 622, June 10, 1809. Supporting Power of Piles. E. P. Goodrich. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. n, p. 220, Part I. Pile Driving Without Leads. L. C. Lawton. Ry. Age Gaz., v. 53, p. no, June 19, 1912. Pile Driving in Two Stages. C. E. Smith. Proc. Am. Ry. Eng. Assoc., 1913, v. 14, p. 238, Part II. Piles Driven with Butt Ends Down. Ry. Age Gaz., v. 49, p. 787. Con- strutting a Braced Pile Bulkhead. Eng. Rec., v. 59, p. 571, May i, 1909. Method of 'Spotting' Foundation Piles for a Bridge Pier. Geo. A. McKay. Engr.-Contr., v. 33, p. 607, June 29, 1910. Cutting Off Piles by Dynamite. Eng. Rec., v. 36, p. 291, Sept. 4, 1897. Durability of Piles Driven in Tidal Waters and Cut Off above Low Water. L. Y. Schermerhorn. Eng. News, v. 47, p. 70, Jan. 23, 1902. Screw-jacks for Pulling Piles. E. M. Malmquist. Pile-Pulling Rig Used in Kansas City. Wm. P. Parker. Eng. News, v. 49, p. 348, April 16, 1903. Methods and Costs of Pile Pulling and Pile Blasting. Eng. News, v. 49, 57 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX p. 338, April 16, 1903. Removing Piles by Blasting. G. W. Stadly Eng. News, v. 49, p. 432, May 14, 1903. Sawing Off Piles under Water. Eng. Rec.,v. 50, p. 437, Oct. 8, 1904. New Portland Bridge. H. A. Crafts. Eng. Rec., v. 53, p. 252, Mar. 3, 1906. Durability of Wooden Piles. Concrete Piles on the Pacific Coast. Eng. Rec., v. 53, p. 525, Apr. 28, 1906. Possibilities and Methods of Pulling Steel Sheet-Piling. W. G. Fargo. Engr.-Contr., v. 27, p. 187, May i, 1907. Under-water Pile Saw with Guide Bracket for Cutting to even Grade. Clarence Coleman. Eng. News, v. 63, p. 696, June 16, 1910. Clarence Coleman. Engr.-Contr., v. 33, p. 605, June 29, 1910. Hand-Operated Device for Cutting Off Submerged Piles to Uniform Level. A. C. Freeman, Engr.-Contr., v. 34, p. 217, Sept. 7, 1910. Sawing Piling under Water. Ry. Age Gaz., Jan. 19, 1912, v. 52, p. 117. Old Piling Rejuvenated. G. Y. Skeels. Eng. Rec., v. 65, p. in, Jan. 27, 1912. Cost of Driving Piles. Eng. News, v. 48, p. 364, Oct. 30, 1902. Cost of Pile Driving and Falsework. Eng. Rec., v. 58, p. 234, Aug. 29, 1908. Notes on Pile-Driving Costs. Victor Windett. Engr.-Contr., v. 35, p. 709, June 21, 1911. USE OF WATER- JET. Water-Jet Pile Driving, Lt. F. V. Abbott. Annual Report Chief of Engineers, U. S. A., 1883, Part II, pp. 1249-1281. Chronology of the Water-Jet as an aid to Engineering Construction. Eng. News, v. 13, p. 104, Feb. 14, 1885. Chronology of the Water-Jet. Edwin Parish. Eng. News, v. 13, p. 124. Screen Dike and Jet Pile- Sinking. Missouri .River Commission. Eng. News, v. 24, p. 498, Dec. 6, 1890. Pile Driving by Water- Jet; Interstate Bridge, Omaha, Neb., Eng. News, v.^i, p. 316, April 19, 1894. Use of a Novel Water-Jet for Driving Piles for the Sandy Hook Proving Ground Railroad Trestle. Sherman A. Jubb. Eng. News, v. 53, p. 456, May 4, 1905. Excavation and Pile Driving for Brooklyn Anchorage Manhattan Bridge. Eng. Rec., v. 52, p. 187, Aug. 12, 1905. Partial History of the Use of the Water- Jet in Sinking Piles. Engr.-Contr., v. 27, p. 233, May 29, 1907. Water- Jet. Proc. Am. Ry. Eng. & M. W. Assoc., 1911, v. 12, p. 281. Use of Water-Jets in Pile Driving. Eng. Rec., v. 63, p. 361, Apr. i, 1911. Refers to report of Committee on Wooden Bridges and Trestles of Am. Ry. Eng. & M. W. Assoc., 1911, v. 12, p. 281. OVERDRIVING PILES. Examples of Overdriving Piles. Jas. W. Rpllins, Jr. Jour. Assoc. Eng. Soc., v. 20, p. 303, Apr., 1898. Safe Limit of Fall in Driving Piles. J. Y. Schermerhorn; G. W. Stadly. Eng. News, v. 48, p. 294, Oct. 9, 1902. Pile Driving. Frank Pidgeon. Eng. Rec., v. 53, p. 465, Apr. 7, 1906; Eng. Rec., v. 53, p. 383, Mar. 24, 1906. Overdriven Piles. Eng. Rec., v. 53, p. 166, Feb. 10, 1906; Eng. Rec., v. 53, p. 192, Feb. 17, 1906. Overdriving Piles. Trans. Am. Soc. C. E., v. 69, p. 104, Oct. 1910; Proc. Am. Ry. Eng. & M. W. Assoc., 1909, v. 10, p. 572; 1910, v. n, p. 196; 1911, v. 12, p. 281. ART. 193 TIMBER PILES AND PILE DRIVING 571 CHEMICAL PRESERVATION OF PILES. Destruction of Piles by Limnoria Lignorum and Limnoria Terebraus in Boston Harbor. Report of Special Examination, fully illustrated by Heliatypes. Report of City Engineer, Boston, 1888, p. 40. Creosoted Piles. J. W. Haugh. Jour. Assoc. Eng. Soc., v. 25, p. 137, Sept., 1900. Destruction of Creosoted Piles. R. R. Gaz., v. 40, p. 531, May 25, 1906. Good and Bad Creosoting. Ry. Age Gaz., v. 45, p. 1270, Oct. 30, 1908. More Evidence of the Longevity of Creosoted Piles. W. G. Am. Eng. News, v. 61, p. 277, Mar. n, 1909. Specifications for Creosoting Piling at the Pacific Creosoting Co. Eng. News, v. 64, p. 473, Nov. 3, 1910. Creosote Piles after 30 Years. Ry. Age Gaz., v. 53, p. 114, June 19, 1912. Interesting Pile Failure. Jno. W. Cunningham. Eng. News, v. 70, p. 465, Sept. 4, 1913. Report of Creosoted Piling in Santa Fe Galveston Bay Bridge. F. B. Ridgeway. Proceedings of Tenth Annual Meeting of Am. Wood Preservers' Assoc., Jan., 1914. MECHANICAL PROTECTION OF PILES. Concrete and Pipe Jacketing for Wooden Piles. R. Montfort. Eng. Rec., v. 30, p. 88, June 7, 1894. Teredo-Proof Sheathing of Piles. Eng. News, v. 31, p. in, Feb. 8, 1894. Protecting Piles against the 'Teredo NavaKs' on the Louisville & Nashville Railroad Company's Lines. R. Montfort. Trans. Am. Soc. C. E., v. 31, 221, Feb., 1894. Form for Applying Concrete Armoring to Timber Piles. Eng. News, v. 55, p. 582, May 24, 1906. Reinforced-Concrete Casing for the Protection of Piles on Wharf Construction. F. A. Koe- titz. Jour. Assoc. Eng. Soc., v. 36, p. 223, May, 1906. Protecting Piles from the Teredo. R. R. Gaz., v. 14, p. 137, Aug. 17, 1906. New Con- crete Covering for Timber Piles in, Teredo-Infested Waters. Philip Aylett. Eng. News, v. 55, p. 21, Jan. 4, 1906. A Large Pile Protection Contract. Eng. Rec., v. 57, p. 474, Apr. 4, 1908. Mechanical Protec- tion of Piles. Eng. News, v. 60, p. in, June 30, 1908. Preservation of Piling against Maine Wood Borers. C. Stowell Smith. U. S. Forest Service, Circular 128, 1908. Protected Piles for use in Teredo-In- fested Waters. Eng. Rec., v. 58, p. 474, Oct. 24, 1908. Timber Pile Protection in San Diego Bay. Eng. Rec., v. 57, p. 174? Feb. 15, 1908. Reinforced-Concrete Wharf. Trans. Am. Soc. C. E., v. 66, p. 289, Mar., 1910. Notes on Pile Protection. T. Howard Barnes. Jour. Assoc. Eng. Soc., v. 47, p. 101, Sept., 1911. Concrete Casings filled with sand as Wooden Pile Protection. . Thos. Englehart. Eng. News, v. 66, p. 412, Oct. 5, 1911. Notes on Pile Protection. Ry. Age Gaz., v. 51, p. 1345, Dec. 29, 1911. Mechanical Protection of Piling against Maine Wood Borers. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. IT, p. 200; 1911, v. 12, p. 305. Covering Worn Timber Piles with Cement-Gun Concrete. Eng. News, v. 68, p. 536, Sept. 19, 1912. Cement Gun for Coating Timber Piles. Morton L. Tower. Eng. News, v. 68, p. 723, Oct. 17, 1912. 572 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX ART. 194. BEARING POWER OF PILES THEORY AND PRACTICE. Formula for Bearing Power. Supporting Povver of Piles. Franz Kreuter. Eng. Rec., v. 33, p. 330, Apr. n, 1896; New Formula, etc., Ed., p. 343, Apr. 18. Supporting Power of Piles. Ernest P. Goodrich. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. n, p. 217; Engr.-Contr., v. 33, p. 371, April 20, 1910. Ultimate Load on Pile Foundations; a Static Theory. John H. Griffith. Trans. Am. Soc. C. E., v. 70, p. 412, Dec., 1910. Formula for Bearing Power of Piles. H. B. Seaman. Trans. Am. Soc. C. E.,v. 75, p. 330, Dec., 1912. Column Action in Files. Eng. News, v. 60, p. 18, July 2, 1908. Column Action in Piles; Stiffening Piles by Riprap. E. P. Goodrich. Eng. News, v. 60, p. 41, July 9, 1908. Supporting Power of Piles. Ernest P. Goodrich. Trans. Am. Soc. C. E. v. 48, p. 180, Aug., 1902. The Supporting Power of Piles. C. BaiJlairge; E. P. Goodrich. Eng. Rec., v. 45, p. 183, Feb. 22, 1902. Formulas for Safe Loads on Bearing Piles. John C. Trautwine, Jr. and Editor A. M. Wellington. Eng. News, v. 20, p. 509, Dec. 29, 1888. Uniform Practice in Pile Driving. J. Foster Crow ell. Trans. Am. Soc. C. E., v. 27, p. 99, 129, 589, Aug. and Nov., 1892. The discussion was reprinted in Eng. News, v. 28, p. 412, 438, 460, Nov. 3, 10 and 17, 1892. Uniform Practice in Pile Driving. A. M. Wellington. Eng. News, v. 28, p. 398, Oct. 27, 1892. Safe Load for Bearing Piles. A. M. Wellington, v. 28, p. 469, Nov. 17, 1892. Safe Load for Bearing Piles. A. M. Welling- ton. Eng. News, v. 28, p. 469, Nov. 17, 1892. Bearing Power of Piles. A. M. Wellington. Eng. News, v. 31, p. 283, Apr. 5, 1894. Pile-Driving Formulas. R. R. Gaz., v. 31, p. 608, Sept. i, 1899. Engineering News Formula, Editorial. Eng. News, v. 55, p. 499, May 3, 1906. Analytical Investigation of the Resistance of Piles to Superincumbent Pressure, Deduced from the Force of Driving, with Application of the Formula to the Foundation of Fort Montgomery, Rouse's Point, N. Y. by Bvt. Lt. James L. Mason, 1850. Papers on Practical Engineering No. 5. Driving Piles. A. M. VanAuken. R. R. Gaz., v. 19, p. 507, Aug. 5, 1887. Driv- ing Piles. E. D. T. Myers. R. R. Gaz., v. 19, p. 521, Aug. 12, 1887. Diagrams to Determine the Bearing Power of Piles. G. F. Stickney. Eng. Rec., v. 56, p. 720, Dec. 28, 1907. Instructions regarding Test Piles on the New York Barge Canal. Eng. Rec., v. 56, p. 720, Dec. 28, 1907. Diagram for Determining the Safe Load on Piles. Arthur S. Milinowski. Eng. News, v. 65, p. 139, Feb. 2, 1911. Pile-Driver Diagram. Eugene F. Kriegsman. Eng. Rec. v. 65, p. 417, Apr. 13, 1912. Diagram of Safe Loads on Piles. Engr.-Contr., v. 37, p. 94, Jan. 24, 1912. Some Facts of Experience in Pile Driving. W. B. W. Howe and A. M. Wellington. Eng. News, v. 28, p. 543, Dec. 8, 1892. Supporting Power of Piles Driven by a Steam Hammer after Standing. Robert Follansbee. Eng. News, 51, p. 542, June 9, 1904. Anomalous Pile Resistance in Soft ART. 195 CONCRETE PILES 573 Mud; Effect of Hammer Shock. W. C. Hammatt. Eng. News, v. 58, p. 173, Aug. 15, 1907. Pile Driving Factors of Safety. A. M. Welling- ton, Eng. News, v. 21, p. 313, Apr. 6, 1889. TEST PILES; RECORDS; SPECIFICATIONS. Lesson in Pile Driving. Eng. News, v. 22, p. 368, Oct. 19, 1889. Some Facts of Experience in Pile Driving. W. B. W. Howe, A. M. Wellington. Eng. News, v. 28, p. 543, Dec. 8, 1892. Test Piles. J. C. Trautwine, Jr. Trans. Am. Soc. C. E., v. 27, p. 148-160, Aug., 1892. Actual Resisting of Bearing Piles. A. M. Wellington. Eng. News, v. 29, p. 171, Feb. 23, 1893. Bearing Power of Piles. Eng. News, v. 30, p. 3, July 6, 1893. Bearing Power of Piles. Editorial. Eng. News, v. 31, p. 283, Apr. 5, 1894. Tests of the Bearing Power of Piles. Eng. News, v. 31, p. 348, Apr. 26, 1894. Test Piles. Jour. Assoc. Eng. Soc., v. 20, p. 269, 271, 283, 312, Apr., 1898; J. P. Carlin, Eng. Rec., v. 43, p. 450, May n, 1901. Test Piles. E. P. Goodrich. Trans. Am. Soc. C. E., v. 48, p. 183, 210, Aug., 1902. Con- crete-Pile Wall Foundations. Eng. Rec., v. 50, p. 431, Oct. 8, 1904. Concrete Pile Foundation of the U. S. Express Co. Building, New York City. 