UNIVERSITY OF CALIFQHBIA 
 
 DEPAKTLIBTT OF CIVIL ENGINEERING 
 STRUCTURAL ENGINEERING. 
 
 NOTES ON FOUNDATIONS AND MASONRY STRUCTURES 
 COURSES C. E. 113 - 114 
 
 By 
 Charles Derleth ; Jr. 
 
 Revised and Enlarged From Earlier Mi t ions 
 Berkeley, California, October 1,1921. 
 
DESIGN 
 
 OF A 
 
 RAILWAY BRIDGE PIER 
 
 BY 
 
 CHARLES DERLETH, Jr., C. E. 
 
 Associate Professor Structural Engineering 
 University of California 
 
 NEW YORK 
 
 THE ENGINEERING NEWS PUBLISHING COMPANY 
 1907 
 
Engineering 
 library 
 
 PUBLISHERS NOTE. 
 
 The following study was prepared by Professor Derleth at the request of the 
 editors of the California Journal of Technology, and printed in the November 
 (1906) number of that magazine. 
 
 It is believed that this article covers the subject of bridge-pier design in a 
 more complete and efficient manner than any text now extant, and recognizing 
 its value, especially to students, it has been thought advisable to reprint it in 
 the present permanent and available form. 
 
Design of a Railway Bridge Pier. 
 
 By CHARLES DERLETH, Jr., C.E. 
 
 I. INTRODUCTION. 
 
 1. Senior students in the College of Civil Engineering of the University of 
 California design completely the metal superstructure for an inclined upper 
 chord, double-track railway bridge, usually about 300 ft. in span length. This 
 article attempts to give the calculations for a first study of an intermediate 
 pier to carry a superstructure like that designed by our senior students. A 
 foundation is selected of a depth not too great to properly employ the pneu- 
 matic process. The pier is assumed to rest on a rock and the caisson proposed 
 is of steel. 
 
 2. The pier from the coping to the caisson roof is not designed in detail, but 
 only in general proportions. Its outlines are proposed and the general type of 
 construction at different levels is clearly indicated ; the article in these particulars 
 attempts to show merely that the proportions assumed give a pier which satisfies 
 all practical considerations, is economical and of good appearance, and that 
 it is stable when subjected to the worst combinations of external loads and forces. 
 
 3. A purely ideal case and fictitious foundation site have not been assumed. 
 In order to give added interest to the problem, the calculations are based upon 
 conditions found for Pier 8 of the Havre de Grace Bridge of the Baltimore & 
 Ohio Railroad. (Consult Fig. 1, Plate 1). 
 
 (See " A Treatise on Masonry Construction," by I. O. Baker, p. 286; also 
 Engineering News, vol 13, p. 14; and " A Practical Treatise on Foundations," 
 by W. M. Patton). The Havre de Grace Bridge is single-track; a double- 
 track bridge is considered in the present text. The actual caisson is of wood; 
 the one here outlined is of steel. 
 
 -I. The writer does not mean to imply that steel is better than wood con- 
 struction for a caisson at this particular pier site. He has arbitrarily chosen 
 steel for the main purpose of explaining tersely the method of procedure. The 
 mechanical principles for calculation are logically outlined and the main parts 
 of the caisson are designed sufficiently in detail to satisfy all stress conditions. 
 In short, the object of the paper is to emphasize the design of a metal caisson. 
 It may be further observed that any one interested may have the opportunity 
 of comparing the results of the present problem with those of the actual con- 
 struction. The actual caisson being of wood lends itself less readily to compu- 
 tation. 
 
 78S4SO 
 
2 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 5. The wood caisson now in the work at pier 8 is 17 ft. 3 ins. in height, and 
 ... in jlaiv m.ea'stf.res 70 ft. 10J ins. x 32 ft. 7| ins. In the actual bridge a 520-ft. 
 ' throtlgft ^'pa^'and a 380-ft. deck span meet at the pier. In the present problem 
 .; ^he^sscrne deftgftis of span are assumed, but both spans are treated as through 
 
 '"types.' Prg.*I,''Plate 1, shows a profile of the complete bridge and the position 
 of pier 8. 
 
 II. GENERAL PROPORTIONS OF PROPOSED PIER. 
 
 6. Plate 2 gives the main dimensions for the pier outlined in the present 
 problem. The base of rail is at an elevation of +94.97 ft. ; 9 ft. 6 ins. lower is 
 the plane of the coping top. The coping measures 27 ins. in thickness. For the 
 next 79 ft. downward, horizontal sections of the pier have parallel sides and 
 semicircular ends with a face batter of -in. to the vertical foot. From this 
 elevation the cut-water extends on the up-stream side for the next 10 vertical 
 ft. with a slope of one in four, while the other sides ret ,in their normal batters. 
 The cut-water sections end 24 ft. above the mud-line. From the base of the 
 cut- water to the mud -line the pier section remains constant; that is, the pier 
 sides are vertical. At the mud-line the pier enlarges by offsets to a rectangular 
 section in order to give proper anchorage and bottom clearances for the detach- 
 able coffer-dam. From the mud-line downward, with batters of one to twenty- 
 four on all sides, the rectangular section continues to the caisson roof, 67 ft. 
 below. The caisson itself has vertical sides, and, measured along its outer 
 side-plates, is 12 ft. 2| ins. in height. From the cutting edge of the caisson to 
 the top of the coping, the pier measures 179.94 ft. Eighty-four and two-tenths 
 feet of the pier are below the low-water line. 
 
 7. In this particular problem the river selected has but a small range in water 
 surface. Bridge piers in the Mississippi valley rivers require the consideration 
 of great range in stage, a condition which often produces a very serious problem. 
 Eighty-six and twenty-four hundred ths (86.24) feet of the pier is above low 
 water. From low water to the river bottom measures 28.95 ft. From the 
 river bottom, or mud-line, to rock, averages 55.05 ft. At low-water stage of 
 the river, therefore, the greatest head on the caisson, that is, when it has reached 
 its destination, is about 55 ft. of material (mud and silt) and 29 ft. of water; to 
 be exact, 84.2 ft. in all. At high stage of the river 2.75 ft. of water must be 
 added to the above figures. 
 
 8. It is plain that the foundation is a rather deep one, but it does not approach 
 the extreme record depths. It would seem that pneumatic work reaches the 
 limit of its application for depths of from 100 to 125 ft. below water surface. 
 
 III. SPECIFICATIONS. 
 
 9. The following important quantities and other specifications are used in 
 the calculations: 
 
 a. The weight of pier masonry = 155 Ibs. per cu. ft. 
 
 b. Weight of yellow pine timber = 50 Ibs. per cu. ft. 
 
 c. Weight of concrete = 140 Ibs. per cu. ft. 
 
 d. Weight of steel and iron = 480 Ibs. per cu. ft. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 3 
 
 e The coping course is of granite. 
 
 /. From the coping to low water the pier consists of a concrete heart [ 1 Port- 
 land cement, 3 sand, 5 broken stone (to pass a 2-in. ring)] faced with limestone 
 ashlar (quarry -faced, joints f-in.). 
 
 g. From low water to the mud-line of river bottom the whole body of the 
 pier is of concrete of the proportions given above. 
 
 h. From the mud-line to the caisson top the pier consists of a permanent 
 coffer-dam of yellow pine filled with timber framing, but mainly with concrete 
 of 1 Portland cement, 2 sand and 4 broken stone (to pass a 2-in. ring). 
 
 i. The steel caisson is eventually filled with a rich concrete composed of 1 
 Portland cement, 2 sand and 4 broken stone (to pass a 1-in. ring). 
 
 /. The total weight in pounds per lineal foot for the main trusses and their 
 bracing is assumed as follows: 
 
 For the 380-ft. span = 10 times the span length in feet, = 3,800 Ibs. 
 
 For the 520-ft. span = 11.5 times the span length in feet, = 5,980 Ibs. 
 
 These weights are for double-track structures and are somewhat light, con- 
 sidering the heavy locomotives now being proposed ; for example, Cooper's E-50. 
 For such heavy loadings the weights of trusses of the above spans should be 
 increased to say 13 and 15 times the span length in feet, respectively. 
 
 k. Weight of floor system = 900 Ibs. per lineal foot. This figure, also, is 
 light. 
 
 /. Weight of track = 800 Ibs. per lineal foot. 
 
 m. Average weight of live-load = 3,500 Ibs. per lineal foot. 
 
 n. Through trusses for general lateral stability should have a spacing equal 
 to or greater than one-eighteenth to one-twentieth of the span. In the present 
 case the spacing has been assumed 28 ft. 6 ins. This would seem rather re- 
 stricted, considering the 520-ft. span, but it is justifiable, since most of the 
 spans of the Havre de Grace bridge are shorter. Heavy train loadings like 
 Cooper's E-50, for proper clearances, would find this spacing of trusses rather 
 scant. Twenty-nine feet six inches, or even 30 ft. would be advisable for post 
 clearances, especially the end-posts. 
 
 The calculations here given were made some time ago for the 28 ft. 6-in. 
 spacing, and the writer has not had the time at his disposal to make a desirable 
 change. This is true of other parts of the calculations. The article attempts 
 to explain a method rather than to give in all cases the most stii table proportions. 
 
 o. The allowable pedestal bed-plate pressure is 350 Ibs. per sq. in. 
 
 p. Specifications for individual materials, for timber construction and stone 
 masonry are not given. They may be found in any standard set of specifications 
 for substructures. Consult, for example, "General Specifications for Bridge 
 Sub-Structure," of the Osborn Company. 
 
 IV. NECK SECTION OF PIER. 
 
 (See Plate 1, Fig. 2.) 
 
 10. The size and shape of the neck section of a pier depend upon the bracing 
 of the main trusses and upon the bed-plate dimensions of the bridge pedestals. 
 The truss spacing has already been given as 28 ft. 6 ins. The bed-plates must 
 
DESIGN OF A RAILWAY BRIDGE PIER. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 5 
 
 now be designed. The total weight of superstructure and train possible upon 
 one pedestal is as follows: 
 
 For the 380-ft. span = 1,187,500 Ibs. 
 
 For the 520-ft. span = 1,908,400 Ibs. 
 
 11. These loads must be carried by the respective pedestal bed-plates. The 
 working values for allowable bed-plate pressure on granite copings vary with 
 different designers from 300 to 400 Ibs. per sq. in. An average value of 350 
 Ibs. per sq. in. is here taken and the bed-plates, therefore, require the following 
 areas : 
 
 For the 380-ft. span - 24 1 sq. ft. ; final 7 ft. x 3 ft. 6 ins. 
 For the 520-ft. span = 38.7 sq. ft. ; final 7 ft. x 5 ft. 6 ins. 
 
 12. It is plain that the area of pier top or neck section must be far greater 
 than is necessary for the masonry to carry the loads. The pedestal plates are 
 made oblong to save width of pier, since its length is fixed by the truss spacing. 
 Where trusses require a very wide spacing, piers sometimes omit a portion of 
 the central masonry. In such cases we virtually have two visible piers, one 
 under each set of bridge pedestals, resting upon a common foundation. In a 
 construction of great magnitude not only the visible piers but the foundation 
 also may become entirely separated from the two sides of the structure, pro- 
 ducing two independent piers and foundations. Much economy may often be 
 possible through a careful study of this problem. 
 
 13. It will be noticed that the bed-plates for both spans are slightly wider than 
 necessary, assuming the 7-ft sides as fixed lengths. This increase allows 
 for expansion and contraction of the trusses, due to changes of temperature. 
 Good practice allows one inch per 100 feet of span for the total expansion from 
 a mean position, and the same amount for contraction, as a horizontal play-room 
 for the roller -ends of the trusses. Eight inches is allowed for the 480-ft. span; 
 the above rule requires 7. 6 ins. A proportional allowance has been made for 
 the 520-ft. span, assuming that both trusses meet at pier 8 with expansion 
 bearings. This may or may not be the case. If desired, therefore, a few 
 inches could be saved in the width of pier by treating one or both pedestals 
 as fixed. The width of the neck section finally adopted is 10 ft. 6 ins , the 
 total width of bed-plates with expansion allowance is 9 ft. 8 ins. It is desirable 
 always to have the neck-section width slightly exceed the bed-plate plans. 
 
 14. This pier has semicircular ends. The diameter of the semicircle for the 
 neck section is taken along the extreme outer edges of the bed-plates. Fig. 2, 
 Plate 1, gives the final proportions for the pier top. Fig. 3 shows a study for 
 the coping and corbel courses. Copings should ordinarily project about 6 ins. 
 beyond the next course below and not more than 9 ins. This being a large pier, 
 the upper limit is taken. In deciding upon the amount of projection, the gen- 
 eral architectural effect should be considered. The corbel course is added for 
 this latter purpose; it reduces projections per course at the same time that it 
 provides, sufficiently large total projection for heavy piers. The introduction 
 of the corbel course causes the smallest section of the pier, which is at the base 
 of the corbel course, to be slightly larger than the neck section. 
 
6 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 V. GENERAL STABILITY OF PIER. 
 
 15. A high pier is subject to the vertical loads of the superstructure and its 
 own weight, and its horizontal section at any level must be of sufficient area to 
 withstand the vertical load at proper working pressure. 
 
 16. At the foundation beds these loads must be carried with proper working 
 factors, depending upon whether the caisson material, or the material upon 
 which it rests, is the weaker, in supporting power. For example, a pier resting 
 on sound, solid rock, will carry loads dependent upon the crushing strength of 
 the caisson materials, but if the same pier rested on sand the crushing strength 
 of the pier concrete would exceed the safe supporting power of the sand. Other 
 things being equal, the bottom plan of a pier would have to be much larger for 
 a sand than for a rock foundation. 
 
 17. In these calculations must be considered the abnormal pressure on the 
 foundation bed, the buoyant efforts of the displaced water and the friction and 
 uplifting forces exerted by the surrounding material against the sides of the pier 
 and foundation. 
 
 18. The vertical loads produce compression, usually of nearly constant 
 intensity upon horizontal sections of the foundation. This condition of loading 
 is practically obtained for a pier of equal batter on all sides. Our pier has a 
 starling on the up-stream face which, for sections below it, throws the resultant 
 weight away from the center of horizontal sections and toward the down-stream 
 edge; therefore the dead weight of the superstructure and pier tends to produce 
 pressures slightly greater at the down-stream toe than at the up-stream. In 
 most piers, as in this example, the variation is slight and commonly neglected. 
 
 19. There are other reasons, however, why the pressures at times may vary 
 greatly in intensity upon horizontal sections of the foundation, especially those 
 at considerable depths. Horizontal forces may act tending to overturn the 
 pier about its down-stream toe and in a plane at right angles to the length of 
 the bridge. Fig. 4, Plate 1, shows the nature and position of these forces. They 
 are produced by the wind on the trusses and train, the wind on the pier, the 
 pressure of an ice-flow through which the pier cuts, and the pressure of the 
 water current moving against the structure. These forces may all act in the 
 same direction and at the same time. Their overturning moment tends to 
 produce compression on the down-stream half of a horizontal section and tension 
 on the up-stream half. Under the most favorable action of these horizontal 
 forces, therefore, we may find a much higher intensity of pressure at the down- 
 stream than at the up-stream edge of a joint. 
 
 20. To study these stresses it is necessary to consider for any horizontal 
 joint the stability of the structure against: 
 
 a. Pressures due to vertical loads. 
 
 b. Overturning about the down-stream toe. 
 
 c. Horizontal sliding down-stream. 
 
 d. Maximum intensity of pressure at down-stream toe. 
 
 21. Calculations of this type present no difficult problem and are well outlined 
 in such books as Baker's " Masonry Construction," Chapter 16, p. 366. In 
 order to design the steel caisson in this problem, however, it is necessary, first. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 7 
 
 to make sure that the pier is stable and economic, and consequently the sta- 
 bilities of joints MN, G H and JK (see Plate 2), are considered. These 
 joints, it will be noted, are at the mud-line, caisson roof and rock bottom re- 
 spectively. Joints above the mud-line need not be considered, because the 
 loads and overturning effects are relatively small. 
 
 VI. HORIZONTAL FORCES ACTING UPON PIER AND SUPERSTRUCTURE. 
 
 (See Plate 1, Fig. 4.) 
 
 22. F , = wind pressure on 520-ft. trusses = 78,000 Ibs. acting at elevation 
 + 120.03. 
 
 F 2 = wind pressure on 380-ft. trusses = 57,000 Ibs. acting at elevation 
 + 115.03. 
 
 F 3 = wind pressure on train = 135,000 Ibs. acting at elevation + 105.03. 
 F t = wind pressure on pier = 23,240 Ibs. acting at elevation + 45.28. 
 F 5 = ice thrust = 743,040 Ibs. acting at elevation + 0.28. 
 F t = current pressure = 13,500 Ibs. acting at elevation 9.72. 
 Total horizontal force tending to produce sliding = 1,049,780 Ibs. 
 
 23. In the above: (1) The vertical projection of trusses has been assumed 
 equal to 10 sq. ft. per lineal foot of span and that of trains at the same figure; 
 (2) the wind pressure on vertical projections of trusses and train is assumed at 
 30 Ibs. per sq. ft. and on the pier at 20 Ibs. per sq. ft., because the ends are round 
 and tend to deflect the wind; (3) the ice- flow is assumed to be 1.5 ft. thick of 
 melting ice with a crushing strength of 200 Ibs. per sq. in. ; (4) the current 
 pressure is computed by formula, Art. 569, p. 367, of Baker's " Masonry Con- 
 struction." 
 
 24. In determining the elevations for the horizontal forces, the 520-ft. truss 
 is assumed 60 ft. in depth and the 380-ft. truss at 50 ft. ; the lower chord of both 
 trusses is taken 5 ft. below thebaseof rail, the train wind 10ft. above base of rail; 
 the ice-flow is considered to occur at high-water, and the resultant current 
 pressure is placed 20 ft. above the river bottom for a river depth at high-water 
 of about 32 ft. 
 
 These figures are not exact, but greater accuracy is not necessary. 
 
 VII. STABILITY OF SECTION MN. 
 
 25. Elevation = 29.72 at the mud-line or river bottom. 
 
 Weight of the pier above MN = 13,119,820 Ibs. L , _, 
 
 Weight of live load and superstructure = 6,191,800 Ibs. 
 
 Total weight on section MN = 19,311,620 Ibs. 
 
 Total weight (deducting for empty cars) == 18,186,620 Ibs. 
 
 Area of section MN = 964.9 sq. ft. 
 
 Total horizontal force above MN = 1,049,780 Ibs. 
 
 26. Stability Against Overturning, Section M N. Using similar notation to 
 that for the horizontal forces, the moments of these forces about axes in the 
 section MN are as follows: 
 
 M, = 78,000 x 150 = 11,700,000 ft.-lbs. 
 M 2 = 57,000 X 145 = 8,265,000 ft.-lbs. 
 
8 .DESIGN OF A RAILWAY BRIDGE PIER. 
 
 M, = 135,000 X 135 = 18,225,000 ft.-lbs. 
 M 4 = 23,240 X 75 = 1,743,000 ft.-lbs. 
 M s = 743,040 X 30 = 22,291,200 ft.-lbs 
 M t = 13,500 x 20 = 270,000 ft.-lbs. 
 Total overturning moment for section MN = 62,494,000 ft.-lbs. 
 
 27. The lever-arm, with respect to MN of the resultant of all the horizontal 
 forces acting upon the structure = 62,494,000 + 1,049,780 = 59.5 ft. The 
 resultant of this maximum horizontal overturning force and the vertical load 
 above MN cuts that joint at the point E, Plate 2, far within the middle third. 
 There can never be tension in the section, and there is no danger from over- 
 turning. 
 
 28. Stability Against Sliding, Section M N. The resultant at E makes an 
 angle with the vertical whose tangent = 1,049,780 + 18 186,620 = 0.058. 
 
 At the limit for sliding stability the value of this tangent for masonry is 
 0.75, which shows that the joint has a frictional resistance to sliding thirteen 
 times greater than is necessary just to balance the horizontal forces. Besides 
 the frictional resistance the joint offers also a shearing resistance, usually neg- 
 lected in calculations of this kind, though it is a very large quantity. These 
 results emphatically show that sections like MN are abundantly able to resist 
 sliding. 
 
 29. Safety Against Crushing, Section M N. The vertical loads acting alone, 
 assuming a uniform distribution of pressure, produce a compression in the 
 joint MN of an amount: 
 
 p = 19,311,620 *- 964.9 = 19,900 Ibs per sq. ft. = 10 tons per sq. ft. Good 
 concrete may safely carry 15 tons per square foot. The value of p is not exact 
 because the load is probably not uniformly distributed and because the resultant 
 load does not cut the center of the joint, but passes slightly to the down-stream 
 side of the center a distance, e. This eccentricity is due to the cut-water. 
 
 30. A moment Pe therefore tends to produce tension in the up-stream half 
 and compression in the down-stream half of the joint. P is the total load on 
 the joint; the maximum intensity of pressure occurs, consequently, at the down- 
 stream edge. Its amount is 
 
 where / is the longer side of the joint, and / the moment of inertia of the joint 
 about its shorter center line. In the present case e is small and the value of p t 
 is assumed essentially equal to p. 
 
 31. It has already been shown that the horizontal forces produce an over- 
 turning moment, M = 62,494,000 ft.-lbs. (Art. 26). This moment produces a 
 similar effect to that discussed for the moment Pe, but it cannot be neglected. 
 In general, 
 
 ' 
 
 Neglecting Pe, the greatest compressive intensity for the joint M N is 
 p t = 19,900 + 6,900 = 26,800 Ibs. per sq. ft. = 12.4 tons per sq. ft. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 9 
 
 Again these calculations are not exact, but were roughly made to save time 
 and labor. The relatively high values for the pressures indicate an economic 
 design. 
 
 32. The calculations in Arts. 25 to 31 show that the section MAT, at the mud- 
 line, is perfectly stable in all respects. 
 
 VIII. STABILITY OF CAISSON-ROOF SECTION. 
 
 33. This section GH, see Plate 2, is 43 ft. below section MTV. The total 
 weight upon GH is 28,600,000 Ibs. The area of section GH = 68X27 = 1,836 
 sq. ft., therefore the average pressure, p = 15,600 Ibs. per sq. ft. =.7.8 tons 
 per sq. ft. The total horizontal force is the same as for MTV; the factor of 
 safety against sliding (neglecting shearing tenacity) is about 18. Since the 
 joint is 43 ft. below MTV, the total overturning moment is readily obtained as 
 follows: M = 62,494,000+ (1,049,780X43) = 107,700,000 ft.-lbs. Substituting in 
 Equation (2), again neglecting the small amount Pe, the maximum pressure 
 at the down-stream edge is p 2 = 15,600 + 5,130 = 20,730 Ibs. per sq. ft. = 10.3 
 tons per sq. ft. The most eccentric position of the resultant cuts the joint at 
 F (see Plate 2), far within the middle third. 
 
 IX. STABILITY OF PIER AT BED ROCK. 
 
 34. The total weight of superstructure and pier resting upon bed-rock is 
 33,000,000 Ibs. The caisson plan is 68X27 = 1,836 sq. ft. The average in- 
 tensity of pressure due to weight alone = 17,900 Ibs. per sq. ft. = 9 tons per 
 sq. ft. In the two previous joints the strength against sliding was shown to be 
 great; as it must be even greater in this case, the computations are omitted. 
 Bed-rock is 55.2 ft. below section MTV, hence the total overturning moment is 
 
 M = 62,494,000 +(1,049,780X55.2) == 120,694,000,ft.-lbs., and p 2 = 17,900 + 
 5,700 = 23,600 Ibs. per sq. ft. = 12 tons per sq. ft. 
 
 35. The.se pressures are safe for concrete and bed-rock, but would be too 
 high for a foundation on sand. If this pier rested on sand, it would require 
 a much larger caisson plan to reduce the loads on the sand. A steel caisson 
 would be out of place in such a case. Wood beirg lighter and of larger volume 
 would be far more suitable material. The pier at bed-rock is very safe against 
 overturning; the resultant load may be shown to pass far within the middle 
 third of the section. 
 
 36. The stiffness of the surrounding material must assist the structure against 
 sliding and overturning for joints below the mud-line, but such resistance cannot 
 be considered, since the pier must never appreciably move. Nevertheless, 
 piers deeply imbedded in materials like mud, silt, sand, clay and hardpan, and es- 
 pecially the last three materials, must be made additionally stable against 
 overturning. 
 
 37. The pressures computed above for bed-rock perhaps never exist and are 
 in excess. They neglect buoyancy of water and displaced materials and omit 
 the supporting effect by side friction from the surrounding material. If no 
 water can get under the pier, a condition rarely obtained, buoyancy will not 
 enter to reduce the pressures on bed-rock. The following figures are significant: 
 
10 
 
 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 PLATE 2. 
 
 
 f C> ^^ 
 
 te*/ Ao V f ^X \ . 
 
 GZWZftAZ. 7ZAN 
 
DESIGN OF A RAILWAY BRIDGE PIER. II 
 
 Total load of structure on bed-rock = 33,000,000 Ibs. 
 
 Buoyancy of displaced water = 1,750,000 Ibs. 
 
 Immersed weight = 31,250,000 Ibs. 
 
 Buoyancy of sand and silt at 120 Ibs. per cu. ft. = 77,325,000 Ibs. 
 
 Fatigue weight = 19,925,000 Ibs. 
 
 Side friction at 400 Ibs. per sq. ft. of surface = 4,075,000 Ibs. 
 
 Actual probable fatigue measure = 15,850,000 Ibs. 
 
 = 8,600 Ibs. per sq. ft. 
 
 = 4.3 tons per sq. ft. 
 
 X. BATTERS AND THEIR EFFECT ON THE STABILITY OF PIERS. 
 
 38. The computations for the three joints here studied show that it is unnecessary 
 to consider the stability of sections above the mud-line. Such sections will 
 be more than strong enough, especially near the pier top. In fact it may be 
 said that very deep piers, piers that have sufficient neck section to carry the 
 superstructure, which have side batters of 1 in 12 to 1 in 24, will be found stable 
 in most cases. Exceptions to this rule will be found for very deep and high 
 piers resting upon poor foundation material. Such cases would require large 
 bottom plans and therefore large caissons, and such caissons had better be of 
 wood than of steel. Low piers requiring large neck sections will generally be 
 of excessive strength. 
 
 39. In this case the batters, for simplicity of calculation, have been taken at 
 J-in. per vertical ft. on all sides. End batters are often made larger than the 
 side batters, being perhaps f-in. per vertical ft. as against f-in. per vertical ft. 
 for side batters. Batters are indispensable for appearance, but where stability 
 does not warrant a batter, there is no reason why piers may not have vertical 
 sides below permanent low water. 
 
 XI. FLOTATION OF CAISSON. 
 
 40. The caisson is to be built on scows which are to be weighted and sunk 
 when launching time comes. Care must therefore be taken to design the 
 caisson to float, cutting-edge downward, in order that it may be towed to the 
 pier site, accurately located, and held in position by cables and piles preparatory 
 to the work of sinking. 
 
 41. The metal weight of steel caissons is found by experience to equal usually 
 from 11 to 13 Ibs. per cu. ft. of enclosed volume. Using the average figure of 
 12 Ibs., the approximate caisson weight is 68X27X12X12.2 =269,000 Ibs. 
 Assuming a thickness of 4 ft. of concrete over the roof-plate of the caisson's 
 working chamber and between and above the roof girders to give stiffness and 
 flotation stability, gives a weight of concrete of 68X27X4X 155 = 1,138.320 Ibs. 
 The total weight of steel and concrete to be floated, therefore, is about 1,400,000 
 Ibs., requiring a displacement of 22,400 cu. ft. Neglecting the volume of the 
 working chamber, which may be assumed filled with water, the volume of water 
 displaced between the roof level and the top of the caisson side-plate is 27 X 
 68X4.8 = about 8,810 cu. ft., leaving 13,590 cu. ft., of displacement to be 
 produced by adding to the caisson top a sufficient height of timber wall of the 
 
12 'DESIGN OF A RAILWAY BRIDGE PIER. 
 
 permanent coffer-dam. A height of 7.4 ft. of such timber wall is therefore 
 necessary to secure flotation with a 4-ft. layer of concrete. 
 
 42. It is highly improbable that the caisson will be loaded with a weight 
 equivalent to a 4-ft. thickness of concrete, but for flotation safety it would seem 
 advisable that at least 7 ft. of permanent coffer-dun wall should be in place 
 and calked when the caisson is launched and towed to the pier site. 
 
 XII. WEIGHT NECESSARY TO SINK CAISSON. 
 
 43. After the caisson is moored in position at the pier site it becomes necessary 
 in order gradually to sink the structure, to weight it by increasing amounts, at 
 the same time adding to the height of the permanent coffer-dam wall to keep 
 water from entering the pier volume from above. Until the cutting-edge 
 reaches the river bottom or mud-line, the only weight necessary for sinking is 
 that required to overcome water buoyancy. Such sinking weight is readily 
 obtained by adding in layers the concrete of the permanent coffer-dam. But 
 when the caisson has once reached the river bottom, the sinking weight necessary 
 must not only overcome water buoyancy, but also side friction and resistances 
 at the cutting-edge offered by the materials through which the caisson is being 
 sunk. As the structure proceeds downward from the river bottom to bed-rock, 
 the frictional resistance rapidly increases in amount, so that the necessary 
 sinking weight becomes rapidly larger, reaching its maximum during the last 
 operation of sinking, when the caisson is just about to reach its final position. 
 
 44. The exact value of this sinking weight cannot be accurately computed 
 because the conditions which determine the uplifting and resisting forces are too 
 complex and uncertain to allow of close calculation. The designing engineer 
 must therefore provide a caisson strong enough to carry a load safely in excess 
 of the probable maximum sinking weight. When the pier has once reached 
 bed-rock no further weight is added to the structure until the caisson volume ' 
 has been filled with concrete and the air-locks and as much as possible of the 
 air-shafts for men and material have been removed. It is plain, therefore, 
 that the caisson stresses are not due to the final pier weights. 
 
 45. The stresses acting in the caisson frame are temporary and cease to exist 
 after the caisson has been firmly seated on bed-rock and its working chamber 
 filled with concrete. High working stresses, at least one-half the elastic limit 
 of the metal, are consequently justifiable. This explains the relatively high 
 values in the following design calculations: 20,000, Ibs. per sq. in. is used for 
 direct stresses and 10,000 Ibs, per sq. in. for shearing stresses. 
 
 46. Sometimes the maximum necessary sinking weight is not all produced 
 by materials of the actual final pier. Loads of pig-iron are often used rather 
 than the weight of materials of the completed structure. The pig-iron acts as a 
 live-load, so to speak, and may be varied, increased, and also decreased, if found 
 desirable. The engineer thereby obtains a greater command over the sinking 
 operations, especially when the foundation tends to careen or turn from its 
 proper alinement. 
 
 47. Side frictional resistances offered by materials like those encountered 
 at Havre de Grace will usually be found between 350 and 450 Ibs. per sq. ft. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 
 
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 DESIGN OF A RAILWAY BRIDGE PIER. 
 
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 of surface, although there are cases on record where frictional resistances of 
 600 Ibs. and over have been recorded. The maximum area over which the fric- 
 tional forces act is 10,192 sq. ft. Assuming a frictional intensity of 400 Ibs. per 
 sq. ft., the maximum frictional resistance equals about 10,492 x400 = 4,076,800 
 Ibs. The volume of pier under water is 114,312 cu. ft., causing a buoyant 
 force due to displaced water of about 7,154,500 Ibs. The greatest resultant 
 frictional and buoyant force is therefore in the neighborhood of 11,231,300 Ibs. 
 To this amount should be added resisting forces at the cutting-edge. 
 
 48. The approximate weight of steel in the caisson has already been stated 
 as 269,000 Ibs., Art. 41, and the weight of pier materials between the caisson 
 roof and the water-line is about 14,303,400 Ibs., so that were the pier to be 
 built to the level of the river surface at the time the cutting-edge reached bed- 
 rock, the weight of pier available to cause sinking would be approximately 
 14,500,000 Ibs. The above figures show that such a weight would only slightly 
 exceed the probable maximum resistance to sinkage. This design, therefore, 
 assumes that under the worst conditions the steel caisson must be able to support 
 a load of 14,500,000 Ibs., and that at the same time it must be capable of with- 
 standing the maximum lateral pressures from the surrounding material tending 
 to thrust inward the side walls of the working chamber. 
 
 XIII. DESIGN OF CAISSON. 
 
 49. The important parts of the steel framing of the caisson are: (1) the roof- 
 plates, (2) roof-beams, (3) side-plates, (4) side-wall brackets, (5) side-wall beams, 
 (6) cutting-edge and (7) splice-plates, corner-plates and other important details. 
 
 50. Roof-Plates The roof-plates carry no important stresses; they are f-in. 
 thick and, like the side-plates, must be carefully calked at all joints to secure 
 as nearly as feasible a water-tight air-chamber. 
 
 51. Roof-Girders The roof -beams are plate-girders spanning the shorter 
 side of the caisson plan and are supported by the side-wall brackets. The 
 masonry above them has considerable supporting power itself. The steel 
 girders are designed to carry only the weight of a wedge of material whose base 
 is the caisson roof and whose sides make angles of thirty degrees with the vertical. 
 See Fig. 5, Plate 1. The height of wedge h = 12 tan 60 = 20.8 ft. Due to 
 to the carrying capacity of the side- wall brackets, the effective span of the girders 
 is taken at 24 ft. ; the wedge base is therefore also 24 ft. The weight of 1 ft. 
 thickness of wedge = 12X20.8X 155 = 38,700 Ibs. 
 
 52. Design of Flanges; Roof -Girders With roof-beams spaced 4 ft. center to 
 center, the effective reaction for one girder = R = 38,700x2 = 77,400 Ibs., 
 while the maximum bending moment in the span equals 77.400X8=619,200 
 ft.-lbs , nearly. For a beam-depth of the span the plate-girder web is 36 ins. 
 in depth. Assuming flange-angles 6x4 ins., with the 6-in. leg horizontal, gives 
 an effective depth of girder = 34 ins. If the flange-angles be considered to 
 carry all the bending, the maximum flange-stress for a 34-in. effective depth 
 
 = 219,000 Ibs. For a working intensity of flange-stress of 20,000 Ibs. the 
 flange-area required at the center of the tension flange = 10.95sq. ins. Two6x4x 
 j-in. angles, deducting for two rivet-holes, give a net area of about 12.4 sq. ins. 
 
16 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 53. Design of Web; Roof-Girders The maximum end shear of 77,400 Ibs., 
 at a working-stress intensity of 10,000 Ibs., requires 7.74 sq. ins. of available web- 
 section. Assuming J-in. rivets with 3-in. pitch in the stiffener-angles gives an 
 effective web-depth of 24 ins., and therefore a necessary web-thickness of 0.322 
 in. A f-in. web-plate is used. Stiffener-angles and rivet details are shown on 
 Plate 3. Since these girders are imbedded in concrete, their webs and com- 
 pression flanges are considerably reinforced. The stiffener-angles are conse- 
 quently light, being two 3 X 3 X $ in. angles occurring about every 3 ft. Strictly 
 speaking, there are no end stiffeners. Three sets of stiffener-angles are found 
 over the brackets. The stiffeners at the extreme ends of the girders are made 
 heavy, of two 6 X 6 X J-in. angles, to give solid connections to the side-plates and 
 for vertical reinforcement to assist in carrying the extra loads which come upon 
 the brackets. 
 
 54. The drawings show no transverse bracing between girders. This is 
 deemed unnecessary because of the binding strength of the concrete. For 
 security, however, two lines of bracing could readily be introduced along lines 
 AB and CD, see Plate 6. 
 
 55. Side-Plates The side-plates are f-in. in thickness. As they are rein- 
 forced every 4 ft., horizontally, by the main side-wall brackets, and, vertically, 
 every 27 ins. by the Z-bars, they must simply be of sufficient strength to resist 
 the pressures of material from without tending to bulge 27 X 48-in. plates inward. 
 The maximum head on the caisson is about 82 ft., of which about 30 ft. is 
 water, and the rest water and material. Assuming a blow-out to occur in the 
 working chamber and that the 82 ft. head of water, mud, sand and silt causes 
 a hydrostatic pressure equivalent to a material of four-thirds the density of 
 water, the normal intensity of bulging pressure has a maximum value of about 
 0.434X82X1.33X144 = 6,830 Ibs. per sq. ft. = 47.5 Ibs. per sq. in. 
 
 56. The intensity of pressure is roughly obtained and may be very excessive. 
 Yet it would be unsafe to consider a smaller pressure, as the following additional 
 calculation shows: 30 ft. of water at 62 5 Ibs. per cu. ft. + 52 ft. of material at 
 120 Ibs. per cu. ft. produce a vertical intensity of pressure at bed-rock = (30 X 
 62.5) + (52X120) =8,100 Ibs. per sq. ft., nearly. The horizontal conjugate 
 pressure, according to Rankine, is 
 
 . 1 sin< 
 
 p=wh- ; (3) 
 
 1 + sm <f> 
 
 where wh = 8,100 Ibs. per sq. ft. in this case and </> the angle of repose of the 
 material surrounding the caisson. The value of < must lie between zero and 
 about 30, approaching the former, the wetter the material. 
 
 For = 0, p = 8,100 Ibs. per sq. ft. 
 
 For = 15, p =. 8,100X0.588 = 4,780 Ibs. per sq. ft. 
 
 For <j> = 30, p = 8,100X0.333 = 2,710 Ibs. per sq. ft. 
 
 Any considerable percentage of water permeating the material around the work- 
 ing chamber when near bed-rock must tend to cause the lateral pressure to 
 approach' 8,100 Ibs. per sq. ft. 
 
 57. The unsupported dimensions of plate are 27 X 48 ins., Art, 55, These 
 
DESIGN OF A RAILWAY BRIDGE PIER. 
 
 17 
 
18 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 edges cannot be said to be simply supported, nor can they be assumed entirely 
 fixed. The theory of stress in bulged plates is a very complex subject. Consult 
 Burr's " Elasticity and Resistance of the Materials of Engineering", Art. 105, p. 
 184, Edition of 1903. For Burr's notation, a = 27 ins., b = 48 ins., w = 47.5- 
 Ibs. per sq. in. Assuming fixed edges, the greatest intensity of fiber stress is 
 
 a 2 b 4 w . 
 
 1 ~ * < 4 ' 
 
 and t-t.VfflV-jp, (5> 
 
 Here t is the necessary plate-thickness in inches, and .K", the allowable intensity 
 of stress in Ibs. per sq. in. 
 
 58. If K l be taken at 20,000 Ibs. per sq. in., t = 0.952 ins. The above calcu- 
 lations are only roughly approximate. A formula expressing the thickness t 
 should be based in form upon Equation (5) , but should be fitted with experimental 
 constants. (Consult further, " Applied Mechanics," 4th Edition, by G. Lanza, 
 Art. 300, on the Strength of Flat Plates. See also Engineering News, Vol. 
 43, pp. 10 and 162). More elegant treatments might here be referred to; the 
 intention is to suggest rather than to solve the problem. 
 
 59. The values of a and b could be taken somewhat smaller than 27 ins. and 
 48 ins. because the bracket-angles and Z-bars by their stiffness and riveting 
 reduce the effective values of a and b. Moreover, the pressure, 47 5 Ibs. per 
 sq. in. is high. For these reasons a f-in. side-plate is used. Even this is probably 
 too generous and bold, and designers might advocate the use of a J-in. plate. 
 Local boulders can at times produce pressures against the side-plates and cutting- 
 edges of excessive amounts over restricted areas, and reasonable provisions 
 should be made for such possibilities. 
 
 60. Side-Wall Brackets These brackets must carry their portion of the 
 sinking weight as vertical struts and must resist the pressure against the side- 
 plates as cantilever triangular frames supported along the lower chords of the 
 roof-girders. 
 
 61. The maximum sinking weight has already been fixed at 14,500,000 Ibs.. 
 Art. 48, therefore the load on one bracket = 426,000 Ibs. Allowing a compres- 
 sion of 20,000 Ibs. per sq. in., and assuming the load carried wholly by the 
 vertical leg of the bracket requires a cross-section at that leg =21.3 sq. ins. 
 The design provides: 
 
 2 6X4Xf-in. angles = 13.88 sq. ins. 
 
 1 12iXi-in. filler-plate = 6.25 sq. ins. 
 
 Total 20 . 13 sq. ins. 
 
 In addition, as reserve strength, we may count to some extent upon the side- 
 plates, the ^-in. bracket web-plate and the two 6X4Xi-in. angles on the inner 
 inclined flange of the bracket. 
 
 62. In designing the side-plates it was concluded that a maximum pressure 
 of 47.5 Ibs. per sq. in., might be experienced against the sides of the working 
 
DESIGN OF A RAILWAY BRIDGE PIER. 
 
 19 
 
 
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20 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 chamber. 'This would bring upon the bracket a horizontal load. = 27,400 Ibs. 
 per lin. ft. of vertical leg. Considering the bracket as a cantilever, the resulting 
 bending moment in the plane of the roof-plates of the working chamber would 
 equal 7.5X27,000X3.75 = 769,000 ft.-lbs., while the horizontal shear for the 
 same plane would be 207,000 Ibs. The bending stress in the vertical leg of the 
 bracket is a tension of 769,000 n-4.5 = 171,000 Ibs.; and in the inclined leg a 
 compression of 769,000 -3.7 = 208,000 Ibs. The tension of 171,000 Ibs, in the 
 vertical leg can never exist because that leg is subjected to a far greater com- 
 pression from the pier loads. There should, however, be a considerable tensile 
 strength in the joint between the end stiffeners of the roof-girders and the 
 vertical legs of the working-chamber brackets. Allowing 20,000 Ibs. per sq. in. 
 compression in the inclined leg requires 10.4 sq. ins.; two6X4Xl-in. angles 
 provide 13.88 sq. ins. The horizontal shear of 207,000 Ibs. at the top of the 
 bracket is well taken care of by the two 6X4Xi-in. angles along the top, to- 
 gether with the further stiffening which may be relied upon from the roof-plates 
 and lower chord-angles of the roof-girders. 
 
 63. The -in. web-plate of the bracket has an effective top length of about 
 48 ins. and a net shearing area of about 18 sq. ins. At 10,000 Ibs. per sq. in. 
 the shear of 207,000 Ibs for the horizon of the roof-plates, requires 20.7 sq. ins. 
 These figures would indicate a weakness in shear for the -in. web-plate; it is 
 used, remembering that the pressure of 47.5 Ibs. per sq. in. against the sides of 
 the caisson is excessive. To strengthen the web-plates against buckling it 
 would be well to stiffen them along lines AB and BC, Plate 3, with 3 X 3 X f-in. 
 angles. 
 
 64. Side- Wall Beams. In the 7 ft. 6 ins. of vertical height of working chamber, 
 the caisson main side-plates are reinforced along vertical lines, at intervals of 
 4 ft., by the main brackets. These side-plates have been calculated to resist 
 bulging inward by considering them subdivided into rectangular parts, 27 X 
 48 ins. each. They must therefore be reinforced along horizontal lines at 
 intervals of about 27 ins. Two lines of Z-bars are used for this purpose. See 
 Plate 3. Each Z-bar is assumed to support the pressure against one-third the 
 height of the working chamber or a load of 6,830 X 2.5 = 17,200 Ibs. per lin. ft. 
 For a span of 4 ft., this load gives a bendingmoment = 34,400 ft.-lbs. = 412,800 
 in. -Ibs., which, for a working fiber stress of 20,000 Ibs. per sq. in., requires a 
 Z-bar whose section modulus = 20.6; a 6|X3f X J-in. Z gives a section modulus 
 
 = 16.4 and is used. Again, the design would appear weak. The Z is strength- 
 ened by a 3f X J-in. filler and by the side-plates and the pressure or load used 
 has already been stated as generous. Only two lines of Z-bars are needed. At 
 the roof of the working chamber the side-plates are amply supported by a 
 6X6Xi-m- angle and by the concrete above the roof -plate. At the cutting 
 edge the extra plates and a 6X6X J-in. angle provide sufficient support. 
 
 65. Cutting-Edge. It is not possible to give figures for the design of a cutting- 
 edge. Locally where a boulder is encountered the stresses may be enormous. 
 Unequal sinking or uneven excavation under the cutting edge may produce similar 
 effects. The cutting-edge often may be badly damaged in a restricted length 
 and require repair. It must be stiff and tough and in the present design is 
 
DESIGN OF A RAILWAY BRIDGE PIER. 
 
 I? 
 
 I 
 
22 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 formed by reinforcing the J-in. side-plates by two plates, each 18 ins. in depth, 
 the one on the outside -in., the one on the inside ^-in. thick. A 6x6X$-in. 
 angle, on the inside and slightly above the cutting-edge, adds to the general 
 stiffness. This angle extends continuously about the caisson and supports the 
 lower ends of the side-wall brackets. Stout timbers bolted to this angle often 
 further reinforce the cutting-edge. See Plates 4 and 5. 
 
 66. Details. Since the caisson is to be sunk through compact silt in which 
 few boulders occur, no great precautions need to be taken to reduce side friction. 
 Rivets are therefore boiler-headed on the outside of the caisson. In bad materials 
 rivets are sometimes countersunk on the outside and water-jets supplied over 
 the imbedded sides of the foundation through holes in the side walls (See 
 Eng. Record, Nov, 23, 1893, p. 410, Foundations of the East Omaha Bridge). 
 Rivets are f-in. in diameter throughout and the pitch so far as possible is about 
 3 ins. The caisson is to be thoroughly calked at all joints to secure as nearly as 
 feasible a water-tight air-chamber. Splice-plates and corner-angles are carefully 
 considered in this respect. The side-plates are spliced vertically every 8 f t. , 
 that is, at every other bracket. The brackets at the shorter sides of the caisson 
 do not carry as much load as those against the longer sides; they are therefore 
 somewhat lighter, (See Plate 4). Similar remarks should apply to the girders 
 along the short sides of the caisson; they are built channel-girders whose webs 
 are the main side-plates. 
 
 67. Plates 3, 4, and 5 give all the important detailed features of the caisson 
 design. Plate 6 shows the general plan for roof-girders and bracket-framing; 
 it also shows the positions of air-shafts and the main pipes for air, water, and 
 sand- or mud-lifts. 
 
 68. A caieful bill of materials for the steel-work of the caisson has not been 
 prepared, nor could it be, since the design has been roughly made. The amount 
 of steel in the caisson is about 305,000 Ibs. The volume of caisson from cutting- 
 edge to top of side-plates is 22,480 cu. ft. The metal weight therefore is 13.5 
 Ibs. per cu. ft. of volume. The assumed weight, in discussing the caisson's 
 flotation, Art. 41, was 269,000 Ibs., a considerable smaller quantity, but it will 
 be at once noted that the discrepancy in no way seriously affects the design. 
 Our caisson is heavier than an average example, partly because of the depth of 
 foundation , and partly because the design is uniformly conservative, using, as 
 has been repeatedly noted, high values for the stress-producing loads and forces. 
 
 XIV. COFFER-DAMS, SHAFTS, LOCKS, AND POWER PLANT. 
 
 69. The permanent coffer-dam, detachable coffer-dam, the air-shafts and" 
 locks for material and men, supply-pipes to the caisson for air and water, sand- 
 lifts, mud-pumps, etc., are only shown in outline. See Plates 2, 6, and 7. These 
 parts of the structure have been sufficiently considered by the writer to make an 
 approximate estimate for the complete cost of the pier, but it is regretted that 
 time was not available to develop further their design in these pages. 
 
 70. The power plant, the equipment and methods for sinking the foundation, 
 the anchoring and guiding of the structure during its descent, the handling of 
 the men, the physiological effects of compressed air upon the workmen, and 
 many other important matters can here be stated in closing this article. 
 
DESIGN OF A RAILWAY BRIDGE PIER. 23 
 
 XV. BILL OF APPROXIMATE COSTS. 
 
 71. Pier below mud-line. 
 
 1. Concrete below cutting-edge = 675cu. yds. at $12 $ 8,100 
 
 2. Caisson steel = 305,000 Ibs. at 3.5 cts 10,700 
 
 Concrete = 510 cu. yds. at $12.00 
 
 320 cu. yds. at 8.50 8,845 
 
 3. Permanent coffer-dam: 
 
 Timber = 150 M. ft. B. M., at $40 6,000 
 
 Metal: bolts, spikes, etc., = 22,500 Ibs. at 3 cts 675 
 
 Concrete = 2,200 cu. yds. at $8.50. 18,700 
 
 Shafts, pipes, etc.. = 36,480 Ibs. at 3.5 cts 1,280 
 
 4. Sinking cost = 138,130 cu. ft. displacement at 20 cts 27,900 
 
 5. Detachable coffer-dam: 
 
 Timber, 101 M. ft. B. M. at $40 4,040 
 
 Ironwork = 15,100 Ibs. at 3 cts 450 
 
 Total cost of foundation below mud-line, $86,690 
 
 Foundation volume below mud-line = 3,490 cu. yds. 
 Cost of foundation below mud-line, iri eluding detachable 
 coffer-dam = $24 85 per cu. yd. 
 
 72. Pier above mud-line: 
 
 6. Coping = 49.5 cu. yds. at $40 $ 1,980 
 
 7. Limestone ashlar = 1,625 cu. yds. at $15 24,375 
 
 8. Concrete = 1,450 cu. yds. at $6.50 9,425 
 
 Total cost of pier above mud-line $35,780 
 
 Pier volume above mud-line = 3,125 cu. yds. 
 Cost of pier above mud-line = $11.40 per cu. yd. 
 Total volume of foundation and pier = 6,615 cu. yds. 
 
 Total cost of foundation and pier $122,470 
 
 Cost of foundation and pier, = $18.50 per cu. yd. 
 
 73. In the above estimate the following prices were used: 
 Concrete under cutting-edge at $12 per cu. yd. 
 Caisson concrete at $12 per cu. yd. 
 Caisson steel-work at 3.5 cts. per Ib. 
 Yellow pine for coffer-dams at $40 per M. 
 
 Excavating and sinking at 20 cts. per cu. ft. displacement below low- 
 water line. 
 
 Permanent coffer-dam concrete at $8.50 per cu. yd. 
 Hardware in coffer-dams, 150 Ibs. per M. at 3 cts. per Ib. 
 Limestone ashlar masonry, f-in. joints, at $15 per cu. yd. 
 Pier concrete above mud-line at $6.50 per cu. yd. 
 Granite coping at $40 per cu. yd. 
 Steel in air-shafts, left in work, at 3.5 cts. per Ib. 
 
24 DESIGN OF A RAILWAY BRIDGE PIER. 
 
 XVI. REFERENCES. 
 
 1. Baker, I. O.; A Treatise on Masonry Construction. 
 
 2. Patton, W. M. ; A Practical Treatise on Foundations. 
 
 3. Fowler, C. E. ; Ordinary Foundations, Including the Coffer-dam Process 
 
 for Piers. 
 
 4. Engineering Record, June 17, 1893, p. 38, vol. 27; 
 
 Pneumatic Caisson for Seventh Avenue Bridge, New York City. 
 
 5. Engineering News, vol. 13, 1885, pp. 14, 41, 63, 83, 122, 228, 244., 262, 274; 
 
 Foundations, Havre de Grace Bridge. 
 
 6. Morison, G. S. ; The River Piers of the Memphis Bridge; 
 
 Proc. Inst. C. E., vol. cxiv, p. 289. 
 
 7. The Forth Bridge Report. 
 
 8. The Memphis Bridge Report. 
 
 9. The St. Louis Bridge Report. 
 
 10. Railroad Gazette; Jan. 13, 1893, p. 19. vol. 13; 
 
 Seventh Avenue Drawbridge. 
 
 11. Engineering Record; Nov. 23, 1893, p. 410; Construction of Pivot Pier, 
 Interstate Bridge, Omaha, Neb. 
 
 12. General Specifications for Bridge Substructures; The Osborn Co. 
 
 13. The Hawkesbury Bridge. 
 
 14. The New East River Bridge. 
 
 15. The New York and Brooklyn Bridge. ,, 
 
 16. Engineering News; Dec. 7, 1893, p. 458; Pneumatic Foundations for the 
 
 Manhattan Life Building, New York. 
 
 This list does not presume to be complete nor does it intend to give all of the 
 best and most important references. The writer has given references at his 
 immediate command without seeking to make the table exhaustive. It will 
 help the student to find other articles relating to the subject. 
 
 Computations have been made with the aid of a slide-rule. The arithmetic 
 is not exact. Errors, it is believed, are far within one per cent, and therefore 
 more than small enough for a first study and estimate. 
 

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 22O Broadway, New YorR 
 
UNIVERSITY OF CALIFORNIA 
 DEPARTMENT OF CIVIL ENGINEERING. 
 
 STRUCTURAL ENGINEERING 
 
 I 
 
 NOTES ON FOUNDATIONS ANfl MASONRY STRUCTURES 
 COURSES 113 - 114. 
 
 By 
 
 Charles Derleth, Jr. 
 
 ll 
 
 Revised and Enlarged From Earlier Editions 
 Berkeley, California, October 1, 1921. 
 
 J 
 
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TABLE OF CONTENTS 
 
 ) -" 
 
 FOUNDATIONS. 
 
 Part 1. 
 Explorations Shallow Foundations. 
 
 Chapter 1. Examinations and Explorations . . , . , ...... I 
 
 1. Digging Test Pits . 2 
 
 2. Driving Pipes or Solid Iron Bods ...... 2 
 
 3 , Borings with Post Diggers end Augers . .. . . . . 4 
 
 Sather Tower ................... . .... 5 
 
 Calaveras Dam . . . . ......... . . , ...... 6 
 
 4. Test Piles ........... . ...... 8 
 
 Harbor Development at South San Francisco ........ 9 
 
 Oalcland Auditorium. ......../. 12 
 
 Calaveras Dam .............. 13 
 
 5. Borings v.'ith the Sand Pump ... * . W 
 
 Civic Center, San Francisco 15 
 
 6. Sinking with \Vr.ter-Jet 16 
 
 7. Drilling v/ith Artesian \7ell Boring Tools 18 
 
 8. Drilling with the Diamond & Stoel Shot Drills 20 
 
 General Precautions for Test Borings ..21 
 
 Sub-Aqueous Borings , "33 
 
 References '*.. 
 
 Problems 27 
 
 Chapter 2. Classific.tion of Foundation Soils - Bearing Power ...... 28 
 
 1. Solid Rock 29 
 
 2. Gravel and Kardpan ........................ 31 
 
 3. Sand .......... ............... 32 
 
 4. Clay . . . . 35 
 
 5. Ordinary Soil Earth Pressure. ............ . t . ... 35 
 
 6. Semi -Liquid Soils, Quicksand . ~58 
 
 Methods of Increasing the Bearing power of Earth Foundations ...... 42 
 
 Drainage and Confinement ..................... 42 
 
 Sand Piles ..................... . '43 
 
 Stock Ramming ................... 44 
 
 Sand Layers '. . . 44 
 
 Testing the Bearing Power of Soils .................... 45 
 
 Pressures on Foundation Beds Abnormal. Pressure 47 
 
 Examples of Pressures on Foundations and Boundation Beds in 
 
 Sand and Ear.-th ..'............,... 47 
 
 Summary - Foundation Soils: Their Supporting Cape city 49 
 
 References; Foundation Soils and Pressures ... ....... 49 
 
 Problems ..*....................... . . 50 
 
 Chapter 3. Classification and Requirements, Foundation Designs ...... 51 
 
 A. According to the Material Upon 7,/hich the Foundation Rests . .' , 51 
 
 B. According to Tjrpe of Structure Designed ,,,,.. , ... .51 
 
 Foundation Requirements .....'................... .51 
 
 References - Specifications - Problems .................. 53 
 
ii 
 
 Chapter 4, Distribution of Foundation Pressures - Spread Footings, ... 54 
 
 Table - "/eight of Masonry , . . 55 
 
 Table - live Loads for Buildings 56 
 
 Center of V/eight Vs. Center of Figure for Building Footings ....... 57 
 
 Table - V/all Thickness t ............ 58 
 
 Eccentric Foundation Loads .*..... 4 .'............... 58 
 
 Treatment for Center of Pressure "./ithout tlie lliddle Third .......<, 61 
 
 Pressure on the Foundation Bod of a Ifesonry Pier ............. 62 
 
 Stability Against Sliding ............. .^ t ......... 64 
 
 Spread Footings . ... : ; ............ 66 
 
 1. Timber Footings , . . .66 
 
 2. Masonry Offsets, Rubble ;Brick or Concrete .............. 67 
 
 Table Shov.'ing Offsets for i-Iasonry Footing Courses ......... 68 
 
 3. Timber Grillages or Rafts , . . . 71 
 
 4. Inverted Arches of Stone, Brick, Concrete or Reinforced Concrete. 72 
 
 5. Footings, of Structural Stec-1 Beams and Concrete , 73 
 
 Cast Iron Bases, Steel Pedestals, etc 76 
 
 Other Design Llethods for Steel Grillage Footings 77 
 
 6. Footings of Rejnforced Concrete Slabs 79 
 
 V/all Foot ings,. Bear ing, Shear 79 
 
 Bending, Design for Reinforcement .80 
 
 Interior Column Foot ings,. Bearing, Shear,. Bend ing 81 
 
 General Comment on the Design of Footings Under Interior Columns 82 
 
 7. Combined. Footings 83 
 
 Call Building, San Francisco 84 
 
 Washington jlonument ...... .84 
 
 Singer Building Foundati on . .86 
 
 Trapezoidal Combined Footings ................. 87 
 
 Combined Footings of Structural Steel I-bea'ms and Core re te . . .90 
 Tvvo Unequal Column Loads Supported upon a Rectangular Grillage 91 
 Two' Unequal Column Loads, the Greater Load at the Lot Line, 
 
 Supported upon a Trapezoidal Grillage of two ffiers of ffieams 93 
 Three or More Unequally Loaded Columns., in One Line,, Unequally 
 
 Spaced, Supported upon a Rectangular Slab 95 
 
 Partial Application of the Principle of Three .'.foments. .... 97 
 Eccentric Steel Beam Grillage Foundations, Native Sons 
 
 Hall, San Frcncis co - 99 
 
 Cantilever Spread Footings of Reinforced Concrete 100 
 
 References, Problems .... 101 
 
 Chapter 5. Sheefr Piling 104 
 
 Light Wooden Sheet Piling 104 
 
 Effect of Cohesion 107 
 
 Heavy Wooden Sheet Piling 109 
 
 Steel Sheet Piling .............' 
 
 Requirements for Metal Piling ..... 114 
 
 Spacifi cat ions for Steel Sheet Piling 115 
 
 Reinforced Concrete Shoot Piles .... 116 
 
 Hennobicue Shoot Piling , Fig. .55 
 
 Reinforced Concrete Sheet Piling; U.S. Naval Coal Depot, Tiburon, Calif. . 
 
 Extracts from the Specifications H" 7 
 
 Extracts from the Specifications for Pile Driving 
 
 Concrete Sheet Piles for Docks 
 
 An Analytic Problem . 
 
 The General Case., Continuous Spans . 
 
 Simpler Case, for One Continuous Span I 23 
 
 Practice! Case, One Simple Span 124 
 
 Additional References; Problems .... 
 
ill. 
 
 Chapter 6, Bearing Piles 127 
 
 Introduction , 
 
 Timber Piles, Timbers Available ............ 129 
 
 Specifications for Timber Piles ........ 129 
 
 Preparing Piles ..............,..] '.'.130 
 
 Driving Piles, .............. ,151 
 
 Pile Hammers ........ . . . . 133 
 
 Sinking Piles by Water Jet , . . . . . .1^5 
 
 Bearing Power Of Piles .............].] ] *156 
 
 l. r /here Driven to a Fir.i Bottom. ........... . . . . 136 
 
 2, ?/here No Bottom is Ree.ciied . , . . . . . . 156 
 
 Example ...,...'.....;....,......... 157 
 
 3. Usual Pile Formula . . . . , . . 137 
 
 Special Pile Formulae ......................... 141 
 
 Table by J.Foster Crowell ............... ..!.,.. 142 
 
 Specified Loads for Piles, Details, General Remarks . . . . . . . . 143 
 
 Preparation of Pile Tops, Capping of Piles .............. 146 
 
 Piles in Soft Ground ............ ....... . ... 148 
 
 Effect of Lagging on the Bearing Power of Timber Piles ........ .149 
 
 Screw Piles .......;.,........'............. 151 
 
 Disk Piles . . . ....... . . . . . . . . . . . . ....;. 153 
 
 Protected Piles ...*...................... 153 
 
 Chemical Preservatives for Timber . . . . . .. , . . . ..... '. . . . 154 
 
 Protected Pile Clusters . . . . ......... . ...... . . 157 
 
 Protected C^/linder Pile (Howard C. Holmes , Pctent Kol92006lO> 159 
 
 Sumnary .',,......... 160 
 
 Additional References ....... , % ......... i ........ 1601 
 
 Problens - Bearing Piles ............... ^ .... V ...... .161 
 
 Chapter 7, Concrete and Reinforced Concrete Piles ............. 163 
 
 Their Advantages and Disadvantsges . . . .............. .163 
 
 Classification - Concrete Piles .................... 165 
 
 1, Piles Loaded in Piece, . . . ................ 165 
 
 Raymond Piles ........................ 165 
 
 Simples Piles ............... ^ .....>.. 167 
 
 Clark Piles ....... ....... . ......... 168 
 
 Abbott Piles o ...:... ^ ................ 168 
 
 2, Piles Molded and Then Driven .:......... ..... .170 
 
 Hennebicue Piles ...................... 171 
 
 Corrugated Piles 171 
 
 Cole Piles ...... .................. 172 
 
 Specifications, Reinforced Concrete Pile . ........ .173 
 
 Protection of Embedded Steel end T'ood-. ............... 175 
 
 References, Concrete Structures Exposed to Sea T 7rter(o 1-17.) .... 176 
 
 Concrete Piles, References Kos. 18-22 ............ v . .176 
 
 Problems . ' .............. .......... ....... 177 
 
 uRT II, FOU1'H'.TIO:;S UhDLH '7..TLR. 
 
 C hr.pt er 8. Concrete Deposited Under V/ater ......... i ....... 178 
 
 Examples of Concrete Deposited Under r /cter .............. 180 
 
 1. Concrete Deposited by Chute. .... o ............ 180 
 
 Tremie Concrete .............. . , . , . . . . . .182 
 
 2, Concrete Deposited by Bucket . . 183 
 
 Lr.itr.nce .......................... 184 
 
 Additional References .......,*.**.> 185 
 
iv. 
 
 .Chapter 9. Coffer Dz.:is ..*.,.,.. .......... 186 
 
 Pivot Pier, Harlem Ship Cr.nr.l Bridge ...... . . 186 
 
 Variations of 'c"::3 Confer Bar- Process ....... . 190 
 
 Pivot Pier, Seventh Ave. 3v/ing Bridge, Few York City ...,.... 191 
 
 Dumbarton Bridge Foundations ....'........ , . . . . . . 191 
 
 Additional Eefererjces ...... <,-............. , . 192 
 
 Chapter 10. Open Caissons . . . . . ..................... 193 
 
 Pier III, Harlem Ship Canal Bridge, lev/ York City . . . . .'-... 194 
 
 Open Caisson Supported on Piles ................ ^ ., 196 
 
 Additional References ........ ^'. ............. ... .197' 
 
 Chapter 11. Pneumatic Caissons. ........... ......... 198 
 
 History of the Pneumatic Process .....>.......'....... 199 
 
 Pneu:-.r..tic Piles ........................... 199 
 
 Vacuum Process ..*..;.......;.*........., 199 
 
 Plenum Process ............................. 200 
 
 Caisson Design arc 1 . Operation ..................... 201 
 
 Sinking Weight ......................... 203 
 
 Caisson Flotation . . . . . ...... c ............ 205 
 
 Sinking Caisson . ....................... 203 
 
 Excavating Lifts and Pumps ......'.......'..... ,204 
 
 Physiological Effects of Compressed Air; Precautions in Kriidling Hen,, 204 
 Caisson Concrete , = 0.0....................... 205 
 
 Crib ",'ork aix 1 . Coffer Darn ....................... 205 
 
 Sew East River Bridge ........................ 206 
 
 Seventh Avenue Swing Bridge, Eew York City ...*......*.... 206 
 
 Additions.1 References ........................ 207 
 
 Chapter 12. Deep Well Dredging ........... . .00...... 209 
 
 Pougl-keepsie Bridge, Rev; York, OJtniber Crib Well ........... .209, 
 
 East Omaha Bridge, Ilissouri River; I.Ietr.1 Caisson ........... 209 
 
 Efewkesbury Bridge, Kev; South Wales .................. 216 
 
 Concrete Caisson Spillway, Calaveras Dam, Spring Valley Water Co. . 216 
 Additional References ......................* 219 
 
 Chapter 151 Deep Foundation Pressures .................. .220 
 
 References ..... ,'............'. % . ..... 220 
 
 Analysis .......... ^ . . . . . . . . . . ......... 221 
 
 Additional References ......................... 225 
 
FOUNDATIONS AJM'D MASONRY STRUCTURES 
 
 1 
 
 Chapter I. 
 
 EXAMINATIONS AND EXPLORATIONS 
 
 Structures of great weight and height usually give rise to difficult 
 foundation problems. The design of proper sub-structures for high office buildings 
 
 ,x 
 
 and bridge piers, when founded in treacherous material, often will present serious 
 cases. Before attempting the design of any important sub-structure, careful exam- 
 inations and explorations should be made of the mass of material in or on which 
 the work is to be founded. 
 
 In many engineering projects soil examinations are as necessary a part 
 of the preliminary study as are surveys and office computations. Results obtained 
 from testing foundation soils may materially influence, not only the foundation 
 design of important structures, but even their location. A conservative and 
 thorough engineer will insist on having the time and funds available for obtain- 
 ing ample and accurate data regarding the character of foundation material before 
 proceeding v/ith design or construction, sometimes- even before finally deciding on 
 location. In many important bridges the cost of the sub-structure may approximate 
 or exceed that of the super-structure; that is, may be one-half or more of the 
 total cost. As favorable soil conditions may affect, very largely, savings in 
 the cost of the sub-structure, a final choice of bridge site and truss type may 
 be influenced mainly by the results of foundation examinations. When the site of 
 a structure is definitely assigned beforehand, as for city buildings, a careful 
 examination of the soil becomes particularly important, since the general design 
 and scheme of foundation and thus that of the entire super-structure may depend 
 upon the exploration; for example, the site may require piles instead of footings. 
 It is usually inadvisable to proceed with a design, and still more so with the 
 actual execution of any important structure until adequate tests have completely 
 and accurately determined the character of foundation material. 
 

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 The methods pursued for making examinations will vary greatly with the 
 character and condition of the subsurfacd material and the depths to be reached. 
 They may be classified, in general, under eight principal headings, depending 
 chiefly on the type of the implements used. 
 
 1. Digging test pits 
 
 2. Driving pipes or solid iron rods 
 
 3. Boring with post diggers and augers 
 
 4. Test piles 
 
 5. Sand pump borings, either with or without casing 
 
 6. Sinking pipes by water- jet 
 
 7. Drilling v/ith artesian well tools 
 
 8. Diamond drill and steel-shot drill borings 
 
 ! Digging Test Pits. This method is used for important structures 
 where the strata are of uncertain character and the foundation bed is at no great 
 depth. It is slow and expensive so that it is usually employed only when the exact 
 location of the proposed structure has been determined. Pits are dug from 4 or 5 
 to 10 or 12 feet square, preferably to the depths to which the actual foundation 
 will reach, requiring in many locations constant pumping to keep the pits from 
 flooding by percolating water. The great advantage 6f this work is that it shows 
 the strata penetrated in their natural position and character, convenient for any 
 examination desired. If the pits are deep, it may be necessary to use heavy timber 
 bracing and lagging, just as in actual foundation pits or trenches to prevent the 
 sides from caving. The construction of this sort of bracing is discussed in later 
 articles (consult sheet piling and coffer-dams). The method, while costly, is 
 jnore satisfactory and certain than any other and has been used extensively for 
 important buildings and dams. It is frequently possible to locate test pits to form 
 a portion of the permanent excavation so that the labor of digging them is not 
 entirely lost. 
 
 2. Driving Pipes or Solid Iron Rods. This is a common method for shallow 
 or unimportant work. It is used satisfactorily to determine, for long trenches, 
 such specific information as the depth to rock or gravel. Data secured in this way 
 are oftea sufficiently reliable to fix the grades of sewers or drains or to enable 
 
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 contractors to bid intelligently on trench work. Solid iron rods or pipes from 
 3/4" to 1.5" in diameter can be driven in ordinary soils from 10 to 40 or 50 ft. 
 by repeated blows with a maul, the rods or pipes being constantly turned. As 
 ordinary water pipe will not stand much driving it is best to use double strength 
 pipe with hydraulic couplings. These couplings extend beyond and protect the pipe 
 threads. They also allow the sections of pipe to be screwed up till their ends abut 
 at coupling centers. When the pipes can be pulled at intervals they usually bring 
 up samples of the material to be found at the bottom of the test hole. If either 
 solid rods or pipes are used it is best to upset them at the lower end, in order 
 to decrease the friction of the sides while driving. The information obtained by 
 this method is rather .neager and liable to lead to erroneous conclusions. It is 
 difficult to distinguish the different strata except rocic and gravel. It is 
 difficult to penetrate compact formations, especially sand and gravel. In order 
 to force a line through gravel it is usually necessary to use at the lower end 
 a chisel bit of hardened steel, and to rotate the apparatus constantly. Boulders, 
 logs, roots or other obstructions may cause the rod to glance and wander, or the 
 pipe to split. More commonly they will stop the driving altogether and th$s may 
 be mistaken for solid rock. A number of holes rather close together should be 
 driven before definitely concluding that solid rock has been reached. Y/hen a 
 foundation bed profile plotted from these drivings shows erratic features, it is 
 wise to question the results and to resort to further investigation, either by 
 driving additional rods or pipes or by selecting a more reliable method of 
 examination. 
 
 The method is used more for obtaining negative than positive results. If 
 solid rock is desired for the foundation of an important structure, it is seldom 
 safe to rely upon information obtained in this way. If, however, a contractor seeks 
 the probable average depth to rock in a proposed sewer trench in order to guide 
 him in estimating a unit cost for the work, errors -nade by this method of testing 
 may not "be so serious since they are apt to be on the scfe side. The method is 
 
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 used as a preliminary to a more thorough program while the results obtained may 
 indicate locations where it is advisable to make other tests, or may assist in the 
 choice of final methods for continuing the exami nation. 
 
 3. Borings With Post Diggers and Augers. This is a safer method than 
 the preceding, especially in compact soils. Samples of clay or other stiff material 
 can be brought up from a great depth and satisfactorily examined, though they will 
 be somewhat more consolidated than in their natural state. If very loose 'or wet 
 surface soil is encountered it may be necessary to encase the top of the hole by' 
 driving light boards, (sheet piling, Chapter V), or iron or terra cotta pipe. The 
 holes may be 2 to 6 inches in diameter and may be illuminated by reflecting sun- 
 light into them by means of small mirrors. 
 
 Tools. A heavy carpenter's auger can be used for shallow borings. For 
 deeper work, steel prospecting augers may be made by twisting rectangular bars of 
 
 
 
 steel 1/4 to 1/2 inch by 3 to 6 inches and 3 to 6 ft. long. The stem is made 
 either from pipe or solid rods, sdrewed or locked together in sections 5 to 20 ft. 
 in length. A good stem can be made of double strength pipe 1 to 2 inches in diam- 
 eter, preferably with hydraulic couplings, provided with keys to prevent unscrewing 
 The top section may be square with a specially provided wrench (see Fig. 1) for 
 turning, or the wfeole apparatus may be easily tux-ned with pipe wrenches. It is 
 extremely difficult to bore through compact sand or grsvel. Narrow strata of gravel 
 
 can be penetrated by substituting a chisel bit for the auger, churning the vhole 
 
 rapidly 
 apparatus,, up and down. If the holes are more than 12 to 15 ft. deep, a derrick 
 
 should be used with a block and tackle or windlass to re ise the auger. A simple 
 three-legged derrick, or a two-legged derrick with guy ropes (see Figs. 2 and 4) 
 will suffice. Care should be taken not to bore too deeply before raising to the 
 surface. By coupling the stem and casings in sections ecch time the auger is 
 lowered., depths of 100 ft. or more can be reached. As the auger usually sinks 
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 formations, if its stem is marked each time it is let down into the hole, one can 
 prevent the tendency to go too far each time. For shallow holes 5 to 15 feet, 
 common post-hole diggers 6 to 8 inches in diameter may be used advantageously 
 if the material is stiff enough to prevent the holes caving in from the sides. 
 : ' .: H a *.lL Tower 
 
 Examinations for the Sather Tower foundations, University of California, 
 were made by hand boring, using the heavy tools just described (see Figs, 2,3,4). 
 This Tower consists of a steel frame with reinforced concrete floors and curtain 
 walls, the concrete wall backing being faced with granite and marble. The 
 structure is 302 ft. high with a base plan 34 ft. square at the ground line. Its 
 16 columns penetrate the ground to elevation -10 ft. , where their steel shoes 
 rest upon a grillage consisting of two tiers of 24" 80# I-beams; 12 beams in each 
 layer. (See Fig. 4A). The steel grillage is imbedded in a solid slab of concrete 
 48 ft. square, 8 ft. thick, the lower 4 ft. tinder the steel beams being reinforced 
 for shear and bending stresses. The foundation bed is at elevstion -18 ft. The 
 total dead and live weight resting upon this level is 13 760 000 Ib. , or 5950 Ib. 
 per sq. ft. , neerly 3 tons. A wind pressure of 20 Ib. per sq. ft. produces an 
 overturning moment = 25 000 000 ft. Ibs. , and a pressure transfer of 1360 Ib. 
 per so, ft., or a maximum qf 7310 Ib. per sq. ft. = 3.6 tons. With a 30 Ib. wind 
 the similar figures are 2040 Ib. per so. ft.; 7990 Ib. per sq. ft., and 4 tons. 
 
 Five borings were made; three, Kos. 1-3-4, being stopped by boulder 
 obstructions at the relatively shallow depths of 20, 18 and 29 feet; (see Fig.4B); 
 while borings Hos. 2 and 5 penetrated each 63 ft. The material traversed in all 
 cases is gravelly clay with boulders. Borings INOS. 2 and 5 probably struck sand- 
 stone. 
 
 Until the complete exccvations for the foundation were made, the engineers 
 
 were uncertain whether holes Kos. 1, 3 and 4 were stopped by boulders or by solid 
 rock. It was possible therefore that bedrock at the site shelved rapidly or con- 
 a precipice- 
 
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 With v/ell boring tools or the diamond drill such uncertainties would 
 vanish. In this case hand boring apparatus was selected b ecaiE e the price bid was 
 90 cents -per ft., while for power machines the minimum charge asked was &300. 
 for 100 ft. or less and >2.50 extra per linear foot for total length of holes 
 drilled exceeding 100 ft. Considerable was known about foundation material in 
 the immediate vicinity through earlier building. The records obtained left the 
 exact levels of rock bed uncertain. 
 
 
 
 Calaveras Dam. 
 
 In March 1918 the Calaveras Dam, Spring Valley Y/ater Company, failed. 
 The upstream toe was pushed into the reservoir by the presaire of the liquid 
 clay core- In order to repair the damage it became immediately necessary to 
 study the character of the material, not only in those portions of the dcm which 
 did not move, but also in the embankments which did. 
 
 In the softer clay portions hand augers inside steel casings were used 
 for a number of test 1-oles. These were sunk with difficulty because the clay 
 contcined many stones e.nd rock fills which had sloughed from the toes into the 
 liquid central core during the building of the dera and also at the time of the 
 failure. The following is the log of well No. 15. Sand pumps were used to lift 
 churned material from the well. 
 
 \7ell KQ_. 15; Drilling Log; Hand Rig_ C_. 
 
 Final location co-ordinates = XXXIV + 44, 23 + 45; elevation 661.4 
 
 Note: This v/ell is near two test pits dug on June 6, 1918, end is 
 surrounded by test piles Kos. 23, 24, 25, end 26. 
 
 June 12, 1918, second location. 
 
 - 8 ft. flowing clay 
 
 8 - 9.5 ft. clay end stones 
 
 9.5 - 1C ft. solid rock, drilled 
 
 10-13 ft. rock fill, herd packed. 
 
 At 13 ft. encountered large boulder; driller decided to move to new 
 location. 
 
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 June 14, 1918, third trial. 
 
 0-10 ft. liquid clay 
 
 10 - 29 ft. rock fill. Big boulder at 23 ft. Used 12.5 ft. 
 of 10" casing, then changed to 6" casing. 
 Material exceptionally clear of mud and 
 stands up well. Water at surface of ground. 
 Driller had to throw clo$.s of clay into well 
 to bring up stones on auger. Casing sometimes 
 3 ft. behind bottom of hole. The 6" casing 
 became jammed between 29 end 30 ft. and 
 could not be driven with the tools available. 
 Casing finally driven to 33 ft. at about 
 6:00 p.m. 
 
 29 -35 ft. rock fill. June 18, 6 p.m., well 40 ft.; June 
 
 20, 2. p.m., well 49 ft. deep. At 35 ft. 
 struck boulder, casing glanced by its side. 
 
 35 - 49 ft. rock fill. Difficult to pump material out of 
 
 well. 
 
 49 - 51 ft. gravel, said and some wet clay. Boring is 
 
 getting eesier. 
 
 SI - 58 ft. June 21. Rock fill and clay. At 58 ft. 
 
 encountered 9" of solid rock; drilled 
 through it. 
 
 59 - 62 ft. June 22. Rock fill; hole 62 ft. at 5:40 p.m.; 
 
 casing et 61 ft.; usually 1 to 2 ft. behind 
 hole. At 8:30 a.m. June 23, hole at 61 ft. 
 Material filled in 1 ft. over night. Y/ater 
 at 8 inches from top. 
 
 62 - 65. ft. Rock fill and clay. June 23, 4:45 p.m., hole 
 
 67.5 ft, , cesing 64 ft. 
 
 65 - 68 ft. Stiff clay with some sand end a few stones; can 
 
 hardly bore it with three men. Difficult to 
 get material up after boring. Material 
 squeezed in over night from 67.5 to 65 ft. 
 June 24, 6 p.m., hole 70 ft., casing 68 ft. 
 
 68 - 70 ft. Yellow clay end sand, some rock disintegrated 
 
 aautl Btotio. rt'ator inches. June 25, 8- a.m. 
 manorial equoczc<l in ovor night to 68 ft. ,. 
 
 At 72.2 ft. June -2S,: -lo*t jEOgor down rail, casing 68 ft. 
 
 Fiahedout auger end moved to v;ell No. 21. 
 Used 12.5 ft. 10" ceding, 68 ft. 8" casing. 
 Took 6 cr.mplec. Yfcter level 8". from curf.ce 
 of ground at hole. 
 
' . : J 
 
 '$'. 9< : 
 
 sa-lt .- Ut-te^ai 
 
 - .'; : --' ' :. tfllMfl 
 
 -- ci-?:\-.t3 f-y; -... iiii ,?? 
 :;>- ;.XC^ftC rs-:i^;;C .?1 .1 
 - ;.oe^ r ;od ..c--;^; :;:. . 
 : ij ;. . o.; a? u^ 
 
 -.. - 
 
 A 1 1 aw . . : c ,QI flajcft .ili ., , 
 
 -,. , -,, c._ . ' tlw . r ; : ; OS 
 ' I-^.: 1 ;-^:' ^Jj . :; ,10l'IUO< :.'...;; 
 
 '"c 
 
 '--'j'-ii:: -;{oo: Si/oa jc 
 
 .3:1. eve; I 
 
 : . ; i- . 
 
 i' ." 
 
 - 
 
 . J -' * 
 -TrrCf i , I'* 
 
 tt s; c^ f,.,.i/'. :uv,j -n. ' ^ 
 
 /-- .; - 1 to- t./ -vvui-, .' . 
 
 -:.K..,D ? ,-- 0e ,;;.-T.,.-3 "o: 
 
 <;:,., cVt ;} Isrei xe^.'/> . . 
 
 .r ";. 
 
 7*1 . ?S a 
 
 : i -uo r -?.'.-'i 
 
 3 :-'oo'0 
 .TTO j,c 
 
6, 
 
 .ANALYSES OF SAMPLES 
 
 
 
 
 Wet Sample 
 
 Dry Sample I 
 
 Sample 
 
 Depth 
 
 Moisture 
 
 Sand and , 
 
 Clay by 
 
 Sand and 
 
 Clay by 
 
 No. 
 
 ft. 
 
 , I 
 
 gravel % 1 
 
 subtract % 
 
 gravel % 
 
 subtract $> 
 
 1556 
 
 56 
 
 18.5 
 
 I 
 
 i 
 68.5 
 
 13.0 
 
 84.0 
 
 16.0 
 
 1560 
 
 60 
 
 17.2 
 
 64.0 
 
 18.8 
 
 77.5 
 
 22.5 
 
 1561 
 
 61 
 
 15.4 
 
 72.8 
 
 11.8 
 
 86.0 
 
 14.0 
 
 1565 
 
 65 
 
 22,4 
 
 34.3 
 
 43.3 
 
 44.2 
 
 55.8 
 
 1568 
 
 68 
 
 16.7 
 
 58.4 
 
 24.9 
 
 70.1 
 
 29.9 
 
 1572 
 
 72 
 
 18.1 . 
 
 39.1 
 
 42.8 
 
 47.9 
 
 52.1 
 
 Consult for CalaM'eras Dam failure Engineering News-Record, Vol. 80, 
 pp. 631, 679, 6$2, and 704; Vol. 81, p. 1158. 
 
 It is sometimes advisable to use wooden piles for the 
 purpose of making examinations at a foundation site. As many piles as may be 
 considered necessary are driven to refusal or as nearly as that can be determined, 
 in order to discover at what depths at different locations in the foundation bed 
 underlying rock or other hard stratum lies. Frequently it is necessary to use 
 shod piles. In work of this character, wherever possible, the pile should be 
 pulled so that the depth of penetration may be verified; otherwise it is question- 
 able whether the pile may not have been broken; or the point of the pile may have 
 wandered. A misinterpretation of results due to faulty data must be prevented. 
 
 A few test piles may be driven outside the proposed foundation plan in 
 order to determine whet depth of penetration it is advisable to specify for the 
 actual foundation. In this way it is possible to r.void specifying or ordering 
 piles of greater length than it is necessary to use. Test piles also are 
 frequently driven, either singly or in groups, and are then heavily loaded, to 
 determine their safe bearing po^or. -: For, important structures this is a necessary 
 part of the preliminary work as it determines the number of piles required; henca 
 governs very largely the design of the foundation; and may have considerable 
 influence on the typo of super-structure. The formulas for determining bearing 
 power of pilos arc doscribod in Chapter VI. 
 
" *-'< ' '' ' - c Jj 
 
 3 ?-^ o; "v 1 
 
 j M J . ii'j 
 
 .OT ':.-& ^.c : fi V.-! 
 
 , Q-; .JoV . c*r--;-. i -}fi-3v/s;i p. 'i i ; o en x; : fii f-tr;Ij ;1 rr.;! e ;:-. "...-.. 10' f^h.ic' 
 
 '.Bill! .q ,Ii- . Cj" . *i>? -..- ?vO ,C'. 
 
 ecf <;<*.-. ,;..-.: . :.ii|q x^j^r- sh.,ttiz no i ,t ;vb:vol 
 
 ^ti : 
 
 9cf Ju.Jc- 
 
 s.-fv . - Trri 
 
 -.-v:-, " - f ^:.. : . ^ .;. 
 
 -t ...iti$ 3 :, ..- . av"i:"o J'rrsc' 
 
 ir ..-! ;-.jTi-._.--9l * ; AU/T L. itH,*fiJ** #- -. ;-i 
 . frf.:io''i<:^Q2 i'V^r: v: 1 -^'-'^* 11 ,^'. - -.--': jo'l . v- i ,-Mis. 
 
EXAMPLES OP TEST PILE EXAMINATIONS 
 
 Harbor Development at South San Francisco. 
 
 For proposed harbor developments in San Francisco Bay near South San 
 Francisco, it became necessary to study the bearing power of the bay bottom to 
 determine (1) bulkhead construction (2) capacity of the soil to support hydraulic 
 fill and buildings, and (3) ability to sustain proposed earth jetties. 
 Nine test holes sunk by boring gave the following results :- 
 
 TEST HOLES 
 
 No. 
 
 Depth, ft. 
 
 Material 
 
 1 
 
 0-34 
 
 soft blue mud - still mud 
 
 2 
 
 0-34 
 
 soft blue mud - still mud 
 
 3 
 
 0-34 
 
 soft blue mud - still mud 
 
 4 
 
 0-62 
 
 soft blue mud - drill stuck 
 
 
 at 62 
 
 probably sand 
 
 5 
 
 0-35 
 
 soft blue mud - nearly lost drill, 1 ft. in send; 
 
 
 
 very fine, packed 
 
 
 at 35 
 
 find gray sand 
 
 6 
 
 0-50 
 
 soft blue mud 
 
 
 at 50 
 
 fine gray sand 
 
 7 
 
 0-35 
 
 soft blue mud - still mud 
 
 8 
 
 0-20 
 
 soft blue mud 
 
 
 20 - 20.5 
 
 fine green sand 
 
 
 20.5 - 25 
 
 sand and mud 
 
 
 25 - 30 
 
 mud 
 
 9 
 
 0-17 
 
 soft blue mud 
 
 
 at 17 
 
 fine green sand 
 
 The table shows that with few exceptions the site consists of soft blue 
 mud for depths of 35 ft. or more. The ground is compressible, both for the 
 harbor and tide lend areas. Under loading the ground flows laterally, indicating 
 thet supported structures should be of light weight. For instance, earth jetties 
 would be more permanent if stable, but the lighter weight of creosoted pile y 
 jetties caused their recommendation, though of greater cost and shorter life. 
 Bulkheads for piers, wharves and retaining dikes were designed to retain earth, 
 diminish lateral flow of mud and restrict settlements. 
 
 Eight test piles were driven. The hamaer used weighed 3200 Ib. , fe.lling 
 from 10 to 20 ft. The total pile penetration, excepting pile fco. 3, was large, 
 being 58 ft. or more. The average bearing capacity wes not high; for test pile 
 
. . 
 
 .: -o- cr;,- re 
 
 ' .%,. 
 
 v -, r rf , ;;+ 
 
 ; - /v:ij 
 
 J-7". - -.i 
 
 /, .^JL.'.:; - :j. ; -j.-/'J 
 
 '- - - : - ~ '.' '-. 6.-;.: ! j-i 
 
 - r ' '' "' ' " ''' : - !!. e;, ;' &; . 
 
 --' -' " , 2f. ;V - V; V 
 
 ~ ; '^ ';. C ..f ^ 
 
 -.iLi:: - jyr j. -..',: t>;r 
 
 er. , 
 
 ;' c - ' 
 
 ."- 
 
 j.j!>X- _- .'_: \;_ i-Li i 
 
 .- :",', 
 x^-i-O " t ^ -y 
 
 d.'i:* 
 
 J i ^= . -; : .i- ^r i.;fi , -j._- _ : . ;_, ..., , 
 
 v - - fA. -.. , ..' ;. 
 
 o^cs-i..lc , Ww,-*s 
 
 
 ... fe 
 
 " : 
 
Eo. 6 it was exceptionally low. 
 
 JBEAKING PC77SEL 0? r ;'I 
 
 PI^ES 
 
 No. j Penetracion, ft. Beaming Pov/er, 
 
 Tons 
 
 1 
 
 58.5 
 
 12.7 
 
 
 2 
 
 61. 
 
 11.7 
 
 
 5 
 
 37.6 
 
 35.0 
 
 
 4 
 
 59, 
 
 35.5 
 
 
 5 
 
 58. 
 
 33.0 
 
 
 6 
 
 56.7 
 
 3.5 
 
 
 7 
 
 60 ' 15.0 
 
 
 8 
 
 75 25,5 
 
 
 As examples of the actual field data the fecords for tost piles I*os- 3 
 
 I 
 
 and 6 are submitted: 
 
 Examination of Site , South San Francisco Harbor Project 
 Test Pile t.o. 5 
 
 Nature of soil - soft blue niud on surface 
 Condition of pile - sound 
 
 length = 61 ft. 8 in. diam. at middle = 10 in. 
 
 diam. at butt = 13 in. difui. et point = 8 in* 
 
 Time of Test, Feb. 2Q, 1912. Began driving 9:30 a.m.; finished driving 
 10:30 a.m. 
 
 Penetration, ft. 
 
 18.85 
 20.75 
 21.60 
 22.40 
 23.00 
 23.75 
 24.50 
 25.25 
 25.90 
 26.60 
 27.35 
 28.10 
 29.00 
 29.85 
 30,50 
 31.35 
 32.00 
 32.70 
 33.15 
 33.60 
 34.05 
 34.95 
 35.55 
 
 Fall of H.m.'.ier a ft. 
 
 7. 
 
 4 
 
 to 
 
 3.3 
 
 
 9. 
 
 3 
 
 to 
 
 10. 
 
 1 
 
 10. 
 
 1 
 
 to 
 
 11. 
 
 
 
 11. 
 
 
 
 to 
 
 11. 
 
 5 
 
 11. 
 
 5 
 
 to 
 
 12. 
 
 3 
 
 12. 
 
 3 
 
 to 
 
 13. 
 
 
 
 13. 
 
 
 
 to 
 
 13. 
 
 8 
 
 13. 
 
 8 
 
 to 
 
 14. 
 
 4 
 
 14. 
 
 4 
 
 to 
 
 15. 
 
 1 
 
 15. 
 
 1 
 
 to 
 
 15. 
 
 9 
 
 15. 
 
 ,9 
 
 to 
 
 16, 
 
 6 
 
 16. 
 
 6 
 
 to 
 
 17, 
 
 5 
 
 17. 
 
 5 
 
 to 
 
 18. 
 
 4- 
 
 18. 
 
 4 
 
 to 
 
 19. 
 
 1 
 
 19. 
 
 1 
 
 to 
 
 19. 
 
 9 
 
 19. 
 
 9 
 
 to 
 
 20, 
 
 5 
 
 20. 
 
 5 
 
 to 
 
 21. 
 
 2 
 
 21. 
 
 2 
 
 to 
 
 21. 
 
 7 
 
 21. 
 
 7 
 
 to 
 
 22. 
 
 1 
 
 22. 
 
 1 
 
 to 
 
 22. 
 
 
 
 22.0 
 
 to 
 
 23. 
 
 5 
 
 18. 
 
 5 
 
 to 
 
 IS. 
 
 1 
 
 19. 
 
 1 
 
 to 
 
 19.3 
 
 iio. of Blov/s 
 
 4 
 
 5 
 
 5 
 
 5 
 
 5 or 6 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 
 5 
 

 . V -. 
 
 '-..- 
 
11 
 
 Penetration., ft. Fall of Hammer , ft . Ho. of Blows 
 
 35.75 
 
 19.3 
 
 to 19.7 
 
 5 
 
 36.20 
 
 19.7 
 
 to 19.9 
 
 5 
 
 36*40 
 
 19.9 
 
 to 20.1 
 
 5 
 
 36.60 
 
 20.1 
 
 to 20.8 
 
 10 
 
 37.30 
 
 20.8 
 
 to 21.1 
 
 5 
 
 ^7 fiO 
 
 
 
 
 
 
 
 
 Kote: Stopped driving because the pile point appeared to be splintering 
 ind brooming. 
 
 Fall of tide during driving about 1 ft. 
 
 Test Pile Ho. 6. 
 
 Nature of soil - soft blue mud. 
 Condition of pile - sound 
 
 length of pile =63 ft. in. die.ni. at middle = 10 in. 
 
 diam. at butt = 12 in. die.ra. at point - 7.6 in- 
 
 Time of Test - Feb. 27, 1912. Began driving at 8:00 a.m.; finished 
 driving at 8:45 a.m. 
 
 Penetration, ft. Fall of Hamaer. ft. Mo. of Blows 
 
 29.4 9.6 to 25.3 5 
 
 45.1 20.7 to 32.3 
 
 56.7 19.7 to 24.0 
 61.0 
 
 At penetration 61. o a puach wes put on but was not successful ss driver was 
 not prepared. 
 
 63.8 14.2 to 17.0 
 
 Bearing Po-.ver Computations 
 To compute bec.ring pover, Engineer ing l\ie\vs formula vc.s uced, see Chr.p. VI, 
 
 equation 5. 
 
 r = 1.8 tfh 
 
 3 + 1 
 
 r = pile resistance in Ibs., \7 = hc.mmer veight in Ibs., h - hr.nmer fall in ft., 
 a = pile penetr: tion in inches. The coefficient 2 in the usual formula is replr. 
 by 1.8 on the resumption thc.t ten per cent of the hrmmer fell ia lost in friction 
 civl from other causes. 
 
 For pile Mo. 3, s for the Ir.st 5 blo-./s is one-fifth of 37.6 - 37.3 = 0.3 
 ft., or 0.72 inches; V/ = 3200 lb., h - 20.95 ft.; hence r = 70 ' ^b, or 35 tons 
 
*- v .-,-. ........ ,* r , ' 
 
 wi Jt3. j.iZii, - --*:_-. . 
 
 "; oo T-C. 
 j ,OS o:r y /f 
 8, OS C' - , ,. 
 .,0i ; 
 
 
 o, ,r. 
 
 AX'.. ...: ' i :,. - _*: i-^ . : : 
 
 T.Vv, ' - vii." :"' i?i_'- X J 
 
 i. C.U. io - 0': 
 
 c -civ c: 
 C -.,. id 
 
 t- .->-; -^ - - to.-. - 
 
 - .t . - , *; .t -' ~ i Y r -; r -j- ^ u-i :_; 
 
 C.V1 ; 
 
 1- .. 
 
 :;j .i, ./.. . J . ~ Ci 
 
 ^ay erfj - 
 
12. 
 with a safety fcctor of 6. For pile No. 6, r = 6900 Ib. , at 56.7 ft. penetration. 
 
 In studying the above field reoorde it. is to be note: that pile Ho. 6 
 represents the worst cc.se ant! pile No. 3 one of the more favorable cases of bear- 
 ing capacity on a treacherous foundation site. Some of these piles sanfc under 
 their own weight an-", the dead weight of the hammer from 10 to 20 ft. or more 
 and also in the progress of driving. For instance, pile Ko. 6 penetrated from 
 29.4 to 45.1 ft. in 5 blows; an average of about 3.1 ft. per blow. At a depth of 
 62 ft. the same pile, urT.er a hrmmer fall of 15 ft,, in the finr.l five blows, was 
 driven 2.8 ft., an average of 0.56 ft. per blow. On the other hand in the begin- 
 ning of .driving pile No. 3 in four blows penetrated from 18.85 to 20.75 ft., an 
 average of 0.5 ft. per blow. Pile No. 3, under a hammer fall of 21 ft. recorded 
 a penetration of 0.3 ft. from the last five blows, or an average of 0.06 ft, 
 per blow. 
 
 Auditorium Building, Oakland, California 
 
 As another example of foundation examination bj test piles, reference is 
 made to the Auditorium Building, Oakland, California, which structure rests on 
 filled ground south of Lake Merritt. Fig. 40 shows the location of six test piles 
 in an area 186 ft. x 400 ft. The field recor-' for only one of these piles is 
 
 given below. 
 
 Test Pile, Ho. 6. 
 
 Date - July 22, 1912 butt end = 14.5 in. 
 
 Dimensions - tip end = 8 in, length = 72 ft. 9 in. 
 
 Mo. of Blows Drop of Hammer Distance , Total Penetration i Remarks 
 
 21 
 
 5 ft. 
 
 : 23' 
 
 0" I 
 
 23' 
 
 0" soft 
 
 7 
 
 5 
 
 i 6 
 
 o \ 
 
 29 
 
 
 
 15 
 
 10 
 
 11 
 
 
 
 40 
 
 
 
 18 
 
 12 
 
 11 
 
 i 
 
 51 
 
 ' hard mrterial 
 
 16 
 
 12 
 
 3 
 
 6 
 
 54 
 
 6 
 
 17 
 
 14 
 
 2 
 
 2 
 
 56 
 
 8 
 
 10 
 
 20 
 
 1 
 
 5 
 
 58 
 
 1 
 
 10 
 
 20 
 
 1 
 
 4 
 
 59 
 
 5 
 
 Stjopped driving; pile went down 1.6 in. for the last blow; pile started to 
 split. Berring value 
 
 r = 2 x 2550 x 20 = 19.5 tons- 
 2.6 x 2000 
 
..; . 
 
 '- r 
 
 .-.-, 
 
 .-I c- - 
 
 - 0- : ^C 
 
 ' ' 
 
 : .- 
 
 . . . ; ; 
 
 r - - 
 
 A * x.' 
 
 ? 
 
 "civ; . ?""- 
 
13. 
 No reduction was here made for loss of energy in the drop h. 
 
 This steel frr.med, concrete and masonry building has its structural 
 columns supported upon reinforced concrete footings which in turn act c.s grillage 
 cr.ps to clusters of piles driven to depths of from 60 to 75 ft. 
 
 Test Piles ot^ Cqlaverr s Dam. 
 
 Eighty-four piles v.ere driven in r. centre 1 pool of clay. From these 
 records end the logs of r. number of v/ells estimates v;ere male for the quantities 
 rnd locations of material o Different grades of solidity. The field, notes for 
 one of these piles is submitted. 
 