'Eng. News, v. 52, p. 348, Oct. 20, 1904. Test Loads of Piles Driven with a Steam-Hammer. J. J. Welsh. p Eng. News, v. 52, p. 497, Dec. i, 1904. Test Piles. W. B. W. Howe. Trans. Am. Soc. C. E., v. 54, p. 413, June, 1905. Applying a Load to Test Piles by Means of a Lever. Dewitt C. Webb. Eng. News, v. 65, p. 172, Feb. 9, 1911. Pile Record Forms. Proc. Am. Ry. Eng. & M. W. Assoc., 1910, v. IT, p. 185; 1911, v. 12, p. 278. Form for Pile-Driving Records used on the Norfolk & Southern Ry. Thos. W. Cothran. Eng. News, v. 57, p. 596, May 30, 1907. Pile-Driving Records. Thos. W. Cothran. Eng. Rec., v. 55, p. 638, June i, 1907. Anothe. Form for Pile-Driving Records. Tyrrell B. Shertzer. Eng. News, v. 58, p. 66, June 18, 1907. Pile Records. Eng. Rec., v. 57, p. 429, Apr. 4, 1908. Foundations of the New Post-Office and Government Building at Chicago. Eng., Rec., v. 39, p. 66, Jan. 27, 1898. Pile Driving, Editorial. Eng. Rec., v. 53, p. 383, Mar. 24, 1906. ART. 195. CONCRETE PILES TYPES OF CONCRETE PILES. Bulkhead and Pier for- the New Port of San Diego, Cal. Eng. News, v. 69, p. 498, Mar. 13, 1913. Comparison of Concrete and Timber Piling on Basis of Cost. E. W. Gaylord. Engr.- Contr., v. 32, p. 486, Dec. 8, 1909. Concrete Piles. Proc. Am. Ry. Eng. Assoc., 1910, v. n, p. 203-216. Concrete Piles. Howard J. Cole. Trans. Am. Soc. C. E., v. 65, p. 467, Dec., 1909. Reconstruction of the Atlantic City Steel Pier in Reinforced Concrete. Eng. News, v. 56, p. 90, July 26, 1906. Shop-made Reinforced-Concrete Piles. L. J. Mensch. Eng. News, v. 60, p. 620, Dec. 3, 1908. Sixth Street Viaduct, Kansas City. E. E. Howard. Trans. Am. Soc. C. E., v. 65, p. 42, Dec., 1909. 574 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Concrete Piles used in the Steamship Terminals at Brunswick, Ga. and in Navy Yard Pier at Charleston, S. C. M. M. Cannon. Jour. Assoc. Eng. Soc, v. 42, p. 24, Jan., 1909. Reprinted in Eng. News, v. 61, p. 549, May 20, 1909; reprinted in Eng. Rec., v. 59, p. 358, Mar. 27, 1909. Pen- horn Creek R. R. Viaduct, Jersey City. Eng. Rec., v. 61, p. 401, April 2, 1910. Seventh Street Viaduct at Des Moines, la. Ry. Age Gaz., v. 53, p. 627, Oct. 4, 1912. Pennsylvania Ore Unloading Dock at Cleveland. Ry. Age Gaz., v. 52, p. 335, Feb. 23, 1912; Eng. News,v. 67, p. 320, Feb. 22, 1912; Eng. Rec., v. 65, p. 199, 212, Feb. 24, 1912. Reinforced-Concrete Piles on the Chicago, Rock Island and Pacific Ry. Eng. Rec., v. 67, p. 606, May 31, 1913. Approach to Municipal Bridge, St. Louis. Eng. News, v. 69, p. 95, Jan. 16, 1913. Reinforced-Concrete Pile Foundation for the Lattewan Building, Brooklyn, N. Y. Eng. News, v. 54, p. 594, Dec. 7, 1905. Method of Manufacturing Reinforced-Concrete Piles by Rolling. Eng. News, v. 56, p. 105, July 26, 1906. Description of the Manufacture of the Chenoweth Pile. Eng. News, v. 56, p. 105, June 26, 1906. Use of Concrete Piling in the Boardwalk at Atlantic City. Aldrich Durant. Ry. Age Gaz., v. 45, p. 99, June 17, 1908. Notes on the Design and Manufacture of Concrete Piles. Eng. Rec., v. 6 5, P- 379, April 6, 1912. Constructing a Concrete Pile Foundation. Eng. News, v. 67, p. 840, May 2, 1912. Concrete Quay Wall on a Cora] Foundation. Eng. Rec., v. 66, p. 526, Nov. 9, 1912. Notes on the Economics of Concrete Pile Foundation Work. Engr.-Contr., v. 28, p. 297, Nov. 27, 1907. Concrete Pile Foundations at Aurora, 111. Eng. News, v. 48, p. 495, Dec. n, 1902. Reinforced-Concrete Piles with Enlarged Footings for Underpinning a Building. J. Albert Holmes. Eng. News, v. 51, p. 567, June 16, 1904. Concrete Pile Foundations at Washington Barracks, D. C. John Stephen Sewell. Eng. Rec., v. 50, p. 360, Sept. 24, 1904. Details of Concrete Piling at Washington Bar- racks. D. C. Eng. Rec., v. 50, p. 463, Oct. 15, 1904. Simplex System of Concrete Piling. Constantine Sherman. Proc. Engr's. Club, Phila- delphia, v. 22, p. 347, October, 1905. Simplex System of Concrete Piling. Thomas MacKellar. Jour. Assoc. Eng. Soc., v. 39, p. 266, Oct., 1907. Concrete Piles with Enlarged Bases. Hunley Abbott. Eng. News, v. 62, p. 684, Dec. 16, 1909. Fifth Avenue Viaduct at Seattle. Eng. Rec., v. 63, p. 200, Feb. 18, 1911. Concrete Pile Footings for the 42- Story L. C. Smith Building, Seattle, Wash. Eng. News, v. 68, p. 914., Nov. 14,1912. Abutment No. 5 of .Substructure of the P. &L.E. R.R. Bridge over the Ohio River at Beaver, Pa., by A. R. Rayner. Proc. Eng. Soc. W. Pa. v. 26, p. 16, Feb., 1910. Tests on Cast-in- Place Concrete Piles. Fran- cis L. Pruyn. Eng. News, v. 69, p. 592, Mar. 20, 1913; Eng. Rec., v. 67, p. 328, Mar. 22, 1913. Methods of Constructing and Driving Combina- tion and Timber Piles with some Results of Tests. Engr.-Contr., v. 33, p. 122, Feb. 9, 1910. Concrete Pipe Failures. Causes and Remedies. ART. 196 METAL AND SHEET PILES 575 C. S. Ho well. Eng. News, v. 68, p. 589, Sept. 26, 1912. Some Ex- periences with Concrete Piles in Chicago. J. Norman Jensen. Eng. News, v. 69, p. 416, Feb. 27, 1913. DRIVING CONCRETE PILES. Heavy Hammer Desirable for Driving Concrete Piles. E. P. Goodrich. Eng. News, v. 53, p. 98, Jan. 26, 1905. Improved Forms of Steam-Pile Hammers for Steel Sheeting and Concrete Pile Work. J. R. Wemlinger. Engr.-Contr., v. 34, p. 325, Oct. 12, 1910. New System of Concrete Piles. W. P. Anderson. Eng. Rec., v. 50, p. 494, Oct. 22, 1904. Corrugated Concrete Foundation Piles for a Seven-story Building. Eng. Rec., v. 54, p. 150, Aug. n, 1906. Concrete Piles at Brunswick, Ga., and Charleston, S. C. M. M. Cannon. Jour. Assoc. Eng. Soc., v. 42, p. 24, Jan., 1909; Eng. News, v. 61, p. 549, May 20, 1909. Driving Concrete Piles. Eng. News, v. 63, p. 623, May 26, 1910. Method of Jetting down Concrete Piles and Records of Output. Engr.-Contr., v. 34, p. 228, Sept. 14, 1910. Concrete Pile- Driving Practice on the Burlington Railroad. L. J. Hotchkiss. Eng. Rec., v. 64, p. 258, Aug. 26, 1911. Driving Concrete Piles with a 12 ooo- pound Hammer. Eng. Rec., v. 64, p. 763, Dec. 30, 1911. Concrete Piles for Bridge Foundations. Ry. Age Gaz., v. 51, p. 480, Sept. 8, 1911. Seventh Street Viaduct at Des Moines, Iowa. Ry. Age Gaz., v. 53, p. 627, Oct. 4, 1912. Concrete Pile Footings for the L. C. Smith Building, Seattle, Wash. Eng. News, v. 68, p. 914, Nov. 14, 1912. Manufac- turing and Driving Concrete Piles. S. W. Bowen. Eng. News, v. 69, p. 95, Jan. 16, 1913. Concrete Piles. Eng. News, v. 54, p. 441, Oct. 26, 1905. Cost of Making and Placing Reinforced- Concrete Piles at Atlantic City, N. J. Eng. News, v. 56, p. 252, Sept. 6, 1906. Cost of Piles and Pile Driving. S. E. Thompson and Benjamin Fox. Jour. Assoc. Eng. Soc., v. 42, p. i, Jan., 1909; Engr.-Contr., v. 31, p. 218, Mar. 24, 1909; Eng. Rec., v. 59, p. 357, Mar. 27, 1909. Municipal Bridge Approach. ,S. W. Bowen. Eng. News, v. 69, p. 95, Jan. 16, 1913. New Pile Formula. Eng. Rec., v. 65, p. 248, Mar. 2, 1912. Data and Opinions on Sustaining Power of Concrete Piles. Engr.-Contr., v. 32, p. 308, Oct. 13, 1909. Test Loading. E. E. Howard. Trans. Am. Soc. C. E., v. 65, p. 61, Dec., 1909. Testing Piles. Trans. Am. Soc. C. E., v. 65, p. 476, 1909. Value of Test Loading. Eng. News, v. 67, p. 1229, June 27, 1912. Cast-in-Place Concrete Piles. Irwin and Witherow. Eng. Rec., v. 67, p. 591, May 24, 1913. Driving Record of Piles Tested. Eng. News, v. 70, p. 555, Sept. 18, 1913. Concrete Pile Specifications. Eng. Rec., v. 68, p. 581, Nov. 22, 1913. ART. 196. METAL AND SHEET PILES TUBULAR, DISK, SCREW, AND SAND PILES. Foundation of Hotel Albert, New York. Eng. Rec., v. 51, p. 293, Mar. u, 1900. Use of 576 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Pile Foundations in the East River Tunnel of the New York Rapid Transit Subway. Eng. News, v. 57, p. 717, June 27, 1907. Experience in Molding and Sinking Concrete Piles for Foundation Work. Engr.- Contr., v. 28, p. 298, Nov. 27, 1907. Special Foundations for a New Edison Substation. Eng. Rec., v. 57, p. 425, Apr. 4, 1908. Deep Foundation Construction in an Occupied Building. Eng. Rec., v. 61, p. 503, Apr. 9, 1910. Using Steel Foundation Piles and Girders in very Narrow Clearance. Eng. Rec., v. 64, p. 710, Dec., 16, 1911. Driving Steel Piles near Insecure Foundations. Eng. Rec., v. 66, p. 271, Sept. 7, 1912. Action of Salt Water on Wrought-Iron Piles. Peter C. Haines. Eng. News, v. 19, p. 143, Feb. 25, 1888. Iron Coal Pier at Norfolk, Va. W. W. Coe. Trans. Am. Soc. C. E., v. 27, p. 125, Aug., 1892. Iron Wharf at Fort Monroe, Va. John B. Duncklee. Trans. Am. Soc. C. E., v. 27, p. 115, Aug., 1892. Hydraulic Pile-Screwing. C. W. Anderson. Eng. Rec., v. 41, p. 570, June 16, 1900. Cienfuegos Screw Pile Pier. Eng. Rec., v. 53, p. 80, Jan. 20, 1906. Novel French Method of Making Foundations in Soft Ground. Eng. News, v. 44, p. 209, Sept. 27, 1900. Compressol System of Making Concrete Founda- tion. Engr.-Contr., v. 28, p. 220, Oct. 16, 1907. Large Concrete Piles. Win. F. Johnston. Eng. Rec., v. 60, p. 362, Sept. 25, 1909. TIMBER SHEET- PILING. Wooden Sheet- Piling. Proc. Am. Ry. Eng. & M. W. Assoc., 1909, v. 10, p. 569; 1911, v. 12, p. 298. Wakefield Sheet-Piling. Eng. News, v. 53, p. 331, Mar. 30, 1905. Improved Scarfed Point for Sheet Piles. A. A. Parker. Eng. News, v. 55, p. 609, May 31, 1906. Sheet-Piling of Square Timbers with Combined Guide and Water Jet Tube. Eng. News, v. 70, p. 552, Sept. 18, 1913. STEEL SHEET-PILING. Metal Sheet-Piling for Foundations and Coffer- dams. Eng. News, v. 45, p. 122, Feb. 14, 1901. New Metal Sheet- Piling. R. R. Gaz., v. 37, p. 386, Sept. 30, 1904. Behrend Steel Sheet- Piling. Eng. News, v. 52, p. 286, Sept. 29, 1904. Steel Sheet-Piling. Eng. News, v. 54, p. 545, Nov. 23, 1905. Steel Sheet-Piling for Large Engine Foundations. Eng. Rec., v. 54, p. 401, Oct. 13, 1906. Experi- ence with Steel Sheet-Piling in Hard Soils. Wm. G. Fargo. Eng. News, v - 57 P- 374) Apr. 4, 1907. Bracing of Trenches and Tunnels, with Pactical Formulas for Earth Pressures. J. C. Meem. Trans. Am. Soc. C E., v. 60, p. i, June, 1908. Steel Sheet-Piling Costs. Eng. Rec., v. 57, p. 804, June 27, 1908. Steel Sheet-Piling for Retaining Earth under Spread Footings. Eng. Rec., v. 58, p. 15, July 4, 1908. Steel Sheet- Piling for a Short Trench. Eng. Rec., v. 58, p. 40, July n, 1908. Steel Sheet- Piling for Pipe-Line Trench. Ry. Age Gaz., v. 45, p. 430, July 3, 1908. New Uses for Steel. Ry. Age Gaz., v. 45, p. 821, Aug. 28, 1908. Devel- opment and Use of Steel Sheet-Piling, with some Data on the Preservation of Steel Buried in the Ground. J. R. Wemlinger. Engr.-Contr., v. 31, p. 406, May 19, 1909. Steel Sheeting and Steel-Piling. L. R. Gifford. ART.,iQ7 COFFERDAMS 577 Trans. Am. Soc. C. E., v. 64, p. 441, Sept., 1909. Principal Types of Steel Sheet-Piling. Proc. Am. Ry. Eng. & M. W. Assoc., 1909, v. 10, p. 570. Hand-Driven Steel Sheet-Piling, Bush Terminal, Brooklyn. Eng. Rec., v. 62, p. 209, Aug. 20, 1910. Chisel Point for Driving Steel Sheet-Piling. H. M. Morse. Eng. Rec., v. 66, p. 704, Dec. 21, 1912. Foundations for the Tunkhannock Viaduct. Eng. Rec., v. 67, p. 484, May 3, 1913. OTHER TOPICS. Brooklyn Tunnel of the New York Rapid Transit Railroad. Driving Sheet-Piling. Eng. Rec., v. 48, p. 530, Oct. 30, 1903. Methods and Cost of Operating Pile-Drivers and of Driving Steel Sheet- Piling. Engr.