 Test Pile l<o. 82. 
 
 Location XXXVIII +29; 27 + 35. East line. Elevation of ground 658 ft. 
 Pile dimensions: V/eight of pile = 1420 * 100 Ib. 
 
 length = 41.83 ft. 
 
 butt circumference = 3.38 ft. 
 
 middle circumference = 3.00 ft. 
 
 point circumference = 2.58 ft. 
 Nature of ground = soft, wet surface of submerged portion of clay pool 
 
 in dam. 
 
 Penetration due to ov/n v/eight = 9.0 ft, 
 Penetration due to hr inner v/eight = 7.5 ft. 
 Total stc.tic penetrrtion = 16.5 ft. 
 
 Driving Log 
 
 . B10\7 
 
 i\o. 
 
 iDrop:. of 
 ''hammer, ft. 
 
 Pen. Pile TOLal 
 per blov; ft. pen. ft. 
 
 Avg, of 5 blov/s Elev. 
 
 Re narks 
 
 '.rop ham. Pen, of of pt, 
 ft, pile, ft of 
 pile 
 
 static 
 
 
 16.5 
 
 642 
 
 Date 
 
 :. 
 
 3.0 
 
 1.2 
 
 
 July 22. 
 
 2 
 
 15.8 
 
 2.8 
 
 
 1918; 
 
 
 
 : 14.0 
 
 1.7 
 
 i 
 
 time of 
 
 4 
 
 16.5 
 
 1.6 
 
 
 start 
 
 5 
 
 15 . 3 
 
 1.5 25.5 
 
 12.9 1.8 632 
 
 10:25 
 
 5 
 
 . 17.6 
 
 l.G 
 
 a . m . 
 
 7 
 
 16.1 
 
 1.4 
 
 
 
 8 
 
 16.6 
 
 1.1 j 
 
 
 c 
 
 17.4 
 
 1.2 
 
 
 
 1C 
 
 17.8 
 
 1.3 32.1 17.1 1.3 G26 
 
 
 11 
 
 - 18.3 
 
 1.3 
 
 
 
 12 
 
 18.5 
 
 0.5 
 
 
 
 13 
 
 . 19.0 
 
 0,6 
 
 
 
 14 
 
 : 19.0 
 
 0.4 
 
 
 
 15 
 
 ' 19.8 
 
 0.7 35.6 
 
 18.9 0.7 623 
 
 
- ' : 
 
 - ; -- - 
 '*: " ' ' 
 
 :0:: a 
 
 
 i : .v".- : i 
 
 .v ^ 
 
 '-'" ' 
 
 ,;j ,v--I_ - 
 re .-.V.- 
 
 '.v* j^-- 
 
 .-__ . 
 
 t .; -C Ov f .:> 
 
 . .. ' 
 
Driving Log Test Pile Ho. 82, continue-: 1 . 
 
 14 
 
 J Blow 
 
 rDrop of 
 
 jPen. pile j Total pen-r 
 
 Averr.ge of 5 blows 
 
 Elev. 
 
 fiemarks 
 
 } No. 
 
 .hammer,ft. 
 
 ; per blow : etrr.tion 
 
 rlrop ham- pen. of ; 
 
 of 
 
 
 \ 
 
 i 
 
 ft. ft. 
 
 mer, ft. pile, ft* 
 
 pt. 
 
 
 j 
 
 
 
 
 of 
 
 
 
 
 
 . 
 
 
 
 
 I 
 
 i 
 
 
 
 pile . 
 
 
 : 16 
 
 18.8 
 
 0.4 
 
 
 
 
 ! IV 
 
 19.0 
 
 0.6 
 
 i 
 
 i 
 
 
 18 
 
 18.9 
 
 O.G 
 
 > 
 
 i 
 
 
 19 
 
 17.2 
 
 1.1 
 
 t 
 j 
 
 
 s 
 
 20 
 
 16,5 
 
 0.9 39.2 
 
 14.1 0.7 
 
 619 '. 
 
 Time of enc. 
 
 : 21 
 
 18.0 
 
 0.9 
 
 1 
 
 
 10:33 a.m. 
 
 : 22 
 
 8.3 
 
 0.4 40.5 
 
 15.8 0.78* j 
 
 618 ! 
 
 Sticking 
 
 
 
 
 
 ! 
 
 out 1.5 ft. 
 
 1 
 
 
 i 
 
 
 i 
 
 *Avg.of 
 
 j 
 
 
 
 
 | 
 
 last 5 
 
 
 
 
 
 
 bl ov;s . 
 
 Berring power of pile = 1.8 x 2500 x 15.8 = 3.4 tons 
 
 (9.36+1) 2000 
 
 5- Borings \7ith the Sand-Pomp. Sand, when dry or compact, is one of the 
 most difficult materials to penetrate. It is readily traversed when wet. The 
 sand pump (see Fig. 3) is a hollow cylinder 1 - 6 ft. in length r.nd 3 - 8 or 10 
 inches in diameter, fitted with a simple flap valve at the bottom, opening in- 
 ward; the whole suspended from a stout rope or wire, or coupled to rods or pipes. 
 The sand pump is lowered into s. hole, the latter containing v/ater at the bottom. 
 The pump is churned rapidly up and down by hand until it partially or wholly 
 fills with mud or sand and water. It is then drawn to the top where the collected 
 material is examined rnd emptied. The method determines the material passed 
 through but does not exhibit it in its natural condition. For exrmple, stiff clay 
 is churned into soft pasty mud. The condition of the .material , especially its 
 compactness, may be inferred however by an experienced operator from the diffi *.'-. 
 culty and rate in sinking a test hole. 
 
 Quicksand, the most troublesome of all foundation materials, is composed 
 of excessively round sand grains mixed with water. If this material, in its 
 native condition, be found held between layers of clay, it may easily be taken 
 for compact sand, giving no intimrtion of its dangerous character. Fine sand shouln 
 
.?.- 
 
 -,-VC-LJ 
 
 -j-oo K? , ''.'tv/ t 
 
 - 
 
 r, -..;j i :; ijr R . .. -7 .'.', ^ri- ': VJ 
 -* .' 
 
 ..>-:--.. ;.noo ci . -; r 
 
 II.: 
 
 : .,'f --t ? 
 
 J; . ..'-.0 ". 
 
15 
 
 be very closely examined with a microscope. A solid core, showing the actual 
 condition of the material in place at any depth desired may be obtained by 
 driving down a smaller open ended pipe to the bottom of the hole excavated by the 
 snnd pump. It is sometimes necessary to use a vacuum pump to keep and lift the 
 .material in this drive pipe. If the material is soft, the hole must be cased 
 with iron or terra cotta pipe, which usually will have to be driven by hammering 
 with a heavy wooden maul, a lever press, or a light improvised pile driver, the 
 material being simultaneously excavated from the inside of the casing, and a 
 little in advance of its botto m, with the sand pump. The apparatus will not pen- 
 etrate gravel and goes very slowly in compact or indurr.ted clay. It gives the 
 best results in comparatively loose soils using light casing. It is ersily 
 stopped by boulders, logs, roots or other obstructions. 
 
 Sand-Pump Borings 
 Civic Center, San Francisco 
 
 The Civic Center, Van Ness Ave. and Market St., San Francisco, presents 
 a foundation site in what was once swamp. The ground water level is within 10 ft. 
 from the surface. For depths of 100 ft. or more borings encounter sr.nd r.nd clay 
 in lasers with numerous thin seams of peat or soft vegetable earth. The site is 
 compressible. The City Hall and Auditorium buildings rest on reinforced concrete 
 footings with a soil pressure of 2,5 to 3.0 tons per sq. ft., figuring dead load 
 and 10 Ibs. per sq. ft. live load on each floor. Figs. 4D f.nd 4E show ten borings 
 for the City Hall and eleven for the Auditorium building; also typical profile 
 foundation sections assembled from the boring records. As examples of the field 
 notes the logs are submitted for hole No. 6, City Hall site, and No. 1, Auditorium 
 site. 
 
 Record _of_ Boring, City Hall Site, San Francisco 
 Hole Ho. 6, October 30, 1912 4 elevation top of hole = 51.51 ft. 
 
 Depth. Ijatnre of Soil Jar No . 
 
 12 '6" dry yellow sand 1 
 
 12 6 water 
 
 19' yellowish wet sand 2 
 
. J..ii*3'; 3;i* 3fi jr.xrf a , OIGC, in/tja A .: cd 
 
 " i. .jF'-ffiTS ,d"0:> fiirs A .tv'jo?-";ur." : rftrv.- : -- =; ' .- 
 
 ..#<?.. jo > :r-,;Mc, i ^rf./^w^&gxtufl) .jJJro.b Y , go; . nO-iJibnoo 
 
 - ''-' - ' ' '- ! '*"- u-- ^"X-X-'V 1 / It '-. ^* ,-f' j j OC."i.i.y '-! * , 7 ' "' -' ' , 
 
 !? i'a. &e?ysoxs aiorr aiiilc .TEC . . . . 'oi gaivI-J) 
 
 ' '. . ;.. *:;:.. ,~t&' ;,..! ' . -f.\ 
 
 - .?* -WlijT- 0-' 
 
 Ji& : -,j c ; nk.r Vj;;,-: .: --;;j c? -^-.-.aoov- : .-. . ^t rl <$... 
 
 ^^Z*??^^^?**,; ,-.. sf^^rf^f'V^r'.O^- -^f^ :! .r's?* 
 
 .ii -^ t r?v:-i:> c-.t' -.:J 9V:x-.In-' Kilc-us;; ,ri;u^v . -. ' ic noii rfrfi'.v 
 
 vtv:,i :? -i evr5r. :rr.* ;&.:::.!! osftT 1 ,*r. -? ?vo ;;if- 
 
 .*^ : ' t^J V Tte' rliv-, P: . . j - : i ^-' 1O .38510 TOVOi : ,i. - J0.' r ^--eri Jl.fiJtW 
 
 C ' -i ''' , r / . i". T I '-! .i ^ '- vi--r !> :..'/.! - , . . > , _ ." 
 
 fl 
 _. - r -,;V-" - =,.-.- . .- - .' '*? vJr 1 rf-',,.!T;>f^ 
 
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 . !>'.'-- -^T- ; ^-t.~ t ^B-r.^-^'P-'*-^ S^-i.'i?Cf >; .. . 10? . SO-YiT'.'S Cfrtd' .TlCli 
 
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 M-i^P-'t'^-QASjWJ-* .', ^E-:.'I . -. . '.- ta". -' 
 
 -' -^-* soTxtnJ:iyi -'.o ;?>. i .ix/j. i " : .'; !:?. at..., 
 
 ^r c J^ ^ v 8Ji> s*ixiiiSiil ..**^ o-'- -Ort. 0..?> oi 
 
 -f-i E.TC* k;.-.. '.v c... i-u , _. -.. . . j-.:-- 
 
 y'i^:'c[._.;;;i?,..\vL:p:a { t . .. . . n,o ;. ?<5 j ' : fl ' 
 
 --. "^t'yj o.-:'. ,... ... 'irtt -iol 
 
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 t .E ... ' .lyr.r/oJ 
 
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 "- * v .- '* L - ' - J - t ' f *' ' . lOl *,', , . ... ". 
 
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16. 
 
 Depth Nature of Soil j ar Ko. 
 
 19' 6" decomposed vegetable substance, hard 2 
 
 25' yellowish wet sand 3 
 
 47' grayish wet sand 4 
 
 47' 6" decomposed vegetable substance, hard 5 
 
 78' fine grayish wet sr.nd 6 
 78' 1" 1-in. strata decomposed vegetable substance, hard 7 
 
 fine grayish wet sand 8 
 
 80* encountered firm blue clay 9 
 
 104' tough blue clay 9 
 
 108' tough yellow clay 10 
 
 109' soft yellow clay and sand 11 
 
 coarse sand, yellow clay 12 
 
 coarse sand, and yellow clay 12 
 
 122' hard sr.ndy yellow clay 13 
 
 Record of Boring, Auditorium Site A San Francisco 
 \7ell Ko. 1, Jan. 1913, elevation to? of hole - +47.60 ft. 
 
 2' 0" fill 
 
 2' 6" soil 
 
 18' 4" yellow sand (dry) 1 
 
 gray s and (wet J 2 
 
 67' 11" green sand (v/et ) 3 
 
 68' 1" soft vegetable errth 4 
 
 70' 9" green sand (wet) 3 
 
 71' 9" vegetable earth 5 
 
 73' 9" green clay 6 
 
 80' 0" hard sandy clay 7 
 
 81* 0" hard green clay 8 
 
 92' 8" green sand (hard) 9 
 
 These borings were all mrde with a hand power apparatus. The 6-in. 
 casing was sunk under pressure from a wooden lever . The boring tool or plunger 
 was operated by using a small derrick similar to ffig. 2, to which a windlass was 
 attached. At intervals the .naterial was lifted with a sand pump; sonples being 
 taken as above indicated. 
 
 In some holes in hard ground, as those at Bcalt Hall and the Agriculture 
 Building, cited under heading No. 7, it was necessary to supply water from time 
 to time to ease sinking. At the City Hall and Auditorium sites the ground water 
 and loose soils made this unnecessary. 
 
 6* Sinking with V/'ater-Jet. In this method a pipe 2.5 to 6 in. diameter 
 is driven into the soil r.nd a smaller pipe inserted inside, through which vr.ter 
 is forced under pressure. 
 
:. ' - -.; 
 
 
 srf "a'SIqarJB i 
 
 fV-hi-j^X/V:^ 
 
 t t. - 
 
 ----.- y ,.*-., . 
 
 ' - - ^* 
 
 -'"'' 
 
 iOTfi, -.;.:. 
 
17. 
 
 Plant required consists of two sizes of screw pipe, cut to convenient 
 lengths of 6 to 20 ft., and threaded at "both ends, a simple frame or derrick 10 
 to 20 ft. high, fitted with block and tackle, or winch, to enable a 100 to 200 
 Ib. weight to b e raised a few feot. v.^tically and dropped; a force pump, usually 
 worked by hand, with heavy rubber hose connections. The procedure is as follows: - 
 the outer larger pipe is driven into the ground a few feet by dropping the weight 
 on a cap temporarily screwed to its top. The smaller or v\e.sh pipe is then inserted 
 and water forced downward through it under pressure flowing up in the annular 
 space between the pipes, bringing to the surface dislodged mud, sand and pebbles 
 where they maybe caught in a bucket and exan ined after settling- 
 
 If it is desired, to examine material in the condition in which it is 
 found, drive down an open ended pipe a foot or two and pull up a cylinder of 
 clay or sand. Vacuum is sometimes used to retain the specimen cylinder of 
 material in the inside of the drive pipe. 
 
 Hydraulic or inside couplings should be used if much driving is to be 
 done. If the soil is reasonably firm the wash pipe may be dispensed with and 
 one pipe connected directly to the force pump, the vr.ter and loosened material 
 rising to the surface in an annular spree which is formed around the pipe. The 
 pipe i:T.y sink of its own weight, or it mr.y be necessary to alternately raise 
 and lower it and perhaps rotate it to secure the best reailts. The pump should 
 be worked continuously as the soil is apt to settle comprctly r round the pipe 
 if the sinking is stopped* even for a few minutes. This method is probably more 
 rapid and economical where it C'nbe used, than rny other, A derrick is un- 
 necessary, though it is advisable, if depths grerter than 30 to 40 ft. are to 
 be reached, in order to permit the use of long lengths of pipe. Fig. 4 (Engineer- 
 ing iiews, Vol. 21, p. 423)shows a simple frame suitable for this work or for a 
 sand pump, 
 
I ;UuOO 9' 
 
 *i ; --<!>.i> 
 
 . 
 
 ec i 1 si :! 
 
 fii - 
 
 ioc 
 
 PaC ; ;iol ur 
 
13. 
 
 7. Drilling with Artesian V/ell Boring Tools. For a complete discussion 
 this subject in itself would require an extensive description. It cr.n only be 
 mentioned briefly here. It is employed for special cases of deep or difficult 
 foundation tests where simpler methods are deemed insufficient. The apparatus 
 consists principally of heavy steel drills, suspended by steel cables or' ropes 
 and raised and lowered rapidly by hoisting engines, together with a special form 
 of pile driver for driving iron or steel casing. Large numbers of other tools are 
 used for special purposes or particular formation; such as sand, pumps, ehisel 
 bits, augers. Holes can be drilled through any formation except the hardest rock 
 and to depths of 3000 ft. or more. The casing is usually from 4 to 18 ins. in 
 diameter. The reader is referred to descriptions of apparrtus for s inking 
 'artesian wells for mter, oil or gas; he should also consult the trade literature 
 
 for artesianwell boring tools. Cf. V/ater Supply Paper No. 257, U.S.G.S. ; a 
 
 ty 
 descriptive and excellent-/ illustrated article on "V/ell Drilling Methods" by I. 
 
 Bowman. This paper describes the diamond drill also. 
 
 Sinoe these tools may sink wells readily to 3000 ft. and more, the 
 usual foundation examination offers a simple application because the depths 
 required for foundation explorations rarely exceed 100 to 200 ft. In ordinary soil 
 formations it is commonly possible to dispense with any driving apparatus and to 
 sink the casing by weighting it while it isb eing worked back and forth with 
 plenty of water to decrease the friction of earth on its sides. A simple lever is 
 frequently used to force the casing down by loading its outer end with bags of 
 sand. The casing may be heavy screw pipe, mr.de of steel or cast iron. If inside 
 couplings are used, there is less friction on the sides. The "stove pipe" casing 
 more commonly used consists of two concentric cylinders of sheet iron or steel, 
 one of them fitting closely inside the other. These are lap riveted or welded 
 in common lengths of 2 to 3 ft,, frequently being made from sheet iron or steel 
 at the site of the work. The casing is formed in place so that the inner and outer 
 
 casings break joints, forming a continuous column stiff enough for ordinary 
 purpose So 
 
:-!-- -.-; - ^&3r#&: 
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 ocU: c/^rt^^v^-i ^ --vie :. . --j8 -: 
 
 .: ,-iy-rov s '-Vc '-^j. .-scv.- -aio .' ? , ..- 
 
 i 3 i:i'.f '^.^^'..i'.Mi >/'i W.-s-i-:-. : -or/o^; 
 
 ,,.'!cf ;:o-. - Ir-.- ;->i::c; :.Ji ; . . i '.. ' - t v t f .r. ... : ..[ 
 
 i"''' 1 .' '' .: ;: V; :,'O.'. :.-' " '" '"--' :> 
 
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 : f ." J 5.: &*i .-i :::-., 
 .: -.. '&t . '. . 
 
19. 
 
 Boalt Hall , Universi ty _of California 
 
 Fig. 4F indicates four borings sunk in 1909 on the site of Boalt Hr.ll, 
 University of California, using machine power well tools for 6-in. holes. For 
 part of the depth it vr.s necessary to sink casings. At intervals the material was 
 taken out with a large sand pump, 
 
 Agriculture Hall, University ojf California 
 
 Borings of similar nature were nade in 1910 for the Agriculture Bldg. , 
 University of California. In this case one hole was driven 42 ft. to test the 
 nature of the foundation soil which was gravelly clay for the entire depth. The 
 three other holes were stopped at much smaller depths. In every case the top 
 soil was adobe; the gravelly clay, yellow, and identical with that found at 
 Boalt Hall. 
 
 Calaveras Dam 
 
 In July 1918 about 25 wells were sunk by power rigs. The following is the 
 record of a well driven in the center or core of the dam. 
 Well No._23_; Drilling Log; Power Big A. 
 
 Location XXXIV + 00 Elevation 661.3 (referred to water surface; 
 22 + 21 ground 0.1' lower at well) 
 
 July 1, 1918, started drilling at 4:50 p.m. 
 
 0- 8.5 ft. liquid clay, very wet and muddy due to nearby excavation 
 
 and water submergence 
 8.5 to 14 ft. rock fill; this material will-not stand up; caves in 
 
 readily, 
 Hole 14 ft. Casing 14 ft Uater at ground surfrce. 
 
 July 2, 1918. 
 
 14 to 51 ft. rock fill; ;nr.teiir.le aves in re.-dily, but stands better 
 
 than that between 8.5 and. 14 ft. Casing hrd to be kept 
 
 close down. 
 51 to 57 ft. rock fill with some soft clay. Y/ill not stand up. Took 
 
 a sample at 57 ft. Material flows into casing. 
 57 to 60 ft. clay, rather stiff; sample at 59 ft. This clay is of 
 
 medium stiffness. 
 
 Hole 60 ft. Casing 60 ft. " : Jater at surface of ground. 
 July 3, 1918. 
 
 60 to 68 ft. sluiced shale and clay. Took samples at 66 ft. 
 
 68 to 74 ft. sluiced shale with very little clay, will not str.nd alone.. 
 
^^.. ,,-.... .-, ;.:-- 
 
 -:>- : ..-U:- ::-. : 
 
 joU-\- " " 
 
 j .; - :!: . " --'. ' ., ." 
 
 ; .- . '- '" ": 'fpj 
 
 --' ! ' S- -w-wotf 'jf- ) ^Sins- : ' ^i-c.- 
 
 -b-'e.'-'lV fr ^ ' .TV-: l 
 
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 ^-- i 
 
 c e '" ' 
 
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 : 
 
 aov -^3 ^i"^' ' -" : " 
 
 " : '"''SfS:>rt5 TH? ' ^ 
 
 :^/oI>'- 
 
 *i ; , :?;v C,j 
 
 i;-^ ii, _ .^ ,..; 
 
20. 
 
 stiff; 
 74 to 77 ft. clay with a little gravel;* Took sanples at 557 ft. 
 
 \7ater 8 inches r.bove ground at 12:00 M. 
 77 to 80 ft. clay; squeezed into hole; rather stiff; sample at 79 ft. 
 
 July 8, 1918. 
 
 80 to 84 ft. clay; very stiff; pure clay 
 
 84 to 87 ft. clay rnd some gravel; took a sample at 85 ft. 
 
 87 to 88 ft. 11:00 a.m. gravel, boulders rnd some clay. Could not get 
 
 sample, struck a boulder with auger. T/ater 1 ft. rbove 
 ground., 
 
 Stopped drilling. Hole 88 ft. Casing 85 ft. 85 ft. of 8" casing used; 
 6 srmples taken. 
 
 Analyses of Samples 
 
 Sample 
 
 Depth 
 
 Viet Samples 
 
 Dry Samples 
 
 
 ft. 
 
 Momsture 
 
 Sand & 
 
 Clay by sub- 
 
 Sand and 
 
 Clay by 
 
 
 
 % 
 
 gravel % 
 
 traction % 
 
 gravel % 
 
 subtraction % 
 
 2357 
 
 57 
 
 2 1.5 
 
 22.3 
 
 56.2 
 
 28.4 
 
 71.6 
 
 2359 
 
 59 
 
 81.8 
 
 21.0 
 
 57.2 
 
 26.8 
 
 73.2 
 
 2366 
 
 66 
 
 18.9 
 
 40.5 
 
 40.6 
 
 50.5 
 
 49.5 
 
 2377 
 
 77 
 
 24.2 
 
 12.1 
 
 63.7 
 
 15.9 
 
 84.1 
 
 2379 
 
 79 
 
 25.5 
 
 9.7 
 
 64.8 
 
 13.0 
 
 87.0 
 
 2385 
 
 85 
 
 25.7 
 
 5.4 
 
 68,9 
 
 7.3 
 
 92.7 
 
 July 10, 1918, Perforated casing at levels 10, 20, 30, 40, 50, 60, 70 and 
 
 30 ft. below ground surface 
 
 July 17,1918, water level 0.2 ft. belov/ ground surface = elev. 661.1 
 July 24, 1918,V/ater level 0.0 ft. 
 
 At intervals the well drill was removed and the hole cleaned by sand 
 pump. Then samples were taken by letting down a steel auger. Later the crsing vr.s 
 perforated to study seepage. Thewellwrs pumped and allowed to fill agrin. These 
 records determined the degree of porosity of .irterials in different parts of the 
 dam. 
 
 8. Drilling with the Diamond Metal _or_ Shot Drills. The diamond drill 
 ie an expensive apparatus, used chiefly in mining and tunnel operations to drill 
 through solid rock. It is used for foundation tests, only in connection with other 
 methods to distinguish with certainty between solid rodk and thin Ir.yers of rock 
 or boulders. It is required for important structures such as iiarine foundrtions 
 for lighthouses, for bridge piers, dams and tunnels, where it is essential thrt 
 a good rock foundation be secured. 
 
, 1 I 1. J 6 
 -2 >IcoT .. 
 
 .*; (X.i;.i . 
 
 .. .-v.>_ 
 
 ... ... .. . ...v,. 
 
 .-- 1 3 
 
 
 
 8 err 
 
 T.i.0 
 
 . ., 
 
 
 
 r 
 .... . <. 
 
 ;.," . f,i 
 
 la- CT ,05 ,02 ,0^ ,0i' ,OS , .01 
 
 :;*#3J v'V 
 
 0!"T -,ru -".'.; lii'l .j,. 
 
 vI .r;c -.- U .. -:; j;o-r/uil ^ . 
 
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 crW^ Jbno . 
 
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 i - 
 
 .;.< . . ' 
 
 -- 
 
21. 
 
 A diamond drill is a heavy steel cylinder 3 or 4 ins. in diameter nnd 
 about 1/2 in. thick, with black diamonds or other very hr.rd substances imbedded 
 in^Lts lower toothed end (see Fig. 5). It is rapidly revolved and cuts out a 
 solid core which maybe broken off from time to time, caught by special tools 
 and brought through the hollow stem to the surface. Sometimes hardened steel 
 tools without diamonds are used, or hollow drill rod apparatus with a combination 
 of vertical churning and rotating motions. 
 
 Core rotary drilling apparatus with steel shot instead of diamonds is 
 now common practice. Because of the continually increcsing cost of black carbons 
 or diamonds, at first steel cutters were introduced, of many forms of cutter, but 
 found inexpedient except for the softest shales. Stone sawyers were the first to 
 study substitutes for sand in sawing stone and finally introduced the use of 
 chilled steel shot of varying size, according to the work' to be done. These shot 
 were found to but the rock very fast and at smaller cost, and as the rock 
 increased in hardness their efficiency increased. It v/as but a step to the use of 
 steel shot under circular hollow bits for cutting a core. Consult trade catalogues 
 
 Q-eneral Precautions for lest Borings, 
 
 Erroneous impressions may be received when the lower end of a pipe or 
 rod is deflected from its course or stopped by boulders. Boulders are frequently 
 removed or broken up by small charges of dynamite dropped into the hole. The 
 outside or inside pipe, auger, casing or sand pump may be easily stopped by 
 boulders, large roots and buried logs. Pipes may be clogged at any moment by small 
 stones or gravel and the consequent sinking conditions thus mry give the 
 impression of too firm a material. 
 
 It is difficult to use any methods of test boring in compact sand or 
 gravel, and then only in the presence of plenty of water. Uater nr.kes it difficult 
 to judge the character of the sand in place, especially of its comprctness. Any 
 method of test boring which uses a considerable quantity of water, such as the 
 Y/ash Drill, -Sand P^mp.. or \7ell Boring Tools, makes it uncertain to judge of the 
 
,* fc 
 
 'PI ^f.i.ir.-"T -s-f .a 
 
 -1C 
 
 v'-- -.,.', 
 
 r*7,* c . .v, :c .,> 
 
 _,_. 
 
 C 
 
 - : : 
 :,OC'4 &., . 
 
 :r. 
 
 --0 f-*;i 
 
 ' 
 
 : "i ! "'.:.' 1- . 
 
 :----*| fev ".. -S: 
 
 ' ^ '"- '-..;'.. "-- *.. 
 
 c^ jjoi /' .- :- 
 
 -iv'jUJ. 
 
 
character of the material in place. It is advisable in such cr.sos to frequently 
 bring up samples dry by the use of special apparatus. This is difficult and some- 
 times impcs sible in sand or gravel, or in mixed gravel and clay or indurated clr.y, 
 
 A c'onsiderable number of borings should be mr.de and if results apperr 
 erratic the examination should be continued. For importrnt foundations on solid 
 rock, borings should enter into the rock for several feet by employing the diamond 
 drill or heavy well boring tools, otherwise the facts crnnot be accepted with 
 confidence. In every case careful and complete records of the material passed 
 through should be kept. Test borings should be located by surveying. A special 
 form of field notes for keeping a log of borings should be prepared and used. 
 Examples of forms have already been given in what precedes. On large work involv- 
 ing many borings, a printed field form should be adopted for ready reports to 
 be made by the foreman. Consult an article by Smile Low, "Cost of \7ash Drill 
 Borings in Kew York State Barge Canal"; on Deep Y/aterways Surveys, 1897-1900; 
 Eng. Hews, Vol. 57, 1907, p. 54. If sufficient borings are made, a contour map 
 can be drawn showing subsurface conditions, the arrangement and extent of strata 
 and the position of solid rock. Profiles or cross -sections of river channels and 
 bays or swamps are frequently made from records of test borings. Sometimes samples 
 of material are kept in glass tubes or bottles with the layers of material in 
 regular order. Mrps may be drawn to show columns of strrta in the positions of the 
 borings, the conventional signs and printed .natter depicting clearly the nature 
 of the ground, All methods, except "drilling with heavy well tooring tools, offer 
 difficulties when working in grrvel or compact sand. The number and location of 
 test borings depend entirely on the magnitude of the particular work in hand. The 
 engineer should be guided by the importance of the structure, by the uniform or 
 non-uniform character of the test results and by the characteristics of the 
 formation examined. A study of the local geology is frequently a great help. 
 
-Ti S 
 
 r-:o,. 
 
 : " . - " ' 
 
 .:' 3T:;~vV IT 
 
 - -.. - 
 
 '" [ ' -'' -"C. V" 
 
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 -'-"' '"' 
 
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 .;..- - 
 
 
 1 
 
 n 
 
22 
 
 Sub-Aqueous Borings 
 
 It is frequently necessr.ry to make borings of the chr.rr.cter already 
 described in ground under water. In such cases the boring outfit is placed upon 
 a scow or barge. In mrjiy instances in deep.vvr.ter or in swift tides or currents, 
 or where the water may be rough, it is necessary to use a power pump for forcing 
 water through the small pipe. These examinations, as well as borings into rock by 
 diamond drill or other processes, mr.y be successfully executed in swift currents 
 and even in the open ocean. They have been made in connection with examinations 
 for harbor improvements; in the rr.pid tidal currents of the East River, New York 
 City, for bridge pier sites; along both the Atlantic and Pacific Coasts of the 
 United States; and in similar foreign loortione. If the water is quiet, as in the 
 slips between docks and piers, a sar.ll scow, 15 by 20 ft. plan, with a well in its 
 center, and fitted with a hand pump will be found satisfactory for ordinary cases. 
 V/hen the water is likely to be rough, or where the currents are strong, it will 
 be necessary to make use of a larger sew/, strongly built and fitted with a pov/er 
 pump. A pile driver scow is a very good vessel for the purpose. The regular pile 
 driving leads are not required although they may be used if they are in place. A 
 much smaller but similar frrme, not more than 15 or 20 ft. high, is ample for the 
 purpose. If the water is deep, necessitating considerable length of pipe, it is 
 advisable to use the pile driver or hoisting engine for handling the pipe, 
 although a winch worked by hand is usually sufficient. 
 
 The scow 40 or 50 ft. long and 20 to 25 ft. wide, fitted with suitable 
 appliances already indicated, is towed to the position where the eicaminations are 
 to be made. If the current is always in one direction, as in a river, it will 
 only be necessary to anchor the scow from one direction, a.s shown in Fig. 6, 
 If, ho- ever, the work is done in a tidal current likely to run in both directions 
 before the position of the scow is changed, it becomes necessary to anchor from 
 both directions. The lines running from the scow to the anchors should have 
 considerable inclination to the axis of the scow, so that it vja.y have the 
 
- --^ X'C 
 
 - ' 
 
 - -Si -- l.r.;..- . r .. t; _ " % 
 
 l: -"' : -'^i::' .-,; ' -.4. ' "*"* "' "--. -'i ~. 
 
 Sl 4 -'- T;;ga -,- .- : . -.-^O' v 
 
 '-JCSOO;.-v 5j . .., . 
 
 - ' i 
 
 '"' ' ''- >1'ati.' . . '. ; 
 
 i lie-'-- ;;^. r f _. r - ''- f.".:/c- . r.. . ,..._. 
 
 ds! i -' - ^^ l ' "' 3 r - : '" "' 
 
 --' ., ---T '-": -' -,. .- 
 
 "'/:,^ ; .;-., "'-"i^> ..-i-'_- _ ' t / ' r 
 
 , tIJ a.^fefitat ...:q, t ^j . 
 
 - i '. ; .';- . vT' .. 
 
 i .u^.'iAV 
 
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 ' ' ' 
 
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 :--'- :, . -,. -. ... ^' 
 
 ' ~ f ' '"" --C-.S; ... 
 
24 
 
 .requisite lateral stability of position. The anchors may be ordinary iron or 
 steel ship anchors, or what are known as Chinese anchors (snrll cribs filled with 
 stones), or such other devices may be used as the localities afford. It will be 
 found advisable, as it is usually most convenient, to handle the pipes and make 
 the borings at one end of the scow rather than through a well in the center. If 
 the Cunsnt is strong, it will also be necessary to make the borings at the 
 down stream end of the scow. The pipes are projected downward from the handling 
 frame in tho manner shown in the figure. In order to hold the pipe against the 
 current, lines or cables are carried from the upend of the scow underneath it, 
 around the pipe and back again, as shown. If the water is deep or the current 
 very strong, two or more loops of the line or crble may be required. In the manner 
 described and by the means indicated, the scow can be held stiffly in position in 
 almost any current and in water of considerable roughness, although when the water 
 becomes too rough it is necessrry to suspend operations. 
 
 Considerable lateral variations in the position of the scow may be 
 secured in the manner shovm in Fig. 6, without moving the anchors. If the cable A 
 running from one corner of the scov/ be lengthened while the others, B, be 
 shortened, the scow will be moved laterally to the position shovm by the broken 
 lines without movement along the current. A judicious selection of position for 
 the anchors will materially facilitrte the operations to be conducted 1 , in taking a 
 line of borings .c-jcross the current. 
 
 The number and location of borings will depend on the features of each 
 particular case and they are to be determined by the judgment of the engineer* 
 For a location of a break-rater they may at times be as much as 1000 ft. apart, 
 or as near as 25 ft. or less for other purposes. 
 
 In these submarine boring operations it is necessary to use soniev/hat 
 heavier pipes thrn in ordinary jet boring work. Three to four in. pipes carrying 
 an inner pipe of 1 1/2 to 1 3/4 ins. diameter have been found to b e very satis- 
 factory for some <^ n r> work in strong tidrl currents or the Pacific Coast. Consult 
 
:;., "/ v: : -;. ;..-. . - ,^ r .. . . .; ....... -...- 
 
 ^"": 5 ' ' ff'w ' "^' - .- -- 
 
 i =' ^vutoi^y-'*-' veift- 
 
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 -f c ^ 
 
 f ct/ - *'-i 
 
 *acif*lv-'-.'-5 
 
 ' ' " 
 
 
 
 " 
 
25 
 
 "Report of Board to Locate a Deep V/ater Harbor at Port Los Angeles or at Port 
 San Pedro, California, 1897"; Appendices D and E; also Pis. 8, 9, 10, 11, 12. 
 A steam pump was used for farcing the water through the inner pipe and operations 
 were conducted in water 50 ft. deep or more. 
 
 In submarine work, as in borings on land or under rivers, it is 
 necessary to guard against being misled by a wrong interpretp+ton of conditions 
 at the bottom of the pipe. In one case rock had been reported beneath a layer 
 of mud and sand at a harbor entrance and the harbor had been reported as being 
 incapable of much improvement in consequence of the excessive cost of removing 
 the supposed rock. At a subsequent date the locality was more carefully examined 
 and it was found thet the supposed rock was little more than a layer of hard 
 cemented gravel a fev/ inches only in thickness; also that down to a depth of at 
 least 42 ft. below mem low water, there was no rock whatsoever. 
 
 Throughout all these boring operations conducted by means of a jet, 
 or in boring through rock by whatever process, a scrupulously careful record of 
 the material passed through should be kept, and in boring on land, the elevation 
 of the subsurface water, if any be found, should be observed with equal care. 
 After complete data have been secured, a profile pL.n should be made showing each 
 boring in its proper location; the depth to which it was carried below datum 
 and the accurately placed, strata of all material found, including the subsurface 
 level of water. This plan could be preserved as a part of .the permanent records 
 of the contemplated work; see Figs, 7A, 7B, and 8. 
 
 If subaqueous borings through rock are to be made, the diamond drill 
 or other rock boring process must be employed. (See Diamond Drill Borings, fiew 
 East River Bridge; Eng. News, Sept. 24, 1896, Vol. 36, p. 198), For this purpose 
 the scow on which the boring outfit is supported must be held much more exactly 
 in position in rough water than is required for jet boring. Specirl means and a 
 more elaborate frame vork for handling the boring appliances will also be needed, 
 The devices required will depend upon the degree of exposure of the location ~nd 
 
~e '' ' 
 
 '.et c l osi", . u ar; C 
 
 * j :vfi :>-'. 
 
 ;,'.. -t^- 
 
 c.":.' 
 
 .yLO:" -; V>S* -** '" 
 
 -GT-'' r 
 .-.- : ~'3<. 
 
 r - - "f ' 
 
 .re" . ". ' "' " x'a 
 
 . * icJirjt 
 
 fins ^i 
 
 xs 
 
 rf: x.v- ' ' - :' e 
 ' ' 
 
 >- ^*^ 
 
 . :'J a.v : 
 
 :'* ca"l~ ; seoi.r^iiif .ti vino ssriacl "-'el fl f.y ^15 f^.'ioi.es 
 
 _ . -v ' * 
 
 Oft 
 
 - * f - 
 
 * ..-; i ..;;j.r ; - - ' . - 
 
 w'Lnco *:itoi j.-re-rc 3; ; . . 
 
 .". ,03.. Y^ 2*00 * ' ai 10 
 
 < jr no "gnrfbtf ai 5ft~. ,*q93t t-y. a<J 
 
 *-'fc &d -^n.". ^x ie^.'w : li/e a4* 5p 
 
 '' r/iiroiq '. i>9:tJJO0a. need errri pJ'.iS e: o t8*'.T. 
 " c* ri^qab 
 . II r 
 
 ir.ifcerf* 
 
 ? 
 
 airf* -ieri (861 ,q ,dC '.IoV 
 
 revifl 
 
 
 36 OJ 
 
26. 
 
 other local features, which will need careful consideration for the conduct of 
 any given piece of work. It will not generally be practicable to conduct these 
 operations in as rough water as that in -which jet boring may be done. 
 
 Additional References. 
 
 1. A Treatise on Masonry Construction; 1. 0. Baker, 10th ed. , 1909, 
 .Chap. XIII, pp. 330-334. 
 
 2. A Practical Treatise on Foundations; V/.il. Patton; pp. 166-170, Arts. 
 25-27; p. 373, Art. 91. 
 
 3. Sewer Design; H.ft.Ogden, Chap. II, pp. 18-24 
 
 4. Borings in Broadway, N.Y, ; \7,B, Parsons, Trans. Am.Soc.C.E. , Vol. 28, 
 p. 13, 1893. 
 
 5. Apparatus for Obtaining Borings by Direct Pressure; T. Allen, Trans 
 Ani. BOC. C,E. , Vol. 2, p. 41, 1873, 
 
 6. Deep Borings; Eng. Kev/s, Apr. 13,1893, p. 505. 
 
 7. Consult General Index, Eng. Hews, 1895-1899 1890-1904; 1905-1909; 
 Borings and Drilling. 
 
 8. Sev/erage; A,P,Folwell, p. 109. 
 
 9. Explorations, H.idson River Crossing, Catskill Aqueduct; A,DElinn; 
 Eng. Kev/s, Vol. 59, p. 358; Apr. 2, 1908; see Fig. 7A, 
 
 10. Diamond Drill Borings, Olive Bridge Dam, Ashokan Reservoir; Eng, 
 Record, Vol. 58, p. 25, July 4, 1908, 
 
 11. Memorial Bridge Across the Potomac River; 55th Congress, H. of R 
 Doc. 388, 1898. 
 
 12. Diamond Drill Boring Costs; Eng. -Contracting, Jan. 9, II" r. 13, 1907, 
 April 29, May 6, 1908; April 21, July 23, Sept, 8, 190S ; Jrn. 5, 1910, 
 
 13. Cost Keeping Systems and Blanks for Diamond Drill '.York; see 
 Cost-Keeping and Llanagenient Engineering, by Gillette &.Dana, 
 
 14. Diamond Drill Borings for a Dam on the Clackamas River, Oregon; 
 Eng. Kews, Vol. G4, Dec. 22,1910, p. 684. 
 
 15. Borings for the Panama Railroad Dock at Cristobal, with table of 
 costs; Eng. Kev/s, Vol. 63, June 1C, 1910, p. 691. 
 
 16. Profile of Spuyten Duyvil site for proposed Kenry Hudson Memorial 
 Bridge; plans showing strata ^nd diamond drill borings on a line 50 ft. west 
 of asis of bridge; Eng. News, Vol. 58, p. 50, i><ov. 21,1907 = 
 
 17. Inclined Diamond Drill Borings under the Hudson River; Eng. Record., 
 Vol. 61, p. G8, Jrn. 15, 1910, 
 
 18. Recent Practice in Diamond Drilling and Borehole Surveying; J,I 
 Hoffman, Eng. Eev/s, Vol. 68, Aug. 29, 1912, p. 404 
 
 19. Freitrg; Architectural Engineering; Chap. 9, FP- 284-309- 
 
 20. Drill Outfit for Light Blast Holes and for Rock Soundings; Eng. 
 
 21. Pile'lests Indicate Type of Substructure for Technology Building; 
 Eng. Record, Vol. 72, p. 235 
 
~f~, r ~ \ . . ". 
 
 - - 
 
 
 
 
 1 
 
 
 
 . .. - 
 
 ."r .. .-) ; '7. ,--.-:; :f ;>- ' rr. J 
 
 ' ' " ' ' i .,;. 
 
 - 
 
 : 
 
 = '. : -. I , v ;:i>-0-.vf ::--; . 
 
 5- 
 
 - -V '. .,?.-; 
 
 :.". . .^ ; : . '.', ."v - - i j' 
 
 . . 
 
 ... . , 
 
 ; 
 
 : hf, 
 
22. Geology of New York City Revealed in Core Boring Exhibit; by H. E. 
 Zipser; Eng, Nees-Record, Vol. 85, p. 60 
 
 23. Foundations of Bridges r.nd Buildings; Jacoby & Er.vis, Chap. 17, 
 p. 518, Explorations rnd Unit Lor.ds. 
 
 24. Engineering and Building Foundations; Fowler, Chap. 12, p. 232, 
 Location and Design of Piers. 
 
 25. Practical Treatise on Sub-Aqueous Foundations; Fowler, Chap. 22, 
 p. 424. 
 
 26. Ordinary Foundations; Fowler, Chaps. 12 and 13, p. 182. 
 
 PROBLEMS 
 
 1. Tell how you would sink a test boring to rock by the water jet 
 process; the site, a river location for a bridge pier; the probable depths of 
 materials in order being, water 30 ft.; silt 15 ft.; mixed sand and clay, 40 ft.; 
 total depth 85 ft, to rock. Describe the apparatus; give sketches; state the 
 precautions to be observed before finally interpreting results. 
 
 2. Describe method of sinking a foundation boring on land into soft 
 materials requiring casing and water jet process for 30 ft., then drill boring, 
 using chilled shot process in order to penetrate 20 ft. further, to be certain of 
 rock foundation. Give stale sketches. Consult texts, references and trrdc 
 catalogues. 
 
 3. A test pile penetrated 6 3/4" totrl under the last five blov/s of a 
 3500# hammer, falling freely from a point 22' above the head of the pile. If the 
 loss of hammer energy per blow is estimated at Q%, co^.ipute the probable safe load 
 by the Engineering weus Formula using a factor of srfety of 4 instead of that 
 involved in the formula given in the Rotes. If the material penetrated is a 
 viscous mixture of sand, clay and earth, how does the above calculated figure 
 co-ipare to lo*d ccpacitjr one month after driving? 
 
- 
 
 :j " - ? 
 
 - 
 
 ;; 
 
28 
 
 CHAPTER 2 
 
 CIASSIFICATIOIT OF FOUKBATION SOILS 
 
 BEARING- POVflER 
 
 The locction of important engineering works is influenced by such varied 
 conditions that it razy b3 necessary to construct foundations on widely different 
 classes of rjateriai. Kence, a general discussion and classification of soils 
 
 should precede a detailed study of the design of foundation types; particular 
 
 i 
 
 reference being ;rade to tho bearing capacity of the soil. 
 
 A classification of this nature must be mere or less arbitrary, and 
 general rather than specific. The different kindscof foundation soils grade into 
 each other so gradually that the classification in any particular case is fre- 
 quently a matter of individual opinion or judgment. Certain materials, such a s 
 hardpan and quick sand are particularly difficult to describe accurately. 
 
 There is no line of engineering work in which there is mere room for the 
 exercise of judgment and exp?rionce than when assigning allowable foundation 
 pressures. The unit soil pressure affects largely the design of the substructure; 
 to a lesser extent, the superstructure, so that it is commonly necessary to fix 
 values in advance of the design, from data obtaired from test boiings. For 
 important structures these values should always be checked where possible by 
 direct tests of the bearing pov.'cr of the soil after the foundation excavations 
 have boon made. Such tests often are difficult to make and the results obtained 
 so uncertain that their interpretation requires almost as much judgnent and 
 experience as 'would be needed to arbitrarily fix the values without such tests. 
 ^ny material, except solid rock, will yield when heavily loddad, especially on 
 such small areas as it is necessary to use when m.- king tests. This yielding \vill 
 be;:in under moderate loads. It is a matter of opinion how much settlement is 
 allowable; the amount being largely affected by tho character of the proposed 
 structure. 
 
 Foundation, materials listed in the order of their desirability are:- 
 

 . .ri- 
 
 .' : 
 
 -r. . 
 
 . .-. * i .^ . 
 
 1 . ; .. - - - 
 
 ^J *--->""' - 
 
 : '. x ; ' 
 
 ' "' 
 
 
29. 
 
 1. Solid rock 
 
 2. Grave 1 and hardpan 
 
 3. Send 
 
 4. Clay 
 
 5- Ordinary soils, usually riore or less compressible. 
 6. Semi -liquid soils - qyicksand, 
 
 For a comprehensive list of soils, their definition, mineralorjical compo- 
 sition, characteristics, color, settlement, laboratory tests , etc., see Proc. 
 Am. Soc. C.E. , Feb. 1921, Progress Report of Special Committee to Codify Present 
 Practice on the Bearing Value of Soils for Foundations, p, 11. Consult also Proc. 
 for Aug. 1920, Table 1 and Plates XI and XII for Bearing Power and Loading Test 
 Apparatus . 
 
 1. SOLID ROCK 
 
 The ultimate crushing strength of a 2-inch cube of any rock hard enough 
 to resist the wearing action of running v/ater, when t ested "by a standard laboratory 
 machine is at least 180 to 200 tons (of 2000 lb. j per sq. ft. The h ardest and . 
 best building stones v;ill withstand, for selected specimens, 2000 tons per sq. 
 ft. Consult, Burr, The Elasticity and Resistance of the Materials of Engineering 
 1915, seventh edition, Art. 69, pp. 420-425, 
 
 The strength of masonry blocks in large masses in place usually is 
 assumed to be considerably greater than that of 2-inch cubes, since the stones 
 are prevented from yielding laterally. If this were not so, high rock cliffs, 
 such as are frequently found in nature, like El Capitan, Yosemite Valley, 
 could hot exist. 
 
 As tl>o maximum pressure upon any footing course of an engineering structure 
 seldom, or never, v/ill exceed ten or twelve tons per sq. ft., the softest stone 
 will give a safety factor of nearly 20. It may be concluded that any ordinary 
 rock foundation bed, v/hen cleared of disintegrated surface material, iscoapablc 
 of carrying any load produced by an engineering structure founded upon it. 
 
 The rock should first bo laid bare by open excavation, or excavation 
 within sheet piling or cofferdams, or for deep foundations, bgr other more 
 difficult methods, such as pneumatic and desp-v/ell dredging; after which the rock 
 
* 
 
 ': ." 
 
 ... ! -vF . '- .. :':-. 
 