-Contr., v. 27, p. 193, May i, 1907. Some Suggestions on Methods of Driving, Cutting and Pulling Steel Sheet Piles with Figures of Cost. R. B. Woodworth. Engr.-Contr., v. 32, p. 296, Oct. 6, 1909. Safeguarding Wall Foundations by Sheet-Piling. Eng. Rec., v. 64, p. 412, Oct. 7, 1911. Test of Driving Steel Sheet-Piling, Cleveland, 0. Engr.-Contr., v. 37, p. 721, June 26, 1912. Costs of Driving Steel Sheet- Piling on 45 jobs. Engr.-Contr., v. 38, p. 196, Aug. 14, 1912. Cost of Driving Steel Sheet-Piling by a Novel Method. J. R. Wemlinger. Engr.-Contr., v. 38, p. 395, Oct. 9, 1912. Bracing Trenches and Tunnels. Eng. Rec., v. 56, p. 494, Nov. 2, 1907. Sheet-Piling and Earth Pressure. Eng. Rec., v. 56, p. 608, Nov. 30, 1907. ART. 197. COFFERDAMS EARTH COFFERDAMS. Cofferdams of Cement Bags Half Filled with Sand. Eng. Rec., v. 64, p. 82, June 15, 1911. Clay Cofferdam. Eng. Rec., v. 57, p. 460, April 4, 1908. Earth Cofferdam for West Neebish Channel of the St. Mary's River. Eng. Rec., v. 56, p. 113, Aug. 3, 1907. Cofferdam made of Fascines. Eng. Rec., v. 49, p. 189, Feb. 13, 1904. Earth Cofferdams. Eng. News, v. 24, p. 413, Nov. 8, 1890. Cofferdam for Dam No. 48, Ohio River. Eng. Rec., v. 67, p. 412, April 12, 1913. WOODEN SHEET- PILE COFFERDAMS WITH GUIDE PILES. Cofferdams for Charles River Dam, Boston. Eng. Rec., v. 53, p. 300, Mar. 3, 1906; Eng. News, v. 53, p. 31, Jan. 12, 1905; Eng. News, v. 55, p. 244, Mar. i, 1906. Repairing a Leaking Cofferdam. Eng. News, v. 46, p. 187, Sept. 19, 1901. Cofferdam Enclosing the Thirty- ninth Street Sewage Pumping Station, Chicago. Eng. Rec., v. 52, p. 580, Nov. 18, 1905; Eng. News, v. 50, p. 546, Dec. 17, 1903. Cofferdam for Cambridge Bridge. Eng. News, v. 46, p. 283, Oct. 17, 1901; Eng. Rec., V; 51, p. 52, Jan. 14, 1905. Cofferdams for the Gilbertsville Bridge Piers. Eng. Rec., v. 51., p. 265, Mar. 4, 1905; Eng. Rec., v. 51, p. 570, May 20, 1905. Large Sheet-Pile Cofferdam. Eng. Rec., v. 50, p. 636, Nov. 26, 1904. Cofferdams for Six Lift Bridges. Eng. Rec., v. 57, p. 39, Jan. n, 1908. Deep Cofferdam for Key ham Dockyard Extension. Proc. Inst. of Civ. Engrs., Dec. 17, 1907. 37 578 REFERENCES TO ENGINEERING LITERATURE CHAP. .XIX WOODEN SHEET-PILE COFFERDAMS ON FRAMES. Cofferdam for Mare Island Dry Dock No. 2. Eng. Rec., v. 57, p. 428, April 4, 1908. Coffer- dam for Pier at Kilbourne, Wis. Eng. News, v. 53, p. 330, Mar. 30, 1905; R. R. Gaz., v. 38, p. 258, Mar. 17, 1905. Some Lessons from a Coffer- dam. Eng. Rec., v. 57, p. 243, Feb. 29, 1908. Cofferdams for Potomac River Highway Bridge, Washington, D. C. Eng. Rec., v. 53, p. 103, Jan. 27. 1906. Cofferdams for Piers of the Chattahoochee River Viaduct. Eng. Rec., v. 58, p. 233, Aug. 29, 1908. Cofferdam for Concrete Bridge at Goat Island. Eng. Rec., v. 43, p. 147, Feb. 16, 1901. Cofferdams for Kentucky and Indiana Railway Bridge. Ry. Age Gaz., v. 51, p. 210, Aug. 4, 1911. Cofferdam for P. B. & W. R. R. at Wilmington, Del. Proc. Engrs. Club, Phila.-, 1908, v. 25, p. 333. WOODEN SHEET-PILE COFFERDAMS ON CRIBS. Heavy Cofferdam Construction at Niagara Falls. Trans. Can. Soc. C. E., v. 19, p. 62, 1905; Eng. Rec., v. 49, p. 180, Feb. 13, 1904; Eng. News, v. 54, p. 561, Nov. 30, 1905. Cofferdam for Pier No. 4 of the Aqueduct Bridge, Georgetown, D. C. Eng. Rec., v. 44, p. 125, Aug. 10, 1901. Cofferdam for Great Kanawha Dam. Eng. News, v. 36, p. 98, Aug. 13, 1896. Cofferdam for Hydro-Electric Development at Kilbourne, Wis. Eng. Rec., v. 60, p. 321, Sept. 1 8, 1909. Cofferdam Construction of the Hydro-Electric Plant of the Rockingham Power Company. Rockingham, N. C. Eng. Rec., v. 57, p. 423, April 4, 1908. Cofferdam Excavation for a Power Station. Eng. Rec., v. 57, p. 92, Jan. 25, 1908. Cofferdam Construc- tion for the Neals Shoals Power Plant. Eng. Rec., v. 53, p. 272, Mar. 3, 1906. Cofferdam Construction for Spier Falls Dam. Eng. Rec., v. 47, p. 689, June 27, 1903. No sheet-piling was used in this work, a fill of stones being made on the upstream face of the dam, and over this a heavy gravel fill was placed. Cofferdam Construction of the Connecticut River Power Co. Eng. Rec., v. 59, p. 443, April 3, 1909. Cofferdam Construction of the Holler Dam. Eng. Rec., v. 62, p. 480, Oct. 29, 1910. Plan for Building Cofferdams for River Piers. Eng. News, v. 56, p. 560, Nov. 29, 1906. STEEL SHEET-PILE COFFERDAMS. Cofferdams of a Chicago Bridge. Eng. Rec., v. 49, p. 413, April 2, 1904. On guide piles. Cofferdam Construction for the Substructure of a Swing Bridge. Eng. Rec., v. 67, p. 268, Mar. 8, 1903. Steel sheet piles with guide piles. Steel Sheet- Pile Cofferdam at Power-House Intakes at Omaha. Eng. Rec., v. 59, p. 17, Jan. 2, 1909. On frames. Steel Sheet-Piling for Bridge Pier Cofferdams. Eng. Rec., v. 55, p. 246, Mar. 2, 1907. On frames. Steel Sheet-Pile Cofferdam for a Ship Lock at Buffalo, N. Y. Eng. News, v. 60, p. 394, Oct. 8, 1908; Eng. Rec., v. 57, p. 747, June 13, 1908; Eng. Rec., v. 59, p. 385, April 3, 1909; Bulletin No. 103, Lackawanna Steel Co. Tunkhannock Viaduct Cofferdams. Eng. Rec., v. 67, p. 485, May 3, 1913. On frames. Steel Sheet-Pile Cofferdam for Bridge Piers over the ART. 197 COFFERDAMS 579 Cuivre River at Moscow Mills. Eng. Rec., v. 49, p. 557, April 30, 1904. Steel-Piling Cofferdams for Bridge Piers. Eng. Rec., v. 53, p. 505, April 21, 1906. On frames. Interesting cost data. Large Cofferdam Built with Steel Sheet-Piling. Eng. News, v. 66, p. 330, Sept. 21, 1911; Eng. News, v. 67, p. 340, Feb. 22, 1912. Cofferdam Construction for Raising the United States Battleship Maine. Bulletin No. 102, Lackawanna Steel Co.; Eng. News, v. 64, p. 424, Oct. 20, 1910. Steel Sheet-Pile Cofferdam for Kaw River Bridge Piers. Eng. Rec., v. 67, p. 435, Apr. 19, 1913. On frames. CRIB COFFERDAMS. Cofferdam for New Inlet Tower of the St. Louis Water Works. Eng. News, v. 26, p. 4, July 4, 1891. Crib Cofferdam for Arthur Kill Bridge. Trans. Am. Soc. C. E., v. 27, p. 475, Oct., 1892. Methods of Depositing Concrete Under Water. Report of Committee on Masonry. Proc. Am. Ry. Eng. Assoc., 1912, v. 13, pp. 487-502. MOVABLE COFFERDAMS. Movable Cofferdam for Rest Pier of the Kinzie Street Drawbridge, Chicago. Eng. News, v. 64, p. 562, Nov. 24, 1910. Removable sides on grillage. Movable Cofferdam Con- struction for Pequonnock River Bridge. Eng. Rec., v. 50, p. 127, July 30, 1904. Removable sides on grillage. Movable Cofferdams for Bellevue Boiler House Foundations. Eng. Rec., v. 64, p. 421, Oct. 7, 1911. Removable sides on grillage. Cofferdam with Removable Sides on Grillage. Eng. News, v. 43, p. 217 (see inset), Jan. n, 1900. Cofferdams for the Hackensack River Bridge Piers. Eng. Rec., v. 63, p. 224, Feb. 25, 1911. Removable sides on grillage. Cofferdam for Cape Cod Canal Bridge. Eng. Rec., v. 63, p. 288, Mar. 18, 1911. Re- movable sides on grillage. Circular Cofferdam for Highway Bridge Pier across the Passaic River, Newark, N. J. Eng. Rec., v. 67, p. 268, Mar. 8, 1913. Removable sides on grillage. Cofferdams for Queens' Bridge, Melbourne, Australia. Eng. News, v. 33, p. 230, April 4, 1895. Movable cofferdam. Cofferdam for Falls of Schuylkill Bridge. Eng. News, v. 31, p. 423, May 24, 1894; Proc. Engrs. Club, Phila., v. 12, p. 163, May, 1895. Movable cofferdam. Cofferdams for Florida East Coast Railroad Piers. Eng. Rec., v. 54, p. 424, Oct. 20, 1906. Movable cofferdam. MISCELLANEOUS COFFERDAMS. Use of Canvas in Water-tight Bulk- heads. Trans. Am. Soc. C. E., v. 31, p. 524, May, 1894. 'A-Frame' Cofferdams. Eng. Rec., v. 66, p. 374, Oct. 5, 1912. Cofferdam Con- struction for Dearborn Street Bridge, Chicago. Eng. Rec., v. 56, p. 278, Sept. 14, 1907. Combination of wood and steel sheet-piling. Cofferdam Construction for Enlarging Lachine Bridge Piers. Eng. Rec., v. 63, p. 84, Jan. 21, 1913. Combination of crib and sheet-pile cofferdam. Cof- ferdam for Bridge Piers in Maine. Eng. News, v. 37, p. 327 ,May 27, 1897. Cofferdam sunk through ice. Metal Cylinder Cofferdam. Eng. 580 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX News, v. 64, p. 25, July 7, 1910. Cofferdams with Water-Tight Linings. Memoires de la Societe des Ingenieurs Civils de France, 1900, p. 472; Proc. Inst. C. E., v. 144, p. 347, 1900-01. Cofferdam in Reinforced Concrete. Revue Technique, Paris, v. 26, p. 226; Proc. Inst. C. E., v. 163, p. 409, 1905-06. Freezing Process as Applied to Cofferdams. Revue Technique, Paris, v. 26, p. 57; Proc. Inst. C. E., v. 163, 1905-06. p. 408. Cofferdam Construction for the Periyar Dam, S. India. Eng. News, v. 46, p. 300, Oct. 24, 1901. GENERAL ARTICLES ON COFFERDAMS. Construction of Cofferdams by Thomas P. Roberts. Eng. News, v. 54, p. 138, Aug. 10, 1905. Gives interesting personal experiences. Experience with Steel Sheet-Piling in Hard Soils. Eng. Rec., v. 55, p. 175, Feb. 16, 1907. Economy of Steel Sheet- Piling for Cofferdams. Eng. Rec., v. 53, p. 557, May 5, 1906. Construction of Cofferdams. Eng. Rec., v. 65, p. 244, Mar. 2, 1912. Recent Practice in Cofferdam Work. Reports of committee and discussions. Proc. Assoc. Ry. Supts. Bridges and Bldgs., 1901, v. n, p. 45; 1906, v. 16, p. 92; 1907, v. 17, p. 89; 1908, v. 18, p. 201. ART. 198. Box AND OPEN CAISSONS Box CAISSONS. Box Caissons of Wood. Trans. Am. Soc. C. E., v. 29, p. 634, Sept., 1893. Circular Box Caisson. Eng. Rec., v. 64, p. 720, Dec. 16, 1911. Timber Crib Caissons for a Break Water. Eng. News, v. 40, p. 50, July 28, 1898. Reinforced-Concrete Box Caissons for a Break Water. Eng. News, v. 60, p. 421, Oct. 15, 1908; Eng. News, v. 62, p. 34, July 8, 1909. Reinforced-Concrete Caisson at Glen Cove, N. Y. Trans. Am. Soc. C. E., v. 70, p. 450, Dec., 1910. Sinking a Foundation Caisson with Post-Hole Augers. Eng. Rec., v. 52, p. 570, Nov. 1 8, 1905. Sinking Machinery Foundations in Quicksand without Excavation. Eng. Rec., v. 52, p. 526, Nov. 4, 1905. SINGLE-WALL OPEN CAISSONS. Single-Wall Open Caissons for the French River Bridge. Eng. Rec., v. 59, p. 118, Jan. 13, 1909; Trans. Can. Soc. C. E., v. 22, p. 204 (see Plate 20), 1908. Single-Wall Open Caissons of the Columbia River Bridge. Eng. News, v. 66, p. 392, Oct. 5, 1911. Single-Wall Open Caissons of the Fraser River Bridge. Eng. Rec., v. 49, p. 679, May 28, 1904. Caisson Construction Rio Conchos Bridge of the Kansas City, Mexico and Orient R. R. Ry. Age Gaz., v. 46, p. 164, Jan. 22, 1909. Caisson Construction for the Pivot Pier of the Coteau Bridge. Eng. News, v. 26, p. 524, May 30, 1891; Fowler's Sub-aqueous Foundations, p. 45. Caisson Construction on the Atchison, Topeka and Santa Fe Railway. Eng. Rec., v. 66, p. 52, July 13, 1912. Draw Foundation of the Charlestown Bridge, Boston. Eng. Rec., v. 38, p. 186, July 30,^1898. Pivot Pier Foundation of the Chelsea Bridge North, Boston. Eng. Rec., v. 68, p. 138, Aug. 2, 1913. ART. 198 BOX AND OPEN CAISSONS 581 CYLINDER CAISSONS. New Chittravati Bridge Caissons. Proc. Inst. C. E., v. 103, p. 135, Dec. 9, 1890. Masonry caissons. Field Engineer- ing Abroad.