 . pflfe 
 
 :( 
 
 rs-. -- .;- : ., , I" I, ... :. 3SS:' ; :': 
 
 .-. - t ,. .. '. : 
 
 :.jLCii-. jufcaxk;": 
 
 
30 
 
 bed should bo examined, thoroughly in order to determine the shape and condition 
 of its surface and its general character. If soft spots are found, or if tls re 
 are crevices, cracks or fissures, filled with softer or rotted raster ial, they 
 should be cleaned out to their deepest points ar.c. filled with concrete. All soft 
 rock should be removed, if necessary by blasting, so that perfectly sound and 
 hard material is exposed to receive t he foundation bed. For vertical or gravity 
 loads all sloping rock should be roughly benched in steps with treads, 5 to 8 
 ft. horizontal or sloping slightly backward and downward and with vertical 
 risers, so that the entire surface receiving the foundation will be approximately 
 at right angles to the pressure which is to come upon it. For inclined lodds 
 or thrusts, as in arched rib abutments or retaining wall footings, the rock 
 should be stopped on an incline. The rock surface in all cases should be so 
 roughened or broken that the footing course docs not rest upon a perfectly 
 smooth surface, unless that surface happens to be practically normal to tie 
 resultant pressure. The main end to be attained is to secure a perfect bond 
 between the footing course and the rock, to avoid completely any possibility 
 of sliding between the footing course and the bed. Blasting is frequently 
 resorted to to clean the surface of the rock; it has the advantage of not only 
 removing all loose and disintegrated material, but also of leaving the bed 
 rough and jagged so that a good bond may be secured with tiro concrete. 
 
 If water percolates into the foundation excavation, it should be pumped 
 out or drained away by some method which will enable the footing course a nd 
 foundation masonry to be laid dry and maintained so tmtil the mortar is 'set, 
 after which the presence of water in the material overlying the rock may be 
 disregarded so far as any effect upon the foundation is concerned. Sometimes it 
 is impossible to remove the water; in such cases at least the lowest part of the 
 substructure must be laid umer water. The methods to bo usod are treated later 
 in Chapter 8. 
 
. iff 
 
 r;x .o:' : >.. ; 
 
 .!< : -- 
 
 '. . '.. 
 
 >-..' pcf Li'cooo ..=,::.; 
 
 -i; * 
 
 aorr 
 
 
31 
 
 2. GRAVEL AHD HARDPAN 
 
 "Hardpan" is a compact or cemented gravel, composed of irrogulat stones, 
 of all sizes, mixed with clay and sand, the latter filling the voids in the 
 gravel. The torn is also rather loosely applied to indurated clay, which usually 
 occurs mixed with sand. Hardpan grades off on one hand into cemented gravel 
 or hard, compact, conglomerated rock. On the other, it passes through indurated 
 clays containing smaller and smaller proportions of grr.vel and dand, to a 
 clr.y which, on exposure to air and water, may become soft and unreliable. A 
 material of this nature is liable to occur irregularly in valleys formed by 
 sv/ift silt -bearing rivers. It is deposited by sudden freshets at the mouths of 
 crooks or tributary streams, and when mixed with sand and clay becomes in time 
 very hard and compact. It frequently is so hard, approaching the condition of 
 natural concrete, that it is necessary to resort to blasting before it can be 
 excavated, even with heavy dredging machinery. 
 
 If there is a sufficient volume of hardpan, it makes an excellent found- 
 ation bed. It is apt to occur in rather thin layers; often between strata of 
 seni-liquid sand or silt. Borings for bridge piers in the Mississippi Valley 
 have oBten disclosed such examples. Consult Report, The Memphis Bridge, by 
 George S. Morison. Compact grr.vel, without cementing nnterial, also will gifce a 
 perfectly satisfactory foundation. The gravel is best v/hen coarse a,"d finer 
 particles are intermixed to leave as siT^all a percentage of voids as possible. 
 Layers if gravel ttro feot >r more thick and well compacted, rti.ll bear very heavy 
 loads, even thopgh overlying poorer material. Adequate foundations can be 
 secured sometimes by dumping gravel into quicksand, or into boggy or marshy 
 la^d, when nothing else vd.ll suffice, though this is liable t? cause the 
 adjacent land to rise. Gravel has the advantage over s and , for as the grains 
 become larger, it has a greater resistrnce to running or percolating water. This 
 is expecially true if the gravel is mixed with a sand or clay, vhich prevents 
 water seeping through it. Compact grr.vel will safely bear from 8 to 15 tons per 
 sq. ft. A Brooklyn Bridge Pier, vdth a pressure of 5 1/2 tons per sq. ft. is 
 

 .'" 3 ' 
 
 
 
 V t: 
 .-. j ?-i ...... .jjj 
 
 :" c^ iiosc'-s -. "fi aci'l O^OT:O 
 
 :o*1o ;2r,-''-;"w . = 1 ^.1 
 
 ^ 
 : " -><* CET ;: 
 
 . r . 
 
 ; '-' ;: - '-' ''.".:. 
 
 . ffl . ;; 
 
 -- r ^ .: . .i- 
 
32 
 
 founded on a two-foot layer of cor.ipact gravel, overlying rode. 
 
 5. SAKE. 
 
 Sand can be divided into three general classes, according to its chemical 
 composition. 
 
 a. Argillacious sand is forrrad by the disintegration of clay, slates and 
 shales. If very fine, or thoroughly disintegrated, it grades into clay. If the 
 grains are granular or hard, it may be called sand, though it is the poorest 
 kind of sand for founiation purposes. 
 
 b. Calcareous sand is used for making hydraulic cement, but is not fcund 
 commonly. It is formed by the disintegration of lime rocks. It is a poor 
 material for foundations, liable to decompos e after exposure to air and to 
 moisture. 
 
 c. Siliceous sand , composed principally of a lica, is more common than 
 any other, and makes a nuch more satisfactory foundation bed. The strata should 
 be reasonably thick and extensive in area. Coarse, angular river sand is better 
 than water-worn rounled sea sand. 
 
 It is stated often that high grade siliceous sand will support any 
 practical load if the sand car. be held laterally. V.Tien securely retained it is 
 nearly incompressible. It has been leaded, confined in trenches, to 100 tons 
 per sq. ft. V/here difficulty has been experienced with sand foundations, it 
 has usually been due to the tendency of the material, mixed with water, to 
 act under the laws of hydraulic pressure, yielding in any direction along the 
 line of least resistrnce. Sane 1 ., if compact and well drained, especially if 
 mixed with a cementing material, such as a small percentage of clay, oay grr.de 
 into hardpan, intermediate in supporting strength to sandstone. Sand is porous 
 and unless confined between clayey rocks or by artificial barriers, water may 
 pass through and scour it, undermining the structure above it. The process of 
 scouring is greatly aided by the pressure from the abnormal loads transmitted 
 to the sand by the foundation. If an excess of water is present, especially 
 if the sand grains are find ar.d well rounded, a quicksand results which has 
 
33. 
 
 little or no bearing power, unless prevented from spreading laterally. The coar- 
 ser the grains of sand, the less the danger of scouring and the greater is the 
 bearing resistance. 
 
 It is especially, advantageous to carry foundations in sand to a consider- 
 able depth. The sand $ill then be more compact because in its natural position 
 it is subject to a greater overlying loac . There "frill also be less possibility 
 of lateral spreading or exposure to running or percolating water. 
 
 In general, if sand can b e drained and confined, it will safely hold 
 from 2 to 15 tons per sq. ft. The Chicago Building La' s permit 2 tons per sq. 
 ft. on dry sand in strata 15 ft. or more in tMckness. Pressures from 2 to 2.5 
 tons per sq. ft. are allowed in Berlin for buildings founded on sand or sandy 
 soil. The Washington Monument, 555 ft. high, with a foundation pressure of 11 
 to 14 tons per sq. ft. is founded on a layer of fine sand 2 ft. thick. The San 
 Francisco Building Ordinance, section 57, allows 3 tons per sq. ft. on loam or 
 fine sand, 4 tons on co;npact sand. 
 
 4. CLAY 
 
 I 
 
 Clay is formed from the disintegration and deposition below water of 
 aluminum rocks, ar..d is one of the commonest materials found in nature. It varies 
 greatly in character, passing grrdually from slate to shale, to indurated clay, 
 to soft, samp or wet clay, and finally, with an excess of water, to a semi- 
 liquid material, which yields in all directions to pressure, and will flow almost 
 like water. The percentage of voids is larger than in almost any other material, 
 b$-b they are exceddingly fine, so '.hat, while clay is usually almost impervious 
 to running water, it v/ill slowly absorb' large quantities of vater and become' 
 semi-liquid in time. Clay normally contains much water , some of which it is 
 impossible to remove. If allowed to freeze, it expands with a " bearing" effect 
 upon imbedded foundations. In cold climates it is necessary to carry the foun- 
 dation well below the frost line or cracks end unequal settlements will develop. 
 Dry clay rapidly absorbs moisture, even from the air, and 'swells, attended with 
 
34 
 
 great pressure. Disastrous effects have sometimes resulted from ramming dry 
 clay behind retaining walls. Railroad embankments or levees built of wet clay 
 may be seriously endangered by the formation of large, deep cracks as the 
 material drys out. 
 
 The Calaveras dam- liquid clay core, which caused the failure in Alarch 
 1918, was very wet and supersaturated 1 . Samples of this flowing clay, when most 
 liquid, gave percentages of moisture by weight from 50.0 to 56.6 percent; or 
 73 to 77 percent moisture by volume. This clay core therefore was an emulsion 
 containing about 39% finely divided clay, tho -est of tte volume being water. 
 Samples of air-dried material from the top of the clay-ppol in the destroyed 
 dam, when cut out and e xamined, contained on an average about 35% voids. In 
 other words when baked dry by the sun the clay had 65% by volume of solids iri it 
 instead of the 30% in the original emulsion or supersaturated -material. 
 
 . * 
 
 The least compacted material remaining in position in the dam a fter the 
 slip contained from 45 to 50% voids. See an article by A. Hazen "A Study of the 
 Slip in the Calaveras Dam"; Engineering liews-Record, Vol. 81, p. 1158. 
 
 ' - 
 
 In general, wet clay is very treacherous and unreliable, so that 
 foundrtions constructed upon this material should be thoroughly drained, if 
 possible, and water ncj allowed to stand on, or especially to run over, them as 
 some clays are very easily washed away by running v;ater. On account of the 
 expanding effect, it is absolutely necessary that foundations must be kept from 
 
 | 
 
 being alternately wet and dry. If foundations must be established in under- 
 drained clay, every .precaution should be taken to prevent the material from 
 oozing or flowing away laterally, especially into adjacent foundations. The 
 material tends to flow in .all directions. In deep railroad cuts, or similar 
 construction in soft clay, the weight and pressure on the sides tends to make 
 the bottom rise, the effect being especially marked in cofferdams or caissons, 
 where the sides are held. Excavations for tunnels, trenches and alafts tend to 
 close in on all sides slowly, hence they should be made -larger than ultimately 
 
35 
 
 required. When beds of clay occur in definite strate, inclined at any consider- 
 able angle, especially if resting on tipped rock, the problems presented are 
 extremely grave. Percolating water tends to fill the contact, or stratification 
 planes, causing the whole mass to slide. This tendency has given much trouble 
 at the Panama Canal, and has been the cause of the failure of irany retaining 
 walls. It is sometimes impossible to prevent the sliding of Icrge masses of clay 
 along inclined stratification planes. Slidings of this sort .nay be so extensive 
 that the pressure will gradually tip over the strongest, haaviest retaining v/ alls 
 The only remedy in such cases may be to keep removing the material as fast as it 
 
 slides and until a condition of stability or equilibrium is reached. 
 
 i 
 Clay is so variable in quantity and behavior that it is one of the . . 
 
 most difficult materials to judge and v/ith which to deal. If, instead of pure 
 clay, we have clay mixed, with coarse sand orgravel, or both, it is one of the 
 b^st foundation materials. The Capitol at Albany, 15. Y. is founded on blue clay, 
 containing from 60 to 90 percent of alumina, the balance fine, siliceous send. 
 The supporting power-, under tests, exceeded 6 tons per sc. ft., the safe load 
 being assumed 2 tons per sr . ft. The Congressional iibrery at \7ashington , D. C. , 
 is founded on yellow clay mixed v/ith send. The ultimate supporting power v,s 
 13.5 tons per sq. ft., the safe load taken at 2.5 tons per so. ft. The Missouri 
 River Bridge at Bismarck, South Dakota, gave an ulti -ate bearing strength of 
 15 tons per sc. ft. At Chicago, the safe bearing power for buildings founded on 
 
 ^/ 
 
 thin layers of clay, hard abo v e and soft be-low, resting on thick layers of quick 
 sand, is taken at 1.5 to 2 tons per sq. ft. In general, the safe pressure for 
 thick beds of clay ccn be assumed about as follows: 
 
 If always dry, from 4 to 6 tons per sq. ft. 
 
 If moderately dry,, from 2 to 4 tons per sq. ft. 
 
 If wet and soft, fror; 1 to 2 tons per sc. ft. 
 
 L. OSDIEABY SOIJt 
 Under this heading is included a con si?. erable variety of sedimentary 
 
 soils, usually co:npose\d of mixtures of clay and send, in all proportions, or 
 very fine send, also certain varieties of black or blue clays containing con- 
 
36 
 
 siderable organic matter, frequently known by local terms, such as "adobe", or 
 "gumbo" soils. These are materials most commonly found in valleys built up by 
 sedimentary deposits from river action. Similar conditions result in most coast 
 cities when a portion of their area is compos? 1 of artificially filled land, as 
 the water front is gradually advanced. Such materials are less uniform than soil 
 
 * / 
 
 normally formec", more compressible and unreliable. They are quite apt to slowly 
 settle under the prolonged action of their own weight and may suddenly settle 
 
 A t 
 
 a considerable amount from violent earthquake shocks. These materials are com- 
 
 / 
 pressi ";le so that foundationsbearing heavy loads are apt to settle slowly through 
 
 them. This settlement is not particularly injurious if it occurs uniformly 
 underneath an entire structure. To insure equal settlement it is necessary to 
 have the unit soil pressure under different portions of the entire structure 
 uniform if the soil is uniform. To insure this condition upon a varying material 
 where for example a large building rests on a soil of changing composition, 
 requires viuch study and analysis; a subject which is trpated in considerable 
 detail in Chapter 4 
 
 In Chicago high buildings founded on thick beds of clay and sediment 
 soil, &ry above and wet below, have settled as much as 3 or 4 inches, in 
 extreme cases, even 6 inches without damage to the buildings. It is necessary to 
 have the foundation bed homogeneous throughout for each s tructure, otherwise 
 unecfual settlement will occur, causing the foundation to tip or crack. This is 
 much more important for tall, narrow structures such as chimr.0ye and towers than 
 for massive buildings or heavy foundations, such as are required for docks or 
 
 quaywalls. 
 
 EARTH PHLSLUT.S IK SOILS. 
 
 For sediment soil, or clay, and to a limited extent, for the softer 
 soils considered later, a mathematical analysis f.-\r pressures transmitted in 
 granular masses can b e made which will assist in determining the allowable loads. 
 
 -) 
 
 For material like dry send or the ideal mass of granular earth whose grains are 
 held in equilibrium by the force of frictiononly, a formula expressing the proper 
 
37 
 
 depth of foundation for a given load intensity can be written in accordance 
 with Eankine's theory of earth pressure. If w is the w eight in Ibs. per cu. ft. 
 of earth, x the depth in feet from a horizontal ground surface, and p the great- 
 est load in Ibs. per sq. ft. which can be placed upon the horizontal earth bed 
 at the depth x without disturbing or lifting the surrounding material, then, 
 see fig. 9, } 
 
 P = 
 
 l+sin0)"' = TO (1+sin 0')) 2 ------- - ---- (1) 
 
 (l-sin0) (1- sin 0} 
 
 here p x = v/x (1+sin 0J_ 
 (1-sin 0) 
 
 ~t 
 
 Consult Rankine's Mechanics, Art. 199, p. 219, 13th ed. , 1901. The 
 angle of repose of the material is 0". Table I shov.'s the values of p for 0" 
 betv.-een 5 and 33*42'. 
 
 i 
 
 TABLE I 
 
 
 p 
 
 5 
 
 1.418 
 
 vx 
 
 1O 
 
 2.017 
 
 v:x 
 
 15 
 
 2.885 
 
 voc 
 
 20 
 
 4.16 
 
 T.-X 
 
 25 
 
 6.07 
 
 \vx 
 
 30 
 
 9.00 
 
 v;x 
 
 3542' 
 
 12.20 
 
 -wx 
 
 C. Prelini, in his book "Earth Slopes, Retaining 'Vails and Dams" gives 
 a good elementary treatment of the effect of cohesion; see pp. 1-27. Examine 
 also Cain's later v:ork "Earth Pressure, Walls s nd Eins", Chap. 1, pp. 1-26. 
 The limitations of earth pressure theories, such as Rankine's are excellently 
 portrayed by an article by H. G. Moult on, entitled, "Earth and Rock Pressures" 
 Trans. An. Inst. Mining Engineers, Feb. 1920; this paper bears particularly 
 upon the problems of tunnels, deep excavations, mining, etc. 
 
 Small angles of repose are found v/ith vet material; foi that reason , 
 Table I shov;s hov: important it is to have a foundation bed dry. The angle of 
 repose, 3342' is that far the standard slope, 1 1/2 : 1. While formula (1) 
 cannot be relied, upon always to give practical value;, it may be used v.isely and 
 
 ^f 
 
 prudently to guide the engineer's judgment. 
 
.,.,- .- ;. - 
 
38. 
 
 The formula neglects the cohesion of the material and usually gives 
 results too lov;. In New Orleans and other cities similarly situated, the foundat- 
 ion pressures in common use are greater than v.'ould be indicated by the formula. 
 For a further discussion of the assumptions upon which such formulas as (1) are 
 based, consult:- Practical Designing bf Retaining Walls, by V/m. Cain, Van Nostrand 
 Science Series Ko. 3, pp. 1-16. See also, Church, Mechanics of Engineering, 
 edition 1909, part IV. Chap. 3, Earth Pressures and Retaining \Valls, pp. 572-585. 
 
 The Building Laws of Chicago permit a maximum load of 4000 Ib. per sq. 
 ft. when the soil is a layer of dry sand 15 ft. or more in thickness, v.'ithout a 
 mixture of loam or soft foreign substance; or 3000 Ib. per sq. ft. as a maximum 
 intensity v/hen the soil is a mixture of clay and sand, the foundation in no case 
 to extend less than 4 ft. below the ground surface. Assuming the mixture of clay 
 and sand to weigh 100 Ib. per cu.ft. and talcing = 33"42', Table I shov/s that 
 the ultimate supporting power of such a material at a depth of 4 ft. is 4880 Ib. 
 per cu.ft.; consequently an allowed pressure of 3000 Ib. corresponds only to a 
 1.6 safety factor. This latter value is too small, settlement is likely to take 
 place. At a depth of 10 ft. Table I shov/s a.Tiple sustaining 'power for the same 
 niaterial, but there is no assurance of freedom from snail settlement as time 
 elapses, in consequence of the load squeezing out the water or from slow subsid- 
 ing motions due to other causes. 
 
 6. SEMI-LIQUID SOILS 
 
 Quicksand. Semi-liquid soils include soft, marshy and alluvial deposits 
 composed usually of fine sand, and clay intermixed with agricultural mold, or 
 hunras, and saturated with water. Such soils' are found along the sea coast, at 
 stream mouths, along lake or river banks , and in river deltas. The particles have 
 little or no permanent cohesion; therefore the soil has snail bearing power, 
 lailroad embankments or levees constructed on soft marshy ground of this character 
 u-o liable to settle slowly for long periods of time. It is important to have 
 flat side slopes in Order that the foundation area may be increased and the unit 
 
 

 . 
 
 .-. 
 
 
 ' r 
 
 , 
 
 
 :.' V 
 
 ....... . . 
 
 * <J. ; . .' :"': ; .*"'" 
 
 -.'ft' .. . . .. 
 
 - '* ^*' * '-' '' ' f .: 
 
 
 
 nbi 
 
 .li^S arfT 
 R 8 ai Ilos sifc? nad-. 
 
 nr 
 
 . 
 
 
 I ' .r. 1. 1 . 
 
 ' :..:.t'? 
 
 " 
 
 - JA .031 
 
 3i OT ' I 
 
 ^cto 5 
 
 
 ^Ilf. 
 
 - f'.r 
 
 ; 
 
39. 
 
 pressure correspondingly decreased. Settlement is frequently accompanied by 
 rising or bulging of the soil adjacent to the feet of such structures. This danger 
 may be greatly increased where einbanlmients or levees are built v/ith dredges, by 
 the location of the borrow pits too close to the embankment. This is especi&lly 
 tKue in levee construction if the borrow pits are placed on the inside. 
 
 Such ground generally requires special treat, nent before it will support 
 important structures. If possible, foundations should be sunk through it to more 
 stable material underneath. Piles, steel or pneumatic caissons, masonry wells and 
 similar structures are used to attain this purpose. When foundations are sunk or 
 floated so to speak in semi-liquid soils alone, a major part of the supporting 
 
 ? power for the foundation comes from skin friction exerted as the sjdes of the 
 sub-structure tend to sink; kence, the lateral area exposed by the foundation 
 should be made as large as possible. The efficiency ofa pile foundation on marshy 
 ground depends primarily on skin friction. The piles are driven very easily, 
 especially if kept in continuous downward motion by light but rapid blows of the 
 hammer. After a period of rest, however, which allows the mud or silt to close in 
 
 \ around the piles, the foundations can be settled or the indifidual piles settled 
 
 ! only v/ith the ~roatest difficulty. In o xtreme cases of excessively liquid silts 
 
 ! 
 it may be necessary to depend chiefly on the buoyant effect of the material. The 
 
 heaviest structures could be const, ucteii even on water if rafts were built large 
 i enough to float them; the same principle applies in a measure to semi-liquid 
 
 soils. Formula (1) of the previous article could be adapted to the extreme con- 
 j ditions of floatation for semi-liquid soils by making the angle of repose zero, 
 1 in which case the formula becomes p = wx, the same as for hydraulic pressure on 
 
 submerged surfaces. Hence under the vorst possible conditions the poorest material 
 
 is able to support by flotation alone nearly twice as great a load as could be 
 | supported on water because its weight per cu. ft. is nearly twice as great. It 
 ' should be noted that both skin friction and buoyancy, -vary directly with the depth. 
 
 of foundation. 
 
40. 
 
 A serious objection to this class of foundations is that they may con- 
 tinue to sink slowly for many years, as in New Orleans and San Francisco. Consult 
 also the experience at the Lucin Cut-off : ' S.P,H,R. , Salt Lake Division. In San 
 
 x 
 
 Fraraisco the old fipevills swamp which extended inland to Market and Seventh 
 Streets, and along most 6$ the water front mainly to the south of the Ferry Bldg. 
 has been sinking gradually at a rate of from one-half to two inches per year. In 
 this swamp particularly in Islais Creek Basin, marked subsidence occurred at the 
 time of the greet earthquake in April, 1906, 
 
 The term "quicksand" is not easily defined, but is applied commonly to 
 very finely powdered or divided sand mixed with water, the mfc ture sometimes 
 containing a small percentage of clay or very fine silt, such as would be 
 deposited only in quiet water. Almost any vary finely pulverized substance when 
 saturated will flow under pressure like water. Quicksand, confined in place, 
 often gives indication from test borings like that of a solid compact material. 
 When exposed to air and water, it will flow indefinitely and transmit great 
 pressures. Strata of euicksan?. sometimes are found of great d imens ions or such 
 extent that they are very difficult to drain or to penetrate by an open excavation 
 especially when occurring at any considerable depth. Strata of cuicksand may 
 be unexpectedly penetrated. In such cases they slowly flow into an open excavae- 
 tion, causing the superincumbent material to settle, crushing the walls of an 
 excavation, or at least throwing them out of line. It is soneti.ies possible to 
 stop the flow by very heavy bracing and sheeting, with a generous use of brush, 
 
 s 
 
 straw or burlap. 
 
 Where it is necessary to penetrate strata of quicksend to any consider- 
 able depth, resort is had frequently to one or two processes, which, though 
 expensive, are certain of success. In the "Poetsch" freezing process (consult 
 Baker's Masonry Construction, Arts. 909-913, p. 455; 10th ed. , 1909) a proposed 
 shaft is surrounded by a series of pipes eight to ten inches in diameter, inside 
 of which are inserted similar pipes com .Tunica ting directly with a tank. A freezing 
 
; '- ". . - 
 
' 41. 
 
 liquid is circulated by pumping through the smaller, pipes freezing the soil in 
 the form of increasing cylinders around each pipe, \vhich gradually unite, forming 
 a solid frozen v/all enclosing the shaft, or the entire space eventually may be 
 frozen solid. The frozen material can be excavated by ordinary methods, frequently 
 requiring no bracing* The method is expensive because it is necessary to keep the 
 material frozen during the entire progress of the ivork. It seems to have had a 
 rather limited application, donfined principally to the sinking of shafts for 
 mining operations, principally in Germany, and has not been used to any extent . 
 in this country. Consult Eng. Record, July 16,1910, Vol. 62, pp. 62-69, giving a 
 description of the use of t ha freezing method for tunneling the Metropolitan 
 
 Subway at Paris. ,ead Patton, "A Practical Treatise on Foundations, ed. 1906, 
 Arts. 54 and 55, pp. 332-342. Read Jacoby & Davis, Art. 128. 
 
 In the second method, the area to be excavated also is surrounded v:ith 
 pipes, v.'hich need not be more than 1 to 2 inches in diameter, and Portland cement 
 
 
 
 grout is forced under pressure into the material surrounding the pipes. As the 
 cement sets, it forms v.'ith the quicksand a solid mass v/hich can be excavated. 
 It is sometimes necessary, before injecting the cement grout, to establish a 
 fafee circulation betv/een the bottoms of the pipes by pumping v.ator into alternate 
 pipes and allov/ing it to rise in the adjacent ones. This method has the advantage 
 over the preceding one of requiring a, simpler plant and of permanently solidify- 
 ing the -material. This principle may be successfully used to solidify gravel and 
 boulders dumped und-ir v.ater to form a foundation for a dam or other heavy struc- 
 ture. It has been repeatedly proposed for solidifying sand and boulders found in 
 place in the beds of sv/ift bearing streams to form a permanent foundation for 
 impounding dav.s or diverting v/eirs. It may readily ma'::e -possible the construction 
 of important structures in the beds of sv.'ift bearing streams under conditions 
 heretofore deemed prohibitory. The chief difficulty to be encountered in such 
 casos comes from the compactness of the material as found in place, a difficulty 
 
 d 
 
 v.'hich it ought to be possible to overcome by the use of substantial pumping 
 
42 
 
 machinery to force the cement grout at considerable pressure into the surrounding 
 material. 
 
 In alluvial semi-fluid river silt or quicksand, loads of from one-half 
 to one ton per sc . ft. cm be appliod \vith s.-sall settlement. The bearing paver 
 of the material as shov.Ti by ..lathematical an** ."sis is dependent largely upon the 
 depths to -.-Inch foundations are carried. 
 
 METHODS OF HjgHMSIMi TEL BLAHILG PO'TER 
 
 OF S/iRTH FOUNDATIONS 
 
 
 
 1. Depth; sea discussion (fig. 9) 
 
 2 Dra inage 
 
 3. Confinement 
 
 4. Sand Piles 
 
 5. Stock Ramming 
 
 6. Sand Layers. 
 
 DRAINAGE AIJD CONFIEEuEL T 
 
 The bearing povrer of clay, sand or sediment soil is increased greatly 
 
 i 
 by drainage. As tho v/ator is v/ithdrav/n, the bearing pov:er is improved. Surface 
 
 rater can be excluded from a foundation bed b}- using surface or subsoil drains, 
 laid st the bottom of a trench 'surrounding the structure, backfilled v'ith gravel 
 or other porous material. Common unvitrified agricultural or drain tile (simple 
 C3'lindors vith plain ends, usually in 1 ft. lengths) should be used at the bottom 
 of the t rcnch at 1; vcls somov/hr.t bolov: the foundation footings. This is a common 
 procedure for v/alls of buildings. The exclusion of underground, or percolating 
 v.Titer is often a more difficult problem, especially if the v.atcr rises under 
 pressure from bcloir;. It ie very important that the problem be solves, especially 
 for clayey soils or fi'nc sand. If thoro is evidence of vat or percolating from 
 below oror an entire foundation bed, a layer of coarse grovel c an be spread below 
 the foundation and a system of opcn-jointoc! tile drains imbedded vheroin to lead 
 off the vator. If the percolating \.ater comes laterally from higher ground, or 
 follows horizontal scams, trenches filled v:it> coarse grr.vol and the drains may b 
 dug around the foundation site as described for the exclusion of surface v;atcr. 
 oomcti.nos instead of filling the trenches \vith g;avol, they are backfilled v.'ith 
 
43. 
 
 an impervious material, such as puddled clay or concrete, tiles being laid at 
 the bottom of the trenches, and perhaps, halfv.r.y up, to carry off the v;ater. 
 Springs are frequently encountered in deep trenches, and may cause 
 trouble. The worst cases occur at the junction of strata of compact clay \vith 
 gravel, or coarse v.atcr bearing sand. In clay or find, sandy soil, precaution 
 should be taken to plug or stop springs or permanently drain them, otherwise the 
 flowing water may eventually \vash awey the fiioer materials and undermine the 
 foundation, \7here complete drainage is impracticable, springs frequently are very 
 ti ouTblesome during construction, impeding the workmen and, where concrete or 
 .nasonry is used, washing out the cement bc-forc it has had time to set. If the 
 water Cc.n b e gathered into one stream, it :&.- bo led av.ay by a pipe, permanently 
 jmbedded in the foundation. In firm material, such as rock, hardpan, or compact 
 clay, springs may be plugged by masses of hydraulic cement 1 mortar. In the con- 
 struction of dams, or retaining \7ells, vent holes sometimes crc built in the 
 masonry and the water allov;ed to flov; freolv until the structure has been built 
 to such a height that the water roe.chos its natural level. At times masonry is 
 laid on heavy tarpaulins, cove-red with pitch., or other waterproof material, to 
 prevent the sashing away of the cement. In extreme cases, springs or the entire 
 foundation 'site may have to bo surrounded with tight sheet piling to exclude the 
 water from the space enclosing construction. 
 
 Sand Pilo.g_ 
 
 The bearing pov/or of compressible soils e en be increased by method's 
 which compact the material as veil as by draina-je, thereby increasing the support 
 ii:g power and materially decreasing the liability to settlement. Soils can be 
 co-pacted by sand piles and "by stock ramming, iieither of these methods is common, 
 altho'ugh they have' been used advantage ously ir so no cases. The sand pile is 
 
 formed by driving an ordinary timber pile into -c Jo soil to the desired distence, 
 chen quickly withdrawing it and immediately filling tl:.e jolo wit> sharp sand. The 
 density of the soil is increased if the sand is pk-.ced in the I ole in layers and 
 
44 
 
 rscmed; because seme of the send vdll be forced laterally into the surrounding 
 mat-rial, thus largely augmenting its supporting pa; or. The increased solidity 
 secured vill depend upon the number of sand piles driven, the piles being more 
 numerous as the original compactness of the rate-rial is less. The piles may be 
 placed from 2 1/2 to 6 or 8 ft. apart on centers. If too many sand piles are 
 
 driven the ground, is liable- to hea.ve 
 
 % > 
 
 STOC::-: RU/DIIES 
 
 The process of stools ramming consists ii; forcing clay or clayey 
 natc-rial into the interior of the yielding nass of earth v/hich is c". o signed to 
 carry the structure. :: pipe 2 to 3 or 4 inches in diameter may b o driven to any 
 required depth from 5 or 6 to 25 or 30 ft. into the foundation bed. An iron or 
 stoel rod closely but freely fitting its ':>oro is used as a ranncr from a frame 
 erected over the uppc: end or uouth of the- pipe. Balls or cartridges of the clay 
 
 * 
 
 ar clayey matorirl made from 6 to 12 or 15 inches in length are tlx-n put into the 
 pipe and rammed into the material adjacent to its lav or ^nd. '.hen a sufficient 
 
 quantity lias boon thus forced into t~...e surrounding .ur.ss., the pipe isv: ithdrav/n 
 
 . 
 from 2 to 4 or 5 ft. and. the process repeated. In this r.ianncr the required amount 
 
 of sfcbck may be ramrod into the foundation bed at such depths and elevations as 
 
 are 
 vill produce the desired degree of compactnesc. If sane and gravel : ::nixcd v;ith 
 
 the clayey stock to b.. ranged, it must be in sufficient ly moderate amounts not to 
 jam or choke in the pipe. This process, like all similar operations, vrill d opend 
 for its extent and frequency of applicrtion to any giv..n found.ation bod, upon tho 
 judgment of the engineer in charge of the v;ork. 
 
 SAIflD IAYERS 
 
 Soft and yielding material frequently maybe very much improved in its 
 bear ing -capacity by an cjccavatio: vom 1 or 2 to even or 6 ft. beloi,' the bottom 
 of. the proposed foundation, and r-filling vith cloa. , shcjrp send. The send, should. 
 
 be placed in layers, moistoncd and relied so as to be forced into tho surface of 
 
 -i 
 
 tho surrounding material and cxipactcd. The foundation pressure which acts upon 
 
 ouch a base or bed v/ill be transmitted in lateral directions so as to increase 
 
45 
 
 / 
 
 very considerably the aroa over vhipJi tlio presaire Is ultiinatcly distributed. 
 
 It is sonctinos necessary to found, structures like railroad embankments 
 
 upon semi-liquid soils in marshy or sva;npy land, at levels so lov: that drainage 
 
 / 
 
 is i .practicable. In such cases great improvement results by dumping in sand, gravel 
 and broken rock, allowing tho materials to fine their ov.n levels and distribution 
 by settling i.: tho :nud. This method > s boon used extensively for some of the 
 .larger structures on tho Panama Canal? also v;hero California Railroads have been 
 built across lovlying laarshus. Railroad embankments, aqueducts and outfall sev;eis 
 sometimes have been supported; i:. svr..;ps, on fascines or mattresses of brush and 
 lo^s. The bearing povrer ov even a fairly solid soil usmally v:ill be increased by 
 spreading upon its surface a layer of sand or gravel* 
 
 TEST IKS TEE B^iaiEG PCTSS .OF SOILS. 
 
 of 
 Direct tests of tha bearing -per: or soils are made frequently, especially 
 
 in nc-v; and untried Ix at ions, before completing tlio design of foundeticms for 
 
 important structures . Tho tests should bo conducted, if practicable, at the bottom. 
 
 % 
 
 of trenches, excavated to the sc.r.a depth as is proposed, for tlw actual foundctions, 
 and vith tho soil in its nonnal condition. The test load should cover as large 
 an area as possible (one q. ft. is frequently used). The a at hod commonly 
 anploycrV is to dig a laolo 1 to 2 ft. squaic-, several fo.t deep, to'placo in it 
 a heavy timber post, 12 by 12 rnches, in cross section, 5'*.o 10 ft. long. Tho 
 post is supportoc by gay ropes, a strong platform built on top of it, to be 
 loaded vith pigiron, rails., or sacks of cement. A number of stakes should bo 
 driven in the immediate visit? it y and their elevations carefully determined. The 
 tests should bo continued for several days or \vcoks , rnd accurate observations 
 made of its sottle.:iont, also of any changes in the level of the surround. ing soil. 
 If earth saves form nerr the trenches, it is an indication that tHe soil is 
 disintegrating or unstable. Frequently, t\vo posts arc sot, connected by a saddle. 
 or four posts, supporting a hoavy table 3 to 5 ft. square. Tho soil sometimes 
 is lce-ot 'moist c.rd the Iced shaken in order to :;ivo tr.3 i/orst possible condioixs. 
 
46 
 
 The foundations for the St. Paul building in Nev; York (Eng. Record, May 2,1896) 
 were tested with a" single post loaded to 6.5 tons per sq. ft. The load v/as shaken 
 ?nd water poured into the trench for sovarr.1 v.eeks, the final settlement being 
 19/32 of an inch. The foundations for the largest chimney in the world at Great 
 Falls, Montana (Eng. Record, Nov. 23, 1903) were tested with four cast iron plates 
 
 2 ft. square; 200,000 Ib. of steel rails, equal to a pressure of 6.5 tons per 
 
 sq. ft. were required to er.usc a settlement. This chimney is 506 ft. high, weighs 
 18,000 tons; the diamater varying from 50 to 80 ft. With a wind allowance of 
 33 1/3 Ib. per sq. ft. corresponding to a velocity of 135 miles per hour, the 
 narimum pressure on the .foundation bod, of uniform shale 22.5 ft. below the 
 surface, is 4.83 tons per sq. ft. 
 
 In August 1907 a test v/as made in Oakland, California, by the Board of 
 Public \7orks, for a foundation site to carry a fiv,. story, Class B, reinforced 
 concrete building. The soil under tha proposed footings consists of a mixture of 
 clay and sand, about in the proportion of 7 to 3. The subsoil had been excavated 
 to a depth of 10 ft, over the entire lot area of 10,000 so. ft. ; the footing bed 
 at 10 ft. r.epth had been graded and the loose soil made firm and compact by 
 frcruent wotting. It was questioned v.'hethor this soil could carry 5 tons per sq. 
 ft. A large sugar pine stick, 12" x 12" x 10' was supported on tvo sides by 
 scantling. After tho loo&e surface material had boon scrap;'." away to a depth of 
 
 3 inches' the bo'ttom of the- ^inc stick wrs allow ,d to rest on the soil The load 
 
 t 
 
 acmsistoo. of old stool rails and barrels of ce..icnt. The. cement was rolled upon the 
 jlatform with much shock. A 'record of tho tost is as follows: (see page 47) 
 
 For a total load of 31,000 Ib. or 15.5 tons per *. . ft. representing a 
 ?actor of safety of 5, tho total settlement was 0.85 inches-, whicl. increased to 
 A .87 inches in 48 hours. It v/as concluded that "the soil v/as amply safe to carry 
 '-ho footings to be installed and tho structural loads thereon". 
 
.- . ': 
 
47 
 
 Date 
 
 Timo Load in Ibs. 
 per sq.ft. 
 
 Depression 
 inches 
 
 Aug. 12, 1909 
 
 2:30 p.m. 
 
 
 
 0.0 
 
 12 
 
 3:30 p. 3. 
 
 2175 
 
 0.0 
 
 12 
 
 4:00 p.m.. 
 
 4256 
 
 0.0 
 
 12 
 
 4:15 p.m. 
 
 6426 
 
 0.1 
 
 12 
 
 4:30' p. .- ; . 
 
 8501 
 
 0.15 
 
 12 
 
 5:00 p.m. 
 
 10576 
 
 0.2 
 
 15 
 
 5:00 p.'.a. 
 
 10576 
 
 0.2 
 
 16 
 
 8:30 a.m. 
 
 12651 
 
 0.25 
 
 17 
 
 3:30 a.m. 
 
 31000 
 
 0.85 . 
 
 17 
 
 5:00 p.m. 
 
 31000 
 
 0.85 
 
 19 
 
 8:30 a.m. 
 
 31000 
 
 0.67 
 
 In Engineering News -Record, Vol. 89, July 13, 1922, p. 73, is described 
 a continuous mat foundation for a 22 story building, the Standard 041 Building, 
 San Francisco, founded 1 on an inverted floor of reinforced concrete 3 ft. thick, 
 reinforced by girder ribs b etwocn column footings. The article illustrates the 
 test apparatus used to determine the bearing quality of the soil, Bush and Sansome 
 St. Cf. also Proc. Am. Soc. C,. , ifarch 1922, p. 523, for a more elaborate 
 discussion. 
 
 PRESSURES ON FOUNDATION. BEDS 
 
 Abnormal Pr e s sur o . The abnormal pressure on a foundation bed produced 
 by a structure; , is the pros sur ^ which is in excess cf that v.'hich existed there 
 before any excavation v/as .?ade.It is equal to the total final load on the found- 
 ation bed, minus the original weight on the bed caused by the pressure of tho 
 earth, sand, rock, mud, water, originally above it. 
 
 EXAMPLES OF PRESSURES ON FOUj^mTIONS. AND 
 FOUNDATION BEDS IN LAH?H AN p_ SAHD 
 
 Example Tons per sq.ft, 
 
 Pressure on concrete and granite masonry, Brooklyn Bridge 26 
 
 .abnormal pressure on firm sane, in ba~s and estuaries 5.0 to 5.6 
 
 .Abnormal pressure on firm sand and sandy gravel 616 to 7.8 
 
 Vbnormal pressure on firm shale and gravel 6.7 to 9.0 
 
 ' bnormal pressure on compact gravel . 7.8 tc 10.1 
 .Washington .Monument: 
 
 1 = Excluding wind, average pressure on base . 5.67 
 
 2. Average of same under concrete base, upon sandy and gravelly 
 
 ground 6.5 
 
 3, Maximum pressure possible v;ith wind 9.0 
 bunker Hill Monument, hard sand and gravel 5.5 
 
 lurch Tower, Fifth Avo. and 27th St., New York City, hr.rdpan 7.0 
 
48 
 
 Bridge over Ohio River, Cairo, 111., piers 50 ft. into sand: 
 
 Max. abnormal pressure under piers 4.0 
 
 Mas. v:hen allowing for skin friction 3.0 
 
 Proposed Korth River Bridge; abnormal pressure on send: 
 
 Promoter proposed 7.16 
 
 Finally limited to 5.0 
 
 Hawksburg Bridge, Mew South V/ales; water 70 ft. deep, foundation 
 
 bed 162 ft. belov; water line; 8 ft. into sand, abnormal pressure 5.7 
 Summary, pressures upon earth and sand 
 
 Average for good deep foundations 5.0 
 
 Average for good shallow foundations 3.0 
 
 The above are all for deep foundations upon sand. , gravel or granular 
 deposits. Belov,- are average values for light, shallow foundations in clay, sand 
 and earth. 
 
 T7ell drained clay, always practically drgr 
 Clay> moderately dry 
 
 Clay, soft, moistened (Chicago conditions ) 
 
 Coarse sand or gravel, in strata, undisturbed and well bonded 
 Ordinary sand, thoroughly compacted, bonded, and well held 
 in place 
 
 Tons, p. sq.ft 
 4.0 to 6.0 
 2.0 to 4.0 
 1.0 to 2.0 
 6.0 to S.O 
 
 2.0 to 4.0 
 
 The pressures on a number of deep foundations, in tons per sq. ft. 
 of 2000 Ib. as 'determined or listed by E. L.Corthell, are as follows: 
 
 Material 
 1 
 
 . 
 
 Pressure, tons pe 
 
 c sq. ft. 
 
 No. of 
 examples | 
 
 rain . ' 
 
 max. ! avg. 
 
 ! Fine sand \ 2.25 | 5.8 
 
 4.5 10 
 
 Coarse sand and gravel j 2.4 
 
 7.75 
 
 5.1 
 
 33 
 
 Sand and clay 
 
 2.5 
 
 8.5 
 
 4.9 
 
 10 
 
 Alluvium ani silt 
 
 1.5 
 
 6.2 
 
 2.9 
 
 7 
 
 Eard clay 
 
 2.0 ! 8.0 
 
 5.08 
 
 16 
 
 Hardpan 3.0 ; 12.0 
 
 8.7 : 6 
 
 See reference No. 7 at the close of this chapter. 
 
 Corthell further finds the following frictionr.1 resistances between 
 pier sides and. foundation materials. For steel cylinder piers, thoyaiethe 
 least for .nud, the mofet for gravel. For masonry piers the figures are lov/est for 
 sand, and gravel, greatest for sane: and clay. 
 
 Fractional Resistance, Ibs. 'oor sq.ft. 
 
 Ho. of Examples 
 
 l.lin. 
 
 1 I/lax, i -kvoraso 
 
 300 
 300 
 
 205 
 
 i 
 
 1500 
 1000 
 450 
 
 540 
 522 
 270 
 
 10 cylinder piers 
 23 r.iasonry piers 
 5 walls, quays, etc. 
 
 For average values of the coefficient of skin friction, Corthell s 
 
 
 sheet iron on sand 
 sawed lumber on sand 
 masonry on sand 
 
 0.4 
 
 0.65 
 
 0.65 
 
49 
 
 1.0. Baker in his Treatise on Masone-y Construction, 10th ed. , 1S09 ; 
 p. 464, gives r, more o:Lhaustive table of values for coefficients of si: in friction 
 Seo also Tablo 59, p 342, on safo boar ins power of soils. Examine Tables 1,2,3, 
 by A.C.Alvarez, on properties of materials. 
 
 PiY; FOUNDATION SOILS: TEEIH SUPPORTIK3 CAPACITY 
 
 1. Any material vrhicl: can be called rock, vhen its bod is properly 
 cleaned and prepared foi the foundation, vill bear safely any stricture liable 
 to b e placed upon it. 
 
 2. Boulders and gravel, usually are able to support any ordinary 
 structure, especially when they arc cemented into hardpan by mixing v.lth small 
 quantities of sand and clgy or earth. 
 
 3. Ordinary (siliooous) sand vill bear safely heavy loads if the sand 
 is properly confined; but great care must bo taken to prevent it from spreading 
 laterally; also, to prevent scour from the action of running, or even percolating 
 v/ater. 
 
 4. Clc.-y makes a satisfactory/ foundation bed when it is kept dry. 
 Particular care should be taken to prevent clay from being alternately v;ot and 
 dry; a Iso to carry foundation trenches v;cll b elov; the frost line, 
 
 5. Good foundations can be constructed on sediment soils or loam if the 
 material is homogeneous throughout tr..e entire rrea undoi lying each structure; 
 and v.cer in addi.ion the design provides ane^ual intensity of load under all 
 footings. Some settlement I/ill occur, but it v.lll not bo particularly injurious 
 if Si7r.ll in amount, ard uniform for each structure. 
 
 6. By special treatment ,, quicksand or semi-liouid marshy soil can 
 support moderate .lor, ds. iiuch of its'boaring pov/er depends on t v ,e principles of 
 flotation and skin friction; hence the foundations should be sunk as deep a s 
 possible. It may be necessary to employ unusual processes, such as freezing or 
 cement grouting, but o :on excavations can bo tadCv 
 
 7o Except for a structure founded on solid rock., the base bed or 
 footing should be spread sufficiently to keep the foundation pressures per sq. 
 ft. t.'ithin allov.rble safe limits for soil bearing capacity; the foundation should 
 bo carried bolovtho frost line, and in soft materirl, as much deeper as prac- 
 ticable. For substructures resting on rock or hard.pan c: ro should be exercised 
 to limit pressures on foundation b-^ds so -chat they do not exceed safe compress- ' 
 ivc stresses for the materials used in the footings 
 
 . . < t 
 
 ADDITIONAL REFERENCES 
 FOUNDATION SOILS AND 
 
 1. A Practical Treatise on Foundations; V/MLPatton; art 1, pp. 1-^ 
 
 2. A Trortisc on Liasonry Construction; I.O.Balcer, Part III, pp. 333-347 
 
 3. The Foundations of the Kcv; Caiitol at Albany, W, J.ilcAlpine; Trrns, Am. Soc. 
 
 C.E. , Vol. 11, p. 287, 1873. 
 I.. Description of the Iron Viaducts erected across the Tidrl Estuaries of t:.e 
 
 k Rivers Leven and Kent, in Moreccmbe Bc.-j, for the Ulver stone and Lr.ncaster 
 
 Ry> ; by Jrmes Brunlcos, Proc. Inst of Civ. Engineers, Vol. 17, p. 442, 
 1858, 
 
50. 
 
 5. Cleeman's E, R. Practice, pp. 193-104., 
 
 6. Professional Papers, Eayal Engrs. Vol. 20, p. ISO, Quicksand Foundations. 
 
 7. Allov/able Pressures on Docp Foundations; L,L.Corthell; see particularly p. 37 
 
 for 58 references from Ermine or ing Index, 1896-1900. 
 
 8. Architects' and Builders' Pocket book, F.L.Xidder, Chap. II > pp. 155-146, 
 
 9. The Station B Chimney of the 17 av; York Steam Co. Chas. E.Emory; .Trans. Am. Sx . 
 
 C.E. , Vol. 14, p. 182, 1885. 
 
 10. The Y/eight on Foundations of Buildings; H.Leonard; Engineering, Vol. 20, J.103; 
 
 1875. 
 
 11. Proc. Inst. C.3. Great Britain, Vol. CLZV, 1905-6; Part 3, 
 
 12. fi conrpositc sr.nd and rode foundation; :,lunicr3al Bldg. , Net; York City; Eng. 
 
 Nev/s, Vol. 63, Jan. 6, 1910, p. 24; also Vol. 64. Nov. 17, 1910, p. 523 
 
 -13. Hardpan.'" and other Soil Tests; by J.M, Jensen, Eng. Kev/s, Vol. 69, i-iarch 6,1913, 
 p. 460. 
 
 14. Testing Rock Bearing by Leverage Load ing 'Machine ; Eng. News -Re-cord, Vol. 85, 
 
 Aug. 26,1920, p. 417 
 
 15. Foundation Tests for Nebraska State Capitol; Eng. Hev/s -Record, Vol. 85 Oct. 12., 
 
 1922, p. 606. 
 
 16. Tests of the Bearing Capacity of Soil; St. Paul Building; Eng. li'ovvs , Vol. 35, 
 
 p. 310 
 
 PROBLEMS 
 
 1. State different methods for consolidating soft and compressible soils to 
 increase their bearing capacity for shallot? foundations. Illustrate where necessary. 
 
 2. Give range in each ease of numerical values for sr.fo bearing pov/er of 
 various foundrti on soils from took to the most treacherous types. 
 
 3. The greatest slops of an earthy hillside 3s 24*. If the angle of repose 
 is 32* , compute by Ranlcino's formulas the passive intensity at a depth of 34*. 
 7/hr.t is the abutting intensity? Compute by the s arae theory the position, c'irectim 
 and amount of the total passr-ve and abutting thrusts respectively exerted against 
 a vortical surface 3' V by 1' H, 38'. belov/ the surface. Submit a scale diagram, 
 Cf. KG t churn, I/alls, 'Bins and Grain Elevators, Chap. I, particularly oqs. 7 and 8. 
 
 4. In v:et sand v;hosc top surface is horizontal, \vhat vertical pressure everted 
 upon a foundrtion bod 24' belov.' the surface v/ill just tend to heave the surrounding 
 material? 
 
 . 5. Define abnormal pressure for a foundation bed. Bivo skin friction resistance 
 for tho sides Of piles and caissons s.unk in different soils, 
 
 6. A total load of 10.55 tons rests upon a 16" s. 16" timber usoc 1 as a test 
 piece to investigate the bearing 'capacity of a given soil. 'That is the pressure en 
 the soil in ; ,',D' i-f the load is central? YThy is it important to have the load 
 central? If in one direction the load is eccentric 3 1/4", compute the min. and 
 -:a::. pressures exerted upon tho SD il. 
 
 7. In tho throe cases given, \vhat pressure may be allowed untfor a contiguous 
 ;oncrot'' footing \: ich supports a building v;ith brick avails. The foundation soil 
 is (a) earth, (b) dry sand, (c) hardpan. Explain th: effect (on values assigned) 
 )f depth bclor; the surface- of the ground. 
 
51. 
 
 CHAPTER ^ 
 
 CLASSIFICATION AND KEQUIK2MENTS 
 FOUNDATION DLSIC-KS 
 
 Classification. 
 
 After complete explorations and soil studies have boon made to enable the 
 engineer to select a proper scheme of foundation, the plans for the substructure 
 -nay bo olaborrtec". Foundation types do not ad-nit <5f vary distinct classification. 
 They may bo grouped as follov/s: 
 
 A. According to the Material Upon Which they Rest, 
 
 1. Foundations immediately on rock 
 
 2. Foundations on hardpan, confined sand or dry clgty 
 
 3. Earth or soil foundations 
 
 a. ordinary soils 
 
 b. compressible soils 
 
 c. seal-liquid soils 
 
 B. According to Type of Structure Designed 
 
 1. Footings:- timber; offsets of nasonry or concrete; timber 
 
 grillages; inverted arches of brick, masonry or concrete; 
 steel 'Tillages of roiled I or channel beams and 1 , concrete, 
 reinforced concrete, 
 
 2. Shoot piling:- timber, steel, reinforced concrete; light 
 
 and heavy sheet piling- 
 
 3. Bearing Pile Foundations: timbo, , reinforced concrete, metal 
 
 4. Coffer dams 
 
 5. Upon caissons 
 
 6. Pneumatic caissons 
 
 7. Deep v;cll dredging 
 
 8. Combination and miscellaneous foundations. 
 
 In v.'hat follov/s, this classification, so far as feasible, v/ill be observed. 
 Foundations usually arc sufficiently complex to bo included uncer tvo or mere 
 of these headings. Shoot piling, by itself, is not a foundation, but may be a voyy 
 necessary preliminary part v.'hich makes possible excavation in soft material and 
 then protects the real foundation during its construction. 
 Zoundat ion Bco ui roraont s 
 
 1. SJicnevcr possible a foundrtion bed should 1 , bo rough, properly stepped, 
 
 % 
 
 -nd perpendicular to thv, resultant pressure upon it. In general, like a masonry 
 joint, it must be capable of v.lths tending overturning. 1 sliding and crushing. To 
 ".void tension in t>o bed, in no case should 1 'the resulting pressure lie outside of 
 
52 
 
 tho middle third, Usually the slier-ring strength of the bed is neglected; then to 
 
 
 
 prohibit sliding, the resultant pressure must never make v/ith the normal to tho 
 bod an angle exceeding the angle of friction for tho materials of the bod. 
 
 2. A foundation bod must always be placed safely below the depth to which 
 freezing and thawing penetrate. 
 
 3. Always e;:cludc surface wators from a foundation bod; confine, stop 
 or regulate the flow of underground water. 
 
 4. Attempt to prepare a foundation bed. so that it offers a uniform 
 jaatorial; that is, one of equal bearing capacity and equal compressibility for 
 .the entire area of foundation base, 
 
 5. Footings, particularly for buildings, and especially for walls vs. 
 interior columns of buildings, should bo designed of such dimensions that the 
 foundation bod at all places under the structure is subjected to tho same intensity 
 tef pressure, otherwise, even with equal homogeneity or compressibility, unequal 
 fccttlomcnt will take- pir. cc. 
 
 6. For complex 'footings, the resultant lord on the- bod must coincide 
 
 . 'ith the center of gravity of tho foundation plan, assuming uniform pressure on 
 t'-!.o bod; otherwise, the foundation will be subjected to a bending couplo and 
 /."ill tend to tilt or settle unequally. The so-called t.apezoidal or combined 
 irb footing for a building exhibits a si.nplc example of the application of this 
 rinciplo; where, to roruco the magnitude of the pressure intensity on the bed, 
 wall and an interior column, unequally leaded, arc jointly supported on a 
 ounce ting slab, 
 
 7. Tho main t>arts and all structural details or joints for simple or 
 
 . 
 .:pl cm' foundation structures must be designed for the materials used and tho" 
 
 .zinu-.; stresses to be borne. In bridge trusses s building grrmcs and other similar 
 scs, the probable str.sscs cm bo computed, with a considerable degree of accuracy- 
 om the nature of substructure designs, thoy arc more massive than steal trussing 
 LC: --lees it more- difficult to analyze for existing strossos. Usually only 
 
53 
 
 approximate calculations con be made. A sound judgment must bo exercised in fig- 
 uring safe dimensions; for example, for the roof beans, side rails, side v/all 
 brackets, and cutting edge of a modern structural stool pneumatic caisson. Simple 
 methods only can be used \vhon stress calculations are made for the design of v;all 
 timbers, bracing struts and anchorage rods in a typical timber cofferdr,.n. Intoll- 
 ^igent methods for analyses nust be proposed, safe specification for v/orking 
 stresses written and sane selections .rsac'o for the particular naterisls to be 
 employed (whether wood, metal or :iasonry).In one case vood is the logical 
 material, in another, it is steel or reinforced concrete. 
 
 REFERENCES - SPECIFICATIONS 
 
 '1. General Specifications for Foundations ancl Substructures of High-ay Bridges; 
 by T. Cooper, 1902. 
 
 2. General Specifications for Bridge Substructures; oho Osborn Co. 
 
 5. Specifications for Ilasonry; Appendix 3; A Treatise on Ilasonry Construction; by 
 I. 0, Baker, 10th od. , 1909, p. 729. 
 
 4. Sec Appendices - Ordinary Foundations, by C L. Fov/lcr 
 
 5. See Appendices - Subaqueous Foundations, and Lnginooring and Buildirg 
 
 Foundations; by C. E. Forolor. 
 
 ^m 
 
 6. Foundations of Bridges anc! 'Buildings; by Jacob;- & Davis, Chap. IS; references. 
 
 7. Design of Ilasonry Structures r.nd Foundations; by C.C.".illia.rs. 
 
 BROBLE.IS 
 
 1, State the seven .or more important requirements which should bo observed in the 
 
 preparation of foundation bids rue. the- design of foundation structures. 
 
 2, Name tho different typos of foundation structure as enumerated in Chap. 3. 
 
 m List the chief groups of masonry structures discussed in the texts of 
 references 3 to 7 inclusive. 
 
. 
 
 '-; ' '. ' 
 
 f.Jcii;". . . -i : - 
 
54 
 
 CHAPTER 4 
 DISTRIBUTION OF FOUNDATION PRLStURES - SPREAD FOOTINGS 
 
 Unless a structure is founded on solic 3 rock, it is necessary that the 
 foundation have an area sufficient to give safe unit pressures on the bed. ,,iany 
 soils, in any event, will permit of slow settlement, which may not be particularly 
 
 injurious if uniform throughout the entire s true ture. In order to secure uniform 
 
 ** 
 
 settlement it is necessary, if the underlying material is homogemeous , to design 
 
 the footings for various parts of a structure so that the pressure on the bed v/ill 
 be of constant intensity. If parts of a foundation bed are more compressible 
 than others, the footing should be so d esigned that the unit pressure v/ill b e 
 less on the weaker material. 
 
 The major pressures on foundation bed's are produced by the dead 
 weight of the sub- and super-structure plus the live load which they are 
 designed to carry, all acting vertically, ilany s tructures , in addition, are 
 subjected' to various lateral forces; applied horizontally or inclined at any 
 angle. For fcall buildings, chimneys, towers or monuments', horizontal wind pres- 
 sures are important. For slender bridge piers, it is necessary to consider 
 besides wind such forces as the dynamic pressure from running water, and 
 pressure from drift rood or ice. In some cases also tractive or centrifugal 
 forces c ausod by moving loads on the superstructure may not bo negligible. 
 Foundations for docks or quay walls should b e designed to withstand impact from 
 v/avesand moving ships. Foundations for arched b ridges and retaining walls 
 must bo designed to resist lateral thrusts. In archos and suspension bridges 
 it is important to consider temperatuie stresses arising in the superstructure. 
 For anchorage piers of cantilever and suspension spans, there may b o large 
 uplift forces. 
 
 The vortical loads usually are much larger than the inclined or 
 horizontal ones; they frequently cause the only foundation -pressures requiring - 
 consideration. A careful analysis for foundation s tability of a structure 
 
55 
 
 should always be made, considering the dead loads of sub-and superstructure 
 with all possible combinations of live loading, lateral forces and uplifts. The 
 
 m "\ 
 
 magnitude, line of action and point of application of the resultant force on 
 each foundation footing should be determined before accepting the superstructure 
 design. Similar calculations should be made for joints at other levels above 
 
 the bed; particularly in tall piers. The r esultant force, in most cases, is 
 not fixed either in position or amount, because of the constant variation of 
 live loads and lateral pressures, 
 
 In buildings the dead weight of the structure can be .computed from 
 
 the cubical contents and the known weights per cu. ft. of materials. The min- 
 i 
 
 imum live load for which a building should be designed is fixed by the specif i- 
 
 Bridges r.re^ usually designed for s. series of wheel concentrations 
 cations i^which represent more or less closely the loads brought on the Structure 
 
 by moving trains, road rollers or trolley cars. Buildings and highway bridges 
 are designed for a certain minimum specified live load "per sq. ft. of floor 
 surface. 
 
 The following table taken from Baker's Treatise on Masonry Con- 
 struction, od. 1909, p. 348, gives/unit weights of masonry. Handbooks like 
 Trautwine, Kidder and Cambria offer more elaborate, specialized tables for 
 masonry, building details, weights of roofs and floors. Consult Kidder, od. 1908, 
 p. 1343. 
 
 WEIGHT OF MASONRY 
 Kind of Ursonry Ugt. in Ibs. per cu.ft. 
 
 Brickwork, prossad brick, thin joints 
 
 Brickwork, ordinary quality 
 
 -Brickwork, soft brick, thick joints 
 
 Concrete, 1 cement, 3 sand and 6 broken stone 
 
 Oranite, 6% more than the corresponding limestone 
 
 Limestone, ashlar ; largest blocks and thinnest joints 160 
 
 Limestone, ashlar, 12" to 20" courses and 3/8" to 1 1/2" joints, 165 
 
 Limestone, squared stone 
 
 Limestone, rubble, best 14 
 
 Limestone, rubble, rough 
 
 Sandstone, 14$ less than the corresponding limestone 
 
'>.: 
 
56 
 
 ADDITIONAL QUANTITIES 
 
 Typical Structure Ugt. in ftl>s.per._sg. ft . 
 
 Suspended ceilings (metal lath and plaster) ' 10 
 
 Ordinary lathing and plastering 10 
 
 Floors for dwellings (usual wood jojst construction) 10 to 30 
 
 Floors for public buildings (higher figures ere for sto*>l & concrete, 45 to 100 
 
 Floors for warehouses 80 to 120 
 
 Shingle roof 10 
 
 Slate or corrugated iron roof 25 to 30 
 
 Consult Ketchup, Steel Mill Buildings, Pert I, Loads, pp. 5-21; 
 Also Ricker, Design and Construction of Eoofs, Chap. 3, pp. 22-25. 
 
 The minimum live loads for which buildings can be designed will vary 
 in different localities and for different types of buildings. The Cambria Steel 
 Handbook, ed. 1919, p. 328, gives a su.n.iary of floor loads prescribed by the 
 Ordinances of thirty- one American Cities. The following table is compile^ frcm 
 Sec. 54, ed. 1921, San Francisco Building Code: 
 
 LIVE LOADS FOB BUILDINGS 
 Kind of Building Live load,lbs. per sq.ft 
 
 1^ Dwellings, office floors, apartment houses, tenement houses., 
 
 hotels, hospitals 40 
 
 2. School rooms and theatres with fixed desks and seats, stables 
 
 and carriage houses 75 
 
 3. Garages, automobile salesrooms, light machine shops and 
 
 department stores 100 
 
 4. Halls of public assemblages, without fixed seats, hells of 
 
 schools , theatres and hospitals, ordinary stores^and 
 
 floors of light manufactories, warehouses for light 
 
 storage as furniture or other bulky materials 125 
 
 5. Stores -frith heavy loads, stack rooms of libraries, warehouses, 
 
 ordinary manufactories 
 
 6. All sidewalks 
 
 7. Roofs, pitch less than 20, live load per sq. ft.- horizontal 
 
 projection 
 
 8. Roofs, pitch greater than 20, live load per sq. ft. horizontal 
 
 projection 
 
 See also Sec. 57 for allowed foundation pressures; "Soils carrying 
 foundations shall not be leaded more than the following number of tons par sq. 
 ft. : soft clay = 1, sand and c lay mixed = 2, firm dry clay = 3, hard clay = 4, 
 loam Or fine dry sand = 3, compact sand = 4, coarse gravel = 6, shale rock 
 hard rock = 20. Seo also Sec. 58 for allowed unit loads on masonry. Consult 
 Cambria, p. 338, 1919 edition. 
 

 
57 
 
 CENTER OF T/EI3HT VERSUS CENTER OF FIGURE FOB BUILDING FOOTINGS. 
 In general, the most important guiding principle for the design of 
 foundation footings is to make the center of pressure or weight coincide as 
 nearly as possible with the center of area of the base. Footings for different 
 parts of a structure should be proportioned to give the same unit pressure on 
 the soil. In designing continuous footings for t he walls of buildings on homo- 
 geneous ground, the footing widths should vary directly with t he weight on the 
 wall. If a heavy exterior wall, WJL (fig. 10) is rigidly connected to a light 
 cross wall, V/g, and their footings are of the same width, there is a tendency 
 for the inner wall to crack. Suppose that in plan 10A, the line of action for 
 the weight on the walls is in the position indicated by the arrows, A, while 
 the upward pressure B from the foundation bod, equal in amount to the weight of 
 
 
 
 A but opposite in direction, has its point of application at B; then the forces 
 A and B are not coincident. The foundation should bo designed with a narrower 
 footing under the cross wall, as shown in the plan 10B, so that the upward 
 pressure is in t he position indicated by the arrow C, slightly outside the 
 resultant weight A. This gives a tendency to the outer walls to incline inward, 
 a movement usually prevented by the interior construction of walls, W 2 , floors, 
 
 and roof. 
 
 If a portion of a wall is omitted, and thus its weight per lineal 
 foot of length is d ecreased because of w indow, doorother exterior openings, 
 the widths of the footings, fig. 11, should be varied to make the unit foundation 
 pressure uniform. Outward inclinations for walls can bo counteracted only by 
 anchors or tie rods, by the bond of the masonry or by masonry buttresses. Little 
 reliatoo,- should be placed on more walls of thin masonry. If it is necessary to 
 design a footing which tends to produce outward inclinations, a masonry or 
 brick building should bo tied carefully together w ith s teel r enforcement and 
 joist anchors, especially above openings, or at the junctures of walls. In 
 general, when a continuous footing is built, it should be designed so that the 
 
198 W 
 
 eBO?ft9? 
 
 . . * 
 
 : 
 
 . aacrrc 
 
 - . . -r.t erfct - 
 
 la 
 
 ... ''A. 
 
 srf; 
 
 ;.. 
 
 .''.It 
 
 , 
 
 i. . . - 'jJeo^t 
 
 i J /&fr ' 
 
 
 
 
 . 
 to tooef jarf;' 
 
 :- 
 
 
 
 > . i -- 
 
 - 
 
 '. ., 
 
58 
 
 center of loading,, for t he various portions, falls a little inside the center 
 of the base .areas. At Chicago, the omission of 2% of the weight, by window or 
 other openings, together with failure to decrease, correspondingly, t he width 
 of the foundation footings, in numerous cas'os has caused unsightly cracks. 
 
 Consult Freitagj; Architectural Engineering, Chap. 5, exterior vails 
 Piers, pp. 144-166; also International Correspondence School - Structural 
 Engineering Course, Statics of I/Iasonry, Part 2, pp. 1-89. Eoad in the San 
 Francisco Ordinance, Part 9, Special -provisions relating to Class C Buildings; 
 Section 133, which discusses the thicknesses allowed for walls of increasing 
 heights. 
 
 The following table for vr.ll thickness is taken from the 1909 od. 
 of the Building Laws of the City of Oakland. Section 131, - "Exterior, party, 
 division and bearing walls of brick, except as provided for in sections 128, 
 129, 130 and 139, shall be built of thickness given in the following table. 
 Division walls carrying no weight may be four inches less in thickness through- 
 out, provided however that one Story buildings not ovc-r twelve foot higl'.. v;hcn 
 used for storage or manufacturing purposes, may bo enclosed with brick walls 
 eight inches thick". 
 
 Stories 
 
 Building 
 Height 
 
 Basement wall ; 
 thickness ' 
 
 First 
 18 ft. 
 
 i Second 
 ! 31 ft 
 
 Third 
 ,' 44 ft. 
 
 Fourth 1 
 57 ft.; 
 
 Fifth 
 70 ft. 
 
 Sixth 
 83 ft 
 
 i Seventh 
 i 95 ft 
 
 (story) 
 
 (Indie's) 
 
 
 1 
 
 1 
 
 i 
 
 1 
 
 
 
 1 
 
 1 
 
 17 
 
 13 
 
 i 
 
 " 
 
 - 
 
 - 
 
 - 
 
 i ~ i 
 
 ; 2 
 
 17 
 
 17 
 
 13 
 
 i ~ 
 
 
 - 
 
 - 
 
 i - 1 
 
 3 
 
 21 
 
 17 
 
 17 
 
 13 
 
 - : 
 
 - 
 
 - 
 
 
 4 
 
 21 
 
 17 
 
 17 
 
 , 17 
 
 13 
 
 - 
 
 - 
 
 } 
 
 5 
 
 25 
 
 21 
 
 I 17 
 
 : 17 
 
 17 
 
 13 
 
 - 
 
 \ ~ 
 
 1 
 
 } 6 
 
 !,-. 25 
 
 21 
 
 21 
 
 17 
 
 17 
 
 17 
 
 13 
 
 \ 
 
 7 
 
 29 
 
 25 
 
 21 
 
 21 
 
 17 
 
 17 
 
 17 
 
 13 ! 
 
 ECCENTRIC FOUNDATION LOADS 
 
 The shifting position of live loads, even in a building, commonly 
 makes it impossible to compute exactly the point of application of the resultant 
 foundation thrust for combined dead and live loads, especially for bearing walls 
 or wall columns. ^ common case is that shov/n in Fig. 12, where the resultant 
 
'' . ' 
 
59 
 
 pressure P, including the live load, is considerably removed from the line of 
 action Q for the dead load only. 
 
 Frequently it is specified that the resultant from any possible 
 combination of dead and live Icx'ds must fall v/ithin the middle third of the 
 foundation bed. Therer.son for this spocificrtion is nr.de clearer by the follow- 
 ing analysis. Many times, it is impossible or impracticable to get the centroid> 
 of the foundation area opposite the center of lording on account of the varying 
 live lords. In such cases tho pressure intensity is not uniform over the 
 foundation area, but varies linearly from a maximum at that edge of the footing 
 which is nearer to the center of pressure, to a minimum at the other toe. In 
 Fig. 13, with a full live load acting, lot the resultant of the beam reaction 
 PI, and the wall load P W equal P., acting at the point b, whose distance from 
 either of the loads can b e found by the principle of the lever. Suppose b to 
 be within the middle third of the base. Let A be the area of tho rectangular 
 foundation bed, whose width is d and length 1. The stress diagram for the 
 foundation pressure intensities is trapezoidal. A semigraphical solution for the 
 maximum and minimum foundation pressures s^ and sg in terms of the average 
 pressure and the eccentricity p, of the applied load, gives:- taking static 
 moments for the stress diagram ares-.s about b, 
 
 p (ds ? ) =(d/6 - p )( d(ai-B2) ......... ....... (1) 
 
 2 
 Solving for p, 
 
 p = d/6(si-s p ) ........................ (2) 
 
 Hi- i 
 
 l*l+2' 
 But P r = A (BI + s 2 ) . ........................ (3) 
 
 2 
 
 Equating (2) and (3) asjsiraultaneous equations: 
 
 S-L = P r /A (1 + 6p/d) .................... (4) 
 
 s 2 = Pr/A (1 - 6p/d) ..... ................. (5) 
 
 Equations (4) and (5) maybe derived from Fig. 13 more simply by 
 talcing moments about the third point of the joint which is nearer si. The 
 static moment of the rectangle s 2 d about a point d/3 from si is precisely the 
 
' ' 
 
 ' 
 
60 
 same as the static moment of the trapezoidal about the same point, because 
 
 the moment of the triangle (BI - sg)d about that point is zero Hence, since 
 
 ~~Z~ 
 
 the moment of Pr and that of the upward pressures must balance about any point, 
 
 P r (d/6 - p) = s 2 Ad/6. 
 
 Solving for S we g et equation (5); substituting that value of 3% in equation 
 (3) and solving for s^ gives equation (4). Consult V/egman, Design and Con- 
 struction of Dams, Chap. 2, pp. 8-13; Morrison and Brodie, High Masonry Dam 
 Design, pp. 7 - 14. 
 
 If the total loed P were axial, so that p = 0, the pressure in- 
 tensity on the bed would be constant and s = P r /A . (6) 
 
 In this case the pressure diagram becomes a rectangle of breadth d and height s. 
 
 x he increase and decrease of pressure intensity due to an eccen- 
 tricity p is 6pPr/dA. For usual calculations a unit length of wall is 
 considered. Making 1 ~ 1, A = d, equations (4)., (5) and (6) become: 
 
 S;L = Pr/d (1 + 6p/d) .....;.,......... (4 1 ) 
 
 s 2 = Pr/d (1 - 6p/d) . . . (0 1 ) 
 
 s = Pr/d . . (6') 
 
 In equation (4 1 ), (5') and (6') Pr becomes the lord per lineal foot of wall. 
 
 When p = 0, s = Si = S2 = Pr/d ........ ......... (7) ) 
 
 V/hen p> bpt ^ d/6, equations (4), (5), (4') and (5') stand. 
 
 When p = d/6, s- L = 2Pr/d; s 2 - .- ' (8) 
 
 When p^ d/6 bpt^d/2, consult a later paragraph and fig. 17 
 
 Notice in the above demonstration., if p = d/6, so that the load Pr 
 is at the middle third, thct BI is twice the average pressure end s 2 is zero. 
 The pressure diagram becomes a triangle; see Fig. 14. If p is greater than d/6, 
 S2 changes sign or becomes a tensile stress, which ordinarily cannot exist at 
 the junction 'of masonry and the foundation soil, and should not exist at higher 
 levels in the masonry itself; see Fig. 15. A possible exception is found in the 
 case of a pile grillage fbunC.E.tion with the tops of the piles imbedded in con- 
 crete. Here a small t ensile stress occas ionally -might be allowed. If p ^ d/6 
 
' f" t " 
 
 - 
 
 3 3ffio 06 d 'irrASSi i> " &' - ? . n I 
 
 ' $ ~ 
 
 a-ixa. ?' 
 
61 
 
 Fig. 13, the resultant pressure lies within the middle third of the foundation 
 base, the stress diagram is trapezoidal, and the analysis shows that no tensile 
 stresses can exist. It is usually specified that the footing must be spread, 
 making d sufficiently large, so that, under all possible conditions, the 
 resultant pressure will pass through or within the middle third of the area of 
 the foundation base, thus avoiding a possible tension for S2 
 
 An analysis for foundation pressures differing from the preceding 
 treatment, but leading to the seme conclusions can be made by assuming the 
 foundation pressure, Fig. 16, caused by a load Pr acting at the center of the 
 footing C, resisted by the rectangular portion, ajcf, of tha pressure diagram 
 considered as concentrated in R = 1/2 (s^ + SojcLl; and by a couple Pr x p, 
 resisted by the triangular portion, hfghie, of the diagram. The foundation bed 
 
 * 
 
 then may be analyzed for stresses as a beam of rectangular section subjected to 
 direcfi compression PL and to cross bending stresses; max. fiber stress k = ei = 
 fg = (s - sg) caused by the bending moment M = Prp. Let k = (s^ - s^} a . 
 
 ' 
 
 . 
 
 the maximum unit fiber stress due to the bending moment; I = Id 3 /12 = the 
 moment of inertia of c roe s section of dimensions 1 x d; then, from the general 
 formulae for flexure in b earns , neutral axis at C, the external bending moment 
 
 is : 
 
 M - Prp = +(si - s?.)l = (si - sp. ) Id 2 . . . . ....... (9) 
 
 d 12 
 
 k = si -82 ~ 6Prp/ld 2 = 6Prp/Ad ' 
 
 The resultant stresses Sj and s 2 equal the average stress Pr/A 
 caused by the central load Pr, respectively plus and minus, the bending stress 
 k, giving values for s x and s 2 identical with those in equations (4) and (5) 
 
 TREATMENT FOR CEHTSR OF PRESSURE WITHOUT THE MIDDLE THIRD 
 
 Fig. 17 ; see also Fig. 15. When the ecceiitricity p is greater 
 than d/6, the center of loading b for the resultant Pr falls outside the third 
 point t. Ordinarily it is assumed that th.e joint Id C .n tcJce no tensile s tresses, 
 
62 
 
 It is assumed that tho Jiodror 'oaooarjr JeinJ cracks from f to h, fig. 17. The 
 tensile stress diagram hfg is neglected. By analogy to the case, when p = d/6, 
 see fig. 14, the effective joint length ho_ is taken equal to 3 u. The unit 
 stresses, diagram hei, for the foundation bed he, area = 3 u x 1, will vary 
 uniformly from a maximum value sj. to zero at h. The average stress is sj/2, end 
 
 acts upon the area 3 ul. Pr = 3 s-jul , hence S} * 2 Pr . 
 
 2 3 ul 
 
 In general, to design a foundation bed without tension, if u is the 
 
 minimum allowable distance from the outer toe e to the point of application b of 
 the resultant load Pr, fig. 17, then 3u is the maximum effective width of the 
 foundation.- If ss-^ is the maximum allowable unit foundation pressure, Pr the 
 
 maximum load, then Pr - 5 si ul and 3 u = 2 Pr . It should be noted that the 
 
 2 s x l 
 
 expression 1,1 - Prp = kl_ is perfectly general, v'o may consider 1.1 to be the 
 
 r 
 external bending moment caused by any number of horizontal or inclined forces 
 
 acting above the given bed or joint. I is the moment of inertia of the cross 
 section of the foundation bod or masonry jjoint, which maybe square, circular, 
 rectangular or annular, as in the case of chimneys. Here r in all cases is the 
 distance from the ccntroid of the cross section to the extreme point or too, at 
 which the raximum intensity of pressure s-^ exists. S..c Turneaure & I.Iauror, ed. 
 1919, p. 435, Fig. 12, 
 
 PBESSURE ON THE FOUNDATION BED OF A ii'.SQMBY PIR 
 
 A general problem will now be outlined for t he design .f the foun- 
 dation for a masonry bridge pier. Structures of this typo arc subject to a 
 variety of horizontal forces, such as wind, ice pressure, dynrmic pressure frcm 
 flowing water, tractive forces from moving "trai ns , r.nd possible blows frtnm ships 
 or drift wood, a detailed consideration of which more properly belongs to the 
 treatment of the design of mrsonry structures. V/ind pressure only will be assumed 
 here. If other horizontal forces were acting, it vould bo necessary to compute 
 for their the total sum of the moments at the foundation bod. For simplicity a 
 
-v ;. /i-rii'.i-j '; 
 
 ........ 
 
 
 : ..' - 
 
 '-Tf j 
 
63 
 
 Consult Brkor, A Treatise on nasonry Construction, Chap. 20, 
 Bridge Piers, ed. 1909, pp, 551-563; r.lso the Irter reticle in these notes 
 entitled Design of a Railway Bridge Pier, particularly paragraphs 15-37 inclusive. 
 
 In Fig. 18 let H.= the resultant of the horizontrl wind pressures 
 on pier and trus.es considered as applied at a distance a above the pier footing. 
 Let d = the length of pier footing. Let P = the resultant w eight of the bridge, 
 bridge pier, and footing, applied at the center C of the footing bed. The 
 
 length d must be so adjusted by design calculations that the ;naxiraum pressure 
 
 due to P and to the moment of the wind pressure H, 
 
 will not exceed the allowable b earing power on the soil. The problem is incapable 
 
 of a direct solutionbecau.se the weight P is not known definitely until the 
 length d is determined. Let S]_ = the max. allowable bar. ring power of the soil, 
 a value to be reached at the leeward toe A. It is composed of two components, 
 
 s and k. s = si + 53 is caused by the direct lord P, k by the bending 
 
 ~~2~ 
 moment' Ka from the v/ind -ores sure. The bending moment Ka = gkl . If 1 = the vddth 
 
 d 
 of the pier footing, normal to the plane of the figure, the moment of inertia 
 
 for neutral axis at C is Id 3 /12 . The area of the foundation bed is Id. Hence: 
 
 s l = s + k = P/ld + Had/21 
 Similarly s 2 = s - k ....... 
 
 Suppose D is the point of intersection of the forces K and P. By 
 constructing the rectrngle of forces, the diagonal R represents completely 
 resultant thrust upon the bed dl. It cuts the bed in the center of pressure D, . 
 wjiich for the stress diagram as dravm lies within the third point B. rvith the 
 point fl determined the distance CO is the eccentricity p. For-milr.s (4) rnd (5) 
 give the values of s I and s2- These values must check the results obtrined by 
 equati ons ( 11 ) and ( 12 ) 
 
 2 
 
 If s = k, s = 0, the stress dirgram becomes a triangle; ai 
 
 , , (13) 
 
 2P/ld = Had/I .,....... 
 
 When tension in the bed is prohibited by specification, eouation (13) 
 
 determines the mininum allowable v:- lue for d. Solving for d fro* the^laet 
 members of ecuation (IS), d = 6 Ha/P. ...* 
 
64 
 
 Equation (14) shows that d is independent of 1, rs it should be. 
 For soft soils it, usually implies too Ir.rge a value or s^. In such cases, for 
 safety from possible settlement, the point D must lie within the middle point B. 
 Equation (11) then give's the value of d in terms of Sj. Substituting for I in 
 equation (11) :- 
 
 * i 
 
 s l = P/ld + 6Ha/ld 2 = Po/d + 6 H a/d 2 Here P and HQ are values for 
 1 = unity. Solfing for d: d = P /2si A /6H a ~P^~ ......... (15) 
 
 81 
 
 Notice that equations (11), (13), (14) and (15) are perfectly 
 
 general. They cou,M be used to determine the max. stress or joint length in any 
 horizontal section of the masonry. They also are applicable where a moment M is 
 caused in any manner, as by earth or water pressure. In each case the moment is 
 to be calculated for a moment center in the level of the section c ons id or ed. 
 
 STABILITY AGAINST SLIDING 
 
 In Fig. 18 9 is the angle which R makes with the vertical. The 
 
 verticrl component of E is P. If f is the coefficient of friction for the footing 
 upon the foundation b ed, then by the law of friction F = Pf. F is the total 
 frictional force exerted in tho bod. Let q = the intensity of shearing tenacity 
 between the footing rnd ;-bed. Tho total shearing strength offered is Q = qld. 
 For equilibrium against sliding:- 
 
 H- F + Q = Pf + qld ..... ..... . ...... . . (16) 
 
 Commonly in equation (16) the term .for shearing tenacity is neglected or consider- 
 ed a reserve factor for safety. Then 
 
 H^F = Pf 
 
 f H/P = tan 9 ..... , .............. 
 
 Knee for safety tan 9 must be less than the coefficient of friction. Generally 
 f is equal to or less than 0.67 for masonry. For deep foundations the effective 
 load producing friction on the bed should betaken less than P. Buoyancy from 
 water or silt and skin friction on the sides of the foundation vl.3n founded in 
 
 sr.nd, clay or other granulrr masses will reduce the value of P very decidedly. 
 On the other fend, foundations floating in granular deposits will be retained 
 
I 
 
 against lateral movement by the thrust action or abutting power of the surround- 
 ing material. For a bridge pier, like that shown in Fig. 18, the load P cor/nonly 
 is so large compared with H that the safety against sliding is jreat. Usually no 
 investigation for sliding stability isxecpired. An inquiry for sliding should 
 be made when H is large and P small, particularly if the footing is deeply sub- 
 merged in water with no solid material surrounding the structure above the level 
 of the bed. 
 
 Numerical Example; Design of a Pier, Fig. 18. Weight of super- 
 structure 327.5 tons. Let the wind pressure = 30 Ib. per sq. ft. Assume the max. 
 allowable pressure s^ = 3 tons per so. ft. Let h = 40 ft. ; top dimensions of 
 pier 3 x 20 ft.; dimensions at top of footing = 7 x 26 ft. The pier is to be 
 built of concrete weighing 150 Ib. per cu. ft. The approximate weight of pier 
 above the footing is (3 x 20) + (7 x 26) x 40 x 150 = 726,000 Ib. = 363 tons. 
 The unit pressure at the top^of thd footing, for vertical loads only is 
 327, 5 + 363 =3.8 tons per sq. ft. Suppose the wind on the superstructure = 
 
 7 x 26 
 
 300 Ib. per lineal ft. for two 100 ft. spans; then H = 300 x 100 = 30,000 Ib. = 
 15 tons. Let H act 15 ft. above the pier top. For simplicity assume the entire 
 pier exposed, that is, let the ground level be at the top of the footing. The 
 wind pressure on the pier = 1/2 ( 3+7) x 40 x 30 = 6000 Ib. = 3 tons. It acts 
 approximately 20 ft. above the top of the footing. The lever arm of the wind 
 pressure on the pier is really the distance from the footing top to the centroid 
 of the trapezoidal end face of the pier, somewhat less than 20 ft. The total 
 wind moment about the footing -coo is 15 x 55 + 3 x 20 = 885 ft. tons. By 
 formula (11) s x - 3.8 + (885 x IS) -t- 7 x(26) 3 - 3.8 + 1.1 = 4.9 tons per sq.ft. 
 
 12 
 
 * 68. Ib. per sq. in. Concrete ma; safely take 400 Ib. per sq. in. in compression. 
 The pier base therefore is excessively strong. This is usually the cr.se since a 
 pier must have sufficient plan to support the superstructure. 
 
 The footing of concrete is assumed 5 ft. in depth, 12 ft. wide anc 
 30 ft. long. Its weight is 12 x 30 x 5 x 150 = 270,000 Ibs. = 135 tons. The total 
 vertical load on the foundrtion bed = 327.5 + 363 + 135 = 825 tons, giving an 
 average pressure s = 825 = 2.3 tons per sq. ft. For t he founda.tion bed:- 
 
 12 x 30 
 M = 15 x 60 + 3 x 25 = 975 'tons; I = 12 x (30)* = 27,000 ft. 4 ; hence 
 
 12 
 s l = 2.3 + 975 x 15 = 2.3 + 0.5 = 2.8 tons per sq. ft., which is sufficiently 
 
 27000 
 
 close to the r.ssuned allowrble pressure of 3 tons to make further calculations 
 unwarranted. Note that k = 0.5 tons por sq. ft. e 2 r. - k = 2.3 - 0.5 = 1.8 
 per SQ. ft. It is to be observed that for neither joint does tension occu 
 the windward toe. The center of pressure is well within the middle third 
 level; its position may be located easily by graphics, or calculatec 
 moments about the point D. 
 
 Study in Taylor and Thompson, Concrete, Plain and Reinforced, ed. 
 1909, the design for an arch abutment, pp. 583-586. On page 586_is described a 
 graphic method for determining the maximum and minimum inteiisi 
 pressure for eccentric loadings. 
 
,- Si,/ 5 ) '.V 
 
66 
 
 In Fig. 18a let AB be to scale the length d of the foundation bod 
 of Fig. 18; let C and D be the thirdpoints of the joint. is the center of 
 pressure for the resultant thrust R whose horizontal and vertical components are 
 respectively K and P. Find the average unit pressure s by dividing the totc.1 
 thrust R by the area d'l, which area is the projection of the bed dl, drawn 
 perpendicular to the thrust R. The point E is the center of the joint d. Plot 
 the average unit pressure s as FG to any convenient scale, perpendicular to the 
 projection to the base at its center F. Connect the projected third points J 
 and K with G and prolong J(J to M on the prolongation of tlie thrust R. The line 
 GK cuts R at N. QN = S and QM = si. The shaded trapezoid is the unit pressure 
 diagram . 
 
 SPREAD FOOTINGS 
 
 Where building columns or walls are founded upon sand, earth or 
 other loose materials, at shallow depths, it is often necessary to design foot- 
 ings to distribute the total foundation load over an extended plan in order to 
 reduce the intensity of pressure to low values. This result may be effected in a 
 
 variety of ways, by: 
 
 1. timber footings; 
 
 2. offsets of masonry in rubble, brick or concrete 
 
 3. timber jprillages or rafts 
 
 4. im^rted arches of stone, brick, concrete or reinforced 
 
 concrete 
 
 B. footings\of structural steel bea.ns and concrete 
 6. footings of reinforced concrete. 
 
 1. TIMBER FOOTINGS 
 
 Fig. 19 illustrates a simple timber footing designed to support a 
 column load ard distribute it over a foundation bed. Such footings give excellent 
 service for very soft material, but as permanent structures they should not be 
 used unless the timber is always wet. The footing is composed of platforms of 
 sticks in layers laid at right angles. The amount that a course of timbers may 
 project beyond the one next above it is found by treating the projection as a 
 cantilever bean supportad from above and loaded uniformly from be low. (Consult 
 tlie next article, equation (19) and Fig. 20 with accompanying examples). The 
 maximum allowable fiber stress in the timber generally is taken at 1000 Ib. per 
 sq. in., When possible, and costs do not prohibit, the footing is made more solid 
 and permanent by supporting the lowest layer of timbers upon a bed of concrete 
 
 6 to 12 inches in thickness. See Kidder, Architects ai}.d Builders Pocket Book, 
 ed. 1908, pp. 170-171; Froitag, Architectural Engineering, l. 1911, Chsp. 9, 
 
-. 
 
 :; : 
 
 "* 
 
 , 
 
 i .-> 
 
67 
 
 pp. 312 - 314; Jacoby and Davis, Foundations of Bridges and Buildings, Chap. 15, 
 Art. 156; Williams, Design of Masonry Structures and Foundations, p. 445. 
 
 2. I.1ASMBY OFFSETS; RUBBLE. BRICK OE CONCRETE 
 The amount of projection m, Fig. 20, for masonry, concrete or 
 brick offsets is calculated in the same manner as for timber, by assuming the 
 offset to be a uniformly loaded cantilever, fixed at the edge AA of the overlying 
 layer or tier. Let R in Ib. per sq. in. = the modulus of rupture of the material; 
 let t in inches be the depth of footing course. The load intensity per unit of 
 breadth upon the foundation bed is s in Ibs. per qq. in. feting from below, 
 uniformly distributed. The max. bending moment at A is 1.1 = sm2/2, which accord- 
 ing to the common theory of flexure is equal to 2 Rl/t. I = t^/12, is the 
 moment of inertia of the c ross section of the projecting offset, for rectangular 
 cross sections. Hence sm / 2 = Rt 2 /6; and m, the allowable projection, is 
 t YR/SS. If p is the pressure in tons per sq. ft. on the base, 
 
 m = tf_R = 0.155 
 
 J5(20QO)P 
 
 r 444 
 
 It is sufficiently close to assume that m = t/6/\/R/P (20) 
 
 If R in formula (20) is the modulus of rupture it gives a value for 
 m for which thq offset is just at the point of failure at A. A large safety 
 factor usually is imposed for masonry or brick or timber construction, so tha.t in 
 
 using the formula, R should be taken as the safe cross breaking strength, supply- 
 
 A factor of safety of 15 to 20 is not uncommon for masonry. -^ 
 ing a safety factor of 5 to 20, according to the grac".e of rnaterial.^The above 
 
 analysis and the following table are taken from Baker's Treatise on Masonry Con- 
 struction, 10th ed., pp. 356-357. The table gives approximate safe values foi R. 
 
68 
 
 Safe Off -Set -pr Masonry Footing; Courses, Using 10 as a 
 
 Factor of Safety. ( 
 
 For limitations, see Arts. 698-701, Baker.) 
 
 IKind of Stone 
 
 R, in Offset 
 
 in terms 
 
 of the 
 
 - 
 
 
 Ib thickness of the 
 
 course 
 
 I 
 
 
 per for a 
 
 pressure in tons 
 
 j 
 
 
 sq. per sq 
 
 .ft. on the bottom 
 
 
 
 in. 
 
 of the 
 
 course of 
 
 
 j 
 
 
 
 0.5 
 
 i.o | 
 
 2.0 j 
 
 Stone, Bluestone, North River 
 
 
 5026 
 
 4.5 
 
 3.2 | 
 
 2.3 
 
 
 Grani te 
 
 
 1849 
 
 2.7 
 
 1.9 
 
 1.4 
 
 
 Limestone 
 
 
 1377 
 
 2.4 
 
 1.7 
 
 1.2 
 
 
 Sandstone 
 
 1 
 
 1378 
 
 2.4 
 
 1.7 ; 
 
 1.2 
 
 
 Brickwork: good building brick 
 
 in poor 
 
 
 j 
 
 i 
 
 
 
 1:2 natural cement mortar, 
 
 age 50 
 
 
 | 
 
 ! 
 
 
 
 days. 
 
 
 120 
 
 0.7 
 
 0.5 i 
 
 0.3 
 
 
 Under-burned building bi 
 
 ick in 
 
 
 j 
 
 
 
 
 1:3 Portland cement mortar, 
 
 ag^e 76 
 
 
 
 
 
 
 days 
 
 
 706 
 
 1.7 ' 
 * ' i 
 
 1.2 i 
 
 0.8 
 
 
 Vitrified building brick in 1:3 
 
 
 i 
 
 
 
 
 Portland cement mortar, age 76 
 
 days 
 
 3560 4.3 : 
 
 2.7 ' 
 
 1.9 
 
 
 Concrete, 1:2:4 Portland cement 
 
 at one mo. 
 
 300 1.1 
 
 0.8 ' 
 
 0.5 
 
 
 it ti 
 
 11 6 mos. 400 1.4 
 
 0.9 
 
 0.6 
 
 
 For granite maso nry, v/here the modulus of rupture R is taken at 
 
 1800 Ib. per sq. in. if a safety factor of 6 is used and the allowable load on the 
 foundation bed is 2 tons per sc. ft., the formula gives m = t/6/J 300/2 = 
 approximately 2.04 t. In applying the formula to masonry construction, the pro- 
 jecting stones must be imbedded beneath the upper course far enough to firmly fix 
 them, a distance equal tort least one-half their length. In the example the 
 
 granite blocks should have a length = 4.08 t. The safe strength of the mason- 
 ry in direct compression, which depends largely on the Strength of the mortar 
 used, must not for any course be exceeded. Notice in the design of piers, built 
 Yvlth a number of offsets, that as the section area of the pier d ecreases tov/ard 
 the top courses, the unit load increases, hence, the possible length of offset 
 decreases from the bottom upward; Fig. 20, m^ m-j_> mg. 
 
 For timber offsets, if the safe value of R is taken at 1000 Ib. per 
 sq. in. and ? = 1 ton per sq. ft., then m = t/e^jToOO = 5.3 t; if P = 2 tons per 
 sq. ft. , m = 3.7 t, 
 
 This method for determining offsets is as equally applicable to a 
 layer of a timber gri Huge if t/.e timbers are laid close, as to a course of a 
 
'>' - , 
 
 "> ' '> ' ' 
 
 
69 
 
 masonry stepped pier. If timber grillages are designed so that, wide spaces are 
 
 left between the timbers. Fig. 19, the bending moment, M, should be calculated 
 by considering the actual concentrated loads fnum the underlying beams. 
 
 Figures 21, 22 and 23 give examples of simple masonry offsets for 
 light buildings of types common 20 to 30 years .a go. In more elaborate and heavier 
 designs the footings and walls might have a greater number of steps. Footings 
 of this type are now generally constructed of concrete, but they may be made of 
 dimension stone. In either case the amount of projection for any course can be 
 
 determined by the theoretic principles of the preceding paragraph, though such a 
 
 , * 
 
 refinement is hardly necessary. For upper walls general rules prescribe the 
 
 successive thickness. If the depth of any footing course be made at least twice 
 its max. projection, good practice usually will be satisfied. For dimension 
 stones the depths of courses vary from 18 inches to 3 ft.jfor concrete they may 
 be taken 12 to 18 inches. 
 
 The Boston Building Law (of about 1890) requires that the foundation 
 block, Fig. 21, of a pier or column shall be at least 24 inches greater in plan 
 than the pier or pedestal that rests upon it. Thus, the distance AB, Fig. 21, must 
 be 12 inches or more. For rubble foundation walls, Fig. 22. gives requirements 
 of the Boston Law. That law does not allow rubble foundation under walls of 
 buildings over 40 ft. high, with the exception of "third class buildings outside 
 the limits". The bed of foundation must not be less than 4 ft. below the frost 
 line. Two-thirds of the bulk of the wall must consist of through stones, 
 thoroughly bonded. The concrete base must be at least 12 inches wider than the 
 
 
 
 fir^t rubble course above it. For granite block work-, Fig. 23, there c.re similar 
 requirements. In both cases the concrete footing shall not be less than 12 in, 
 thick; if of stone, not less than 16 inches. 
 
 The f o 11 owing table shows the thickness- of brick and rubble found- 
 tion walls and concrete footings, Fig. 22, as prescribed by the Boston regula- 
 ions just cited. For every 10 ft. height of portion b, or fraction thereof, an 
 
f !.: 
 
 ':'. 
 
 > 
 
70 
 
 additional thickness of 5 inches mu5 1 be added. At least the same amount of 
 thickening is also demanded for the footing C. 
 
 Thickness of brick 
 wall, inches 
 
 a j 
 inches ! 
 
 b c 
 
 inches i- inches 
 
 8 
 12 
 16 
 20 
 
 20 
 25 
 
 30 \j 
 35 ! 
 
 25 37 
 30 42 
 35 47 
 40 52 
 
 The following table shows corresponding values for granite block 
 foundations, Fig. 23: 
 
 Thickness of brick 
 wall , inches 
 
 a 
 
 inches 
 
 b 
 
 inches 
 
 c 
 
 inche s 
 
 8 
 12 
 16 
 20 
 
 16 
 20 
 - 24 
 28 
 
 20 
 24 
 28 
 32 
 
 32 
 36 
 
 40 
 44 
 
 The following extracts are from the 1901 New York Building Code, 
 
 Section 26:- "Foundation walls shall be built of stone, brick, Portland cement 
 concrete, iron or steel. If built of rubble stone, or Portland cement concrete, 
 they shall be at least 8 inches thicker than the Trail next above them to a depth 
 of 12 ft. below the curb level. For every additional 10 ft., or part thereof, 
 deeper they shall be increased 4 inches in thickness. If built of brick, -they shall 
 be at least 4 inches thicker than the wall next above them to a depth of 12 ft. 
 below the curb level; and for every additional 10 ft. or part thereof, deeper, 
 they shall be increased 4 inches in thickness". The concrete footings are 
 
 required to be at least 12 inches thick. If footings are built of stone, the 
 stones must be not less than 2 ft. x 3 ft. and at least 8 inches in thickness 
 for walls; and not less tjhan 10 inches in thickness if under piers, columns or 
 posts. Footings of concrete or stone are required to be at least 12 inches wider 
 than the bottom width of walls. If stepped-up footings of brick are used in 
 place of stone, above the concrete, the offsets if laid in single courses, shall 
 each not exceed 1 1/2 inches, or if laid in double courses, then each shall n ot 
 exceed 3 inches, offsetting the first course of brick work back one-half the 
 
 t 
 
 thickness of the concrete base, so as to properly distribute the load to be 
 imposed thereon. Similar requirements for footings are found in other building 
 codes. It is recommended that students consult foundation clauses in the building 
 
 ordinances of the cities -of New York, Boston, Philadelphia, Chicago, St. Louis, 
 
 \ 
 and San Francisco. , 
 
tf. 
 