- Eng. Rec., v. 35, p. 246, Feb. 20, 1897. General description of caisson sinking in the far east. Sinking Cylinder Caissons with Hydraulic Jacks. Eng. Rec., v. 56, p. 454, Oct. 26, 1907. Cast-iron cylinders 4 feet in diameter. Cylinder Caissons for the California City Point Coal Pier. Eng. Rec., v. 57, p. 800, June 27, 1908. Cast-iron cylinders, 4 feet in diameter. Cylinder Caissons for a Highway Bridge over the Kansas River at Fort Riley, Kansas. Eng. Rec., v. 58, p. 75, July 18, 1908. Steel cylinders 5 feet in diameter. Cylinder Caissons for Bridge Piers at North Hampton, Mass. Eng. Rec., v. 42, p. 523, Dec. i, 1900. Steel cylinders 10 feet in diameter. Cylinder Caisson Construction on the Chicago and Northwestern Ry. Eng. News, v. 68, p. 748, Oct. 24, 1912. A valuable article describing a number of instances where cylinder caissons were used. Cylinder Caisson Construction in India. Eng. News, v. 34, p. 143, Aug. 29, 1895. Cylinder Caisson Construction for the Omaha Interstate Bridge. Eng. Rec., v. 47, p. 98, Jan. 24, 1903; Eng. Rec., v. 29, p. 218, Mar. 3, 1894; Eng. News, v. 30, p. 410, Nov. 23, 1893. Double-shell caisson, 40 feet outside diameter. Cylinder Caisson. Sinking for the Koyakhai Bridge, Bengal-Nagpur Ry. Proc. Inst. C. E., v. 145, p. 292, 1900-01; Eng. News, v. 46, p. 493, Dec. 26, 1901. External diameter equals 26^ feet and diameter of well equals 13! feet. Cylinder Caisson Construction for the Pyrmont Bridge, Sidney, N. S. W. Proc. Inst. C. E., v. 170, p. 138, 1907. Caisson 42 feet in external diameter and 32 feet in internal diameter. Caisson Construction for the Curzon Bridge at Allahabad. Proc. Inst. C. E., v. 174, p. i, 1907-08. Caisson Construction for the Netravati Bridge at Mangalore. Proc. Inst. C. E., v. 174, p. 41, 1907-08. Cylinder Cais- sons of the Penhorn Creek Viaduct. Eng. News, v. 64, p. 380, Oct. 13, 1910; Eng. Rec., v. 61, p. 401, Apr. 2, 1910. Caissons of reinforced con- crete. Cylinder Caissons for Pier No. 8, at the Puget Sound Navy Yard. Eng. Rec., v. 65, p. 683, June 22, 1912. Caissons of reinforced concrete. Cylinder Caissons for the Lumber Dock at Balboa, Canal Zone. Eng. Rec., v. 66, p. 60, July 20, 1912. Caissons of reinforced concrete. OPEN CAISSONS WITH DREDGING WELLS. Open Caissons for the Poughkeepsie Bridge. Trans. Am. Soc. C. E., v. 18, p. 199, June, 1888; Eng. News, v. 18, p. 306. Open Caissons for the Copper River Bridge. Eng. Rec., v. 61, p. 642, May 14, 1910. Timber caissons. Open Caissons for the Fraser River Bridge. Eng. Rec., v. 49, p. 679, May 28, 1904; Eng. News, v. 53, p. 612, June 15, 1905. Timber caissons. Open Caissons for the Willamette Bridge. Ry. Age Gaz., v. 51, p. 81, July 14, 1911. Open Caissons for the Hawkesburg Bridge. Eng. News, v. 15, p. 98, Feb. 13, 1886; Eng. News, v. 21, p. 3, Jan. 5, 1889; Eng. News, v. 23, 582 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX p. 114, Feb. i, 1890; Pattern's A Practical Treatise on Foundations, p. 268. Metal caissons. Open Caissons for the Dufferin Bridge over the Ganges River at Benares. Proc. Inst. C. E., v. 101, p. 13, 1889-90. Metal caissons. Open Caissons for the Black Friars New Railway Bridge. Proc. Inst. C. E., v. 101, p. 26, 1889-90. Metal caissons. Open Caissons for the Hooghly Bridge. Proc. Inst. C. E., v. 92, p. 75, 1887-88. Metal caissons. Open Caissons for a Railway Bridge, Fitzroy River at Rockhampton, Queensland. Proc. Inst. C. E., v. 144^ p. 45, 1900-01. Metal caissons. Open Caissons for the Beaver Bridge Piers. Eng. News, v. 63, p. 509, May 5, 1910; Eng. Rec., v. 60, p. 299, Sept. n, 1909; Bulletin No. i, Apr. 1909, by the Dravo Contracting Co. Reinfcrced-concrete caissons. Open-Caisson Construction for the Amer- ican River Bridge. Eng. Rec., v. 62, p. 232, Aug. 27, 1910. Reinforced- concrete caissons. Open'Caisson Construction for the North Side Point Bridge. Eng. News, v.68, p. 706, Oct. 17, 1912. Reinforced- concrete caissons. ART. 199. PNEUMATIC CAISSONS FOR BRIDGES GENERAL. Pneumatic Caissons. R. R. Age Gaz., v. 45, p. 671, Aug. 7, 1908; R. R. Age Gaz., v. 45, p. 703, Aug. 14, 1908. Hughes Air-Lock, Valparaiso Harbor. Eng. News, v. 40, p. 363, Dec. 8, 1898. Special Materials Air-Lock. Eng. Rec., v. 29, p. 170, Feb. 10, 1894. The Use of Compressed Air in Tubular Foundations. Trans. Am. Soc. C. E., v. 7, p. 287, 1878. Description of the Plenum Pneumatic Process as Ap- plied in Founding the Piers of the St. Louis Bridge. Milnor Roberts. Trans. Am. Soc. C. E., v. i, p. 259, 1872. Bridge Foundations in the Columbia and Willamette Rivers near Portland, Ore. Ralph Modjeski. Jour. Assoc. Eng. Soc., v. 49, p. 43, Sept., 1912. Pneumatic Caisson Work in Great Britain. Eng. Rec., v. 59, p. 563, May i, 1909. Lower- ing Large Pneumatic Caissons. Eng. Rec., v. 56, p. 566, Nov. 23, 1907. Reconstruction of Coteau Bridge. Eng. Rec., v. 62, p. 628, Dec. 3, 1910. Reinforced-Concrete Caissons. Ry. Age Gaz., v. 47, p. 492, Sept. 17, 1909. Reinforced-Concrete Caissons. Eng. Rec., v. 64, p. 238, Aug. 26, 1911. North Side Point Bridge, Pittsburgh. Eng. News, v. 68, p. 706, Oct. 17, 1912. WOODEN CAISSONS. Pneumatic Caissons of the Sixth Street Viaduct, Kansas City. Proc. Am. Soc. C. E., v. 35, p. 81, Feb., 1909. Williams- burgh or New East River Bridge Foundations. Eng. Rec., v. 36, p. 491, Nov. 6, 1897; Eng. Rec., v. 37, p. 207, Feb. 5, 1898, Eng. Rec., v. 35, p. 554, May 29, 1897; Eng. Rec., v. 39, p. 419, Dec. 17, 1898; Eng. Rec., v. 39, p. 71, Dec. 24, 1898; Eng. Rec., v. 39, p. 397, Apr. i, 1899; Eng. News, v. 37, p. 331, May 27, 1897. Construction of Pneumatic Caissons for the St. Louis Bridge. Woodward's, The St. Louis Bridge; Baker's, ART. 199 PNEUMATIC CAISSONS FOR BRIDGES 583 "Masonry Construction." Pneumatic Caissons for the Third East River (Manhattan) Bridge, New York. Eng. News, v. 48, p. 455, Nov. 27, 1902; Eng. News, v. 45, p. 171, Mar. 7, 1901; Eng. Rec., v. 43, p. 194, Mar. 2, 1901; Eng. Rec., v. 46, p. 510, Nov. 29, 1902; Eng. Rec., v. 49 > P- 332, Mar. 12, 1904. Pneumatic Caissons of the Cairo Bridge. Morison's, "The Cairo Bridge"; Eng. News, v. 25, p. 122, Feb. 7, 1891; Jour. Assoc. Eng. Soc., v. 9, p. 290, June, 1890. Pneumatic Caissons of the Memphis Bridge. Morison's, "The Memphis Bridge"; Eng. News, v. 30, p. 509, Dec. 28, 1893. Incidents in the Construction of the Miles Glacier Bridge. Eng. Rec., v. 62, p. 763, Dec. 31, 1910. New Cornwall Bridge Piers. Eng. Rec., v. 40, p. 643, Dec. 9, 1899. Quebec Bridge Piers. Eng. Rec., v. 44, p. 74, July 27, 1901. Monongahela Bridge at Pittsburgh. Eng. Rec., v. 47, p. 2, Jan. 3, 1903. Omaha Interstate Bridge. Eng. Rec., v. 47, p. 98, Jan. 24, 1903. Tower Foun- dations of the Manhattan Bridge. Eng. Rec., v. 49, p. 332, Mar. 12, 1904. State Bridge at Hartford, Conn. Eng. Rec., v. 50, p. 764, Dec. 31, 1904. Substructures of Bridges on the Spokane, Portland & Seattle Railway. Eng. Rec., v. 58, p. 555, Nov. 14, 1908. Passyunk Avenue Bridge Piers. Eng. Rec., v. 61, p. 388, Apr. 2, 1910. Pneumatic Caisson Piers in Alaska. Eng. Rec., v. 61, p. 559, Apr. 23, 1910. St. Louis Municipal Bridge Substructure. Eng. Rec., v. 62, p. 427, Oct. 15, 1910; Eng. News, v. 65, p. 320, Mar. 16, 1911. New Quebec Bridge. Eng. Rec., v. 62, p. 372, Oct. i, 1910; Eng. Rec., v. 62, p. 444, Oct. 15, 1910; Eng. Rec., v. 64, p. 199, Aug. 12, 1911; Eng. Rec., v. 66, p. 596, Nov. 30, 1912; Eng. News, v. 64, p. 262, Sept. 8, 1910. New York and Brooklyn Bridge. Eng. News, v. 8, p. 171, April 30, 1881; Eng. News, v. 8, p. 181, May 7, 1881; Eng. News, v. 8, p. 191, May 14, 1881; Eng. News, v. 8, p. 201, May 21, 1881; Eng. News, v. 8, p. 212, May 28, 1881; Eng. News, v. 8, p. 223, June 4, i8i; Eng. News, v. 8, p. 232, June n, 1881; Eng. News, v. 8, p. 262, July 2, 1881; Eng. News, v. 8, P- 273, July 9, 1881; Eng. News, v. 8, p. 283, July 16, 1881; Eng. News, v. 8, p. 291, July 23, 1881; Eng. News, v. 8, p. 301, July 30, 1881; Eng. News, v. 8, p. 313, Aug. 6, 1881. Havre de Grace Bridge. Eng. News, v. 12, p. 245, Nov. 22, 1884; Eng. News, v. 13, p. 14, Jan. 3, 1885; Eng. News, v. 13, p. 41, Jan. 17, 1885; Eng. News, v. 13, p. 122, Feb. 21, 1885; Eng. News, v. 13, p. 228, Apr. n, 1885; Eng. News, v. 13, p. 244, Apr. 18, 1885; Eng. News, v. 13, p. 262, Apr. 25, 1885; Eng. News, v. 13, p. 274, May 2, 1885. Schuylkill River Bridge of the B. & O. R. R. Eng. News, v. 15, p. 85, Feb. 6, 1886; Eng. News, v. 15, p. 195, Mar. 27, 1886. Pivot Pier Caisson for a Heavy Swing Bridge. Eng. News, v. 51, p. 5, Jan. 7, 1904. New Steel Viaduct between Kansas City, Mo. and Kansas City, Kans. Eng. News, v. 58, p. 323, Sept. 26, 1907. Pneu- matic Foundations for a Bridge across the Mississippi River at Clinton, Iowa. Eng. News, v. 61, p. 67, Jan. 21, 1909. Pneumatic Caissons on 584 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX the B. & O. R. R. Bridge across the Susquehanna River. Eng. News, v. 62, 546, Nov. 18, 1909. Caissons of the McKinley Bridge. Eng. News, v. 63, p. 9, Jan. 6, 1910. Caissons for the Sixth Street Viaduct, Kansas City. Trans. Am. Soc. C. E., v. 65, p. 42, Dec., 1909. Bridge over the Tennessee River at Johnsonville, Tenn. Trans. Am. Soc. C. E., v. 33, p. 171, March, 1895. The Substructure of the Glasgow Bridge over the Missouri River. Jour. W. Soc. Engrs., v. 6, p. 104, Apr., 1901. Pneu- matic Foundations of the Thebes Bridge. Trans. Assoc. C. E., Cornell, 1905, p. ii. Construction of the River Piers of the Pierre Bridge. Eng. Rec., v. 59, p. 421, Apr. 3, 1909. METAL PNEUMATIC CAISSONS. Pneumatic Caissons of the Alexander III Bridge. Eng. Rec., v. 37, p. 275, Feb. 26, 1898; Eng. News, v. 39, p. 254, Apr. 21, 1898; Eng. Mag., v. 14, p. 515, Dec., 1897. 35 by 65- Foot Steel Caisson Used in Wear River Bridge, British Isles. Eng. News, v. 62, p. 9, July i, 1909. Substructure of the Seventh Avenue Swing Bridge. Eng. News, v. 30, p. 198, Sept. 7, 1893; R. R. Gaz., v. 24, p. 404, June 3, 1892; R. R. Gaz., v. 25, p. 19, Jan. 13, 1893; Eng. Rec., v. 28, p. 38, June 17, 1893. CYLINDER PIER CAISSONS. Deep Bridge Foundations, Atchafalaya River. Eng. Rec., v. 39, p. 421, Apr. 8, 1899; Jour. Assoc. Eng. Soc., v. 21, p. 81, Sept. 1898. Pneumatic Cylinder Piers, Valparaiso. Eng. Rec., v. 38, p. 556, Nov. 26, 1898. The Merrimac River Bridge at Newburyport, Mass. Eng. Rec., v. 50, p. 2j8, Aug. 20, 1904. Caissons for a Highway Bridge at Trail, British Columbia. Eng. News, v. 68, p. 1057, Dec. 5, 1912. PHYSIOLOGICAL EFFECTS OF COMPRESSED AIR. The Caisson Disease. Eng. News, v. 9, p. 400, Nov. 18, 1882. Limit of Human Endurance of High Air Pressure. Eng. News, v. 34, p. 67, Aug. i, 1895. Rules for Working in Compressed Air. Eng. News, v. 40, p. 405, Dec. 22, 1898. Concerning Caisson Disease and Its Prevention. Eng. News, v. 41, p. 27, Jan. 12, 1899. A igS-Foot Dive in Tacoma Harbor. Eng. News, v. 42, p. 138, Aug. 31, 1899. The Occurrence and Treatment of Caisson Disease. Eng. News, v. 46, p. 157, Sept. 5, 1901; Eng. News, v. 46, p. 167, Sept. 5, 1901. Some Observations on the Deep Pneumatic Work of the New East River Bridge Foundations. Eng. News, v. 47, p. 358, May i, 1902. How to Prevent the Bends. Eng. News, v. 51, p. 226, Mar. 10, 1904. Caisson Illness and Diver's Palsy. Eng. News, v. 51, p. 436, May 5, 1904. Caisson Disease. Eng. News, v. 51, p. 60, Jan. 21, 1904. Slow Decompression is the Best Way to Prevent the Bends. Eng. News, v. 51, p. 282, Mar. 24, 1904. Hospital Air-Locks for Caisson Disease. Eng. News, v. 51, p. 178, Feb. 25, 1904. Disease of Caisson Workers. Eng. News, v. 58, p. 435, Oct. 24, 1907. Possi- bilities of Working at Great Depths Under Water. Eng. Rec., v. 33, p. 222, Feb. 29, 1896. Limits of Pneumatic Caisson Work. Eng. News, v. ART. 200 PNEUMATIC CAISSONS FOR BRIDGES 585 36, p. 112, July 10, 1897. Physiological Effects of Compressed Air. Eng. News, v. 47, p. 125, Jan. 31, 1903. Caisson Disease and a Safety Apparatus for Pneumatic Caisson Locks. Eng. News, v. 49, p. 112, Jan. 23, 1904. New York State Law Governing Work Under Com- pressed Air. Eng. News, v. 70, p. 307, Aug. 14, 1913. Criticism of New York Law (In not providing fresh air in air-lock). Eng. News, v. 70, p. 425, Aug. 28, 1913. French and Netherland Requirements. Eng. News, v. 70, p. 566, Sept 18, 1913. Investigation of the Effect on Man of High Air Pressure. Eng. Rec., v. 53, p. 796, June 30, 1906. The Death Roll Due to Bends. Eng. Rec., v. 55, p. 55, Jan. 12, 1907. Caisson Disease. Eng. Rec., v. 60, p. 617, Nov. 27, 1909. Caisson Disease and Compressed Air. Eng. Rec., v. 63, p. 362, Apr. i, 1911. Compressed Air and Its Effects on Man. Eng. Rec., v. 63, p. 347, Apr. i, 1911. Caisson Disease and Its Prevention. Trans. Am. Soc. C. E., v. 65, p. i, Dec., 1909. Cause, Treatment and Prevention of the Bends as Observed in Caisson Disease. Jour. Assoc. of Eng. Soc., v. 39, p. 283, Nov., 1907. Symposium on Caisson Disease. Eng. News, v. 68, p. 862, Nov. 7, 1912. Caisson Disease Experiences and Records. Compressed Air, 1908. Compressed Air Work and the Hudson Tunnels. Eng. Mag., v. n, p. 937, Aug., 1896. Health of Caisson Workers. Eng. Mag., v. 12, p. 131, Oct., 1896. Caisson Disease. Eng. Digest, v. 3, p. 381, Apr., 1908. ART. 200. PNEUMATIC CAISSONS FOR BUILDINGS GENERAL. Foundations of the Municipal Building, New York City. Eng. News, v. 63, p. 24, Jan. 6, 1910; Eng. News, v. 64, p. 523, Nov. 17, 1910; Eng. Rec., v. 62, p. 522, Nov. 5, 1910. Substructure of the Guarantee Trust Building, New York. Eng. Rec., v. 65, p. 44, Apr. 20, 1912. Reinforced-concrete and steel-plate caissons. Steel Substructure of the Woolworth Building, New York City. Eng. Rec., v. 65, p. 177, Feb. 17, 1912; Eng. Rec., v. 64, 1256, Aug. 26, 1911; Eng. Rec., v. 66, p. 97> July 2 7> 1912. Constructing the Foundations of the Seaman's Church Institute, New York. Eng. Rec., v. 65, p. 105, Jan. 27, 1912. Continuous Caisson Foundations for High Buildings. Eng. Rec., v. 64, p. 318, Sept. 16, 1911. Large Pneumatic Foundations of the New York Telephone Building. Eng. Rec., v. 65, p. 610, June i, 1912. New Foundations for the Old Boston Custom House. Eng. Rec., v. 63, p. 185, Feb. 18, 1911. Testing Foundations at the Municipal Building, New York. Eng. Rec., v. 63, p. 196, Feb. 18, 1911; Eng. Rec., v. 62, p. 46, July 9, 1910; Eng. Rec., v. 62, p. 57, July 16, 1910. Bryant Building Substructure. Eng. Rec., v. 61, p. 665, May 21, 1910. Metal shell and timber caissons. Development of Building Foundations. Eng. Rec., v. 57, p. 412, Apr. 4, 1908. Peculiar Pneumatic Caisson Wreck. Eng. 586 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Rec., v. 52, p. 320, Sept. 16, 1905. Development of Architectural Con- struction: Caisson Foundations. Eng. News, v. 38, p. 190, July 30, 1898. Recent Developments in Pneumatic Foundations for Buildings. Trans. Am. Soc. C. E., v. 61, p. 211, Dec., 1908. Pneumatic Caisson Foundations for the Adams Express Building. Eng. Rec., v. 66, p. 320. Pneumatic Caisson Foundations for the Adams Express Building. Eng. Rec., v. 66, p. 320, Sept. 21, 1912. CAISSONS OF WOOD. Pneumatic Caisson Foundations, Emigrant Bank Building. Eng. Rec., v. 63, p. 568, May, 20, 1911; Eng. Rec., v. 60, p. 528, Nov. 6, 1909. Substructure of the Bankers Trust Company's Building. Eng. Rec., v. 62, p. 677, Dec. 10, 1910. Pneumatic Caisson Foundations, Whitehall Building, New York. Eng. Rec., v. 61, p. 792, June 18, 1910. Describes tests made of the supporting power of the soil. Pneumatic Foundations of the City Investing Building, New York. Eng. Rec., v. 55, p. 267, Mar. 2, 1907. Trust Company of America Building. Eng. Rec., v. 54, p. 470, Oct. 27, 1906. Foundations of the Singer Building Extension. Eng. Rec., v. 55, p. 116, Feb. 2, 1907; Trans. Am. Soc. C. E., v. 63, p. i, June, 1909. Substructure of the United States Express Company's Building. Eng. Rec., v. 53, p. 315, Mar. 3, 1906. Constructing Foundations of the Trinity Building, New York. Eng. Rec., v. 50, p. 283, Sept. 3, 1904. Caisson Foundations for a Large Steel Cage Office Building on Broadway, New York. Eng. Rec., v. 49, p. 284, Mar. 5, 1904. Foundations of the Rogers Building, New York. Eng. Rec., v. 49, p. 362, Mar. 19, 1904. Auxiliary Pneu- matic Caisson Work for the Bank of the State of New York. Eng. Rec., v. 48, p. 245, Aug. 29, 1903; Eng. Rec., v. 46, p. 242, Sept. 13, 1902. Foundations of the Gillender Building. Eng. Rec., v. 35, p. 140, Jan. 16, 1897; Eng. News, v. 37, p. 13, Jan. 7, 1897. CAISSONS OF WOOD AND STEEL. Pneumatic Caisson Dam Foundations, United Fire Companies Building. Eng. Rec., v. 64, p. 334, Sept. 16, 1911. Blair Building, New York. Eng. Rec., v. 46, p. 227, Sept. 6, 1902. Construction of the Hanover Bank Building, New York. Eng. Rec., v. 45, p. 340, Apr. 12, 1902. Pneumatic Caisson Foundations for the New York Stock Exchange Building. Eng. Rec., v. 44, p. 289, Sept. 28, IQCI; Eng. News, v. 46, p. 222, Sept. 26, 1901; R. R. Gaz., v. 33, p. 662, Sept. 27, 1901. Foundations of the Atlantic Mutual Insurance Company's Building. Eng. Rec., v. 42, p. 157, Aug. 18, 1900. Rapid Pneumatic Foundation Work. Eng. Rec., v. 40, p. 509, Oct. 28, 1899. Pneumatic Caisson Foundations Under a Residence. Eng. Rec., v. 39, p. 31, Dec. 10, 1898. Pneumatic Caisson Foundations for Mrs. Shepard's Residence. Eng. News, v. 40, p. 363, Dec., 8, 1898. Good description of air-lock. CAISSONS WITH METAL SHELLS. Substructure Work of the Mutual Life Building. Eng. Rec., v. 45, p. 396, Apr. 26, 1902. Foundations ART. 201 PIER FOUNDATIONS IN OPEN WELLS 587 of the Alliance Building. Eng. Rec., v. 42, p. 272, Sept. 22, 1900. Pneu- matic Caissons of the Standard Block. Eng. Rec., v. 38, p. 108, July n, 1896. Foundations of the Commercial Cable Building. Eng. Rec., v. 35, p. 427, Apr. 17, 1897; R. R. Gaz., v. 28, p. 390, June 5, 1896. Foundations of the Broad Exchange Building. Eng. News, v. 44, p. 340, Nov. 15, 1900. Pneumatic Foundations for the Man- hattan Life Building, New York. Eng. News, v. 30, p. 458, Dec. 7, 1893; R. R. Gaz., v. 25, p. 206, Mar. 17, 1893; R. R. Gaz., v. 25, p. 882, Dec. 8, 1893. Pneumatic Caissons of the American Surety Companies' Building. Eng. News, v. 32, p. 71, July 26, 1894; Eng. Rec., v. 30, p. 104, July 14, 1894. ART. 201. PIER FOUNDATIONS IN OPEN WELLS OPEN WELLS WITH SHEET-PILING. Construction of the New Plaza Hotel, New York City. Eng. Rec., v. 54, p. 553, Nov. 17, 1906. Diffi- cult Foundations of the Hoffman House Extension. Eng. Rec., v. 55, p. 296, Mar. 2, 1907. Deep Open Excavation in Quicksand. Eng. Rec., v. 64, p. 769, Dec. 30, 1911. Excavating Caissons Hydraulically at St. Louis. Eng. Rec., v. 66, p. 262, Sept. 7, 1912. Foundations of the Bamberger Building. Eng. Rec., v. 64, p. 456, Oct. 14, 1911. Foundations of the Kinney Building, Newark, N. J. Eng. Rec., v. 66, p. 445, Oct. 19, 1912. Deep Open Pits for Foundation Piers. Eng. Rec., v. 67, p. 158, Feb. 8, 1913. Deep Foundation Pits in Quicksand. Eng. Rec., v. 67, p. 469, Apr. 26, 1913. OPEN WELLS WITH SHEETING. Foundations for the City Hall at Kansas City. Eng. Rec., v. 25, p. 292, 329, 403, April 2, 16, May 14, 1892. Chicago Foundations. Eng. Rec., v. 52, p. 131, July 29, 1905. Development of Deep Building Foundations, Chicago. Eng. News, v. 52, p. 560, Dec. 22, 1904. Foundation Work on the Cook County Build- ing, Chicago. Eng. Rec., v. 53, p. 800, June 30, 1906. Steel-Piling Foundations. Eng. Rec., v. 53, p. 246, Mar. 3, 1906. Extension Ribs and Jacks for Caissons and Trenches. Eng. News, v. 56, p. 117, Aug. 2, 1906. Foundations of the Northwestern Railway Terminal, Chicago. Eng. Rec., v. 59, p. 595, May 8, 1909. Foundations for the New City Hall in Chicago. Eng. Rec., v. 59, p. 745, June 12, 1909. Piers for Drawbridge over the Calumet River. Eng. Rec., v. 67, p. 208, Feb. 22, 1913. Chicago Foundations. Technograph, No. 19, p. 5, 1904-05. Foundations in Chicago. Journal Western Soc. of Engrs., v. 10, p. 687, 1905. Multiple-Spool Hoist for Foundation Work. Eng. News, v. 6 5> P- *33> Feb. 2, 1911. GROUTING PROCESS. Cofferdam without Timber or Iron. Eng. News, v. 25, p. 249, Mar. 14, 1891; Trans. Am. Soc. C. E., v. 24, p. 234, Mar., 1891. New Process for Dealing with Quicksand. Eng. News, v. 27, 588 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX p. 420, Apr. 28, 1892. Making Concrete Foundations in Quicksand. Eng. News, v. 31, p. 533, June 28, 1894. Grouting the Foundations of the Merrimac River Bridge. Eng. Rec., v. 50, p. 218, Aug. 20, 1904. Grouting Foundations for a Bridge over the Danube River at Ehingen. Eng. News, v. 47, p. 35, Jan. 9, 1902. Grouting Concrete Viaduct Piers at Riverside, Cal. Eng. Rec., v. 52, p. 284, Sept. 9, 1905. Im- proved Methods of Constructing Foundations under Water. Trans. Am. Soc. C. E., v. 29, p. 639, 1893; Trans. Am. Soc. C. E., v. 30, p. 579, Dec., 1893. Tests of Grouting Gravel in River Beds. Eng. News, v. 69, p. 979, May 8, 1913. FREEZING PROCESS. Shaft Sinking by Freezing Poetsch Method. Eng. News, v. n, p. 282, June 7, 1884; Eng. News, v. 12, p. 4, July 5, 1884; Eng. News, v. 18, p. 273, Oct. 15, 1887; Eng. News, v. 21, p. 94, Feb. 2, 1889; Eng. News, v. 21, p. 601, June 29, 1889; Eng. News, v. 22, p. 103, Aug. 3, 1889. Freezing Method for Subaqueous Work. Eng. Rec., v. 49, p. 237, Feb. 27, 1904. Freezing as an Aid to Excavation in Unstable Material. Trans. Am. Soc. C. E., v. 52, p. 365, June, 1904. Sinking a Shaft by the Freezing Process in Germany. Eng. News, v. 47, p. 340, Apr. 24, 1902. Sinking a Shaft in Quicksand by the Freezing Process. Eng. News, v. 50, p. 65, July 16, 1903. Building Foundation Constructed by the Freezing Process. Eng. News, v. 69, p. 214, Jan. 30, ART. 202. BRIDGE PIERS GENERAL. Dimensions of Masonry Piers. Street Railway Journal, v. 28, p. 398, Sept. 15, 1906. Concrete Piers. Ry. Age Gaz., v. 46, p. 165, Jan. 22, 1909. Classified cost. Design and Construction of High Bridge Piers. Eng. News, v. 53, p. 548, May 25, 1905. Valuable article showing method of design, also shows examples of solid piers and hollow pivot piers. Mingo Bridge Approaches. Eng. Rec., v. 49, p. 789, June 25, 1904; Eng. Rec., v. 50, p. 27, July 2, 1904. Gives excellent description of methods of construction, building forms, etc. Concrete Bridge Piers. Eng. News, v. 30, p. 296, Oct. 12, 1893. Early use of all-concrete piers. Stability of Stone Structures. Trans. Am. Soc. C. E., v. 8, p. 238, Sept., 1879. Concrete Piers. Trans. Am. Soc. C. E., v. 29, p. 622, Sept., 1893; Trans. Am. Soc. C. E., v. 30, p. 567, Dec. 1893. Substructure of Piscataquis Bridge and Analysis of Concrete Work. Trans. Am. Soc. C. E., v. 61, p. 377, Dec., 1908. Distribution of Pressure on Piers. Eng. Mag., v. 12, p. 869, Feb., 1897. Design of Bridge Foundations. Eng. Rec., v. 38, p. 376, Oct. i, 1898. Bridge