71 . 
 < 
 
 As concluding examples, Figs. 23A and 23B v;ith discussion are 
 
 extracted, from the International Correspondence School pamphlet, Structural 
 Engineering Course, Statics of Ilcsonry, Pert 2, pp. 12-17. 
 
 The dosign for a heavy foundation pier supporting an interior 
 
 column for a Class C building is shown in Fig. 23A. "The footing, if of concrete., 
 should never be less than 12 inches and is sometimes rrp.de 16 or 18 inches in 
 thickness. The projection of the footing beyond the brick work should not be 
 greater than one-half the thickness of tho footing and nover more than 8 inches. 
 
 The batter of the bripk work at the sides should not be greater than 6 inches in 
 
 . 
 every foot of rise. The thickness t of the capstone should equal 1/4 the length 
 
 of its side, or W/4, though when the capstone is rectangular, t he thickness may 
 equal 1/5 of the longer dimension. In no case however should the capstone be 
 less than 10 inches thick." 
 
 In Fig. 23B Iff t the load on the cast iron base supporting a wood 
 column be 200,000 Ibs. Design for this column a foundation pier made of brick 
 
 work in cement mortar *.ath concrete br.se and granite cap. Tha soil under the 
 
 \ 
 pier, being compact gravel and send, can safely sustain 6 tons per sc. ft. But 
 
 assuming a inaxiiaum, load of only 3 tons the base area is 33.5 sc. ft. or 5'9" sq. 
 If the bearing value of brick work in Portlsnd cement mortc.r is 200 Ib. per sq. 
 
 in., the granite cap must supply a plan area of 1000 sq. in. = 6.94 sq. ft., or 
 j 
 
 2*8" square. For further discussion c onsult the original reference. 
 
 3 TIMBER GRILIA&ES PR HAFTS 
 
 Fig. 24 exhibits a timber grillage cons is tins a? three layers of 
 timbej; (spaces filled with concrete) resting upon piles. The grillage platform 
 supports itone or brick masonry. Such a grillage may be built of timbers, in 
 stepped courses, similar to Fig. If. In designs of this "class the sprees between 
 -ihe timbers always should be filled completely with clay, gravel or core rets, 
 'Ise the sticks should be bolted or drift spiked thoroughly together. This type 
 'f construction is in great part now being superceded r; the use of reinforced 
 oncrete slabs capped over the heads of wooden pilot, I. hsed, in some designs 
 
72 
 
 not only the wooden grillage layers but also the wood piles are being replaced 
 
 with reinforced concrete w ork. On the filled ground areas of San Francisco timber 
 grillage on piles has been frequently used for two 'and three story CJass C brick 
 buildings. For lighter structures piles have been dispensed with; the footings 
 having been based on timber rafts of open layers like Fig. 24, or of solid layers 
 of 12 x 12 inch redwood or Oregon pine sticks. Y/here such construction h.s been 
 permanently under tide water the wood has remained in first class condition 
 after a lapse of 40 to 50 years, and no doubt would remain sound indefinitely. 
 
 Timber under these circumstances should r always be placed at depths below the 
 
 i 
 
 lowest possible ground water plane. As a city grows, its surface b ecomos more 
 impervious and its improved sewers and drains lower the water table, thus some- 
 times exposing timber which was not placed in a sufficiently deep excavation,, 
 
 4. INVERTED APCKES OF STOHE, .BRICK, CONCRETE OR 
 ~ REIKFOECSD CONCRETE. 
 
 Fig. 25 shows a typicsl example of an inverted arch footing. These 
 / 
 
 arches frequently are built under and between the bases of piers. Employed in this 
 way, they distribute the load from the piers A and B over a greater area, and 
 therefore in soft material make shallower foundations possible. For light loads 
 the arch dimensions maybe assigned from experience, or where >the span and load- 
 ing are considerable, the r ing maybe designed by applying arch analysis; but in 
 the case of the inverted aivh, the loads are applied from below and the reactions 
 et the ends are induced from above by t heweignt on the piers. In the best designs 
 the allies rest upon a bed of concrete- of considerable thickness, thereby 
 insuring a thorough distribution of the pressure froiii below upon the arch ring, 
 Care .mist be taken to provide for the end arch thrusts at outside piers. It is 
 assumed that the pressure from below on the surface CJ) is uniform. The weight of 
 the arch ring end footi-ng concrete is not considered as an arch load, since it 
 rests directly upon the foundation bed. The total load on CD is tie sum of the 
 ring and footing weights together with the total loads upon the piers A and B; 
 this toial load aiust not exceed the safe bearing capacity of the soil. The arch 
 
73 
 
 ring is cojnmonly of brick, it may consist of concrete or stone block masonry. 
 Since the advent of reinforced concrete more slender archers of reinforced concrete 
 
 t 
 
 are possible. It is more usual liov.'evcr to dispense w it*,- the crch '.principle and 
 employ instead distributing' slabs of r einf orced concrete acting as simple or 
 continuous beams between the pic r footings; s<| group 6, The construction of 
 inverted arches is difficult. Arches of brick or stone blocks a re now seldom^ used. 
 The pressure on the bed CD is rarely uniform. Moreover even slight uneven settle- 
 ment is especially injurious to an arch construction. , 
 
 The Droxel Building, Philadelphia, and the ';;orld Builfiing, Hew 
 Tork, are among the earliestof the steel office buildings, Where columns were 
 supported on inverted arches. Sec- Eng. Record, Vol. 57, Apr. 4,1908, p. 414. 
 
 Shallow foundations using inverted arches should not be built upon 
 filled ground likely to settle or upon filled ground liable to nerve from earth- 
 quake vibration and swash. Instead, concrete slab and girder footings, hecvily 
 I reinforced, should be used. In San Francisco, on filled ground, v/here two and 
 three story brick buildings had their walls supported upon reinforced c oncrete 
 slabs at shallow depths 4 under earthquake motions the we 11s settled while the 
 basement floor slcbswere forced upward at the center line b etv/een walls. In 
 t one case the max. relative vortical motion was not less than 4 ft. These slabs 
 
 ."ere ruptured, even when considerably reinforced. Under such action a brick 
 
 ' 
 
 inverted arch would fail utterly. Arches cannot withstand earthquake shock. Their 
 
 oystones are easily dislodged. On treacherous ground in earthcucko regions even 
 ooting slabs should never be at shallow depths. In doubtful cases good judgment 
 .ill select a pilo foundation, 
 
 5. FOOTIIoU-S OF S TJUCTUFJi.^ 3TELL BIL-.:i AND CONGESTS 
 Important shallow foundations for he, vy loads on interior building 
 Lumns or outer walls are frequently c onstructed of grillages of steel I -beams 
 jedded inconcrete, THIs method was first used in Chicago, using railroad rails 
 stead of I-beams. Fig. 26 illustrates a typical caso. The base of the footing 
 
. 74 
 consists of a-heavy slab of concrete, 1 to 2 ft. or more t",:iclc to insure cs nearly 
 
 as possible uniform pressure distribution upon tha foundation bed. Upon this base 
 are placed layers of I-beams at right angles, 'each tier in order smaller in plan 
 than the one immediately b Glow it. The beams arc- spaced with at least a three 
 
 
 
 inch flange clearance to a How for the ramming of concrete into the spaces b etween 
 the b earns. 
 
 Let U be the total load that rests upon the base of the footing. 
 Assume that this- same weight rests also upon each tier of b earns and that it is 
 uniformly distributed over each tier. Thos'e assumptions are not absolutely 
 correct but their orror is a Iways upon t he side of safety. Let the plan of the 
 column base bo, a x b; that of the first tier of beams below it, bj x 1-p that of 
 the next lower tier bg x 1 2 , and so on; in other words, let the dimensions of the 
 nth tier from the top be b n x l n - Notice that a = bj,! 1 = bg, lg = 1> 3 , etc. and 
 ^n = b n-t-1- The concrete bed b4 x 14 must be proportioned so that W = pbl4 
 inhere p is the allowable safe pressure upon the soil. In Chicago p ranges from 
 3000 to 4000 Ibs. per sq. ft. It is important to provide a stiff footing, that is 
 one that will not tend to deflect. Deflection prevents a uniform distribution 
 of the load upon the bed. Consecuently the steel offsets must ncc be too great. 
 It is better to use deep I-beams. The depth D should not be too small compared 
 to b and 14. 
 
 In Fig. 28 the half section of the thrrd and fourth tiers of Fig. 
 26 is shown. The lords W/2 from the assumption of uniformity of pressure 
 I/istribution are concentrated at the center points A and B of the respective half 
 tiers. The maximum bending moment % in the fourth tier then obviously becomes: 
 
 % = Wn = W {1 4 - b ) = W (! 4 -b 3 ) = V7 (1 4 - 
 
 22448 8 
 
 similarly for the third tier: 
 
 1L = W (1 3 - 
 
 6 8 
 
 r in general for the nth tier: 
 
 Mn = W (l n - l n _2) ft. Ibs. = 3W 
 8 2 
 
75 
 
 In equation 23 the values of 1 are in feet. In general M = kl/d ~ 
 KR, where k is the max* allowable fiber stress intensity, I = the moment of 
 inertia, R = the moment of resistance or section modulus c.nd d = the distance to 
 the most fibres from the neutral axis of a tier of beams; honcc:- 
 
 Mn = 3W (l n - 1 J * MkB ........ ............... (24) 
 
 n-6 
 
 In equation (24) H ? the number of beams' in any tier, k = 577 ( 1 - l n 2 ) and 
 
 2KB 
 H = 3W (In -.1 ) ................ .=*.; ...... . . (25) 
 
 2kR 
 
 .......... ........ . % ...... ... {26) 
 
 n 
 
 3W 
 
 -' In general, for the lowest course 14 is fixed by dividing the 
 
 ret aired area by b4 for any c ourse K is limited by the length of the overlying 
 course. 
 
 
 
 Example - Steel Grillage Footing. Let W = 800,000 lb.; p =2 tons 
 = 4000 lb. per sq. ft. of bed; k = 15,000 lb. per sq. in. p x = 350 lb. per sq. 
 in. = allowable pressure between cast iron base end first tier of beams. 
 
 The cast iron base area a x b = 800,000 _ = 16 sq. ft.; choose a 
 
 350 x 144 
 sq. base 4x4 ft., assuming W to bo the total load on foundation, bed for an 
 
 interior column for a high building; a - b =4 ft. 
 
 For the first tier of beams li = b + 2JikR/3W. Select 15 inch 42 lb 
 
 .' 
 I-teeams; R = 58.9, flange width = 5.5 inches. Hence K for width bj, = 43 inches, 
 
 / 
 
 is 48/ 5.5 - 3 = about 6, for 3 inch clearance of flanges. Then lj e 
 
 1- + 2 x 6 x 15000 x 58.9 =4+4.4 = 8.4 ft. 
 3 x 800,000 
 
 For second tier, 12 beams with 5.5 inch fl^ige width and 3 inch 
 
 :learance, gives b2 = ll = 8.5 x 11 + 5.5 = 99 inches *= 8.25 ft. This is sfufficient- 
 -vclose to the preceding value, 8.4 ft. to settle too selection of 12 - 15" 42# 
 
 . ' N 
 
 :--beams for the second tier, using a spacing nearly 3 itches. Then 
 
 T-2 = a + 2HkR_ 4 + 2 x 12 x 15000 x 58.9 = 4 + 8.6 = 12.8 ft. 
 3W 3 x 800 000 
 For a third tier, 18 - 15" 42# I-beams provide a reasonable solution 
 
 Disregarding for a moment the necessary dimensions for base area of concrete' 
 
 joting slab on foundation b ad. For N = 18, 13 = !.,+ 2 x 18 x 15000 x 58.9 = 
 
 3 x 800 000 
 
8.4 + 13.2 = 21.6 ft. 
 
 / 
 
 The required area of concrete baso bg x lg = 1^ x lg = V//p = 
 
 800,000/4000 * ?* sq. ft.; hence 1_ = 200/12.8 = 15.3 ft. Consequently the baams 
 
 o 
 
 in the third tier maybe shcr toned from 21.6 to 15.3 ft. and the number required 
 
 is N = 5 x 800,000 (15.3 - 8.41 = 10 beams, with ;; roster spacing than 3 inches. 
 
 2 x 15 000 x 58.9 
 Otherwise a lighter boas, say 12 inch 31.5 # should be used, saving 3 inches depth 
 
 of foundation. 1 
 
 For the final dimensions fractional lengths should not bo used. 
 Thus we might finally select: 
 
 Cast iron baso, 4x4 ft. 
 Tier 1, 4 x 8.5 ft. .. 6 - 15" 42# I-beams 
 Tier 2, 8.5 x 13 ft., 12 - 15" 42 I-beams 
 Tier 3, 13 x 15.5 ft., 10 - 15" 42 I-bca.ns. 
 
 For acolumn a. square plan is desirable; the concrete base requires 
 an area of 200 sq. ft. = 14 x 14 ft. The stool beams of tier 3 neod not hevc a 
 3lan greater than 13 x 13 ft. giving a concrete base 6 inches larger s.ll around, 
 lake the concrete be.sc 12 inches thick. The stool for tier 3 should be redesigned 
 Tor plan, 13 x 13 ft., selecting 10 or 12 inch i's. For an additional oxamplo 
 portraying this method, see Eng. Record, Mar. 3, 1894, p. 223. 
 
 CAST IRON BASES, STEEL rZDESTALS, etc. 
 
 For buildings, column bases usually arc constructed of cast iron; 
 sec area a x b, of Fig. 26. Fig. 27 exhibits one of tho erst iron bases used, in 
 the White House, 1907, a largo Department Store building in S?.n Francisco. 
 
 Fig. 27A illustrates an interior footing, founded on sand, in a 
 ;iass A San Francisco Hotel Building. The total load = 468.000 Ibs; bod aroa = 
 iO sq. ft.; soil pressure = 3.9 tons per sq . ft.; cast iron base = 3'6" square = 
 L ;.2 3 q. ft.; pressure under cast iron base = 265 lb. -or sq. in. The student 
 -.ould calculate the punching shear, concrete compression end rod tension in the 
 ooting b- methods illustrated in the next article. 
 
 Fig. 27B exhibits a cast iron baso for a wall column in the same 
 tructure as Fife. 27A, The base is eccentric because of the nearness of the 
 
77 
 structural column to the party lino. Eccontricity of bases, e.s of footings 
 
 tinder thorn, should bo avoided whenever possible. The total load on this base is 
 380,000 Ibs. = 298 Ibs. por so. in. of bod. ' 
 
 
 
 Large manufacturers publish standards for cast iron bases; their 
 handbooks give tables of standard d otai Is, dimensions, weight, bearing capacity, 
 etc.; consult American Bridge Co., Standards for Detailing; Table 4 is reproduced 
 from the leaflets of the Illinois Steel Co., 1905. 
 
 For heavy buildings and bridges, cast stool is sometimes used 
 
 instead of cast iron. Very largo pedestals, particularly for trusses, are designed 
 of built-up structural shapes. Fig. 27C is taken from Eng. Record, Vol. 65, May 4 
 1912, p. 504, and illustrates a base built of rolled shapes used by E. W. Stern 
 for buildings. The beams per layer are bolted together in the shop including 
 separators, and the two layers of b cams likewise are bolted together, all ready 
 for erection in one piece. LIr. Stern advances four reasons why this type of baso 
 might replace cast iron; which read. 
 
 OTHER DESIGN METHODS FCR STEEL GRILLAGE FPOTIKGS. 
 
 Equations 21 to 23 give the max. bending moment in any tier pro- 
 vided that the deflections of the different tiers do not affect materially the 
 assumption of uniform distribution of load. These max. bo-ding moments occur ct 
 the center sections; ifor example, at C for tier 4, Fig. 28. 
 
 In Fig. 28 lot y = 14/2 - b 3 /2 = the projection for the- beams of 
 the fourth tier. Let D be any section in the fourth tier within tho boundary E 
 of the next upper layer. Section D is a variable distance x from'E; x may vary 
 from zero to. b.g/2. The intensity of uniform load acting downward upon tier 4 
 from E to C is pi = V//b3 ; that below tier 4, acting upward, from F to C is p 2 
 W/14- The bending moment M at D is: 
 
 M = P2 /2 (y * x) 2 - Pl x2/2 
 
 The first derivative of M with respect to x is: 
 
 . dM/dx = (p 2 - !)x + p 2 Y 
 "Placing tho second member of (29) equal to zero r.nd solving for x gives, 
 
-if. :;' 
 
 .j,(! '' ' 
 
78 
 
 -p 1 = v/y = b 3 /2 (30) 
 
 - W/b 3 ) 
 
 Therefore the ;nax. valuo of M 'occurs at tho center section C = 
 Placing x = b3/2 in equation 28, 
 
 Me = W/8(l 4 -b 3 ) = W/8 (1 4 - 1 2 ) = Wy/4 ........ (31) 
 
 Equation 31 is identical with equation 21. 
 
 A more approximate method in general use 'calculates the bending 
 
 moment at E, Fig. 28, assuming uniform loading, and considers that bending as the 
 maximum'. Thus !% = p2y 2 /2 = W/8 (U - 1?.) . . * = NkR . . . . . (32') 
 
 In the numerical example given above, considering tier 2, equation 
 
 21 gives M2 = 800,000 (13-4) /8 = 900,000 ft. Ibs.j oouation 32 gives M 2 - 
 
 2 
 300,000 (13-4 )/ 8 x 13 = 625,000 ft. Ibs., a value only 70$ as large. Obviously 
 
 the approximate method produces a more economic but less conservative design. 
 Consult a contribution with insert sheet in Eng. News, Vol. 26 V p. 116, Aug. 8, 
 i89l. In this article :ir. C. T. Purdy outlines methods for design of Steel beam 
 footings in Chicago. Sec also discussion of .Mr. Purdy's methods, Eng. Kovvs, 
 Vol. -26, pp. 312, 265, 415. 
 
 The analysis, equations (21) - (26) isnot the most accurate, 
 because, except for the lowest tier, the load is 'not uniform. The bending of 
 ihe steel beams in any c oursc throws a greater lor.d on the two outside beams of 
 the course next above. A more accurate solution, producing a considerable saving 
 if materiel is effected by applying in important cases the more exact theory for 
 iontinuous girders. It is eucstionablc however whether one is warranted in ,-naking 
 : \e more involved calculations. In practice, the simpler form of aquations 21 to 
 ) justifies their use, particularly when due consideration is given to s. rational 
 lection of values for working stresses. For a mathematical treatment of footing 
 ress'-s, assuming the beams in eny tier as constrained, sec a^ scries of articles 
 r ilr. , B. Durand, Eng. Record, Vol. 39, 1899, pp.333, 354, 383, and 407. 
 
:;<. 
 
79 
 
 6. FOOTINGS OF REINFORCED COI-jGliETE 
 
 Footings of I-beams or rails laid in concrete have boon in common 
 practice since 1890. Recently alternative designs of reinforced concrete have come 
 into use. In the latter typo the concrete slab is reinforced with rods, cither 
 plain or deformed. Usually the footing consists of one concrete layer beneath the 
 cast iron column base, Fig. 2?a. This layer generally has only one set of bars when 
 the footing supports a vail column, the bars running at right angles to the l~ngtfc 
 of the wall. For footings under interior columns the slab in most cases is square, 
 reinforced by two sets of bars at right angles. , 
 
 VZA.LL FOOTINGS ' 
 
 Fig. 29 gives the details of design for a wall column, Boalt'Hall, 
 University of California. The outer walls of the building consist of concrete- 
 faced with granite and arc self supporting. The stcelcolumn carries only the 
 dead and live leads, P c for floors and roof = 189,000 Ibs. The footing plan 
 GHJK is 10 x 10 ft. = 100 sr. ft.; it carries 10 lineal ft. CDFE of wall load. 
 Between columns the wall loads arc carried by a footing 4 ft. wide. Allowing for 
 window openings, the total wall load on GHJK is P w = 238,000 Ibs. The slab 
 GHJK rests directly upcn the soil, which is sandy clay. It vail be noted that 
 the column axis aa is eccentric a distance n, while the w a 11 center lino bb is 
 acentric m inches to the other side of the footing center line AB. The resultant 
 load P = P c + P W = 427,000 Ibs,, m + n by design for all wall columns in the 
 building was taken equal to 10 inches; again JV/ (m+n) = P* 1 ; hence, 
 
 n = Py;(mn) = 258,000 x 10 = 5.6 inches, m = 10 - 5.6 = 4.4 ins. 
 P 427,000 
 
 BEARING. The axis aa for columns was fixed 4 ft. 6.5 ins. from the 
 .'tmcr side GH of the footing; consequently the lino of the force P lies 4 ft. 
 3.5 ins. -i- 5.6 ins, = 5 ft. 0.1 ins. from that edge. For practice.! purposes 
 ''horeforo it may b o assumed that the resultant lead P is central upon d&JK and 
 'hat it acts in the line AB. The pressure on the bod is uniform, its intensity 
 = 427,000/100 = 4270 Ibs. per so. ft. = 2.15 tons. A pressure of 2 to 2,3 tons 
 
per sq. ft. was tentatively assigned for the foundation bod throughout the 
 building plan. 
 
 SHLAR. The footing depth was taken equal' to 36 inches, with roin- 
 
 t 
 
 forcement bars 6 ins. from the bottom surface. The shear oxortoc. by the wall 
 load acts on the vertical sections CD and EF; their combined area = 2 x 10 x 3 = 
 60 sq.ft.; hence neglecting the stiffness offered by tho bars, the shear applied 
 to the concrete = 427,000/60 = 7100" Ibs. per so. ft. = 50 Ib. per sq. in. This is 
 
 a c onservatiVe calculation; tho shear is below safo working values (100 Ib. per 
 
 I 
 
 sq. in. ) for concrete. Observe that it is hero assumed that the wall CDFE dis- 
 
 \ * 
 
 tributes the column load upon the sections CD and EF. 
 
 BEEPING, DESIGN FOR REINFORCEMENT , 
 
 Considering simple cantilever action, tho ..lax. bending moment in 
 
 \ 
 
 the slab, by equation (23)., roughly is: 
 
 M = 427,000. ( 10_ -_3) = 375,000 ft. Ibs. = 4,480,000 in, Ibs. 
 
 2 44 
 
 Tho gross depth of slab D - 36 inches; effective depth from stool 
 
 bars to top surface of concrete, d = 30 ins. For approximate calculations k = 0.4 
 
 and j = 0.86; consult Turneauro & Maurer's Principles of Reinforced Concrete. 
 
 i 
 
 Unless otherwise stated, those values for k and j will be used in what follows 
 whenever calculations for reinforced concrete beams ETC made. Foundation loads 
 cannot be a ssi gnod accurately; usually the beams are short and thick and do not 
 satisfy closely the common theory of flexure, or they arc constrained as con- 
 tinuous spcvns or act partially as slabs supported on four edges. Tho bending 
 moment M therefore is not a certain value; approximate calculations are justified, 
 Similar remarks apply to investigations for shear, kd = 30 x 0.4 = 12, ins; jd = 
 
 0.86 x 30 = 25.8 ins,; F = 4, '480, 000/25. 8 = 173,000 Ibs. * total fiber stress on 
 
 * 
 stool tars in tension and on concrete in compression; f s = allowable intensity 
 
 of stress in steel = 16,000 Ib. per so. in.; A s = necessary c ross sectional area 
 of steel bars = 173,000/16,000 = 10.8 sr . ins.; use therefore 21 - 3/4 in. sq. 
 bars, 9 ft. long, spaced r.bout 5 3/4" ccntors. At rijht c.nglcs to this group 
 of bars place, as shown in Fig. 29 , 4 - 3/4" sq. bars to stiffen the slab and 
 
81 
 
 hold tho other bars. The neutral surface is approximately kd = 12 ins., below 
 the top surface of concrete; therefore the concrete cross section subjected to 
 compressivc fiber stresses is AC = 10 x 12 x 12 = 1440 so. ins. Upon this area 
 tho stresses vr.ry linorrly from zero to a maximum; hence the uiaximum concrete 
 comprossion = f c = 2F/Ac = 2 z 172,000/1440 = 240 Ibs. per so. in. f c might safely 
 be 400 to 500 lbs= por s q. in., which shcv;s that tho footing slr.b is conservatively 
 thick for bonding, but it is not too thick in shear. 
 
 INTERIOR COLUIflT FOOTINGS 
 Fig. 30 show s details for an interior column, Boalt Hall, University 
 
 of California. 
 
 t 
 
 BEARING. The footing is square in plan, 8 x 8 ft. , it is 36 in. 
 tMck with steel 6 ins. from tho bottom. The total load P = 275,000 Ib. The 
 intensity of pressure on the bod = p = 275, QOO/ 8x8= 4300 Ib. - 2.15 tons per 
 so. ft. 
 
 SHEAR. The cast iron base has a plan = 30 x 39 ins. honco tho 
 total arod $f shearing section ABCD = 4 x 39 x 36 = 5600 sq. ins., shear inten- 
 sity not considering effect on bars = 275,000/5600 = 49 Ib. per sq. in. 
 
 BEHDIKCr. An approximate method for calculations will bo used; 
 
 consult Designing Ilcthods, Reinforced Core rote Construction, Expanded I.Iotal and 
 3orrugatcd Bar Co., Vol. 1, Ko. 2, June 1908, p. 49. Two sets of bars at right 
 .ngles are employed. Tho upward prcs&uro on triangle EOF and the downward, pressure 
 m DOC are each equal to 1/4 of P or to 69,000 Ibs. The max. bending M is in the 
 cortical plane XY; G is the controid of triangle DOC, H that of EOF; OG = 1/3 
 f AD - 13 ins. , OH = 2/3 of XE = 32 ins. ; honco M = P m /4 = 69000 x 19 = 
 .,310,000 in. Ibs. This moment is resisted mainly by the concrete and bars below 
 id within tho confines of the cast iron base. Of course only bars normal to 
 T can be considered, and of these bars, those that arc near the lines XE and YF 
 
 little work. Assume that 11 is resisted in the vortical plane through XY by the 
 
 ' 
 ncrote and bars in a width equal to a side DC of the column base plus -the depth 
 
 f footing; thus the available width w = 39 + 36 = 75 ins. The distance EF is 
 
 ' 
 
82 
 
 96 Ins., not greatly exceeding w, but this is due to the fact that the footing 
 depth of 36 ins. has boon assumed generously. The bending moment per ft, width 
 is MI = M/w = 1,310,000/ 6.25 = 210,000 in. Ibs., B = 36 ins., d = 30 ins,, 
 kd = 12 ins., jd = 25.8 ins., hence F = 210,000/25.8 = 8140 Ibs.; f g = 16,000 Ib. 
 por sq. in., AS = 0.51 so. ins.; use 1/2 in. square bars, 7 ft. long, spcccd 6 
 ins. centers in two groups at right angles. 
 
 &ENERAL COMMENT ON THE DESIC-IT OF FOQTIKuS UEDSR INTERIOR COLUMNS 
 
 The problem of the design of square of rectangular footings, 
 
 reinforced in two directions, is similar to that for floor panels in which the 
 slabs rest on all four cdgos. For ordinary soiJLs the allowable footing pressures 
 range from 2 to 4 tons or 4000 to 8000 Ibs. per s q. ft. Floors usually carry a 
 total load, dead and live, of, only 200 to 500 Ibs. per so. ft. of floor slab. 
 Hence footing slabs are much thicker; in their beam action they are short in 
 span and deep in section ssfi require special attention to provide against excess- 
 ive shear and bond stresses. 
 
 It is difficult to calculate accurately the stroscos in a square 
 footing. Assumptions have- been made in the design, Fig. 30, which give results 
 well on tho side of safety. For more exact analyses, tho theory of stress in 
 square an4 circular plates may bo applied to this problem. See Principles of 
 Reinforced Concrete Construction by Turneannc & Mauror, 3d od. , 1919, Chap, 8; 
 also an article by Prof. H. T. Sdcy, Year Book, Lngincors bocioty, University of 
 Minnesota, 1899. 
 
 Tho following gives mother treatment. As a general principle the 
 pressures should be carried as directly as possible from the edges ABCD, Fig. 31, 
 to the center. The square EF&E 'represents the plan of the cast iron column base, 
 'Jwo sgts of main reinforcing rods aa 1 and bb 1 within tho limits shown, will do 
 oho most work. To reinforce tho corners the two sets of diagonal bars dd 1 arc 
 introduced. In footings of large plan ABCD ard relatively snail column base EFC-H 
 chc groups of bars aa 1 , bb' and dd 1 will not cover the entire area. 'Triangular 
 . - Hire J::L arc 1 loft. To offset this a fc* short 
 
83 
 
 The criticism to be .tado of this scheme of r cinforccm&nt is that 
 it uses considerable steel and congests it under the column base. In making 
 calculations, the total pressure on BFGC is assumed to bo carried to the vertical 
 section at PG whore the bonding moment and shear are maxima and may be studied 
 as in the preceding problem, Fig. 30. 
 
 The max. shear and diagonal tension in footings ere found near 
 
 section QR, Fig. 31. Cracks tend to occur along the curved linos oc 1 . Bent rods, 
 when used, must be bent up as shown just outside the column base. They aro net 
 
 needed near the end of the beam. Stirrups, g, must be spaced closely near QR but 
 
 r 
 
 can be omitted further out. 
 
 For economy large footing slabs may be increased in thickness pro- 
 ceeding from the outer edges toward the center, Fig. 31A, or they may bo stepped 
 as shown. Again, a thin footing slab maybe used, ribbed on the under sMo with 
 beams of greater depth, thus securing the benefit of T-action, as in floors. 
 Tho upward pressure from the foundation bed tends to pull the slab away from the 
 beam,, but the use of sufficient stirrups properly bonded to the horizontal steel 
 bars in slab and beam will give adequate anchorage. See Turncaurc and Maurer, 
 just cited, Chap. 9, fig. 35, p. 337. Consult Engineering News, Vol. 56, p. 30. 
 
 g. COIIBIITEP FOOTINGS 
 
 In large buildings (class A) all the lords, oven of the walls, arc 
 supported dir :ctly by rows of regularly placed columns. If possible tho footings 
 are disposed symmetrically febout tho center of gravity of the column loads; 
 usually they arc squr.ro. Frequently c.n exterior column footing cannot be designed 
 square, because of the limitations to tho size of tho lot. In such a case, tho 
 load of the wall column may be connected with that of the nearest interior column 
 -jy designing a special trepezoidr.l footing. Sometimes three or more columns may 
 
 their footing combined by employing cr.ntilcver and continuous slabs. In 
 ildings on irregular lots, a cluster of columns at a corner or under a tower 
 iay be supported upon a large polygorcl slr.b. Tho main principle to be satisfied 
 
 ,TF-VO 
 
 bua 
 

84 
 
 of gravity of the combined column and footing loads; sec Chap. 3. Combined 
 footings may consist of stool I-beams embedded in concrete.; such designs are moat 
 common for vory hcrvy foundations. Or they may b o off reinforced concrete slabs, 
 girders and beams constituting a floor, similar to a building floor, but reversed 
 as to loads. 
 
 Some- heavy footings arc monolithic slabs 'covering tho entire 
 
 building plan. This typo is usual for tall tower like structures. See Figs. 4A- 
 4B; Sather Campanile foundation, whose concrete slab, 8 ft. thick, 48 ft. sq. 
 in plan, is stiffened by tv/o layers of 24" I-beams supported upon a lower 4 ft. 
 bod of reinforced concrete. 
 
 CALL 3WILDING, SAN FIO'CISCO. Fig. 31A shows tho base of the Call 
 building, Sen Francisco, established on wot, compact, hard sand, in natural 
 place, at a depth of about 25 ft. 9 ins. below the street level. On this sand was 
 poured a bed of concrete 2 ft. thick, 96 x 100 ft. plan. The base of tho build- 
 ing at the sidewalk level is 75 ft. square. Upon the concrete bod rest tv/o 
 layers of 15 inch stool I-bcams, 58 in the first and 63 in thc'second, at right 
 angles, forming a grillage of beams, each spliced beam about 96 ft. long. Those 
 two layers are covered with concrete. Upon the grillage- were placed 28 sets of 
 20" I-beams to carry the columns and pedestals. The cast stc.l pedestals arc 
 firmly held by anchor bars extending down and keyed into the webs of tho lower 
 layer of 15" I-beams. The footing therefore is a great table of reinforced con- 
 crete, 54 inches thick, giving an average soil pressure 4500 Ib. per sc.ft. 
 The superstructure weighs 12000 tons. 
 
 V/ASHIKSTOH MONULENT , In 1878 the monument, Fig. 31B, had been 
 completed to elevation AB, 156 ft. 4 1/8 ins. above the top of its foundation 
 CD. The mean lengths of side and thickness of shell at AB are 48 ft. 9 5/8 ins. 
 and 11- ft. 10 5/16 ins.; at CD, 55 ft. 1 1/2 ins. and 15 ft. 1/4 ins. The shaft 
 consists of white nr.rblc facing and bluest one backing/ The original foundation 
 CDEF, 23 ft. 4 ins. in thickness, of blue gneiss rubble masonry, laid in pure 
 lime mortar, was carried up from bottom to too in 8 offsets or stops. The first 
 
85 
 
 or lowest step vizs 80' x 80' x 2'4" riso; the oighth or top stop, 58'6" x 2*11" 
 rise; the other stpps being more or loss in proportion. 3y rctual experiment the 
 masonry wcs found to average 164.88 Ibs. per cu. ft. in v/fcight 
 
 The w eight then of tho partially completed shaft was: 
 
 weight of shaft 23 794 tons 
 
 weight of foundation 8,139'" 
 
 weight of earth on foundation 243 " 
 
 total 32,176 tons 
 
 This weight distributed or or a bed 6400 so. ft. in area, gave a 
 
 \ 
 
 pressure of 5.027 tons per sq. ft, of 2240 Ib. each. 
 
 In 1878 the Corps of Engineers, U. S. Array, was ordered "to prepare 
 
 ' 
 a project for strengthening tho foundation, to tho ^nd that the monument may be 
 
 ' carried to a height of at least 525 ft. above the present top of the foundation", 
 For this new height, and with earth filled upon the foundation to level CD the 
 total load on tho bed EF would have been- 
 
 weight of shaft 43,421 tons 
 
 woight of foundation 8,139 " 
 
 weight of roof and stairs, etc. 250 " 
 
 weight of earth on foundation 2,283 " 
 
 total 54,093 " 
 < 
 
 or 8.452 tons per sc. ft. 'with a wind pressure of 55 Ib. por sq. ft. acting on 
 the shaft's vertical projection would have given a max. of 9.941 tons per sc-ft, 
 
 ?-t the toe of bed EF. This value was considered unsafe. 
 
 
 The substructure was undermined by sections and now /masses of 
 
 Portland cement concrete ;r.sonry introduced in thin vertical Icyors, not over 
 
 <i ft. in width, having first tunneled under the structure with drifts of that ( 
 I \ 
 .vidth and the. required height and length. The new bed, 126' 6" square has its 
 
 jvel GH at the water lovol, or 12 '4" below the earlier bottom EF of the first 
 oundation. The new masses were extended 18 ft. under the outer edge of the old 
 oundction end 5 ft. under tho outer face of the shaft at its lowest joint. The 
 >d of the final foundation, with the oarth terraced to the Ic-vol of the bottom 
 f the shaft, is subjected to loads as follows: 
 
I-.- 
 
 ' '- ' 
 
86 
 
 weight of shaft 43,671 tons 
 
 weight of foundations 21,160 
 
 weight of earth on top of foundation 14,269 
 
 .weight of earth within foundation 1.278 
 
 total 80,378 tons 
 
 giving a mean pressure of 5.022 tons per sq. ft.; or a re.::, with a 55 Ib. wine, of 
 5.398 tons; which is only 0.371 tons greater than that c::ertcd by the partial 
 
 * 
 
 structure upon the older bed EF. 
 
 The student should read the report of the Chief of Lngineers, Thos. 
 Lincoln Casey, 45th Congress, 3rd Session, House of Representatives, ;,iis. Doc.l\o. 
 7, 8, 9, etc. for detailed accounts. 
 
 SINGER BUILDING FOUNDATION. Consult Trans. A.n. Soc. C,E. , Vol. 63, 
 p. 1, particularly fig. 12, p. 23. At the basement level the tower is 60 ft. square 
 
 
 
 center to center of columns; the CD lumns arc 12 ft. on centers; 6 columns per 
 side, or 36 columns total; the height is 560 ft. above basement to base of lan- 
 tern. The greatest depth of caisson below basement is 73 ft. or 92 ft. below 
 curb. The height of tower from bottom of caisson to top of flagpole is 745 ft. 
 The lantern is 66 ft. in height; the flagpole 40 ft. 
 
 The main tower then is a square prism 63 x 63 x 560 ft. above the 
 basement level. The weight of tower is 18,365 tons. The height of the main 
 building adjacent to the tower is 191 ft. 8 in. from sidewalk to roof. Therefore 
 it was assumed that wind pressure could act only upon the upper 350 ft. of the 
 tower. Though 30 Ib. per so. ft. of wind pressure was proscribed, in the cal- 
 culations this v,as reduced to 20 Ib. on account of a 50^ increase allowed by 
 the building code for wind stresses when compared to dead and live lead stresses. 
 The wind force on the exposed tower above the 14th story then is \7 = 
 = 442,000 Ib. 
 
 Considering the tower to rest on a base 70 x 72 ft. the average 
 pressure by a monolith theory is 18400/70 x 72 = 3.65 tons per sq.ft. The wind 
 force of 442,000 Ibs. moves the center of pressure 4 ft. from the center of the 
 figure, giving E range of pressures from 2.4 on the windward to 5 tons per sq. 
 ft, on the leeward edge of the base. 
 
87 
 
 As a matter of fact the tower rests on caissons about 80 ft. long. 
 Those caissons wore proportioned to t alec a load not to exceed 15 tons per sq.ft. 
 Since tho wind pressure docsnot exceed 50fb of the dead and live load, it was net 
 regarded in figuring the caisson pressures. It was considered in designing tho 
 steel wind f ran ing ard the anchorage of columns to caissons 
 
 TRAPEZOIDAL COMBINED FOOTIK3S 
 
 Let A and B, Fig. 32, be loads carried by columns A and B; x - 
 
 the distance of the point of application of the resultant load A+B from the conter 
 of A; m = distance between center linos of colmrns A and B. Talcing moments about 
 
 A:- 
 
 Bm = (A + B)x Q ; hence x = Bm/ A+B ..... . . . ...... (33) 
 
 The combined footing acts like a beam resisting tho upward pres- 
 sure of the soil. It is supported at tho ends by the downward column leads. By 
 - naking the center of gravity of the footing plan coincide with the resultant of 
 the column loads, a uniform soil -pressure is produced. Strictly this ia only true 
 
 * 
 
 r /Lon the weight Qf the footing is constant per sq. ft. of plan; that is, v/hon tho 
 footing slcb is of uniform thickness. 
 
 Let p = the allowable soil pressure, P = tho total weight of footing 
 and k = tho area of footing plan; then: 
 
 k = P + A + B ....... . ...... ....... ^34) 
 
 p 
 Observe that since the column loads A and B arc resumed unequal 
 
 :;ho footing will have a trapezoidal shape; if A = B, the trapezoid becomes a 
 cctanglo. Let a and b be tho parallel sides of tho trapozoid. If A<B, a<b 
 ISD . Lot 1 = total length of footing, and y = distance from center of wall column 
 to tho lot line. Note that X Q is determined by equation (33) while y is given 
 Torn tho study of the ground plan. Hence the centroid of the trapozoid must bo a 
 istance x +y from the lot line at column A. Usually 1 and z are given from the 
 around plan studies also. 
 
 (55) 
 
 2 
 Consider tho trapezoid composed of a rectangle al and two right 
 
88. 
 angled triangles; take static moments about a. point in the side a: 
 
 Si? (b - a)l3 = k (x +y) . . . . ........ .... (36) 
 
 2. 3 
 
 In practical problems, in equations (35) and (36) all quantities 
 
 are known save a and b; solving for those unknowns: 
 
 b = 2k (3(x +y)_i 
 1 ( I 
 
 a = 2k/ 1 - b ..... ...,..,.....;....,.... (38) 
 
 If B = 2A and it is assumed that y=Z=0;l=m, from (33), 
 
 X = !" from ( 3? ) b = 2k/l; and from (38), a = O/ Therefore the nethod fa Is 
 3 
 
 when the interior column load is tvo or more times that of the- wall column. ' In 
 such cases the footing must bo prolonged beyond column B into the lot area. Then 
 the sle.b of span m becomes continuous' with a cantilever span -projected to the 
 tight side of B. Heavy bending is produced at B. Commonly for this type the plan 
 of footing bod. is made rectangular. The foundation slabs maybe designed in 
 reinforced concrete or in tiers of structural stool beams; 
 
 With "She plan dimensions of the trapezoidr.l footing, determined and 
 its thickness D assumed, the slab should be designed as a reinforced concrete 
 beam of span- m loaded with an intensity A+B/k Ib. per so. ft. It is convenient 
 to consider a 12" width of beam, mcr.suring the 12" horizontally and perpendicular 
 to m. The main reinforcement rods should run parallel to the line AB for the rods 
 
 near the .median, line of the trapezoicl. Proceeding latcfr.lly towerd the sides, the 
 
 f 
 rods should diverge slightly so that the outermost ones run parallel to the in- 
 
 clined sides of the trapezoid. Particular caution should be observed in the design 
 of inclined bars g and stirrups h for the webs of these thick slabs. Bond vrlues 
 r.nd anchorage details for reinforcement metal should be studied carefully at the 
 column ends of the footing. Observe that such a slab must be considerably con- 
 strained at its ends. Heavy reverse bonding must exist under the columns. The 
 value for the maximum bending moment near the center of the span m may bo grossly 
 approximate when the span is considered simply supported. 
 
 Since the footing hrs considerable width at its ends a and b, it is 
 
39 
 
 necessary to distribute the colu/im loads laterally by placing transverse bars 
 under column A for a width at least 2y and under column B for a width of 2z. Such 
 reinforcement is to be calculated as for square footings; see Fig. 30. There is 
 therefore a vertical section like EF at column A. distant about 2y from the edge 
 
 
 
 a of the trapozoid, for which special shear calculations should be made; similarly 
 for a corresponding section near colujnn B. It maybe found that the assumed thick- 
 ness D of slab is excessive or too thin to give required strength; then proper 
 changes must be made, which in turn will affect the v/eight P, thus the area k, 
 equation (34). A second calculation should readily give satisfactory results. Hotc 
 that the load- for which beam stresses are calculated in the slab or span m docs 
 fiot include the deadweight P of tho footing. When the base of column A is small 
 it maybe that tho punching shear exdrted around its edges is grocter in intensity 
 than that along the lino EF; this oc cure when tho length of tho boundary of the 
 cast iron base is loss than EF. 
 
 Numerical Example. Soaring. Suppose column A carries 220 tons, B 
 300 tons. Lot the working pressure under cast iron colum bases bo 350 Ib* per 
 
 sq. in. ; then area base A = 220 x 2000 = 8.75 sq.ft.; similarly area base B = 11.9 
 
 350 x 144 
 sq.ft. Use square plan bases; for A = 3 x 3 ft., for B = 3 1/2 x 3 1/2 ft. Assign 
 
 y = 2 ft. , z = 2 ft. 6 in. Suppose m = 12 ft. Then 1 = m + y + z = 16 ft. 6 in. 
 Consider the safe soil pressure p = 4 tons per s q. ft. Neglecting own v/eight of 
 
 slab, the area of trapezoidal footing required = 220 + 500 = 130 sq.ft. Assume 
 
 4 
 
 the 
 
 slab 4 ft. thick; its approximate weight P = 150 x 4 x 130 = 78,000 Ib. 
 
 Kence k, equation (34), = 140 sq.ft. By equation 33, x = 500 x 12 = 6.92 ft. 
 
 520 
 By equation 37, b = 2 x 140 (5 x 8.92 - 1.) = 10.55 ft.; a = 2 x 140 - 10.55 = 
 
 16.5 16.5 16.5 
 
 6.45 ft. Practically make b = 10 ft. 6 in. , a = 6 ft. 6 in. 
 
 of Sleb. The effective upward pressure producing bending and 
 
 shear is p' = 220 + 300 = 3.72 tons = 7450 Ib. per sq. ft. For a strip 12 in. 
 
 140 
 wide the bending moment is M = p'm2/12 - 7450 x 144/12 - 89,200 ft.lb. < 
 
 1,070,000 in. Ibs. D * 48 ins,, d - 42 ins. kd - 16.8 ins.; jd = 36 ins . F = 
 1,070,000/36 - 29,700 Ibs.; for f s = 16000 Ib. per sq. in., A s -29700/16000 
 

 
 : sd filtforfa enoJ telyol^o tsorfa Islotqe riolrf 
 
 ' - -L - 
 
 orfJ J-'uW Jbtii'ol: scf YS.T; JI .6 actfrloo tsoa rro 
 
 t/pot QVT. o,t KirfiJ' oo^. 1C ovif; 
 
 ft aw?* ,1 Jrfiaw tvf^ *oo'tl;JS Iliv, 1 /nu^ rti Icjl'..' ,. *8i/o 
 
 ' ' 
 
 3 ovijk v,iibsoT br.corls cioi?a' >s A .(Wil 
 
 "; -, , . i; r .^ ; v ! '" ; 
 
 .ic cfafs or!* i 6-otfEl.uol53 OTD iaaao^c 
 
 nmoloo "io eesd- ori* rto/^V .Cfiloa1 orf* lo b c^It ofc 
 
 BVC 
 
 :' riOii. 
 
 foo :foif 3iia . :;OT; s. ^ri* i'oJ .ancJ. 005 
 
 V .'- 
 
 :..i .$"$ S\I 5 x Si\I 5*8 "JOl , .it! S x 1 
 '""ai d ft. dl s * Y + m * X t-rf?" .*! SI 
 
 :r 000, 
 
 o ,?o trei 
 
90 
 
 sq.in. , use 1 in. sq. bars at 6 in. centers; f Q = 2 x 29700 = 297 Ib. por sq. 
 
 12 x 16.8 
 in. Since the concrete could stand 500 Ib. per so. in. the slab is seon to be 
 
 thicker than necessary so far as concrete in compression is concerned. But a thinner 
 slab would require heavier stool bars. Simple calculations would determine quickly 
 the economic value of D considering fiber s tresses alone. A study of shoai and 
 diagonal tension near the columns may show that D = 4 ft. is desirable; moreover 
 
 | 
 
 a thick stiff slab aasures more definitely a uniform pressure distribution p 1 . 
 
 Shear. At section EF the shear roughly is 440,000 Ibs. The concrete 
 section = 7.5 x 4 - 30 sq. ft. Hence neglecting the metal reinforcement the average- 
 
 shear intensity = 440,000 = 102 Ib. per sq. in. The max. shear of the center of 
 
 30x144 
 the slabs' depth would exceed this value and shows that D was not taken too large., 
 
 further, that v/eb reinforcement is required. It is to Tap supplied in the form of 
 inclined bars and stirrups, but the computations will bo omitted. The shear area 
 for columnbaso A = 4 x 3 x 4 = 48 sq.ft. which shows that the section EF in this 
 case gives the greatest web stresses; simit r remarks apply to column base B, 
 In other problems, for smaller column bas^s, the results nay bo reversed. 
 
 The transverse reinforcement under columns also is not calculated; 
 nor 'the amounts of reverse bonding moment bars for the -min reinforcement. The 
 student s hould supply these computations with design sketches. 
 
 Consult Eng. Record, Vol. 64, Oct. 28 ,1911, p. 506, for a description 
 of a Reinforced Concrete Candy Factory. Eoro is illustrated a trapezoidal footing 
 Fig. 32A for whose bottom slab the main reinforcement runs laterally, since the 
 column leads are transmit t cd to the slab by a connecting girder 6'6 ;1 wide x 
 5'0" dee. 
 