Construction. Trans. Assoc. of Civil Engrs., Cornell University, v. i, p. 5, Apr., 1893. Bridge Work on the Kansas City, Pittsburgh and Gulf Ry. Eng. News, v. 40, p. 114, Aug. 25, 1898. Construction of Substructures and Foundations ART. 202 BRIDGE PIERS 589 within a Radius of Sixty Miles of Pittsburgh, by E. K. Morse. Proc. Engrs. Soc., W. Pa., v. 27, p. i, Feb., 1911. SOLID PIERS. Saybrook Bridge on the Connecticut River. Eng. Rec., v. 65, p. 186, Feb. 17, 1912. Stone masonry piers on pile and timber grillage foundations. Substructure of a Double-Track Railroad Bridge at Peoria, 111. Eng. Rec., v. 62, p. 105, July 23, 1910. Reinforced with rods. Copper River Bridge Piers. Eng. Rec., v. 61, p. 642, May 14, 1910. Starling heavily reinforced with old rails. Piers of the Miles Glacier Bridge. Eng. Rec., v. 61, p. 559, Apr. 23, 1910. Heavily rein- forced with rails against ice pressure. Bridge Piers on the Guelph and Goderich Railway. Eng. Rec., v. 57, p. 77, Jan. 18, 1908. Piers of the Columbia River Bridge. Eng. News, v. 66, p. 391, Oct. 5, 1911. Piers of the Cantilever Bridge over the Ohio River at Beaver, Pa., Pittsburgh and Lake Erie R. R. Eng. News, v. 63, p. 509, May 5, 1910; Proc. Engrs. Soc., W. Pa., v. 26, p. i, Feb., 1910. Piers of the McKinley Bridge across the Mississippi River at St. Louis, Mo. Eng. News, v. 63, p. 9, Jan. 6, 1910. Large Concrete Pier. Eng. News, v. 53, p. 330, Mar. 30, 1905. The Mississippi River Cantilever Bridge at Thebes, 111. Eng. News, v. 53, p. 479, May n, 1905; Eng. Rec., v. 51, p. 263, Mar. 4, 1905. New Westminster Bridge over the Fraser River, British Columbia. Eng. News, v. 53, p. 611, June 15, 1905; Eng. Rec., v. 49, p. 679, May 28, 1904. High Concrete Piers for Railway Bridge across Stone's River; Tennessee Central Railway. Eng. News, v. 47, p. 251, May 27, 1902. Cumberland Extension of the Western Maryland R. R. Eng. News, v. 51, p. 304. Mar. n, 1905. Reinforced-Concrete Piers of the GilbertsviJle Bridge. Eng. Rec., v. 51, p. 265, Mar. 4, 1905; R. A. Gaz., v. 39, p. 31, July 14, 1905; Eng. News, v. 53, p. 548, May 25, 1905. Masonry Construction for the Black well's Island Bridge. Eng. Rec., v. 49, p. 307, Mar. 5, 1904; R. R. Gaz., v. 36, p. 319, Apr. 29, 1904. Piers for a Bridge over the Cuivre River, Burlington & Quincy Railway. Eng. Rec., v. 49, p. 557, Apr. 30, 1904. Concrete Piers for the Red River Bridge, St. Louis & San Francisco R. R. Eng. News, v. 19, p. 443, June 2, 1888. Sub- structure of the Cairo Bridge. Eng. News, v. 25, p. 122, Feb. 7, 1891; Morison's, "The Cairo Bridge." New Cornwall Bridge Piers. Eng. Rec., v. 40, p. 643, Dec. 9, 1899. HOLLOW PIERS. Tall Reinforced-Concrete Bridge Pier. Eng. Rec., v. 62, p. 160, Aug. 6, 1910. St. Louis Municipal Bridge Substructure. Eng. Rec., v. 62, p. 427, Oct. 15, 1910; Eng. News, v. 65, p. 320, Mar. 16, 1911. Hollow Concrete Piers on the Louisville & Nashville R. R. Ry. Age Gaz., v. 55, p. 146, July 25, 1913. Design of the Broadway or Sparkman Street Bridge, Nashville, Tenn. Eng. News, v. 62,' p. 570, Nov. 25, 1909; Eng. News, v. 61, p. 199, Feb. 25, 1909. Substructure of the Mingo Bridge. Eng. Rec., v. 48, p. 393, Oct. 3, 1903. Monon- gahela Bridge Piers. Eng. Rec., v. 47, p. 2, Jan. 3, 1903. The Gunpow- 5QO REFERENCES TO ENGINEERING LITERATURE CHAP. XIX der and Bush River Bridges. Eng. News, v. 68, p. 144, Aug. 9, 1913; Eng. & Con., v. 41, p. 195, Feb. n, 1914. VIADUCT PIERS. Construction of the Substructure of the Mulberry Street Viaduct, Harrisburg, Pa. Eng. Rec., v. 58, p. 228, Aug. 29, 1908. Viaduct Substructure, Knoxville, Cumberland Gap & Louisville R. R. Trans. Am. Soc. C. E., v. 34, p. 247, Sept., 1895; Eng. News, v. 33, p. 383, July 13, 1895. Viaduct Foundations. Eng. News, v. 44, p. 379, Nov. 29, 1900. Piers of the Soulevre Viaduct, France. Eng. News, v. 23, p. 606, June 28, 1890. Viaduct in Portland Cement Concrete. Eng. News, v. 30, p. 79. Jan. 27, 1893. Difficult Pier Construction, Man- hasset Viaduct, Long Island Railway. Eng. News, v. 41, p. 18, Jan. 12, 1899. Bridgeport Improvements of the New York, New Haven & Hartford Railway. Eng. Rec., v. 50, p. 104, July 23, 1904; Eng. Rec., v. 50, p. 127, July 30, 1904. Cost of Small Concrete Piers for Viaduct Supports. Eng. Rec., v. 59, p. no, Jan. 23, 1909. Cost of Piers of the Chattahoochee River Viaduct. Eng. Rec., v. 58, p. 233, Aug. 29, 1908. METAL SHELL CYLINDER PIERS. Cylinder-Pier Bridges, C. & N. W. Ry. Eng. News, v. 68, p. 748, Oct. 24, 1912. Cylinder Piers of the Norfolk & Western Bridge No. 5, Elizabeth leaver, Norfolk, Va. Eng. News, v. 61, p. 620, June 10, 1909. Modern Highway Bridge Construc- tion. Eng. News, v. 64, p. 209, Aug. 25, 1910. Substructure of the Dumbarton Point Bridge. Eng. Rec., v. 62, p. 172, Aug. 13, 1910; Trans. Am. Soc. C. E., v. 76, p. 1572, Dec., 1913. Tensas River Bridge. Eng. News, v. 13, p. 386, June 20, 1885. Bridge Foundations in Nova Scotia. Trans. Am. Soc. C. E., v. 29, p. 622, Sept., 1893; Trans. Am. Soc. C. E., v. 30, p. 567, Dec., 1893. Design of Concrete Piers with Metal Shells. Eng. News, v. 48, p. 379, Nov. 6, 1902. Cylinder Piers of the New Portland Bridge. Eng. Rec., v. 53, p. 252, Mar. 3, 1906. Steel Wharves at Manila. Eng. Rec., v. 53, p. 741, June 16, 1906. Dunsbach Ferry Bridge. Eng. News, v. 44, p. 54, July 20, 1901. Greenfield Street Railway Bridge, Greenfield, Mass. Eng. Rec., v. 49, p. 462, Apr. 9, 1904. REINFORCED- CONCRETE CYLINDER PIERS. Piers for Bridge over the St. Croix River at Hudson, Wis. Eng. Rec., v. 69, p. 192, Feb. 14, 1914. Lift Bridges over the Buffalo River. Ry. Age Gaz., v. 54, p. 197, Jan. 31, 1913. Reinforced-Concrete Piers for a Bridge at Stakeford, England. Eng. News, v. 63, p. 193, Feb. 17, 1910. PIVOT PIERS. Substructure of the East Haddam Bridge. Eng. Rec., v. 66, p. 630, Dec. 7, 1912. Substructure of the St. Louis River Bridge. Eng. Rec., v. 65, p. 582, May 25, 1912. Pivot Pier of the Chelsea Bridge North. Eng. News, v. 68, p. 138, Aug. 2, 1913. Pivot Pier of the Gilbertsville Bridge. Eng. Rec., v. 51, p. 265, Mar. 4, 1905; Eng. News, v - 53> P- 548, May 25, 1905. Draw Foundation Pier for Charlestown Bridge. Eng. Rec., v. 38, p. 186, July 30, 1898. Substructure of the ART. 203 BRIDGE ABUTMENTS 591 Dumbarton Point Bridge. Eng. Rec., v. 62, p. 172, Aug. 13, 1910; Trans. Am. Soc. C. E., v. 76, p. 1572, Dec., 1913. The New Portland Bridge. Eng. Rec., v. 53, p. 252, Mar. 3, 1906. Pivot Pier of the Interstate Bridge, Omaha, Neb. Eng. News, v. 30, p. 410, Nov. 23, 1893. ART. 203. BRIDGE ABUTMENTS GENERAL. Design of High Abutments. Eng. News, v. 55, p. 36, Jan. ii, 1906. Economical Concrete Abutment. Eng. News, v. 55, p. 296, Mar. 15, 1906. Heaving of Bridge Abutments by Frost in the Ground. Eng. News, v. 59, p. 260, Mar. 5, 1908. Designing Concrete Abutments for Steel Highway Bridges. Eng. News, v. 65, p. 190, Feb. 16, 1911; Eng. Rec., v. 63, p. 305, Mar. 18, 1911. Gives diagrams for estimating the amount of concrete and the cost of abutments. Abut- ments for a Reinforced-Concrete Girder Bridge at Stakeford, England. Eng. News, v. 63, p. 193, Feb. 17, 1910. Concrete Pedestal Bridge Abutments on the New York State Barge Canal. Eng. News, v. 64, p. 180, Aug. 18, 1910; Eng. Rec. v. 61, p. 154, Feb. 5, 1910. Design of Railway Bridge Abutments. J. H. Prior, Proc. Am. Ry. Eng. Assoc., 1912, v. 13, p. 1086. Discussion of Design and Specifications for a Reinforced-Concrete Bridge Abutment. Trans. Can. Soc. C. E., v. 21, p. 173, 1907. Abutments for the Delaware River Bridge, New York, Ontario and Western R. R., Hancock, New York. Eng. News, v. 66, p. 725, Dec. 21, 1911. Reinforced arch abutments. WING- WALL ABUTMENTS. Concrete Abutment and Parapet Wall for a Skew Bridge, Ulster & Delaware Railroad. Eng. News, v. 50, p. 270, Sept. 24, 1903; R. R. Gaz., v. 37, p. 602, Dec. 2, 1904. Reinforced- Concrete Abutment for a Bridge on the Lehigh Valley R. R., at Towanda, Pa. Eng. News, v. 57, p. 277, Mar. 14, 1907. Buttressed type. Novel Concrete-Steel Bridge Abutment on the Wabash R. R. Eng. News, v. 52, p. 62, July 21, 1904. Buttressed type. Abutments on the Chicago, Milwaukee & St. Paul Ry. Eng. News, v. 63, p. 160, Feb. 10, 1910. Reinforced-Concrete Abutments on the Atlantic, Birmingham, & Atlantic R. R. Eng, Rec., v. 56, p. 100, July 27, 1907; Ry. Age Gaz., v. 45, p. 23, July, 1908. Substructure of a Double-Track Railroad Bridge, Peoria. Eng. Rec., v. 62, p. 105, July 23, 1910. Substructure of the St. Louis River Bridge. Eng. Rec., v. 65, p. 582, May 25, 1912. U-ABUTMENTS AND T-ABUTMENTS. Abutments for Long Span Rein- forced-Concrete Girder Bridges on the West Perm. R. R. Eng. News, v. 63, p. 87, Jan, 27, 1910. Abutments on the Cumberland Extension of the Western Maryland R. R. Eng. Rec., v. 51, p. 304, Mar. n, 1905. New Type of U- Abutment. Eng. Rec., v. 61, p. 100, Jan. 22, 1910. Method of Figuring Foundation Pressures under U-Abutments. Eng. 5Q2 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Rec., v. 62, p. 560, Nov. 19, 1910. Concrete Bridge Abutment of T-Section. Eng. News, v. 57, p. 187, Feb. 14, 1907. BURIED ABUTMENTS. Abutments of the Beaver Bridge. Eng. News, v. 63, p. 510, May 5, 1910. Abutment, for the East Haddam Bridge. Eng. Rec., v. 66, p. 630, Dec. 7, 1912. Design of Concrete Abut- ments Without Wing Walls for Deck Girders. Eng. News, v. 70, p. 816, Oct. 23, 1913. Abutments of the Mingo Bridge. Eng. Rec., v. 49, p. 789, June 25, 1904. Haw Creek Bridge Abutment. Eng. Rec., v. 50, p. 476, Oct. 22, 1904. ART. 204. SPREAD FOUNDATIONS GENERAL. Sand Foundations for High Buildings. Eng. Rec., v. 66, p. 310, Sept. 21, 1912. Development of Building Foundations. Eng. Rec., v. 57, p. 412, Apr. 4, 1908. Tall Building Foundation on Soft Clay. Eng. Rec., v. 55, p. 731, June 22, 1907. Gives results of tests. Reinforced-concrete footings adopted. Permissible Reduction of Live Loads under Footings of Buildings More Than Three Stories High. Schneider's "General Specifications for Structural Work of Buildings," p. 58, 1910. Chicago Foundations. P. C. Shankland. Eng. Rec., v. 52, p. 131, July 29, 1905. Proportioning of Foundations for Columns and Walls. Eng. News, v. 69, p. 465, Mar. 6, 1913. STEEL I-BEAM GRILLAGE FOUNDATIONS. General Features of the Curtis Building, Phila. Eng. Rec., v. 62, p. 41, July 9, 1910. Phelan Building, San Francisco. Eng. Rec., v. 57, p. 366, Mar. 28, 1908. Dis- tributing Column Loads on Irregular Grillage Foundations. Eng. Rec., v. 64, p. 632, Nov. 25, 1911. Curtis Power Building. Eng. Rec., v. 63, p. 17, Jan. 7, 1911. Design of I-beam Grillages for Foundations. See "Cambria Steel," by Cambria Steel Company, also "Pocket Companion," by Carnegie Steel Company. Steel Foundations of the Title Guarantee and Trust Company Building, New York City. Eng. Rec., v. 53, p. 531, April 28, 1906. Foundation Details, New Office Building, New York Central Lines. Eng. Rec., v. 53, p. 224, Feb. 24, 1906. Steel Beam Grillage Foundations. Eng. Rec., v. 38, p. 99, July 2, 1898. Rein- forced Wall Foundations on Yielding Subsoil. Eng. News, v. 60, p. 5, July 2, 1908. REINFORCED-CONCRETE SPREAD FOUNDATIONS. Novel Type of Canti- lever Foundation. Eng. News, v. 68, p. 995, Nov. 28, 1912. Slab and Box Foundation for Chimneys and Columns. Eng. Rec., v. 65, p. 636, June 8, 1912. Inverted- Arch Foundation of Reinforced Concrete. Eng. News, v. 66, p. 763, Dec. 28, 1911. Reinforced-Concrete Raft Foundations for Tall Buildings. Eng. Rec., v. 64, p. 622, Nov. 25, 1911. Foundations of the Logan Building at Youngstown. Eng. Rec., v. 58, p. 278, Sept. 5, 1908. Reinforced-Concrete Work at the New Railway ART. 205 UNDERPINNING BUILDINGS 593 Terminal Station at Atlanta, Ga. Eng. Rec., v. 55, p. 399, Apr. 12, 1906. Spread Foundation of Reinforced Concrete for a Six-Story Building. Eng. News, v. 54, p. 77, July 20, 1905. Reinforced-Concrete Candy Factory. Eng. Rec., v. 64, p. 506, Oct. 28, 1911. Long Foundation Girders for a Loft Building. Eng. Rec., v. 64, p. 580, Nov. IT, 1911. Reinforced-Concrete Footings for the Factories for the Bush Terminal. Eng. Rec., v. 53, p. 36, Jan. 13, 1906. Substructure of the New Meier & Frank Building. Eng. Rec., v. 60, p. 148, Aug. 7, 1909. Cantilever and Raft Foundation for a Twelve-Story Building. Eng. Rec., v. 59, p. 362, Mar. 27, 1909. Method of Enlarging Column Footings. Eng. Rec., v. 58, p. 487, Oct. 31, 1908. The Substructure of the Pope Building, Cleveland, Ohio. Eng. Rec., v. 58, p. 354, Sept. 26, 1908; Eng. Rec., v. 58, p. 489, Oct. 31, 1908. Beam grillages with reinforced-concrete spread footing. Reinforced-Concrete Store Building in Chicago. Eng. Rec., v. 49, p. 7 13, June 4, 1904. Design of Reinforced-Concrete Footing "Concrete, Plain and Reinforced," by Taylor and Thompson. ART. 205. UNDERPINNING BUILDINGS GENERAL. Underpinning the Cambridge Building; New York City. Trans. Am. Soc. C. E., v. 67, p. 553, June, 1910. Underpinning Buildings near Excavations, New York City. Eng. Rec., v. 60, p. 598, Nov. 27, 1909. Underpinning a Leaning Chimney. Eng. Rec., v. 60, p. 27, July 3, 1909; Eng. News, v. 62, p . n, July i, 1909. Shoring and Straight- ening a Four-Story Building in Milwaukee. Eng. Rec., v. 59, p. 480, Apr. TO, 1909. Problem in Underpinning. Eng. Rec., v. 56, p. 94, July 27, 1907. Underpinning a 7o-Foot Wall without Temporary Supports. Eng. Rec., v. 52, p. 90, July 22, 1905. Transferring a 2000- Ton Wall to Columns and Girders. Eng. Rec., v. 52, p. 523, Nov. 4, 1905. Underpinning: Supporting a Brick Wall from One Side Only. Eng. Rec., v. 43, p. 525, June i, 1901. Underpinning High Masonry Struc- tures. Eng. Rec., v. 43, p. no, Feb. 2, 1901. Underpinning without Supports. Eng. Rec., v. 40, p. 415, Sept. 30, 1899. Retaining Walls and Underpinning. Proc. Am. Soc. C. E., v. 28, p. 202, Mar., 1902. Under- pinning Buildings. Eng. Rec., v. 57, p. 420, Apr. 4, 1908. NEEDLE-BEAM UNDERPINNING. Underpinning the Cross Building. Eng. News, v. 68, p. 1134, Dec. 19, 1912. Shoring and Remodeling the Front of a New York Building. Eng. Rec., v. 65, p. 296, Mar. 16, 1912; Eng. Rec., v. 65, p. 392, Apr. 6, 1912. Deep Underpinning Through Sand. Eng. Rec., v. 62, p. 461, Oct. 22, 1910. Underpinning a 300-Ton Column on Quicksand. Eng. Rec., v. 61, p. 649, May 14, 1910. Knicker- bocker Trust Building Substructure. Eng. Rec., v. 59, p. 537, Apr. 24, 1909. Underpinning Buildings Adjacent to The Bridge Loop Subway, New York. Eng. Rec., v. 57, p. 263, Mar 7, 1908. Underpinning 38 594 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Six-Story Apartment Houses in New York City. Eng. Rec., v. 57, p. 689, Miay 30, 1908. Underpinning Adjacent to the Silversmiths' Building, New York City. Eng. Rec., v. 56, p. 346, Sept 28, 1907. Combined Underpinning and Sheeting Job. Eng. Rec., v. 56, p. 254, Sept. 7, 1907. Underpinning Job on the Washington Street Subway, Boston. Eng. Rec., v. 55, p. 266, May 2, 1907. Underpinning Foundations Adjacent to the City Investing Building, New York. Eng. Rec., v. 55, p. 267. Mar. 2, 1907. Cantilever Underpinning in Boston. Eng. Rec., v. 55, p. 700, June 15, 1907. Methods Used in Underpinning the Singer Building, New York. Eng. Rec., v. 55, p. 275, Mar. 2, 1907. Under- pinning a Tall Brewery Wall on Rock Foundations. Eng. Rec., v. 54, p. 20, July 7, 1906. Underpinning the Marshall Field Building in Chicago. Eng. Rec., v. 53, p. 552, May 5, 1906. Underpinning the Criterion Hotel, New York. Eng. Rec., v. 53, p. 692, June 2, 1906. Foundations of the Myers Building, Albany. Eng. Rec., v. 53, p. 802, June 30, 1906. Underpinning the Grand Central Palace, New York. Eng. Rec., v. 53, p. 798, June 30, 1906. ' Underpinning Brooklyn Stores. Eng. Rec., v. 53, p. 58, Jan. 13, 1906. Underpinning Heavy Buildings. Eng. Rec., v. 53, p. 782, June 30, 1906. Underpinning and Protecting the Foundations of the Times Building, New York. Eng. Rec., v. 51, p. 595, May 27, 1905. Underpinning the Sears Building, Boston. Eng. Rec., v. 51, p. 351, Mar. 25, 1905. Underpinning an Old Office Building on Broadway, New York. Eng. Rec., v. 48, p. 698, Dec. 5, 1903. Direct and Indirect Supports for Underpinning a High Wall. Eng. Rec., v. 47, p. 294, Mar. 21, 1903. Complicated Under- pinning. Eng. Rec., v. 46, p. 299, Sept. 27, 1902. Underpinning Buildings Adjacent to the Adams Express Building, New York. Eng. Rec., v. 66, p. 320, Sept. 21, 1912. Lifting and Underpinning a Nine- Story Wall. Eng. Rec., v. 45, p. 373, Apr. 19, 1902. Construction of the East Market Street Subway, Phila. Proc. Engrs. Club of Phila., v. 25, p. 219, 1908. Underpinning the Decker Building, New York. Eng. Rec., v. 45, p. 442, May 10, 1902. BREUCHAUD METHOD. Deep Underpinning in a Very Narrow Clear- ance. Eng. Rec., v. 64, p. 276, Sept. 2, 1911. Underpinning a Fifteen- Story Building on Grillage Foundations. Eng. Rec., v. 64. p, 307, Sept. 9, 1911. Underpinning Buildings Adjacent to the United Fire Companies Building. Eng. Rec., v. 64, p. 334, Sept. 16, 1911. Under- pinning the Astor Building, New York. Eng. Rec., v. 62, p. 17, June 2, 1910. Underpinning the Mt. Siani Hospital Dispensary. Eng. Rec., v. 61, p. 478, Apr. 2, 1910. Underpinning Buildings Adjacent to the Farmers' Loan and Trust Company's Building, New York. Eng. Rec., v. 58, p. 480, Oct. 31, 1908. Trust Company of America Building. Eng. Rec., v. 54, p. 442, Oct. 20, 1906. Underpinning Old Walls with Steel Columns. Eng. Rec., v. 53, 433, Mar. 31, 1906. Substructure Work for ART. 206 EXPLORATIONS AND UNIT LOADS 595 The Mutual Life Building, New York. Eng. Rec., v. 45, p. 368, Apr. 19, 1902. Underpinning of Heavy Buildings. Trans. Am. Soc. C. E., v. 37, p. 31, June, 1897. Underpinning the Stokes Building, New York City. Eng. Rec., v. 34, p. 183, Aug. 8, 1896. Underpinning Heavy Buildings. Eng. Rec., v. 35, p. 144, Jan. 16, 1897. Shoring the Walls of An Old Building. Eng. Rec., v. 37, p. 211, Feb. 5, 1898. New Method of Underpinning Heavy Buildings. Eng. News, v. 37, p. 6, Jan. 7, 1897. Foundations of the New Mutual Life Building. Eng. News, v. 45, p. 221, Mar. 28, 1901. ART. 206. EXPLORATIONS AND UNIT LOADS BORINGS WITH AUGERS. Test Borings for Foundations. Eng. News, v. 21, p. 324, April 13, 1889. Exploration of Soil by Wood Augers. Eng. News, v. 41, p. 175, Mar. 16, 1899. WASH BORINGS. Sinking Foundation Test Holes with a Water-Jet. Eng. Rec., v. 25, p. 95, Jan. 9, 1892. Methods and Results of Surveys and Borings for Oswego-Mohawk Ship Canal Route for U. S. Board of Engineers on Deep Water-ways. D. J. Howell. Eng. News, v. 43, p. 418, June 28, 1900. Borings for the Bohio Dam for the Panama Canal. R. C. Smith. Jour. W. Soc. Engrs., v. 8, p. 372, Aug., 1903. Suggested method of Recording Earth Borings. E. R. Shnable. Eng. News, v. 53> P- 20, Jan., 5 1905. Wash Drill Borings on the New York State Barge Canal. EmileLow. Eng. News, v. 57, p. 54, Jan. 17, 1907. Cost of Wash Drill Borings on the Deep Water-ways Surveys, 1897 to 1900. Eng. News, v. 57, p. 57, Jan. 17, 1907. Wash Borings for the Rapid Transit Commission, New York City. Eng. News, v. 57, p. 58, Jan. 17, 1907. Cost of Boring Five Test Wells for a Double-Track Railway Bridge in California. P. J. Robinson. Engr.-Contr., v. 33, p. 9, Jan. 5, 1910. Borings for the Panama R. R. Dock at Cristobal, with Table of Costs. E. B. Karnopp. Eng. News, v. 63, p. 691, June 16, 1910. Jack for Pulling Drill Rods and Sounding Bars. Eng. Rec., v. 67, p. 37, Jan. n, 1913. Sub-surface Investigations on the Catskill Aqueduct, Board of Water-supply. Robert Ridgway. Eng. Rec., v. 57, p. 522, April 18, 1908. CORE DRILLING WITH DIAMONDS. Explorations for Hudson River Crossing of the Catskill Aqueduct, New York City. Alfred D. Flinn. Eng. News, v. 59, p. 358, April 2, 1908. Sub-surface Investigation on the Catskill Aqueduct, Board of Water-supply. Robert Ridgway. Eng. Rec., v. 57, p. 557, April 25, 1908. Standard Symbols for Borings. Eng. Rec., v. 65, p. 378, April 6, 1912. Diamond Borings. New East River Bridge Foundations. Eng. News, v. 36, p. 198, Sept. 24, 1896. Ex- perience in Diamond Drill Work on the Deep Water-ways Survey, with Statistics of Cost. Eng. News, v. 50, p. 83, July 23, 1903. Cost of 596 REFERENCES TO ENGINEERING LITERATURE CHAP. XIX Diamond Drilling. Eng. News, v. 57, p. 389, April 4, 1907. Testing Diamond Drill Borings at the Site of the Olive Bridge Dam, Ashokan Reservoir. Eng. Rec., v. 58, p. 25, July 4, 1908. Methods and Costs of Testing for Bridge Foundations. F. H.jBainbridge. Engr.-Contr., v. 30, p. 352, Nov. 25, 1908. New Bridge Crossing of the Mississippi River at Clinton, Iowa, C. & N. W. Ry. F. H. Bainbridge. Eng. News, v. 6 1, p. 68, Jan. 21, 1909. Cost of Diamond Drill Work. Eng. Rec., v. 59, p- 346, Mar. 27, 1909. Inclined Diamond Drill Borings under the Hudson River. Eng. Rec., v. 61, p. 68, Jan. 15, 1910. Core Drilling un- der the Hudson River for the Catskill Aqueduct. Wm. E. Swift. Eng. News, v. 63, p. 414, April 7, 1910. Methods of Conducting Test Borings and of Sinking Shafts for the Hudson River Crossing in the Catskill Aqueduct. Engr.-Contr., v. 34, p. 356, Oct. 26, 1910. Cost of Diamond Drilling and Depreciation of Diamonds. Engr.-Contr., v. 37, p. 462, April 24, 1912. Time lost in Diamond Drilling Operations. Engr.- Contr., v. 39, p. 93 Jan. 22, 1913. CORE DRILLING WITHOUT DIAMONDS. Davis * Calyx' Core Drill. Eng. News, v. 45, p. 334, May 9, 1901. Methods of making Test Borings for the Catrkill Reservoirs for the New York Water-supply with some Plant Costs. Engr.-Contr., v. 31, p. 511, June 23, 1909. Pre- cautions in Interpreting Records of Test Borings. Engr.-Contr., v. 33, p. 585, June 29, 1910. See also articles in preceding paragraph on borings for Catskill Aqueduct, Board of Water-supply, New York City. TESTS FOR BEARING CAPACITY. Preliminary Foundation Tests for the St. Paul Building. Eng. Rec., v. 33, p. 388, May 2, 1896. Safe Load on Soil at New Orleans, La. Eng. News, v. 41, p. 3303, May n, 1898 and correction on p. 333. Foundation Construction for the New York Capitol for South Dakota. Samuel H. Lea. Eng. Rec., v. 57, p. 437, April 4, 1908. Bearing Tests for Heavy Foundation Loads. Eng. Rec., v. 60, p. 55, July 10, 1909. Testing Bearing Power of Hard-Pan. Extension Whitehall Building, New York City. Eng. Rec., v. 61, p. 792, June 18, 1910. Tests and Costs of making a Test of the Bearing Power of Soil for a Building. Engr.