 COMBINED FOOTINGS OF STRUCTURAL STEEL I -SHAMS Al-iD COk 
 In proportioning areas for adjacent grillage footings, they are 
 
 frequently found to overlap and in such castss two, three or even four areas may be 
 combined into ono footing. In some of tho more recent designs complex foundations 
 have been built in reinforced concrete but in the majority of instances recourse 
 has been had to the use of grillages of I -beams. In typical examples r number of 
 
:;, i :..' 
 
 
91 
 
 columns rest upon a straight, continuous girder, which in turn is supported by 
 one or more layers of short grillage beams. For exceptionally heavy work the 
 continuous I-girder bocoro s a neat of I-beams, a plate girder or evon a truss. 
 The same principles of design apply whether the type is reinforced concrete slabs, 
 rolled steel I-beams or plate girders. In the following analyses the cases consider- 
 ed picture only groups of I-beams imbodc'od i-n concrete. 
 
 Combined footings of I^becm grillages are much used with the canti- 
 lever construction and where lot linos limit the spread of one part of a foundation. 
 Thore are nrajiy possible combinations requiring special solutions. The problem is 
 much simplified when only two tiers of beams aro used. The examples presented 
 below arc taken in part from Frcitag's Architectural Engineering, Chap. IX, on 
 Foundations. 
 
 TWO UNEQUAL COLUMN LOAlfe SUPPORTED UPON A HECTAHGULAF. GRILLAGE 
 
 In Fig. 33 lot A and B be two column loads spaced a distance m. 
 
 The lot line is adjacent to the lighter column; A<.B. It is required to design a 
 footing of two tiers of I-beams whose foundation bed is rectangular, b x 1. 
 
 If tho weight of grillage P is neglected and the allowable foundation 
 pressure is p, the croa k of footing bed is : 
 
 k = bl = A + B/p (9) 
 
 Let x = tho distance from column A to the line of action of tho 
 o 
 
 resultant load A+ B. Tho value of x is given by equation 33. In order that the 
 controid of the rectangle and the center of loading mr.y coincide: 
 
 1 = 2 xo * 2 fin/ A + B (40) 
 
 Hence, b = k/1 ' ( 41) 
 
 The upper tier of beams will be few in number, of length 1, The 
 group will have a total plan width c. They are continuous beams of two spans, 
 m and a; a being a cantilever span. If w = the uniform pressure per lineal ft. of 
 
 footing: 
 
 w = A + B/l = pb l4 ' 
 
 This is the intensity of load par lineal ft. acting upon tho uppsr 
 
.'"'.' ' --'' ' '*;.'' 
 
92 
 
 tier of beams whoso two spans m and a are supported by the two reactions A r.nd B. 
 If d is tho spacing in ft. of the cross beams in the lower tier, the- total laid 
 
 T 7 on one bean is , 
 
 T7 * wd . . . . . . . . . . . . . , . . . . . . . . . (43) 
 
 and the maximum bonding .nomont LI is by equation 23, M = V//8 (b~c). .... (44). 
 
 For simplicity an appropriation is made by considering the center 
 line of column A as the end of tho footing. The error is slight particularly if 
 tho span m is largo in comparison to the column base which usually is loss than 
 2 (ft. square, since tho bearing is metallic. For the upper tier tv/o rc.x. bonding 
 moments MI and !1% will bo found, one at the section -of zero shear in spai m, the 
 other at column B. If g is the distance of section IIj from A: 
 
 g = A/w o . (45) 
 
 % = Ag - wg2/2 , V . . . (46) 
 
 If the base of column B has a width c, 1,1 = wa 2 / 2 - Bc/8 ......... (47) 
 
 (~j 
 
 ; Thc maximum shears in the upper tior of beams occur at tho columns. 
 A small distance to the right of A the shear is the load A; immediately to the 
 right of column B it may be taken equal to va while to tl::- left of that' column 
 it is B - wa. 
 
 Uhen the wall column carries the Irxgcr load, A> B, this method 
 
 fails since the lot lino would prohibit the projection of a cantilever span to the 
 left of column A. 
 
 / 
 
 Numerical Example. In Fig. 33, let :: = 220 tons, B = 400 tons, m = 
 12 ft, p = 4 tons per sq. ft. By equation 39, k = 155 sq. ft. By equation 40, 
 
 1 = 2 z 400 x 12 ^ 15.5 ft. By qquation 41, b = 10 ft. By equation 2, w = 4:r 10s= 
 
 220 + 400 
 40 tons per lineal ft. By equation 45, g = 220/40 - 5.5 ft.; by equation 46, Ll x = 
 
 220 x 5.5 - 40 x .(5.5) 2 = +605 ft. tons. The metal base of column B rests on stool 
 
 2 
 
 beams; therefore assume a base width c = 42 ins.; this value will give an excess- 
 ively low bearing pressure for steel on steel. By equation 47 M *= - 40 x (3.5) 2 + 
 
 M 
 
 400 x 5.5- = _ 71.Q ft, tons. In this problem it is sc.n that ;/!]_> Lig; with 3 
 
 8 
 larger, tho cantilever length a rould increase till finally LI 2 ^'ould c-xcccd U-,_ . 
 

 
 ' 
 
 PC 
 
 
 .. i 
 
93 . 
 
 The section modulus for tier 1 Is 605 x 2000 x 12 =S08, requiring 5 - 24" 85# 
 
 16000 
 I-beams in bending. The beans must be hold together securely by separators and 
 
 bolts. The spaces bctvoen are filled with, concrete 
 
 Sh_ecr. The shearing stresses in the v/obs of the I -beams of tier 1 
 
 should be investigated. The shear near A * 220 tone; to the left of 3 = 260 tons ; 
 to the right of B = 140 tons. Hence tho greatest shear intensity in the webs = 
 
 S = 3 / x 260 x 2000 IDS. per sc. in,; where n = number of beams in tier 1, d = 
 
 tndt 
 depth" of. those beams in ins., and t = their web thickness in ins. For t he 5 - 24" 
 
 85# I-beams required for the bending moment I^, n = 5, d = 24 ins., t = 0.57; 
 hence S]_ = 11400 Ib. per sq. in., a value which is conservative and indicates 
 about the s ame degree of safety as the 16000 Ibs. per sc . in. working stress em- 
 ployed for bending stresses. Allowing about 2 1/2 in. spaces between flanges to 
 pour concrete, 'c = 5 x 7 + 4 x 2. 5 = 45 ins, 
 
 Design of tier 2 - Consider d = 1 ft.; by eq. 43 \7 = 40 tons, by 
 (44) iJL = 40/8 (10 - 3.75) = 31.2ft. tons, per lineal ft, of footing, section 
 
 modulus = 51.2 x 2000 x 12 = 46.8; use 12" 31. S^ I's at 9 1/4" centers. The 
 
 16000 
 maximum shear is at section QQ = 40 y. 5.12 = 12.5 tons uer lineal ft. of tier 2 = 
 
 10 
 9.6 tons per beam for 9 1/4" spacing. Henco the rax. shear intensity's = 3/2 
 
 9.6 x 2000 = 6850 Ib. per sq. in. of web. 
 12 x 0.35 
 
 TWO UKECUAL COLUf/E LOADS, THE GREATER LOAD AT THE LOT LINE, 
 
 H) upou A TR.PSZOID.'.L GRILLAOZ OF TV/O Tizrs OF 
 
 x 
 
 In Fig. 34 use notation similar to that of Fig. 32. Column A at the 
 lot line has lord. A}> B. The distance y. from the trapozoid's centroid to the line 
 of column A is found by ec. 33. Neglecting tho w eight of footing P, its area k is 
 giveniby oq. 34. By static moments about any point in the lot line, a:- 
 
 bl 2 * (a - b)l 2 = k (x + yj> (48) 
 
 2 6 " 
 
 Equation 35 and equation 48 contain two unknown quantities, a and 
 
 b, solving:Q a = 2k ( 2 -5(x n +y) ) (49) 
 
 1 1 
 
 b = 2k ( 3(v,,+ v) i\ ( 5 ) 
 
94 
 
 In footings for which tho span m is large compared to the dimensions 
 of column bases, tho distance y and z may bo neglected, ifeking y=z=0,m=l,' 
 
 and : - 
 
 a = 2k/l (2- 5x n ) ; b = 2k/l (Sx^ - 1 }...,......**. (51) 
 
 ~1 1 
 
 The upper tier of beams is loaded with an intensity wj at edge b; 
 
 Cu 
 
 w 2 at edge^. The load varies linearly between those lioits. At any intermediate 
 section 'the intensity is proportional to tho width of the trapezoidal footing. 
 Since p denotes tho allowable unit footing pressure, \Vj=pb; v/2 = pa. ........ (52) 
 
 By scaling the pressure diagrr.m, or from similar triangles by 
 
 computation we may got tho values of \v a and w- Q under the respective column centers, 
 If y and z are considered negligible, w-^ = w b and w 2 = w,,. Measure tho variable 
 distance x from column B to the left, then the load intensity at any section is: 
 w = wb + (w a - w b ) x/1 .................... (53) 
 
 Neglect the restraining cantilever effects in tier 1 produced by 
 tho soil pressures at tho dnds y and z. Consider tho girder of tier 1 .simply 
 supported on span m = 1. For t he assumptions the reactions are A and B. The 
 bending moment M at any section XT is:- 
 
 * "V- 
 
 M = Bx]_ - / w(xi - x) dx ....... . ......... (54) 
 
 6 
 
 M maybe evaluated from (54,-) by considering -x^ a c onstant r.nd sub- 
 stituting the value of w from (53); but in what follows X]_ is a variable; see 
 
 equations (55) and (56). 
 
 / 
 M = Bxl - / (wb + (w a - Wb)x/l)(xi-x)dx. 
 
 Expanding and integrating: 
 
 M Bxi -IwwKlX - (w b ~ (w - v/ b (J) x x ) x 2 /2 - (w a -w b ) x3/3 1 
 
 Substituting the limits, wo get tho bending moment at any section: 
 M = Bx 
 
 The m?.ximum bonding moment M occurs at section x x = g, whore tho 
 
 .-hoar is zero. Tho first derivative of M v/ith respect to x is: 
 
 = s = B - v/b*i - (w a - wb ) xi2/ 21 
 
95 
 
 v/hcn the shear s = 0, x = g, henCe: 
 
 = B - w b g * (w a -v.'t>)g 2 ; solving for g, 
 
 
 g = - w b l -i- *f~w~izT< + 2B1 
 
 _ ............... (57) 
 
 MO =/B^-A^bg2J - (w a - w b ) g3/ 6 1 ............... (58) 
 
 c*/L 
 
 iracTical problems it is often b ost .to calculate the value of 
 
 each quantity in turn. By introducing the numerical r. suits in succession into 
 the subsequent equations the complexity of algebraic forms like (57) is eliminated 
 
 The beams of tier 1, v/hon uniform in section throughout the span, 
 are designed for the shear s = A and b ending moment I1 . For very heavy footings, 
 for economy, the beams of tier 1 may be plate girders whose webs and stiffeners 
 vary in dimensions to suit the value s from eq. (56) and whose flanges are pro- 
 portioned to withstand the v rying bending moment M of oq. (55). For an analysis 
 equivalent to t he above, see Frcitag, Architectural Engineering, 1909, p. 331. 
 
 The lengths of the beams in the lower or second tier vary from b to 
 a. The total load on a b earn at a would be w 2 d, where d is f o spacing of beams; 
 similarly at b x the- total load would be w x d. For an intermediate beam at section 
 x the load would b e wd. Separate calculations have been illustrated fully in two 
 earlier examples. As already explained for the trapesoid of reinforced concrete, 
 Fig . 32, here also, the method fails when column load B is equal to or less than 
 one half of load A. For -B = A/2, vq. ' 
 
 '..' 
 
 ' '" , . consult Frog's Architectural En Si neoring, p. S*i International 
 correspondence School, Structural E n S inoerin g Course, Heavy Foundations, p. 24. 
 
 V 
 
 Sec also reference No. 9 at the end o'f this cjjaptoi 
 
 In Fig. 35 consider three columns, loads PI. P 2 , *g> ' 
 
 r 1 Neglecting the footing weight: 
 spaced, supported on a rectangular base b . 
 
 pbl = Pi + P 2 + PS 
 
 Hore p - allege pressure en the soil. For uni. distribution, the center o f 
 

96 
 gravity of the loads P must coir.cide with the centroid of the rectangle, or 
 
 1/2 = P 1:n i + P 2 (rai-H7i 2 J + P 3 (mi-wi2-r-3) ............ .... (60) 
 
 p l + ? 2 + ^3 
 To satisfy these relations the girders must be stiff and suffer 
 
 little deflection. The dimensions m and the loads P must be arranged to fit. If 
 these conditions cannot be fulfilled the pressure p vd.ll not be uniform unless 
 the breadth b israade variable. A changing value of b throughout the footing 
 length introduces further complexity and indetermi nation. For cases v.hich do not 
 ueet the requirements of (59) and (60) easily, the continuous footing type should 
 be discarded. Instead separate footings, pile clusters, or caissons may be 
 
 selected. 
 
 To design the beams of tier 1 it is necessary t o find the max. 
 shears and bending moments. The pressure against the beams from below is pb. From 
 
 above, under Pl it<is PI/XI = p, , under P^ it is p2 = ?2/ x 2 ; and P 3 = P 3/ X 3" The 
 i-.iax. bending moments are 111, 1/12, 143, etc. at distcnces Ij, l2> ls etc - from ^ e 
 left end of footing, at sections for which t he shc-ars are zero. For the notation 
 
 shows:- pbli = PlU]_-yi) fr which 1 = p 1 y 1 (61) 
 
 pb! 2 = PX, or 1 2 = Pi/pb 
 
 = PI * pat is-yi-x-yg). or 1 s = p i-P2(yi >x i *yz) .... (63) 
 
 Similar equations maybe established f or t he remaining sections of 
 zero shear at distances 1 4 and l g . The max. bending moments Ml, M 2 , etc. result 
 by toeing in each case the algebraic sum of moments of pressures to the left of 
 the section about the section. 
 
 MI = pbli 2 / 2 - PiUj-yil? - (64) 
 
 fy 
 
 112 = pbl2 2 /2 - P-.M^-tr. -XT 1 ' t 65 ) 
 
 . ?1 {1 y Xl ) - P2 (l 5 - yi -x r y 2 )^ . '. 166) 
 
 3 -2 ', : 
 
 The expressions for M4 and :.I 5 are easily written. If z^ *2 and x 3 are relatively 
 small and their effects on MI, M 3 and Il g are neglected, the max. shears are th( 
 
97 
 
 following: s^ = pbmi and S2 * SI-PI % .... (67) 
 
 S3 = pb(mi+ra2) - P},s 4 = s 3 - P 2 (68) 
 
 She values for s 5 and 35 are easily written. If the pressures pi, 
 P2 ' P3 are considered, the shears are somewhat reduced, so that the values 
 (67), (68) etc. give results on the safe side. 
 
 If the girder of tier 1 consists of a neat of I-beams the design is 
 decided by the greatest M and sj Aquations (64) to (68). If a plate girder is used 
 the webs and flangos maybe made to vary inr/eights to suit the different paxima. 
 The cross beams under the belumn bases and the transverse bea.ns of 
 tier 2 are designed in the usual manner, see eq. (23). 
 
 PARTIAL APPLICATIOn OF THE PRINCIPLES OF TItEEE MO:fflKTS. 
 Strictly speaking this theorem is inapplicable, particularJ.5' for 
 extended slabs of large length 1 supporting four or more columns. Assuming a 
 uniform soil pressure p, the column shears s, , s 2 , etc. and the column moments 
 M-p MS, M5 etc. result by computation. For unrestrained elastic action of the 
 bending moments throughout the spans mi, m 2 etc. there must be appreciable de- 
 flection which would lessen the pressure intensity p near the span centers and 
 increase it under the columns; Bhus destroying a prime assumption. But furthermore 
 for equilibrium of vertical forces s-^sg = Pj, s 2 + s 3 * P 2 , etc. Such equalities 
 can only obtain after repeated trials. It would be a practical difficulty to pro- 
 portiom the span lengths m and to adjust the column leads P to meet the above 
 conditions at the same time that a uniform soil pressure p was maintained by a 
 coincidence of the centers of loading and footing areas. It would require limi- 
 tations to the architect's freedom in planning floor panels and column positions 
 that might be completely objectionable. Hovover, the preceding analysis, equation 
 59 to 68 in great part is open to the same objections. As an instructive analytic 
 problem the theorem of three moments will be applied to the case of Fig. 35, three 
 
 columns and four spans. 
 
 For simplicity assume that the column bases xi, x 2 ,x 3 are : 
 relatively to m lf m 2 , m 3 , n*, so that the loads from -above are applied essentially 
 
! 
 
98 
 
 at points. Tho two end moments M, and Mg are known because the spans raj and,m 4 
 ere cantilevers:- M]_ = pbm].2/2; M 5 = pbm 4 2/2 ..... ... ....... (69) 
 
 Applying the theorem of three moments to spans m 2 and m^:- 
 
 Mlm2 + M3(m 2 +m3) +151713 = - pb/4 (m 2 3 + m 3 3 j ; -- .......... . (70) 
 
 Eq. 70 contains only one unknown, M^; hence, 
 
 + M].m 2 
 
 ~ - 
 
 (71) 
 
 2(m 2 -17113) 
 For the end spans:- si - pbm]_; 85 = pbm 4 .................. (72) 
 
 In span m 2 , taking external moments rbout column P2:- 
 
 s 2 m 2 - pbm2 2 / 2 - Mi+Mg =0; hence sg '= pbm 2 /2 * Mj-IJg ....... ; . . (73) 
 
 m 2 
 By taking moments, similarly, about Pj, PS and P 2 , 
 
 33 = pbm 2 /2 - Mi-M 3 ......... . ...... ....... (74) 
 
 ^ m 2 
 
 A- 
 
 + 1,1^-1.15. . . . ................. '. . (75) 
 
 mg 
 
 = pbms/2 - J%- 
 ' ra 3 
 
 The maximum moment M 2 in span m 2 is found at section 1 2 v/hore the shear is zero. 
 Lot g]_ = 12-m: S 2 =pbg! = 0; g]= s 2 /pb. ... ............. (77) 
 
 M 2 - -Ml + S 2 gl - pbg^ 2 , ........... ............ (78) 
 
 Similarly M4 = - MS + s 4 g 2 - pbg 2 2 /2 .................... (79) 
 
 The analysis, equations 69 to 79, depends upon the condition that s-^+sg := PI 
 
 ^Z* B & ~ P 2 ; S 5 * S 6 = P3 ' and upon the satisf&ction of equations 59 and 60. 
 
 Special Case. Suppose the design is symmetrical about the line of 
 column P 2 . Then the center of loading and the ccntroid of footing are under that 
 column;- ml + m 2 = 1/2; PI = P 3 , rr^ = m 4 ; m 2 = 'm^ 
 From (69 1, HI - Mg = pbmi.2/2 ....................... ( 8I 
 
 From (71), M 3 = - pb/8 (m 2 2 + Smj 2 ) ..... . .............. 
 
 From (72), si = S 6 = pbm; ......... ................ 
 
 From f73), s 2 = s 5 = pb/8m2(3n?2 + 2ml 2 ) .... ............. ^ 8 
 
 From (74), S 3 = s 4 = P b/8m2(5n 2 2- 2m]2) ...... ............ 
 
99 f 
 
 From (77), g = m 2 -g 2 = 5m^2 4- 2m^_ ....... 4 . (85) 
 
 8mg 
 From (78), M2 = % = pb/lZBa&Z (9rn 2 4 - S^SceS+tal^) .......... (86) 
 
 Further si+s 2 = PI = Pg pb/9m 2 (3m 2 2 + 8mim 2 + 2mi2) (87) 
 
 S3 + 34 = P 2 = pb/4m 2 (5m 2 2 - Sm^) (88) 
 
 numerical Example. Suppose in Fig. 35, p = 3 tons per sq. ft., 
 Pi = PS = 40O tons, P 2 = 250 tons and that the lot dimension 1 = 40 ft. Fron 
 (59) bl = 1050/3 = 350 sq.ft., b = 350/40 = 8.75 ft. For symmetry about P 2s 
 2(m 1 + m 2 ) =40 ft. Hence, m> - 20 - m 2 . ... . . . . .... . . ... (89) 
 
 From (87) 3m2 2 + 8m]m 2 + 2mi 2 = 8Pi/pb ~ 8 x 400 = 122 ft (90) 
 
 ffig ' 3 x 8.75 
 
 From (88), 5m2 2 - 2ai 2 = 4P 2 /pb = 4 X 250 = 38.1 ft. (91^ 
 
 m2 S x 8.75 
 
 Either (90) or (91) combined independently with (89) v/ill give the values of m 
 
 and m 2 . Considering (89) and (91) :t fim 2 2 - 2(20-m 2 )2 = 38.1m 2 
 
 Solving, ra 2 = +10.8 ft. or - 24.8 ft.; the rational value is m 2 = 10.8 ft.J 
 
 hence m]_ = 9.2 ft. Equations 82 to 84 give the max. shears; 80 and 81 and 36 
 
 the :jax. bending moments. If the column loads are distributed upon tier 1 over 
 
 base widths x^ and x 2 , the moments and shears at columns v/ill be reduced. 
 
 ECCEl.'TRIC STEKL BEArl GRILLAGE FOUNDATIONS , 
 NA?IV3 SONS HlLL, SAL' FRANCISCO 
 
 Fig. 35A shova a line of four structural steel wall columns, Nos. 
 
 
 
 3,4,5,6, supported upon a layer of 5 15" 42#I-beavns. The beam layer in turn is 
 imbedded in and upon a concrete base 3'9" \7ide by 50 '4" long. There is a bed of 
 12" of concrete under the beams. The steel columns have their axes 8 1/2 inches 
 from the long center line of the footing, thus producing a tilting moment which 
 would give increased pressure at the lot line. To offset this eccentricity two 
 15" 65irl-beams extend from e^jchwall column to the interior footings Nos. 40,41, 
 42,43. The tilting moment therefore t ends to lift the interior colu.nns, relieving 
 weight upon their bases and_ producing central pressure on the wall grillage. The 
 foundation rests on dry sand; the design pressure being about 3.5 tons per sq.ft. 
 The total load on the four wall c olumns is 1,140,000 Ibs . The largest column, 
 No. 6, carries 313,000 Ibs. which for an eccentricity of 8 1/2 inches gives a 
 
T 
 
moment of 2,650,000 In. Ib. upon the wall grillage. This moment is resisted by 
 the two 15" 65#I-bea7is end produces an uplift at column 43 of about 11,000 Ibs. 
 The total load on the wall footing is increased by the same amounts 
 
 Co nsult Engineering Record, Vol. 64, Oct. 28, 1911, . 508, for 
 foundation girders in the United Fire CompaniesBldg. , Kow York, where the same 
 principle was used as in the iiative Sons Kail, but for much heavier loads, 
 necessitating the use of plate girder grillage and balrnce beams. 
 
 CANTILEVER SPREAD FOOTINGS OF RIII^TOBCLD CONCRETE 
 
 Fig. 35B illustrates a cantilever footing designed in reinforced 
 concrete for the proposed Regents Hotel, San Francisco, using the principles just 
 described in Fig. 35A. To bring the center of the structural steol column No. 59 
 v/ithin 8 1/2" of the lot line required an eccentric cast iron base similar to 
 Fig. 27B. The total load on column 59 is 442,000 IDS., eccentric 1.8 ft. from the 
 center of the rectangular footing, 12 ft. long by 5 ft. wide. Column 48, inhich 
 otherwise would rest upor a footing similar to Fi&. 27A, acts as an anchorage. 
 The load on column 48 is 630,000 Ibs. The relief, 45,000 Ibs. through cantilever 
 action reduces the effective load to 585,000 Ibs. Additional load thus is trans- 
 ferred to the footing under col umn 59, v/hich receives a total of 487,000 Ibs. 
 The tilting moment at footing 59 is 45,000 x 17.5 x 12 = 9,500,000 in. -Ibs. The 
 concrete beam 36" wide by 40" deep, Ag - 14.5 sq. in., is in cantilever bending, 
 the moment decreasing toward column 48. This building rests on dry sand. The 
 footings v/ere designed for a pressure of about 4 tons per sq, ft. The student 
 should check the design to determine the stresses in concrete and. steel for the 
 two footings and their connecting beam. Since the concrete of the foundation 
 rests directly on the sand the weight of the two footings and cantilever beam 
 is not included in the a'^ove bending calculations. In this design rather high 
 working stresses wero used. 
 
 For discussion and illustration of similar concrete footings, see 
 1. Concrete Building with Composite Column Foundations, Eng. Eec. Vol. 65, Mar. 
 23,1912, p. 324; 2, Spread Footings for Large Concrete Factory, Eng. Record, 
 
101 
 Vol. 65, June 22, 1912, p. 682, 
 
 ADDITION!, ICFSBSIjCES, SPREAD FOOTIflSS. ...,*' 
 
 1= Architects and Builders Pocket Book; F.JJ.Kidder, Chap. II, Foundations 
 and Spread Footings; Chap. .Ill, Hasonry Walls and Footings 
 
 2, International Correspondence School, Structural Engineering Course, 
 The Statics of Llasonry, Parts 1, 2, 3; Heavy Foundations. 
 
 3. Foundations for the Phelan Building, San Frr.no isco; Eng. Record, 
 Vol. 57, p. 366, March 28,1908. 
 
 4. Foundations for the Call Building, San Francisco; Architectural 
 Engineering, Freitag, 2d, efl. , 1909, p. 339; also ling. Record, Apr. 9, 1898. 
 
 5. The Humboldt Savings Bank, San Francisco; Eng. Roc. Vol. 58, Uov.21, 
 1908, p. 581. 
 
 s 
 
 60 Development of Building Foundations; F. 77. Skinner; Eng. Eecord, 
 Vol. 57, Apr. 4,1908, p. 412, 
 
 7. Stress?s in Steel Fovndction Footing of I -beams and Concrete, Using 
 the Theory of Continuous Beams; Eng. Record, Vol. 39, 1899, pp. 335, 354, 383., 407. 
 
 8. C,T.Purdy, Steel Foundations; Footings of I-beams ar.d Concrete; 
 Approximate Methods; Eng. Bev/s, Vol. 26, 1891. pp. 116, 122, 265, 312, 415, 
 
 9. Analysis of the Continuous Three-Column Foundation, by C..'-. Ellis, 
 .Ing. News-Record, Vol. 85, Oct. 7, 1920, p. 680. 
 
 PROBLEMS 
 
 1. A retaining wall of concrete, back face vertical, front face battered 
 1 E to 3 V, is 2 ft. thick at top; the earth slope behind wall is plane, sur- 
 charged on angle of 10; $ the angle of repose = 32*, the weight of earth is 
 120 Ib. per c- .ft. Upon a horizontal joint 32 f . from the top find the center of 
 -pressure, the range of pressure intensity and the max. and rain values, the 
 stability agcinst sliding. Use Pisnkine's formulas for earth thrust. 
 
 2- A cement jointed brick wall thoroughly waterproofed is 18 in. thick. 
 If it retains v/ater 'whose free surface is coincident with the wall top, at what 
 depth is the center of prc-s'ure at the :iiddle third of a horizontal joint? For 
 -his joint what is the -.Tax. intensity of pressure? 
 
 3. A sub-be sement v/all of reinforced concrete is 12 ft. 6 in. high between 
 loors A and B; the upper floor A is 7 ft. be^r the horizontal ground surface, 
 he wall t ekes only lateral pressure from ths retained wet earth. Design a ver- 
 % ical strip of 'all 12" wide, using specifications of the San Francisco Ordinance 
 uppose the vail panel rests between two columns 14 ft. 6 in. apart. Compute the 
 Ocds corning upon reinforced concrete bea.is running horizontally between columns 
 ic at the levels A and B if the biams support tl'.e bulging pressures from the 
 T.ll= Design the beams. 
 
 4. A cylinder shell of concrete maso nry has its inside surfece a right 
 ylinder of eicmeter 2 ft. 5 in. Tho shell is 9 in. thick at the top, 24 in. at 
 :;e bottom and of height 85 ft. From dead weight what is the presiure at tl:G bottom 
 
. 
 
102. 
 
 joint assuming the load uniformly distributed? Considering the trapezoidcl 
 meridian section es bringing the weight ecdentric on the circular basal ring, what 
 is the minium::! and v.'he.t the njaximum intensity ^for outer ?nd inner points of the 
 base section? For a wind blowing with pressure 20 Ib. per sc. ft. of vertical 
 projection, v/hat ,nin. and max. pressures are exerted whin combining dead with 
 wind forces? 
 
 5. For the Great -Falls, IJontcna, chimney described in Eng. Record, Nov. 
 28,1908, compute the stresses and investigate stability of a joint 80 ft. from 
 the base, when the wind is blowing v/ith a horizontal pressure of 20 Ib. per sq. 
 ft. 'of vertical projection. 
 
 6. Design a concrete c.butnent to withstand n srcli thrust of 130,000 
 Ib. per lineal ft. of bridge width, if the thrust acts at e. point in the fsce of 
 the kbutment 20 ft. below tha roadway and at an angle of 28" to t ha horizontal. 
 Determine the necessary length of s. joint 40 ft. below the roadway r osting upon 
 hardpan. 
 
 7. If a soil may carry 2 1/2 tons per sc. ft. design a timber footing 
 of yellow pine to support a column load of 300,000 Ibs.., allowable timber' fiber 
 stress 1000 Ibs. per sq. in., compression across grain 200 Ib. per sq. in. 
 
 8. For the timber grillage of prob. 7 substitute a solid c oncrete footing 
 with stepped offsets; allowable cross breaking strength of concrete 30 Ib. per 
 
 sq. in.; compression 500 Ib, persq. in. 
 
 9. The load, ona cast iron colusm base is 300,000 Ib. neglecting the 
 footing weight, design the cast iron b; se, a stepped brick pier laid in cement 
 mortar with a concrete bed end bluestono pap, the safe bearing value of the soil 
 being 4 tons per sq. ft.; of the brickwork 2000 Ib. per sc. in., of concrete 400 
 
 and of the bluestone cap 00 Ib. per so. in. 
 
 10. Design a steel grillage, like Fig. 26, of square bed, total load on 
 foundation bed 500 tons, safe soil pressure = 3 3/4 tons per so. ft., pressure 
 on cast iron base = 375 Ib. per sq. in., allowable shear in beam webs = 10,000 
 Ib. , fiber stress = 18,000 Ib. per sq, in. 
 
 11. Design a square reinforced footing, like Fig. 30, total load 500,000 
 Ibs., soil pressure 4 tons, per sq. ft,, bearing cast iron column base =r 350 Ib . 
 per sq. in,, allowable concrete shear =^-75 Ib. , compression = 500 Ibs,, steal 
 bars in tension = 16,000 Ibs., bond = 125 Ibs. for deforce! bars, all in Ibs. per 
 sq. in* 
 
 12. Design a rectangular rolled steel bea-.n g rillagt , like Fig. 33, to 
 support the loads of prob. 13 upon a rectangular footing bed, using stress 
 specifications of probs. 10 and 11. 
 
 13. Design a trapezoidel footing of reinforced concrete, like Fig. 32, 
 columns spaced 15 ft,, loads respectively 315 and 425 tons, specifications 
 similar to problem 11. 
 
 14. Design a trapezoidal steelbec-m grillage, like Fig. 34, to repl.co tke 
 reinforced concrete slab of piob. 13, 
 
 15. Design a rectangular I-beam and concrete grillage like Fig. 35, to 
 surport four columns, PI = 180, P2 = 210, PS = 230, ?4 = 250 tons, m 2 = 12 ft 
 mj = 14 ft., m4 = 16 ft. ,p = 3 1/4 tons per sq . ft. Determine 1, b, ml end m 5 . 
 Assign the necessary specifications for unit stresses. 
 
0.1 
 
103. 
 
 16. Design a footing like Fig. 32A to replace that of prob. 15. 
 
 17. Design the footing of prob. 12 so 'that the beams in tier 2 of Fig. 
 '33 rtin parallel to the long side of the rectangular bed, replacing tier 1 by two 
 
 lines of short lateral beams , one sot under oech column. 
 
 18. A wall c olumn center line is 1 ft. 3 in. from the lot line. The 
 column carries 378,000 Its. * the interior adjacent column 65,000 Ibs. the column 
 spacing is 20 ft. 4 1/2 ins. Design for thesfc two columns a balanced footing 
 similar to Fig.35A. 
 
 19. Bedesign prob. 18 in reinforced concrete, see Fig. 36B. 
 
 20. In an automobile garage the center line of wall column No. 5 is 
 
 I ft. 3 1/2 ins. from the lot line; spacing of columns Hos. 5 and 6 is 27 ft. 
 
 II in., ?5 = 477,000 Ibs., PS = 619,000 Ibs., allowable bed pressure = 
 
 4 tons per sq. ft. Assume weight of a footing. Design a reinforced concrete 
 spread footing of rectangular plan, using principle of Prob. 17. The footing 
 will be a huge Tee gir,er, stem 30 in. wide x 48 in. deep, Tee 4 ft. 4 in. wide 
 by 24 in. thicl-c; total depth of girder 72 ins. See illustrations, Eng. Rec. 
 Vol. 65, p. 324. 
 
r.. 
 
104 
 
 CHAPTER 5 
 SHEET PILING 
 
 This tern is applied to plan&s of wood, metal, or reinforced concrete 
 i 
 
 driven vertical ly' to form a permanent cut-off v/all or bulkhead; more frequently 
 
 to produce a .temporary onolostzro for an area int.- which it is rr coseary to oxcavato 
 
 
 for foundation purposes. Wooden shoot piling may bo light, consisting of thin 
 
 boards; or heavy, composed of stout sticks, solid or built up of pieces of 
 different sizes. LJetal sheet piling is constructed of rolled shapes so designed 
 that they interlock. There are numerous schemes, ilany of the forms are patented. 
 Concrete piling is built like huge tongue and grooved boards. Both heavy ?.nd light 
 sheet piling often form integral parts of cofferdam c onstruction. 
 
 LIGHT Y/OODEK' SHEET PILING 
 
 The sheet piling used for purposes of making excavations for building 
 foundations need seldom be heavier than 3 or 4 inch plank and frequently 2 or 3 
 inch thickness will be sufficient. If the surface of the ground outside the Units 
 
 of the excavation must r err in undisturbed., the sheet planks 8 to 12 ft. in length 
 fs 
 
 nust be put in position edge to edge around the outside line of the excavation 
 at the very outset and driven, as far as feasible, usually with mauls or sledges. 
 A light pile driver outfit is so.-;etimos used. If this condition is not essential 
 an open excavation rnay be :.irde until the disturbance of the surrounding ..iaterial 
 reaches its permissible li.nits, necessitating then the introduction of the first 
 tier or group of sheet planks in the manner just described, but at some distance 
 jelow the ground surface. The excavrtion is then made within the sheet piling as 
 far as it can b e carrie c" without removing the supporting material at the feet of 
 the planks, or causing the upper portions to get out of proper alignment. Hori- 
 20ntal waling pieces of proper dimensions varying from a single plank of 3" x t 
 :o a scantling of even 10" x 12" are introduced as low down rs will give the proper 
 support to the upper end of the sheeting after it is fully driven. 
 
 The excav-tion is thus carried down as far as possible without endagger- 
 ing the support of 'the lov;er end of the sheeting or until the latter requires 
 
A- r 
 
 - : 
 
105 
 
 another horizontal waling piece, in order to prevent it fro;n being thrust out of 
 position by the retr.ined material. Another waling piece is then introduced and 
 secured in position by proper struts or braces, after which the excavation proceeds 
 as be'fore, with the introduction of 'Other waling pieces f.s recuired and in the 
 manner described, .after the introduction of the waling pieces, the sheeting is 
 again driven as fnr as possible, or until the upper ends of the plank are drawn 
 down flush with She original surface, or until further driving would destroy the 
 upper end of the planks by brooming. 
 
 When the last waling piece put in position is as near 1 3)e lower end of 
 the sheet planks as the excavation cr.n be carried, a new set of sheet piles nust 
 be started and driven inside the first set and in precisely the same nrnner. The 
 excavation is then to be continued, or other v/r.ling pieces introduced successively 
 until the excavation is carried frown to the desired depth. Fig. 36 for wide exca- 
 vations, indicates with sufficient clearness the general arrangement of sheeting, 
 waling pieces and braces, as well as the :.rn;:er of working by this method. The 
 lower ends of the sheet piles should bo bevoled as shown, so as to close tight 
 against each other w hen driven. For nrrrow sewer trenches no brace piles B are 
 necessary; the struts I are placed horizontal .jr; through then, the two walls of 
 the excavation press against erch other and -che whole problem of bracing is much 
 simplified. See the Irtsral braces in Fi^. 38. 
 
 Excavations cm be carried down to d epths of 30 ft. or more by this 
 method with sheeting not n:re thru 3 to 4 in. thick if but little water be en- 
 countered. In such c r.sos is it .essential to the safety of the work that the 
 bracing, including the supports at the feet of it, should be designs d and pieced 
 in position with great thoroughness rnd care. Sheet piling carried successfully 
 to a depth of about 53 ft. has been completely wrecked by the waters of a heavy 
 rainstorm and the leakage of adjacent wrter mains saturating rnrterial back of the 
 sheet Blinking so as to greatly increase the pressure which the bracing hr.d to 
 carry. The possible saturation of the ;.r.terial retained by the sheet planking is 
 therefore one of the exigencies which aus x. always be considered in work of this 
 
106 
 character, and be carefully guarded against as far as practicable. 
 
 The pressure which the bracing will have 'to carry in any given cr.se can- 
 not be determined v/ith any great degree of precision, but the theory of earth 
 pressure affords a means by which at least the approxii'-ate loads on the brrces 
 may be computed. The earth pressure P in Ibs. per lineal ft. Pig. 36, which may r.ct 
 upon any waling piece A, -will be found with sufficient accuracy by tricing the 
 intensity p due to a depth J/2 (xx+xg) below the surface, as acting uniformly on 
 that portion of t he vertical face of the sheeting found between the two horizontal 
 planes Q and Q 1 taken /nidwr.y fcetWQcm each pair of waling pieces. This intensity 
 of earth pressure p is to be found by the Rr.nkine formula :- 
 
 p = w/2 (KI + x 2 ) 1 - sin j ............ . . . . . (1 ) 
 
 1 + s in 
 in which p is the pressure in Ibs. per sc;. ft., w the weight per cu. ft. of 
 
 earth, 1/2 (x]_ + xg) the average depth of earth on the waling piece and tf is the 
 angle of repose of the earth behind- the sheeting. If the material is dry, the 
 angle of repose may b e t aken at 3342', corresponding to a slope of 1 1/2 hori- 
 zontal to 1 vertical-. If on the other hand, the material b ec ones either partially 
 
 or completely saturated with vr.ter, the rngle of repose may be arc. 11 and the 
 
 . . 
 weight per cu.ft. relatively large. The formula sha. s that both of these influences 
 
 large l^r increase the pressure ag: inst the braces. JJnless the latter are de- 
 signed with a, view to this contingency, the work may unexpectedly and completely 
 be- destroyed by access of water to the material retained by the sheeting from 
 .storms, leakage of adjacent wrter pipes or other sources. For the notation given 1 
 the pressure per liner 1 ft. of hsrizontal waling sticlc is, P = p(xg-X]_). , . .(2) 
 
 If the distance between braces is b, the ;.r.x. shear s and bending moirent 
 
 H may be readily calculated. For deep trenches and bold design tho safety of the 
 
 timbers agrinst longitudinal shear and crushing across tr.e grain should be 
 particularly investigated- 
 
 In the determination of the bending strains upon any waling sticlc or of 
 the load T whiclv any brace may carry, both the vrlues of the angle of repose rnd 
 the weight per cu.ft. of t?.:o a tex ial .::ust be assigned with some judgment. Dry 
 
107 
 
 v material may not weigh more than 90 Ib. per cu.ft., whereas wet earth may reobh 
 a weight of 120 Ib. per cuwft. or possibly more. Similarly the angle of repts e 
 maybe reduced fro.:: 3342' to possibly 20" or less. 
 
 The pressure^'P against the waling piece which will be carried by a single 
 brace, T, will be distributed over an area limited by the two horizontal planes 
 Q and. Q 1 , rlrer.dy described and by the midway points to each of the adjr.cent 
 braces spaced a distcnce b. Let thr.t area be represented by A = (xg - x )b, and 
 let the angle -which the brace inaxes v/ith a horizontr. 1 lir.e be represented by . O( 
 then the total stress or load to which the brace is subjected will be represented 
 by T = pA sec ex . 
 
 If the excavation is made v/ith vertical parallel sides, as for deep 
 
 I - 
 
 sewers, or water pipes, the expression for the load which any horizontal brace 
 
 must carry vail be identical with that just given with the secant of the angle 
 
 made gqual to unity. The expression will then beco:::e T = pA. 
 
 The timber or other struts which have to be used for the purposes in- 
 dicated, are then to fee designed under appropriate beam rnd column formulas with 
 the preceding values of p rnd T for loads. If these operations are performed with 
 judgment, it is seldom that the conditions attending the work cannot be sr.fely 
 and economically controlled. 
 
 EFFECT OF COHESION 
 
 The usual formulas for earth thrust consider solely the weight of the 
 viaterial and the force of friction. Thus surfaces of cleavage or rupture are con- 
 sidered plane. As a .natter of fact due to the combined action of friction and 
 cohesion, these surfaces are warped. When cohesion is neglected, pressures exerted 
 appear larger than they rctually occur in nature. Thus, a formula like that by 
 Bankine gives results on tie safe side, often entirely too conservative. 
 Fig. 36a gives tie solution to *he follow ing problem: 
 Consult "Earth Slopes, Retaining "/alls rnd Dams" by Charles Prelim, 
 TO- 1 - 27, Given a bank of homogeneous earth 25 ft. 'high whose cohesion is 110# 
 
108 
 
 per sq. ft. Take $ - 30"41'. Consider horizontal sections at intervals of 5 ft. 
 By Prelini's method, pp. 15-17, determine (a) the proper- stepped slope for this 
 material, (b) the slope of equal stability. 
 
 Embankments along streams often show a frash break of er.rth v/ith an 
 overhanging top, as shown in Fig. 36A, at the point C. 7/ith w sathering' the upper 
 portions of material will, grr.dur.lly break away; thus the earth slope AEC is not 
 stable except for limited periods. 
 
 VThen Irrge excavations in Civil Engineering .n* Mining practice are nr.de 
 for temporary worlc, sheet piling or other bracing :i?.y be omitted, provider tho 
 ground is stepped, as .shown in the fi'gire. In this way considerable quantities 
 of excavation can be saved above the slope AE which fires the angle of repose. 
 To what extent these steps and berr.is may depart from the plane of rupture and 
 approach the slope of equal stability for fresh earth is dependent upon the 
 
 degree of safety desired rnd the length of time during which the excavation is to 
 
 > 
 
 remain unbraced = 
 
 On page 37, Chapter 2 of these notes, reference is r.ade to an article 
 on "Earth and Rock Pressures" by E. G. Moult on, Trans. Am. Inst. Dining Engineers. 
 Feb. 1920. This paper gives an excellent account of the limitations of the classic 
 earth pressure formulas. It is now well loiown that in deep trenches the greatest 
 thrusts do not always exist at the bottom of the excavation. 
 
 In Fig. 36B x represents the depth in feet of a trench where materials 
 are retained by sheet piling and bracing. In his article Moult on explains that 
 the line of rupture approximates the curve shown; the surface of rupture inter- 
 cepting the ground level about x/2 ft. back of the vertical through the lowest 
 -:>oint in the trench. If the sheet piling tends to give, the earth moves along 'the 
 line of rupture, but due to the forfies of cohesion rnd friction, arch action Is 
 induced, as shown in the figure, giving maximum thrusts agr.inst the sheet piling 
 
 
 
 in the vicinity c\f the horizon. . AA, rather than at the bottom of the trench. 
 
 Experience hrs aicvn that frequently the nerviest' bracing is needed at 
 such a level as AA and nobracin- fit all at the bottom of the pit. V/ere the usual 
 
109 
 
 formula for earth thrust followed, the bracing would increase in size and strength 
 with the depth of trench, thus using the material uneconomical!; 7 and improperly. 
 
 These observations apply v/ith particular force in mining and tunnel con- 
 struction, Such properties of granular masses are not limited to earth and sand, 
 but apply also to lurolcen rock, to stored grain, coal piles, etc. The student is 
 urged to read ivloul ton's article; referring particularly to his fig. 14, pp. 22-25 
 
 ELAVY r/OODEM SHEET PILING 
 
 Excavations for bridgepiers are frequently r.irde in saturated material 
 sometimes covered by shallow water; see Figs. 38 and 39. In such cases it is 
 necessary to use the heaviest class of sheet piling consisting of 6 x 12, 10 x 12 
 .or even 12 x 12 inch sticks, driven by an ordinary pile driver. These sheet piling 
 
 sticks are usually tongue-and-grooved, some tines by working them into the required 
 
 or 4 
 
 shapes or more frequently by spiking 2 x Scinch strips to the' 10 or 12 inch sides; 
 see Fig. 38. 
 
 Various types of what may be called c ompound sheet piling are formed by 
 bolting or spiking together 3-12" planks 2, 3 or 4 ins. in thickness, so as to 
 .tirke the two outer ones overlap the middle one by 2 or 3 inches. The '.Vakofield 
 sheet piling, Fig. 32 is perhaps the most prominent example of this type. It has 
 bec-n much used v/ith very satisfactory results; cf. "The Cofferdam Process for 
 ?iors" by C,L. Fowler; for other types, Fig. 38, p. 60. One of the difficulties 
 
 :cperienced in deep driving of this nervy sheet piling is the "wardering" of the 
 ' ; owor points of the individual pieces. In spite of the greatest crro, the lower 
 edge of the resulting sheeting mry be found much out of lino, giving the completed 
 i-heetirnj a warped shape, inducing t/.o opening of joints and l^alcrge of water into 
 
 -ho excavation as the work progresses. 
 
 i In those cases of horvy sheeting for bridge piers, the- volume of oxcava- 
 
 ion must be made larger in plan by 1 1/2 to 2 or 5 ft. on each side then the 
 lass of masonry which is to be built within it, f or t ho purpose of giving the 
 'ocuisite room for the wrling pieces and for the mesons in their operations of 
 
 aying masonry, should the latcer be other than concrete; see distance a in Fig. 39 . 
 
If- 
 
 ; 7here the footing is of concrete, or where the entire :rss of masonry is to be 
 
 of concrete, -^s _. ,; . ,-the entire 
 
 volume between the. sheeting is filled. The concrete is placed jn layers of 9 to 12 
 ins. in thickness reaching the sides of the sheeting, and thoroughly rcnrned, as 
 required for such work. The timber braces /iiay be takon out as tho masonry progresses 
 leaving the sides of the sheeting braced against tho completed -portion of the pier. 
 Dr, if the volume is filled 7/ith concrete, the timber bracing which vill be per- 
 manently saturated with water, may b o left in the concrete mass. All timber bracing 
 however which will not certainly be saturated should be taken out before the con- 
 crete is deposited, leaving the concrete itsolf to hold the sheeting in piece. 
 
 When the plan for the excavrtion for a pier lias been so laid out at the 
 site rs to lerve sufficient clear spree inside the sheeting to meet the require- 
 ments above d escribed, a line of shoetir.3 is driven usually by a pile driver 
 around the entire enclosure, the tongue of each individual piece fitting closely 
 into the groove of the adjrcont piece, as shown in' Figs. 38 and 39. The lower end 
 of arch piece should bo so fooveled as tocrov> T d it closily against its neighbor in 
 driving. At this .beveled end a thin shoulder of the full section of the- original 
 piece should be left so as to partially or wholly close the triangular opening 
 which \vould otherwise -afford unobstructed entrance for water, mud, sand or other 
 flowing laterial. This detail is shown in Figs, 38A and 38B. After the- sheet 
 piling is driven to the desired depth so as to enclose the site to be occupied 
 by the foundations and to b e as nearly vr.ter tight aspossible, the material en- 
 olosed is to be excavated. If it is sufficiently soft, it may to some extant be 
 
 Iredged, but it is usually taken out by .hand, thrown into large buckets, lif 
 
 
 
 >ut by power and either spoiled on ^.ste land immediately adjccent or convoy* 
 )thor points by land or water, As fast as the excav; tion is maOe, heavy horiaoi 
 v/aling strips are put in plrce and properly braced across the entiie pit, or around 
 itif the excavrtion- is polygonal or of curved outlines, so that the sheet pill* 
 ,ay not' be forced inward by the pressure of the outer material. These waling 
 ,ieces (10x12, or 12x12 in. .ieces in heavy work) st be placed closer together 
 
111. 
 
 verticr.lly as the excavat i on proceeds, as the inwr.rd pressure of the surrounding 
 .vater ial increases with the depth in the manner shown by equations 1 and 2, The 
 sizes of the brr.ces (and of the waling pieces also) are to be designed as carrying 
 the loads described in connection with the derivation of equations 1 and 2, it 
 being remembered that in these crscs the retained nateriril v/ill in nerrly or quite 
 alTcases be saturated with water. If the ercavtion is rectangular in plan, the 
 corners must be braced with diagonal sticks suitably placed and s tror.gly held at 
 the ends. Again, if the length of the excavation is so ;;ro:.t u hat it is inadvisable 
 to b race with single pieces of corresponding length, special trussing or brr.cing 
 must be provided, particularly at the ends, or a. t polygorial corners as indicated 
 in Fig. 38, which shows the plans of a piece of work of this chrracter as actually 
 constructed. The tiers of horizontal bracing may be placed as much as 6 to 8 ft. 
 apart at t: e surface, but at a depth of 30 to 55 ft. it ::ay be necessary to place 
 them only 3 or 4 ft. apart verticr.lly. Za:cavations have been carried to depths 
 of over 40 ft. by this method, bu'c unc'er such circumstances, the utmost vigila.nce 
 and continuous care must be 'exercised in order to properly guard against accident 
 or failure. The work should be prosecuted with c he greatest rapidity consistent 
 with suitable safety precautions in order that the period of risk may b e reduced 
 as much as possible. 
 