-Contr., v. 34, p. 31, July 13, 1910. Tests of Bearing Capacity of Sand under Municipal Building, New York City. Eng. Rec., v. 62, p. 46, July 9, 1910; p. 57, July 16, 1910; Eng. News, v. 63, p. 24, Jan. 6, 1910; v. 64, p. 525, Nov. 17, 1910. Device for Making Sub-surface Tests of the Bearing Power of Soils with some Examples of Operation. Eng.-Contr., v. 34, p. 94, Aug. 3, 1910. Testing Soil below the Surface for Foundation Loads. Eng. Rec., v. 62, p. 71, July 16, 1910; v. 63, p. 512, May 6, 1911. Testing Foundations at the Municipal Building, New York. Eng. Rec., v. 63, p. 196, Feb. 18, 1911. Stand- ard Tests of Soil. Rudolph P. Miller. Eng. Rec., v. 66, p. 112, July 27, 1912. Soil-Bearing Tests. Eng. Rec., v. 66, p. 304, Sept. 14, 1912. Hard-Pan and Other Soil Tests. J. Norman Jensen. Eng. News, v. 69, ART. 206 EXPLORATIONS AND UNIT LOADS 597 p. 460, Mar. 6, 1913; see also editorial on p. 463. Building Foundations. J. A. Smith. Jour. Assoc. Eng. Soc., v. 36, p. 155, April, 1906. Results of Tests on Chicago Hard-Pan at a Depth of 57 Feet below Lake Level. Frank A. Randall. Engr.-Contr., v. 37, p. 436, April 17, 1912. VALUES OF BEARING CAPACITY. Supporting Power of Soils. Randall Hunt. Jour. Assoc. Eng. Soc., v. 7, p. 189, June, 1888; Eng. News, v. 19, p. 484, June 16, 1888. Construction of the Buildings, Bridges, Piers, and Docks at Jackson Park. Eng. Rec., v. 28, p. 199, Aug. 26, 1893. Al- lowable Pressure on Deep Foundations. Elmer L. Corthell. Eng. News, v. 56, p. 657, Dec. 20, 1906; Editorial, Eng. Rec., v. 54, p. 647, Dec. 15, 1906. Foundation Pressure on Hard-Pan; Proposed Rule. Rudolph P. Miller. Eng. News, v. 64, p. 727, Dec. 29, 1910; Eng. Rec., v. 62, p. 783, Dec. 31, 1910. Sand Foundations for High Buildings. Eng. Rec., v. 66, p. 310, Sept. 21, 1912. Report on Unit Pressure Al- lowable on Road-Beds of Different Materials. Proc. Am. Ry. Eng. Assoc., 1912, v. 13, p. 388. Failure of the Transcona Grain Elevator. Eng. News, v. 70, p. 944, Nov. 6, 1913. INDEX ABBOTT, H., 139 Abutments, bridge, 433-451 literature of, 588 buried, 449 cubature of concrete, 445 design and construction, 436 form and dimensions, 433 reinforced-arch, 449 T-, 448 U-, 441 wing- wall, 439 Air chamber, concreting, 322, 360, 552, see also pneumatic caissons, working chamber. Air-locks, 309, 352, 556 American Railway Engineering Asso- ciation, 6, 16, 55, 66, 112, 113 Analysis of time and cost, 157 BAINBRIDGE, F. H., 449, 525 Bearing, allowable, under caissons, 559 capacity, tests for, 531 values of, 534 power, effect of rest on, 95 sub-surface conditions, 97 taper, 166 of piles, 75-iiS literature of, 572 BERT, P., 332 Blow-out process, 319 Borings with augers, 519 wash, 520 Box caissons, 239-279 literature of, 580 miscellaneous types, 245 of concrete, 243 of timber, 240 Breuchaud process, 507 Bridge piers, see piers. BURNHAM and ROOT, 458 Caisson disease, 331, 333, 337 Caissons, box, see box caissons. cylinder, see cylinder caissons. definitions and classification, 239 hydraulic, 382 open, see open caissons. pneumatic, see pneumatic caissons. Caps, pile, 27, 30, 147 Chemical preservation of piles, 63 Chicago method, 370 Cofferdam process, 198 Cofferdams, 2, 198-238, 350 choice of type, 238 construction, 300 cost of, 236 crib, 215, 226 design of, 235 double- wall, 203, 213 earth, 199 leakage of, 234 literature of, 577 miscellaneous types, 232 movable, 228 on grillage, 231 self-supporting, 221 sheet-pile, 203, 206, 210, 216, 221 steel, 216, 221 supported by cribs, 214 timber, 203 single- wall, 206, 211 Compressed air, physiological effects, 329 Compressol system, 181 Concrete, 559 Concrete piles, 116-173 advantages of, 118 cast-in-place, 116, 136 choice of type, 163 classification, 116 cutting off, 157 599 6oo INDEX Concrete piles, driving, 152 effect of taper, 166 form and construction, 130 literature of, 573 precautions against injury, 142 composite types, 144 pre- molded, 116 design of, 134 patented, 127 unpatented, 122 specifications, 172 COOPER, T., 391 CORTHELL, E. L., 535 Cost of cofferdams, 236 concrete piles, 157 pile driving, 71, 157 CRAWFORD, J. E., 32 Crib, 350 construction, 298 CUNNINGHAM, A. O., 440 Cutting edge, details of, 294 Cylinder and pivot piers, 417-432 Cylinder caissons, 251, 304 combination, 307 literature of, 581 of masonry, 252 of metal, 254 of reinforced concrete, 257 of timber, 252 Cylinders, concreting the, 513 methods of sinking, 511 pneumatic, 507 transferring load to, 514 Dam, water-tight, of wall piers, 361 Design of bridge abutments, 436 Bridge piers, 411 caissons, 313 cofferdams, 235 cylinder piers, 423 double-column footings, 464 I-beam grillages, 459, 464 needle-beams, 492 pneumatic caissons, 313 pre-molded piles, 134 reinforced-concrete column foot- ings, 477, 479 spread foundations, 474 Design of sheet-piling, 194 DOUGLAS, W. J., 411 Drilling, core, with diamonds, 524 without diamonds, 527 shot, 527 Driving batter piles, 41 concrete piles, 152 piles butt down, 40 timber piles, 37-74 Drop-hammers, 20 fall of, 85 restrained fall, 87 weights of, 85, 148 Engineering literature, 564-597 News formula, 82, 91, 162 Ejector, hydraulic, 278 Explorations, 518 literature of, 595 sub-surface, need of, 529 FAULKNER, E. O., n Followers, 27 Footing, design of reinforced-concrete column, 477, 479 wall, 474 distribution of pressure on base, 468 spread, defined, i Footings, design of double-column, 464 early types, 453 masonry, 453, see also spread foun- dations. Formulas for bearing power of piles, 77, 82, 90, 105, 161 Foundation, placing the new, 503 Foundations, i grillage, see spread foundations. in open wells, 2 open caisson, 2 pile, defined, 2 pneumatic, 2 spread, see spread foundations. Fox, B., 157 Freezing process, 379 Frictional resistance, 326 FRIESTEDT, L. P., 185 '\ INDEX 601 GIFFORD, L. R., 189 GOODRICH, E. P., 13, 56, 77, 88 formula, 77, 105 GREINER, J. E., 113, 172, 389, 391, 397, 410, 436, 535 Grouting process, 373, 376, 378 HARRIS, R. L., 377 Hydraulic caissons, 382 JACKSON, J. W., 371 JAMINET, A., 332 KRIEGSMAN, E. F., 94 Leads, pendulum, 42 pile-driver, 14 clearance of, 10 swinging, 42 Lighting of pneumatic caissons, 544 Literature, engineering, 564-597 Loads, unit, 518 literature of, 595 Lock-joint pipe, 70 Low, EMIL, 523 LUTHER, C. M., 449 MCCLELLAN, G. B., 48 Mechanical protection of piles, 66 MERRILL, O., 517 Metal piles, 174-197 MILLING WSKI, A. S., 94 MODJESKI, R., 402, 403 MORAN, D. E., 460 MORSE, E. K., 386 MORISON, G. S., 291, 294, 389, 395 MURPHY, M., 420 Needle-beams, design of, 492 examples with, 493 supporting wall below, 495 Needles, figure-four, 501 NEUKIRCH, F., 375 NICHOLSON, G. B., 87 NOBLE, A., 403 Overdriving piles, 49 Open caissons, 2, 239-279 literature of, 580 Open caissons of concrete, 272 of metal, 270 of timber, 263 single-wall, 246 sinking, 277 with dredging wells, 262 Penetration per blow, final, 88 total, 100 Pier design, example of, 411 \ foundations in open wells, 366-383 Piers, bridge, definitions, 386 form and dimensions, 388 general requirements, 384 literature of, 588 materials and construction, 394 methods of failure, 411 ordinary, 384-416 specifications, 397 cubature of concrete, 390 cylinder, 417-432 design and construction of, 423 metal shell, 418 on piles, 418 reinforced-concrete, 426 hollow, 403 pivot, 417-432 solid, examples of, 398 stability of, 409, 424 wall, 361 Pile caps, 27, 30, 147 drivers, 14, 42, 147 track, i 6 driving, n, 37-55, 152, 169 cost of, 71 diagrams and tables, 92 literature of, 567 observations in practice, 37 phenomena of, 1 1 hammer, drop, 20, 147, see also drop-hammers. steam, 21, 147 see also steam- hammers, point, 32 records and performance, no rings, 27 shoes, 32 specifications, 112, 172 602 INDEX Pile splices, 32 Piles acting as columns, 75 batter, 3 driving, 41 bearing, 3, 4 bearing power of, 75-115, see also bearing power of piles, classification of, 2 combination, 5, 144 concrete, see concrete piles, cutting off, 58, 157 definitions of, 2 disk, 178 driving butt down, 40 guide, 4, 203, 206 lagged, 8 metal, 174-197 literature of, 575 overdriving, 49 pipe, 174 reinforced-concrete, see concrete piles. removing, 58 sand, 5, 180 screw, 178 sectional, 174 sheet, 3, i74-*97 spacing of, 55 test, n, 105, 169 timber, see timber piles, tubular, 174 Piling, sheet-, see sheet-piling. Plant and equipment, 555 Pneumatic caisson practice, 538-561 caissons, bracing of, 296 building, 315 caulking, 544 cofferdam, 300, 350 construction, 541 crib, 298, 350 cutting edge, 294 design of, 313 development, 338, 539 excavation, 552 for bridges, 280-337 literature of, 582 for buildings, 338-365 literature of, 585 Pneumatic caissons, friction of, 326 joints between, 361, 554 launching, 315, 547 of metal, 302, 345, 347 of reinforced-concrete, 301, 349 of timber, 340, 347 placing, 315, 549 removing spoil, 319 roof construction, 283 sealing, 322, 360, 552 shafts of, 309, 352, 544 sinking, 317, 323, 356, 359, 549 working chamber, 293, 322 360, 552 Pneumatic process, 280 POETSCH, F. H., 380 PRIOR, J. H., 451 Puddle, 234 Pump, sand-and-mud, 321 RAYMOND, A. A., 116 RIDGWAY, ROBERT, 528 ROBERTS, T. P., 237 SCHERMERHORN, L. Y., 48 SCHNEIDER, C. C., 389, 534 E. J., 432 SEAMAN, H. B., 534 Security, degree of, 101 Sheeting in open wells, 370 Sheet-piling, 3, 174-197 concrete, 189 design of, 194 driving, 190 in open wells, 366 steel, 184 strength, 195 supported by cribs, 214 by frames, 210 timber, 181 Wakefield, 182 Sinking open caissons, 277 pneumatic caissons, 317, 323, 356, 359, 549 rate of, 323, 359 SMITH, A. H., 332 C. S., 67 SNELL, E. H., 336 INDEX 603 SOOYSMITH, W., 321 Sounding rods, 518 Specifications for bridge abutments, 436 concrete piles, 172 timber piles, 112 Spread foundations, 452-489 concrete, 487 design of reinforced-concrete, 474 I-beam grillages, construction, 458 design, 459 literature of, 592 modern types, 457 steel grillage, 469, see also foot- ings. Stability of piers, 409, 424 Steam-hammers, 21 advantages of, 24 weights of, 23, 148 TALBOT, A. N., 478 Taper, effect of, on piles, 166 Test piles, 105, 169 pits, 518 Tests for bearing capacity, 53 1 THOMPSON, S. E., 157 THOMSON, T. K., 296, 313, 336, 353, Si5, 538 Timber piles, 6, 567 and drivers, 1-36 brooming of, 29 chemical preservation, 63 cutting off, 58 driving, 37-74 Timber piles, durability of, 8, 63 form and dimensions, 9 literature of, 567 mechanical protection, 66 specifications for, 6, 7, 9, 112 use of, 5 TORRANCE, W. M., 441, 449, 451 Underpinning buildings, 490-517 cantilever method of, 497 literature of, 593 modern methods, 515 needle-beam, 490 remarks on, 560 UPSON, M. M., 162 USINA, D. A., 353, 362, 363 WADDELL and HARRINGTON, 306 Wales, 4 Wall, joining to the old, 506 footing, 474 Water-jet, 147, 278 equipment, 48 literature of, 570 use of the, 43 WELLINGTON, A. M., 82, 84, 91, 105, no Wells, open, foundations in, 366-383 literature of, 587 with sheeting, 370 with sheet-piling, 366 WHITE, L., 528 WHITTEMORE, D. J., 28 14 DAY USE RETURN TO DESK FROM WHICH BORROWED This book is one on tffe la\t Sate sjkmped below, or on the date to which renewed. Renewed books are subject to immediate recall. IJLJAN 4 78 LD21 32m 1,'75 (S3845L)4970 General Library University of California Berkeley 1954 )m-5,'43 (6061s) YC 13429 UNIVERSITY OF CALIFORNIA LIBRARY Rf