 In all such work it is usually necessary to l.:eep pumps constantly at v/orlf 
 
 in order to -naintain the excavation so nearly free of water rs to afford;, opportunity 
 for the requisite excavation. It is not frequently necessary to coTuience pumping 
 
 . * '~; 
 
 until a considerable depth of e ;:.cavation has b--en re;ched, but as the greater 
 depths ara attained, t he wrter is so/.ieti.nes exceedingly troublsso^e. The tongue 
 
 v- 
 
 and gnuorve detail of the piling and the driving of the latter solidly down on 
 the rock, or other hard bottom so as to broom the points of the' piles into as 
 
 many of the s.nall openings as possible, are designed 'to .;ake the enclosure as 
 r.ecrly water tight as practicable. Rotary pumps v/ith their freedo.n from valves 
 .re ac..urc.bl" rdapted to such puniping as it is required in these crses, inasmuch 
 s the water carries much solid matter, 
 
o tj -;: IT 
 
 - 
 
112 
 
 
 
 After the rock has been laid bare by this process, it is to be thorough- 
 ly cleaned off before any masonry is put in piece. Then all soft or other un- 
 satisfactory rock should be carefully and completely removed. If the surface of 
 the rock is sloping, it should either be stopped off roughly, or made rough and 
 jagged if it is not naturally so. Those operations must be completed with care 
 in order that the footing course of concrete or other masonry <r>ay be satisfactor- 
 ily bonded to the rock. If the resultant thrust on the rock is inclined, as in 
 the case of an abutment for an arch;, then the preceding operations can tee sp 
 applied as to make the foundation bed at least npproxi:na.tly normal to the direction 
 of the thrust. After the foundation bed has been thus prepared, the footing 
 course of concrete or other masonry can be put inplace. \7hi2e this is beirg done 
 the water which finds its way into the enclosure should be led by suitable drains 
 to a sump at so ;ne point within the excavation, from which it mus,t ba pummtad in 
 order that the footing nasonr^r may be built up dry. 
 
 Fig. 39 gives diagrammatically an example taken from actual 
 
 -practice showing a use to v/hicli sheet piling mr.y be put. The rectangular enclo- 
 sure is 21 ft. x 64 ft. 5 ins., leaving a clearance "a" for bracing rnd workmen. 
 The figure describes an approach pier founded on piles driven in mud and silt 
 overlying bedrock at a considerable depth. The pier is in two parts, to save 
 masonry. It supports deck latticed approach spans for a large city highway 
 bridge. The sheet piles with pumping kept back the flow of s ilt into the exca- 
 vation and reduced ths water lovel within the enclosure so that the mud and silt 
 could be excavated to elevation - 14.0, A layer of sand 1 ft. thick was trmped 
 upon the finished mud surface. The piles were- cut off rt elevation -10.0, A slab 
 
 
 
 of concrete 3 ft. thick deposited upon the srnd layer formed a plane surface 
 for the completed enclosure upon which, in the dry, the two component pier courses 
 were built, first- three steps o-f concrete, then a fertuiewith limostoie front 
 followed in turn by granite as I", lor for t ho upper visible portion of ti.e pier and 
 
 co-oings. In work like this, rt lorst for appe:ranco, the s heat piles ?hould 
 
 
 
 finally be cut off below the pernanont low tide or water level before backfilling 
 asrainst the ~Dicrs. 
 
113 
 
 STESL SHEET PILING- 
 
 Recently a distinction has been made b etween "sheeting" and "sheet 
 piling". Mr. J. C, ;,Ieem ; Trans.. A~,i. Soc. C.L. ', Vol. 60, p. 1, defines "sheeting" 
 as that class of sheathing which is set or driven coir.-eidently with t n .:e excavation 
 and "sheet piling" as that class of sheathing v:hich is driven aher.d of the excava- 
 tion or beyond its find limits. This article deals only with -sheet piling. 
 
 ill-. P. B- V/oodworth; Jrr.ns. ^.:ioSoc. C,L. . Vol. 64, p, 47^, gives an 
 interesting historical review oi the use of piles a.nd sheet piling. V,ood was used 
 for these purposes ir: the er.rli-eut historical tii.-es. \\ooden sheet piling is 
 
 li.iited in length. It w ill stand little abuse front he pila driver; it cannot be 
 
 ^ 
 
 driven into stiff ."aterials; it cm be used only once; it cannot be .ir.de to inter- 
 lock v/ell and therefore does not insure water tightness. Its joints are werlc; 
 
 
 
 its span cannot be large horizontally or vertically; consequently it requires 
 much interior bracirg for large excavr t i ons It is to be suspectscl theLefore that 
 rnetal sheet piling v.'.?.s thougl:t of in the past though it hrs become coriTiercially 
 practical only in the la st decade, ;-.u . '.."ooovorth describes early for. ns of c ast 
 iron sheet piling, one type by ifc,t thews, 1822; another by i'eter Btvcrt, 1822; 
 others by Janes Y/r liter, 1824; \ia. Cuoitt, 1832; he gives also SOMO later examples. 
 See also Appendix VI, to Ordinary Foundations, by C.E. Fowler. 
 
 Cast iron is an unsuitrble v.r.terial.; it is brittle in driving, it cannot 
 
 stard high bending strains- Seventy years ago it cost more tb-.n wood, prrticularly 
 in this country v/here wood \z.s plentiful. \.Tlnber is now a scarcer a rticle a.nd 
 rolled :.,etcl shapes less costly than they were 20 years rgo. Steel is tough v r.nc" 1 . 
 fitted for driving through stiff :.ia.teri:.ls. Sheet piles of steel i-.r.ybe rolled to 
 give strong joints end reasonable water tightness . .V/ood sheet piles cannot be 
 used a second ti.;e. Liodern sieel sheet piling car. be pulled :nd redriven, On a 
 sewer trench at u.;irdt v i-ev/ Jersey, "100 lin. ?t. of 10 ft. We.nlinger corrugrted 
 sheeting vr s used on 8000 ft. of sewer in a trench varying in depth from 9 to & 
 ft,; thr.t is to say, the sa..ie sheeting wr s driven and pulled at least 80 tines and 
 at the co^ole-cion of the job was still in good condition, This sheeting was made 
 
114 
 
 of 16 gauge mr.terirl, v/eighing 5 Ibs. per sq. ft. in place". Other examples could 
 be cited. Steel she:-t pilesof heavy rolled sections car. be driven readily through 
 obstructions. Instr.nces are not uncommon where they have been driven successfully 
 through buried logs or railway "ties or into compact. hardpan. 
 
 REQUIRE E'. IS FJK :,IB2Al PILING-. 
 
 1. Strength, 2. stiffness, 3. water tightness, 4. economical and prrctical 
 sections, from manufacturers' standpoint. 
 
 Fig. 40 shows a variety of sheet pile sections now used in pr:ctice. 
 Consult article by II;: . L.IL Clifford, Trrns. ^m. Soc.CoS. , Volo 64, p. 441. Ke arranges 
 these sections into three groups:- 1. standard structural, shapes; 2. special 
 rollsd shapes, 3, specirl shapes. It crnnot be argued that Standard rolled shapes 
 are necessarily the cheapest, The cost of sheeting per sq ft. in place is the 
 governing factor. This 'frctor depends Upon the ease with which a specir.l type may 
 be driven into a given ..rvceri: 1 and upo the effective v/idth per sheet pile v.-hen 
 interlocked. In sane designs the interlocking devices consume mueh of the gross 
 v/idth of ar> individual pile. Begulai' rollsd shapes, group 2, require riveting; 
 v/Iiile specirl rolled shapes, group 2, eliminate shop work and give a simple inter- 
 locking ferture. Corrugrted piling, group 3, is expensive per Ib. of metal, but 
 usually is cheap per sc, ft. in plr.ce. "'here water tightness is d eraanded , the 
 type of piles should be selected irrespective of cost per Ib. of ,netal. The pile 
 with -che tightest joint should govern. 
 
 Metal piling .mst resist two groups of stresses;. 1. bending stresses 
 due to earth or water pressure, 2. shear, bending and tension in the Interlocking 
 joints. Steel sheet piling usually it, braced at the top and bottom only, For deep 
 work there nay be intermedia ;e waling sticks. One disadvantage of netal sheet 
 piling is the difficulty in fastening waling sticks r. rd other interior bracing. 
 Ecuations 1 and 2 determine approximately the lord intensities producing bending 
 for verticrl spans b etween waling st:ips. The section modulus should be ".s great 
 as possible for weight of metal p?r lineal ft. of pile. The metal massed at the 
 sides for interlocking purposes should help to give the greatest section modulus - 
 
115 
 
 Strictly a single pile does not act clone in bending. Adjacent piles support each 
 other through the interlocking. Therefore w e must canpute the section modulus 
 per lineal ft, of width of piling interlocked in pt.ce. 
 
 The piles should be sufficiently stiff to drive without buckling or 
 crushing, and particularly without springing under the blows of a hammer. The 
 radius of gyration relative to the pile length should be as large as possible 
 for a given weight of metal in the pile. 
 
 To secure water tightness attempts hr.ve boen Mace to p?.cl: or caulk the 
 
 
 
 joints with wood strips or other in;itorials. That type of piling nay be considered 
 the best which requires no such packing in the interlocking joints. Indeed prac- 
 tice shows that it is impossible to do any effective caulking. 7/hen a line of 
 piling has been driven, it often happens that it re:r.ins in alignment at the 
 bottom and bulges gradually to the maximum displacements at the top. The piling 
 thus offers a warped surface _ toward the excavation. Shearing and bending stresses 
 aswellas tension are thrown upon the interlocking joints. That % type of inter - 
 l^jjking is "best which will resist the opening of joints due to shear and t ension, 
 particularly when the piling bulges. 
 
 The chief disadvantage of metal sheet piling is the difficulty in fasten- 
 ing waling sticks arc 1 , other interior bracing. Such connections can be made more 
 easily to timber than to metal cofferdams- Again, timber sheet piling often is a 
 fixed portion of a foundation, For parts permanently below the water line the 
 timber will b e sound indef initely. Metal sheet piling is subject to corrosion. 
 Considering the problems of bracing and the cuestion of duirbility, one may con- 
 clude that metal sheet piling will never supersede ant ire 13' the us e of timber 
 
 SPECIFICATIONS FOR STEEL SH_i,.:T PILING 
 
 Material. The steel used shall satisfy the specifications of the American 
 Association of Steel Manufacturers for Structural Stenl for Buildings. 
 
 Working Stresses. The allow: ble unit stresses per sq . i:-.. on extrene 
 fibers in bending shall no - c exceed;- for permanent work 16,000 lb,, for temporary 
 work, 20,000 lb. The section modulus in bending is to be fi cured for interlocked 
 piling in place 
 
 St i f fne ss . Sirgle piles driver, separately shall have a ratio of length tt> . 
 least radius of gyration not to exceed 250. 
 
- 
 
116. 
 
 x 
 
 Water Tightness. The sections when r. ssembled in piece shr.ll be water 
 tight at joints-, without the use of auxiliary packing or caulking pieces, unless 
 such packing of caulking pieces are made a part of and are assembled v.ith the 
 sections of the sheeting or sheet piling before driving 
 
 Priving. Care shall b e taken in driving to prevert battering of the 
 heads of the pilas, and if necessarv to prevent this, a tight fitting cap shall 
 be used. Driving shr.ll be done by steam or compressed air hammers. 
 
 REIKFORCED CONCRETE SHEET PILES. 
 Recently, for heavy and durable work, there have been proposed or used 
 
 occasionally, reinforced core rete sheet piles; each pile nr.de of rectangular 
 
 / 
 
 cross section with grooved ends to engage special keys to give a water tight 
 
 joint. In some cases the piles have been specially molded to dovetail into each 
 other. Buel &Hill, "Reinforced Concrete", pp. 162-187, illustrates some examples., 
 among others, the Hennebique system, Fig. 55. Each unit pile is reinforced like 
 a column with rods or structural shapes. Special caps are employed v/ith a false 
 
 
 
 pile to protect the concrete pile from the blows of the hammer. In general, the 
 same problems are presented as for reinforced concrete piles; this subject is 
 treated further under that heading. Reinforced concrete sheet piles must withstand 
 bending strains when in place, also shear and t ens ion stresses at joints, and in 
 addition the s tresses to which an ordinary pile is subjected. Thus far, there has 
 not been a large field for the application of reinforced concrete sheet piling; 
 
 but its use is daily increasing. It is expensive, 
 
 ^ 
 
 HEME3IC.UE SHEET PILIl'S - Fig ,55 
 
 This form is adapted for heavy 'sheet piling, by using a rectangular cross 
 section 5 7/8 x 15 3/4 ins.,, reinforced with 6 vertical rods tied together at 12 
 ins. intervals by wire ties. Semicircular spaces about 2 3/4 ins. in c.iameter are 
 left along adjoining edges ol the sections, ^fter the piling 1-c s been c.^i^sn into 
 place, cement grout is forced into these key spaces, cementing '&-- s -^.tei-i t .l to- 
 gether and firmly uniting the sections of piling into a monolithic wall tff great 
 strength. Two light I-beams have sometimes been used for vertical reinforcement 
 in place of the 6 circular rods. 
 
*>. . , 
 
REINFORCED COHCHBTE SHEET PILING; U.S. NAVAL 
 COAL DEPOT, TIBUEON, CALIFORNIA 
 
 Fig. 40A illustrates the Cioss section of pier a.nd coal pockets. Hrrd 
 bottom is found at irregulr.r deaths rlong the pier length. Both hr.rd and soft 
 bottoms slope to increasing depths rvfc the water side. The coal near the pier 
 rests on a timber mat at elevation +1 ft. This mat of 'itself is incapable of 
 supporting its load without settlement. The pier proper therefore no-t only sup- 
 ports its own weight but resists the lateral flow of the mud fill. 
 
 The pier which is also the foundation for the coal bunkers, has a 40 
 ft. base. Its foundations consist of wooden piling capped with 12" x 12" K 40' 
 timbers. At the rear there are three lines of batter piles to t rke the lateral 
 thrust produced b- the weight of coal. The timber grillage is covered with a 4" 
 timber decking laid continuous over the capsl On this deck was built the front 
 and rear concrete retaining walls. These walls at intervals are widened into 
 piers which support the steel coal bunker columns. At intervals also the walls 
 are connected b~; concrete diaphragms. The pockets between the walls, above ele- 
 
 4 
 
 vation +2.0 weie filled with earth to elevation +10.0. The remaining volumes 
 between and to the rear of piling and behind Ithe reinforced corc rete sheet piling 
 were filled with soft mud dredged in "front of tl:e seawr.ll. This soft mud fill 
 extends to elevation +2.. ft. The harder foundation bed material into which the 
 piles were driven occurred at depths of - 20to - 35 ft. To hold the mud fill and 
 soft original bottom from flowing out into the channel produced, the necessity of a, 
 continuous he. vy reinforced concrete sheet piling. 
 
 EXTRACTS FHOLI THE SPECIFICATIONS..' 
 
 The concrete shall consist of 1 cement, 2 sand, and 4 broken sone, to 
 pass a 3/4" to 1 3/4 ;i ring, Each concrete pile sh: 11 be cast in a separate and 
 distinct form of sufficient stiffness to hole 1 the concrete true to shape. The 
 forms shall be water tight; their surface in contact with concrete perfectly 
 smooth. The platform upon which the piles are cast and cured must be a rigid 
 plane. Reinforcing rods shall be accurately spaced and located a.nd proper means 
 taken to insure them against movement after having been properly placed. The 
 concrete for er ch pile shall be mixed and deposited continuously in order that the 
 nost perfect bond may be secured. Concrete shall be thoroughly worked around all 
 reinforcing rods, The upper free of the pile in the for.-.F shall be cr re fully 
 smoothed off by trowelling. If -necessary, in order to s^c^ra a smooth surface, a 
 
Ill 
 
 coat of mortar, I cement to 2 sand, shall be applied. The pile for/as shall remain 
 in place at least 24 hours. All forms must be thoroughly cleaned for each casting 
 and coated with crude oil or other approved In.bricrtion oach time the forms are 
 used. Concrete piles must be protected from the direct r;.ys of the sun $nd kept 
 damp by proper covering and sprinkling for at least one v/eelc after casting. 
 
 Piles when removed from tha forms and v/hen b eing placed shall be 
 true to form and dimensions., perfectly smooth., free from wind and all defects 
 which affect their appearance or strength in the fi'nishc-c 1 . work. Main steel rein- 
 forcement, Fig.lOB, shall consist of 6 - 7/8" round bars, located as shown, 
 continuous throughout the length of t?-e pile; these- bars to be braced by 3/8" 
 round steel clips or bands at 24" centers. For tha top 5 ft. of the pile, 
 surrounding the 6- 7/8" rods, provide" reinforcement equivalent to expanded 
 metal No. 10, 3 in. metal. This reinforcement shall b e bent into a rectangular 
 form around main bars. The main bars shall protrdde 4 in, at the top of the pile, 
 to bond with the pier concrete. Each sheet pile shall be bolted to the 12" x 12" 
 wood stringers. For this purpose holes are provided in the pile," 
 
 Note: The piles v/ere cast on their side., no mortar v/as required to 
 secure a smooth finish, since the concrete could be worked smooth on account of 
 the small size of the stone used. The concrete was poured wet. It was all mixed 
 by hand. The forms were often stripped after 24 hours, 
 
 EXTRACTS FRO:J THE SPECIFICATIONS FOR PILE SRIVII-IG, 
 
 No piles shall be driven until a.t least 30 daysld, Kone shall be ^oved 
 or otherwise handled until -experience has proved that it may be done with safety; 
 (to be determined by the Officer in Charge), All piles seriously injured in 
 handling or driving must be abrndoned. Piles sSall b e driven by water jet under 
 high pressure, To this end a 2" diameter wrought iron pipe shall be cast into 
 the pile. Ilaximum pile lengths shall b e 40 ft. All piles shorter than this must 
 be driven to refuse:!. To b ring piles to final position only light short blows of 
 the hammer shall fee used with a proper cushion between the ;:>ile and hamnffir 
 approved by the Officer in Charge. Pipe ferules cast into the piles for the 
 purpose of handling them past be properly filled with cement mortar after driving 
 All piles shall fee driven plumb and true to line. They must closely hug the 12" 
 x 12" driving stringer. The tongue of one pile shall clo.sely fill the groove 
 of the next. Any pile driven so that the adjacent bearing surfaces on piles do 
 not come together within 3/4 in. will be rejected. The pile ,r;ast be removed, 
 if injured, and redriven 
 
 Note: 'Piles were beveled at tlie bottom-, sse Fig. 403. Ho piles were. 
 driven under 30 days ege. Most of them were older. At first the 2 in. jet pipe 
 was cast into the pile with its lower end chol-rsc. to a bore of 1 inch, but this 
 jet would beco/.ie stopped as the pile v/as driven, causing the hose connection to 
 the jet to burst. This interior jet proved unsati&frctory r.nd its use was dis- 
 continued. In its -:>. ce two separate jets were user 1 .. These jets were hung loose 
 from the pile driver and could be used over and over again. Two holes Were cast 
 into the pile; one 6 ins. from the top v/as used for bolting the pile to the 
 stringers; the other IS in. lower was used for lifting the pile; the hole 6 in. 
 from the top not being strong enough for this purpose. Very little trouble was 
 experienced in holding piles so that adjacent bearing surfaces were less than 
 3/4 ins/ apart. Host piles were driven tight. 
 
 Fig. 40B shows the pile as designed. A number wfs so cast, but after 
 driving a few, some changes v/ere made* In the figure it will be noticed that the 
 bevel at the pile foot is on the same si", e with the groove. In driving the tongue 
 
119 
 of the pile being driven fitted into the groove" of the pile already in place. 
 
 Tongues stood driving better than grooves. Therefore when failures occurred 
 during driving, it was usually the groove of .the previously driven pile that 
 failed. Consequently two pile<$ had to be pulled. G-enerally the groove of the pile 
 previously driven would break off while the pile juet being driven would be 
 mninjured. The bevel therefore was ch-:.nged -co the tongue's side; Fig. 400. 
 
 The bevel v/as also increased but to too groat an extent, as it caused 
 the foot of the pile to c rowd the other too closely at the bot'tom so that after 
 a number of piles were driven they v;ould not be plumb. The tops would lean in 
 the direction of the driving. It therefore becane necessary to bevel some piles to 
 a slight extent on the opposite side just before driving. It is believed that a 
 bevel intermediate between Figs. 403 and 40C and placed- on the tongue's side 
 would have been an improvement. The bevels on the pile sides, shown in Fig. 40B 
 were omitted in the latter design of Fig. 40C. Side bevels seemed to make the 
 pile drive crooked, 
 
 The greatest difficulty in driving was that the foot : of the pile would 
 go out or move av/ay from the seawall. The concrete piles ? as seen in Fig. 40A, N 
 v/ere driven fairjy close to the wooden piles. The woolen piles having been driven 
 first compacted the material; therefore when the concrete piles were driven their 
 feet would tend to follow a line of least resistance, which, wrs awaj<- from the 
 compacted material around the wooden piles. This tendency to a large extent was 
 overcome by placing the jets between the concrete and the wooden piles, also by 
 beveling the concrete piles on the outer side only. To allow for ..lore freedom in 
 driving the pile tongue was nr.de 1/2 in. thinner than as designed. This allowed 
 the pile to give more without breaking a groove. In only five or six cases did 
 the head of a pile fail in driving. 
 
 Two v/ater jets v/ere used consisting of two inch pies 44 ft. long 
 
 connected to a pump by fire hose. The jets were usually plrcec 1 . one on each side 
 of the tongue of the pile already driven and worked down as far as possible. They 
 
 v/ere then withdrawn and the new pile set in place. The cushion block, follower and 
 
. r 
 
120 
 hammer were next put upon the new pile. The jets were placed one on each side 
 
 of the new pile and worked down to r. bout 3 ft, in advance of its foot when the 
 hammer .started, the jets being worked down as the driving proceeded. The cushion 
 consisted of an or.k block 10" x 14" x 18" with rope rind rubber hcs e nailed to the 
 top and bottom. The oak follower was placed upon the cushion. The steam hammer 
 engaged the upper end of the follower. The bottom of the follov/er was cushioned 
 with rope and rubber hose. The Steam hammer was placed in a special frame work. 
 This frame work moved in the leads of an ordinary pile driver. The frame work 
 was necessary since the leads were 20 inches wide while, the piles were 24 inches. 
 The pile driver was placed crosswise at one end of a barge. At the other end of 
 the barge was placed a derrick to handle the piles. The sterm hanraer weighed 
 6800 Ibs.; its moving parts 3000 Ibs. The weight of a 40 ft. 'pile was 7 ons. 
 
 Most of the piles were driven 5 ft. to 10 ft. into hard material. The 
 specifications stated that no pile longer than 40 ft. would be required. Some 40 
 ft. piles were driven with great ease when down their full length. The depth to 
 mud along the pile face is -9.0 ft. The tops of the piles were to be at +3.0 ft. 
 elevationj thus, 28 linear ft. of the pile penetrated mud and. usually 3 ft. or 
 4 ft. into gravel at the very bottom. The wooden piles to the recr of the concrete 
 sheeting drove 20 ft. to 30 ft. further than tl-.e concrete piles in most places. 
 'Some concrete piles received 400 blows- without injury. At the top the 
 piles were bolted to the 2 - 12" stringers vrith 1 1/2" galvanized bolts; see 
 Fig. 40A. After driving the tops of the concrete sheet piles presented a serrated 
 outline since all ^iles did not drive to exactly the s. -me elevations. Expanded 
 metal was placed over the tops as shown in Fig. 40^-.. \Vhen the concrete of the wall 
 above was poured, the sheet piling and wall mrde one monolithic mass. 
 
 ' The contract price for the piles was $2.00 per lineal ft. delivered, and 
 60 cents per liner 1 ft. for piecing. The actual cost of handling, driving and 
 bolting uo tl:.e piles was 62 cents per liner. 1 ft.; this includes labor only. 9200 
 lineal ft. of "Diles were driven. 
 
. : 'i - " '- ' 
 
121 
 
 CONCRETE SHEET PILES FOR POCKS 
 
 \ 
 
 Recently this type of construction has been repeatedly recommended for 
 seawalls and docks to act not nerely as bearing piles but also to eesist the 
 lateral flow of ,nud as in the preceding descriptions. Consult the plans by 
 Haviland & Tibbetts for the Richmond Harbor Project, plates 6 and 7. Examine also 
 a report by Virgil G. Bogue, 1911, on the Plan of Seattle, plates 15, 16, 17/ 
 
 AH ANALYTICAL PROBLEM 
 
 Equations 1 and 2 hr.ve been .proposed to give sufficiently accurate 
 dioul*t|oxiB for bending stresses in both v;ood and metal sheet piles. Actually 
 the load on the piles is variable, increasing in intensity linearly with the 
 depth. The center of pressure and the maximum bending moment on a span between 
 waling sticks may be considerably in error when figured by equations 1 ard 2 for 
 the long spans ;nrde possible by heavy steel piles. The following study is proposed 
 not as necessary for practical designs but as an analytical d rill for t he student 
 It should be noted that the treatment is similar to that given with Fig. 34 for 
 footings. *. t ' 
 
 The General Case , Continuous Spans , In Fig. 41A, let AD represent a line 
 of steel sheet piling braced by v/aling sticks at levels, A, B, and C. It is re- 
 quired to compute the center of pressure E, and the total pressure P upon the 
 span 1 between ve.1 ing pieces B anci C; also the position F and the mount M of the 
 max. bending moment in the span 1, due to an earth pressure of intensity p. Since 
 the steel sheet piles are in one piece from A to D there is continuity at B and C. 
 The span 1 has fixing moments Mj_ and Mg at these supports with e ffective abutment 
 
 shears s and so. To simplify the analysis assume the slope of neutral curve 
 1 
 
 after flexure to renain vertical et B and C. Equation 1 gives the pressure in- 
 tensity of earth at any head. Consider one lineal foot horizontal length of 
 piling. Then: 
 
 Pl = W hi (1 - sin g[) , p = W (h^x) &l-sin $) , p 2 = whp(l-sin g) . . . (2) 
 (1 + sin 0) fl+sin 0) (1+sin 0) 
 
 The trapezoid of pressure intensities is BGJC. Again, if b = P2 - j>i 
 
-f .-,. 
 
 
 .. . - 
 
 r <:;.r 
 
 /r 
 
the general value of p is:- p = p + bx ............. . . . . (4) 
 
 i 
 Taking momenta about B: 
 
 , s I=h2-hl 
 
 m = /P x <lx = / (Pi + bx)xdx = P!/| (h2^} 2 + tog-Pi ) (h2-^l) 5 (5) 
 
 ~FT~ 
 
 From a summation of pressures: 
 
 1 ........... ................ (6) 
 
 2 
 Dividing equati. n(5)by(6)gives the value of m, the position of the center 
 
 of pressure. Equation (6) gives the magnitude of the total pressure on the span ! 
 Applying the equations of static equilibrium to the external lords acting 
 up an the span 1: 
 
 s.i + s 2 - p = . . ..... . . . ^ . . . ........... (7) 
 
 i 
 
 MI - M 2 + sgl - P m = . . . . . . . . , . , . . . ....... (3) 
 
 These equations 7 and 8 contain four unknowns, 33., s2, MI and ilg. It is 
 necessary to establish two additional equations in order to make a complete 
 solution. -The extra equations .aey be established from the elastic conditions which 
 
 fix the slopes at 3 and C. 
 
 , 
 
 At any section x, the equation for bending moment is'- 
 
 El d 2 w = Ml - s x x + /o'xi dx ....... o ........... (9) 
 
 dx 2 " 6 
 
 In equation 9, x is a constant, X]_ is vari^ble with the limits o and x, 
 p 1 is the pressure intensity at any distance ::]_ from section x. Hence w is the 
 lateral deflection of sheet piling. 
 
 p' = fi + b(x - a^). .............. ...... .(10) 
 
 Substituting the value of p' from (10) into (9): 
 
 / x l 
 El d 2 w = Ml - six +/ /Pl+b(x-X]ll xldx = Hl-six + pjx2 + bx, ....... (11) 
 
 dx 2 " <f , ' -^ 6 
 
 Integrating (11) between the limits o and x for xi, remembering that when 
 x = 0,,dvjF/dac = 0: 
 
.-;..., :;:>.>..-<. -"H; 
 
 . 
 ;X^:: i! 
 
 -.'.TS.-'VJ i-'-Jf ? 1 
 
*r ^ 
 
 /ax r I I- r 
 
 BI / d 2 w = MI / dx - Sj_ / xdx + f i / x 2 dx + b_ /x^dx, 
 
 ^y dx /> "0 -2" >6 6y 
 
 o 
 
 El dw = M]_x - SjX 2 + pix 3 + br.4 . ...... o ... . . o (12) 
 
 dx "IT" -6 - 24 
 
 Integrating (12) between the limits o and x for X]_, remembering that 
 when x = 0, w = 0, 
 
 El w = M-|_x 2 - six3 + p T x 4 + bx 5 . 
 - - ~2T~ 
 
 120 
 Jn (12) when x = 1, d\v/dx = 0; in (13) when - Ij, w = 0; hence: 
 
 - MI - s.,1 + p x l 2 + bl. o ... / .............. ( 14 ! 
 
 2 "T" 24 
 
 = Mi/2 - Sl l/6 + pi! 2 /24 + bl3/120 ....... .... ..... (15) 
 
 Equations (14()) and (15) together with (7) and (8) v.lll give completely 
 the ve.lues of s-^, s 2 , 1.^ and M 2 
 
 The shear S at any section z n is:- 
 
 /JL 
 'dx = &i - i > ?! + b(x - Z^U dx = S]^ = p^ - bx 2 /2 ... (16) 
 J ' 
 
 TO get tlie value of x, for the section of maximum moment MQ, place s 
 in Equation (16) equal to zero end. solve for x = XQ. 
 
 
 Placing this value of XQ in equation (11) gives the amount of MQ. 
 
 Simpler Case, for One Continuous Span. In many cases there is only one 
 span 1; the waling piece B being ct the ground surface, c at tije trench bottom; 
 
 see Fig. 41B. From (3), pi = 0; p = wx (1 - sin $} , and 
 
 (1 + sin 0) 
 
 P 2 = wH (1 - sin gf). ................ ....... (18) 
 
 ( 1 + si n ) 
 
 The pressure diasrem' becomes the triangle BJC. 
 From (4), b = p 2 /H; ? = bx = p 2 x/H .... ..... ............ (19) 
 
 From (5), Prn = P 2 H 2 * wH 3 ( 1 - singf) . . . . . . ..... ...,.. (20) 
 
 ~Z~ S (1 + sin 0) 
 
 From (6), P = P2R/2 = wH 2 /2 (1 - sin j\ .... ..... . . . ....... (21) 
 
 (1+ sin 0) 
 
(- 
 
 c ;, 
 
 - atjtf 
 
 . 
 
 - 
 
 . 
 
124 
 
 Hence m = 2H/3 ...... (22) 
 
 From (7) si - s 2 - P = (23) 
 
 From (8), MI - M 2 + S2H - P m = . . . .'..' (24) 
 
 From (14), M I - siH/2 + p 2 H 2 /24 = (25) 
 
 From (15), Hi/2 - siH/6 + p 2 H 2 /120 ,-. (26) 
 
 Combining (25) and (26), eliminating si end solving for M l9 
 
 M, = P2H2/30 = WH3/30 (1 - sin 0) ............... (27) 
 
 (1 + sin 0) 
 
 Taking moments about bottom waL ing stick C for all external forces, 
 MI - M 2 - SiH + P(H-m) = (28) 
 
 Combining (25) and (28), eliminating si, substituting from (27) the 
 value of Mj and solving for M 2 , 
 
 M = p 2 H2/20 = wH 3 /20 (1 - an 0) . ............... (29) 
 
 (1 * sin 0) 
 
 From (24), s 2 = p 2 H/3 + M 2 - MI = 1/20 wH 2 (1- sin gf) ......... (30) 
 
 *~1T~ (I + sin 0) 
 
 From (28), s- L - p 2 H/6 - Mg - MI = 3/20 wH 2 (1 - sin 01 .......... (31) 
 
 H (1 + sin (3) 
 
 From (17), x g = + Hi] 3/10 = 0.5477 H . (32) 
 
 From (11), we get MQ by substituting the values of Ml frcfin (28), si from (31), 
 
 = V s - :'._ - . ; .' - ' - - .. 
 
 M = - 0.0215 wH 3 (1 - sin gf) . . ........'.......... (33) 
 
 (1 + sin 0) 
 
 Practical Case, One Simple Span. Where bending is calculated in 
 practice it is usual to assume MI = M g = 0, supposing the span H simply supported, 
 The values of pi, p 2 , b, P and m remain unchanged as given by equations (18) to 
 (22). From (30) and (31) 
 
 S2 - p 2 H/3 = v/H 2 /3 (1 - sin jj ................... (34) 
 
 (1 + sin 0) 
 
 s l = P2 H / 6 = wH 2 /6 (1 - sin 0) ................... (35) 
 
 (1 + sin 0) 
 
 From (1C) x o = H/J1/3 = 0.577 H ..................... .(36) 
 

 125 
 From (11), making 1^ = 0, substituting S]_ from (35), x = X Q , 
 
 M Q = - 0.064 wfi3 (1 - sin gQ (37) - 
 
 (1 + si n 0) 
 
 The pressures per lineal foot against the waling pieces are given by 
 equations (34) and (35); equation (57) gives the bending moment for \vhich the 
 section modulus is computed. 
 
 ADDITIONAL REFERENCES, SHEET PI-LI UG. 
 
 1. Steal Sheeting end Sheet Piling; R.L.Gifford, with discussion; Trans. Affl. Soc. 
 
 C.E. , Vol. 64, p. 441, Sept. 1909. 
 
 2. New Systems of Steel Sheet Piling with Clamp Connections; Eng. News, Vol. 59. 
 
 p. 133, Jan. 30, 1908. 
 
 3. A Practical Treatise on Foundations; W.M.Patton, pp. 150-155; Part II, Arts. 
 
 6-9; also pp. 472 and 500. 
 
 4. A Treatise on Masonry Construction, 1. 0. Baker, 10th eel., p. 374, 1909. 
 
 5. The Coffer Dam Process for Piers; C.E, Fowler, Arts, IV, V, VI, pp. 40-79. 
 
 6. The Bracing of Trenches and Tunnels; J.C.Heem, Trans. Am. Soc. C.E. . Vol. 60, p. 1 
 
 7. United States Sheet Piling; Iron i^ge, IJay 28,1908. 
 
 I 
 
 8. Steel Sheet Piling for Retaining Earth Under Spread Footings; Eng. Record, 
 July 4,1908, Vol. 58, p. 15. 
 
 9. Experience with Steel Sliest Piling on Hard Soils, by W.8. Fargo; Eng. News, 
 
 April 4,1907. 
 
 10. The Strength of- Sheet Piling; Eng. Record, Vol. 63 Apr. 1,1907, 'p. 368. 
 
 11. Eng. News, Vol. 59, p. 133, Vol. 63, p. 117, 
 
 12. Drive Inclined Precast Concrete Slabs for Seawall; Eng. Sews -Record, Vol. 81, 
 
 p. 897.' 
 
 13. Notes on the Design of a Single V/all Cofferdam; En~. News-Record, Vol. 82, p. 708. 
 
 14. Building a Sheet Pile Cofferdam in a 28 ft. Tide; Eng. liev/s -Record, Vol. 87, 
 
 p,806. 
 
 PROBLEMS 
 
 1. A building foundation is to be excavated with verticrl sides 23 ft. high 
 in a sandy loam weighing 100 Ibs. per cu.ft. and standing readily on a slope of 
 1 1/2 H to IV. During construction the wells are ^supported by three tiers of 
 vertical woolen sheet piling Jin 15 ft. lengths with horizontal waling pieces 
 spaced 10 ft. vertically; time v/aling piece at the top. Each waling piece is 
 braced by posts spaced 8 ft. horizontally; and inclined st an angle of 45*,v/ith 
 the vertical. Design the light sheet piles end waling sticks as simple beams for 
 an allowable cross breaking stress of 900 Ib. per sq. in. Design the inclined 
 
126 
 
 braces as posts by the column formula for allowable unit stress, s = 1000 - 12 _!_ 
 
 d 
 
 where g is in Ib. per sq. in., 1 is' the length,' cr.d d the least dimension of 
 cross section. 
 
 2. In Fig. 36 compute the probable axial load on the next to t he lowest 
 inclined brace if the struts are spaced 10 ft. laterally. Suppose the retained 
 material is wet clay mixed v/ith some sand. Us sign the strut. Y.'hat pressure comes 
 on the waling piece? V.'hat is the maximum bending moment in the waling piece? 
 Design it. what thickness of sheet .piles is required at tris level? 
 
 3. A sewer trench is to b e excavated 15 ft. deep in saturated silt weighing 
 130 Ib. per cu.ft. with an angle of repose of 1 v. to 4 H. The sides are 
 supported by Vertical sheet piling vith horizontal waling oieces 6, 6, 10 and 13 
 ft. from the surface, braced v/ith horiac ntal braces extending across the trench. 
 
 ' Design waling sticks and brcces for allowable stresses of 1200 Ib. per so. in. 
 of either cross breaking fiber stress or direct compression. Use standard 
 sizes, 3" x 6", Or 6" x 6", of timbers throughout. 
 
 4. In Fig. 38 compute the load ona horizontal stirut of the fifth frame from 
 the top if the retained roaterial is wet river mud. Design this brace. >7nat is the 
 pressure' per lineal ft. against a waling piece in this horizon of bracing? 
 Suppose mud may rise to top of sheet piles. 
 
 5. In Fig. 39 suppose that the concrete slab below elevation - 10 has been 
 placed but that no materials of any kind rest upon it. If the water surface out- 
 side the sheet piling reaches a level +2.0 and has free access beneath the concrete 
 slab, what is the net thrust in los. per sc. ft. tend! n'j. to lift the concrete? 
 \Vhat is the average total pull in Ibs. tending to break the bond between the 
 concrete and one pile head? V/hat is the safety factor for this anchorage? Neglect 
 friction against sheet piling. 
 
 6. A building foundation is to '-> e excavated v/ith vertical v/ alls 10 ft. high 
 in moist loam, weighing 112 Ib. per cu.ft. with an angle of repose of 1 V to 2 
 H. The sides are to be supported -by sheet piling composed of standard rolled 
 steel shapes (channels or I-b-ams) driven far enough so that they .nay be 
 designed as 'cantilever beams 10 ft. long, fixed at the bottom of the excavation 
 and subjected to earth pressure computed by the Rankine formulas. Design with 
 an alloy/able unit stress of 18 000 Ib. per sq. in. .a " 
 
 
 
 7. Suppose the sheeting of prob. 6 is braces 1 , as in Fig. 41B. VJhat is the 
 pressure par lineal ft % on v/aling sticks B and C. Design them of Oregon pine 
 for lateral braces spaced 8 ft. centers horizontally. Compute the position and 
 amount of max. bending moment in the steel sheet piles for ends simply supported. 
 Design the sheet piles of same type shown in Fig. 40 and for the spa cif icr tions 
 given in the text, 
 
 8. In prob. 7 suppose the piling tfonstraine d at 3 arJ. C, analyze and design 
 in parallel. 
 
 \ 
 
 9. In prob. 7, suppose the sheet pile free at B but fixed at C. Supply 
 parallel calculations and designs, 
 
127 
 
 CHAPTER 6 
 
 BEARING PILES 
 Introduction 
 
 Where the soil is so soft that it is impossible or impracticable to 
 obtain sufficient bearing power by spreading the foundation, or whare there is 
 danger of a structure being undermined by running water, heavy loads frequently 
 are supported upon bearing piles. Cf. Figs. 40, 24, 39 and 40A. Hound timber 
 sticks or logs are most common for this purpose, though steel in special forms 
 and lately /reinforced concrete are used. 
 
 The supporting power of piles is due to the. friction of the surrounding 
 material on the sides of the sticks r.nd to the direct bearing power of the 
 material at the pile points. The relative value of these two portions of the 
 
 supporting capacity is extremely variable, but the former is usually the larger. 
 
 ) 
 
 The amount of this friction in Ib. per sq. ft. depends upon the kind of material 
 
 penetrated. Hard compact clay, particularly if gravel b e mixed with it, will 
 permit small penetration of t he piles only, both on account of the side 
 friction and the r esis tance offered to the point of the pile. At the ether ex- 
 treme, very wet mud obviously will afford little side friction and less point 
 resistance. Between these "two extremes, all degrees of side- or skin friction of 
 the piles may be found as well as varying degrees of point resistance. The 
 latter however is relatively so small that it maybe neglected, except in those 
 special cases where the point of the pile /neets rock or other hard nr.terial. 
 
 Many tusta have boon BO.C with piles f or t ho purpose of determining the 
 amount of side or dc in friction offered by the material penetrated. As -a result 
 of those tests skin friction has been found as high as 1850 to 1900 Ib. per sq. 
 ft. of pile surface-. Those high fraluos have been found in compact clay or rnixod 
 clay and gravel or in alternate strr.ta of dry and gravel or sand. In so ft 
 material settled sufficiently solid 1 , to offer satisfactory pilo support frictional 
 resistances ranging from 200 to 300 Ib. per sc. ft. have boon recorded. Those 
 values show that the surface friction of tho piles will vary botween wide limits 
 
128 
 
 for material which may bo considered s atis factory for pilo driving. In ordinary 
 satisfactory material, with hammers varying in weight from 3000 to 4000 Ib. it is 
 probably not far wrong to assume a skin friction on the surface of the piles vary 
 ing from 300 to 500 Ib. per sq. ft. Those values hrve been found for piles driven 
 from 10 to 20 ft. in the stiffcr materials named, and from 40 to (70 ft. in soft 
 material. Tho value of the skin friction will bo materially increased when a few 
 hours have elapsed after the completion of driving. The surrounding .Tutorial then 
 has an opportunity to settle firmly into all tho uncvcnncssos of the pile surface 
 and the frictional resistance will be much increased over that which exists im- 
 mediately subsequent to the last stroke of the hammer. 
 
 When piles are used for building foundations they commonly are driven 
 into compact .material such as sand, hard clay or hardpan, in which cases the direct 
 bearing power of the point may be considerable, although it cannot be accurately 
 estimated. Such quantitative tests as have been made show that this direct bearing 
 power may be taken fro.n 40 to 100 Ib. per sc .in. of tho nor;.E.l section of tho 
 pile at its point. Analyses for the carrying power of piles have been made by 
 Weisbach. Rankino and numerous later authorities; all analyses however are based 
 upon assumptions whicji arc only approxi lately realized in practice and they omit 
 necessarily considerations of some of the complicated conditions which surround 
 the penetration of all piles. Tho best compilation of those formulae is that 
 entitled "Bearing Piles" by Rudolph Horing, published by Enginooring Hews Pub. 
 Co. Lr.tcr discussion of the subject will bo found in "Trans, ^m. Soc. C,E. for 
 August and Nov. 1892. No purely ideal or theoretical c onsidorctions crn be imde 
 to give accurate values for the sustaining par; or of piles; but such considerations 
 may and do load to formulae having much rcr.l value although they cannot bo depended 
 upon under all circumstances and may even bo only loosely approxL--.ae.to under s ome 
 important conditions of actual work. Tho "Engineering News Formula" appears to 
 fulfill the general conditions as well as r.ny formulr yet proposed'. 
 
129, 
 
 TIMBER PILES - TIMBSBS AVAILABLE. 
 
 Tho principal timbers for piles along the Atlantic Const are spruco, 
 yellow pino, white pine, Norway pine and oak. On the Pacific Coast, Oregon pine, 
 or Douglas fir, is much used.- In the interior portion of tho country., t.i\-j 'timber 
 of satisfactory resistance which will afford sticks of requisite length and stri ight- 
 ncss is employed. Piles may be of alr.ost any diameter, not too s;rall, cut from 
 trees v/hichgrow of sufficient length and aro at least fairly straight. They arc 
 of all lengths up to 80 or 90 ft. and usually arc specified to be straight, sound 
 sticks, free from cracks, loose knots or other imperfections which may materially 
 
 wcakon them. Sometimes they may havo tips as snail as 6 ins. in diameter, although 
 8 ins. is often a minimum specification limit, with the butt varying from 12 to 
 
 18 ins. in diameter. Tho vrriation in size will depend to some -xtent upon the 
 
 character of the work for which the piles are to bo used. For permanent work, piles 
 
 are frequantljr required to be freed from bark. 
 
 Eucalyptus lias been much advocated, r.nd used to a considerable extent 
 
 . 
 
 
 
 in the Southern and Western Stctes, especially in marine work, where it is com- 
 paratively immune from the attacks of narine worinsa It crn be obtained readily 
 in long straight sticks. The tree is quickly and cheaply grown. 
 
 Good foundation piles ere usually of white or Norway pine, yellow 
 pine, spruce or white oak. Oak piles rre seldom used, except in specif 1 cases, on 
 account of the extra expense involved. There is little choice rs to pino or spruce 
 piles. V/honwell selected, oithor material gives excellent results. In many places 
 piles are kept in stock afloat so that they become thoroughly v.r.ter-soaked before 
 being used. Sometimes thoy are kept in this condition for a long period of time 
 - without being appreciably dame god. In such cases however they may to some extent 
 become alternately wet and dry by reason of motion duo to winds or currents, rrd 
 hence thoy should bo subject to c?reful inspection. 
 
 SPECIFICATIONS FOR TIIiBER PILES 
 
 Many piles used for building foundations in some cities rrc far too small 
 and their use should not be permitted The "building laws of tl:.o City of liov; York in 
 
. 
 
130 
 
 1900 permitted the use of a. pile- with a 5 in. point, and while- this may not be 
 specially bad practice, 6 ins. is certainly small enough for an absolute minimum. 
 The same building rogut tior.s specified minimum butt diameters ranging from 10 to 
 
 ins. depending upon the pile length. Engineers seldom specify for less than a 
 14 in. butt, although in building foundations v/hore tho supporting arterial is, or 
 ought always to be, flush v;ith the top of tho pile, 12 ins. is permissible as a 
 minimum. A pile with a 12 in. butt and 6 in. tip is ccttainly small enough as a 
 limiting minimum for satisfactory foundation work for any building and nothing 
 smaller should be allowed. It is extremely doubtful whether the smr.ll needle-like 
 piles which frequently have been seen driven in How York City foundrtions really 
 add- much to the supporting power of the sand into whicfc they r.ro drivon. 
 Extracts from tho New York City Building Code, 1901, Sec. 25:- 
 
 "Pilos intended to sustain a wall, pier or post shall be spaced not moro than 
 36 in. or less than 20 in. on centers; they shall be driven to a solid bearing if 
 practicable to do so, and the number of such piles shall bo sufficient to support 
 the superstructure proposed. No pile shall b o used of less dimensions than 5 ins. 
 at the small end odd 10 ins. at the butt fpr. short piles, or piles 20 ft. or less 
 in length; nor less than 12 ins. at the butt for long piles, or piles moro than 
 20 ft. in length. No pile shall be weighted with a load cxcee-ding 40,000 Ib. 
 When a pile isnot driven to refusal, its safe sustaining power shall be determined 
 by the following formula: - Twice tho weight of tho hanrncr in tons multiplied by 
 tho height of the fall in foot divided by the least penetration of pile under the 
 last blow in inches plus one. The Commissioner of Buildings shall be notified of 
 the time when such test piles will be driven, so that h& may be present in person 
 or by representative. The tops of all piles shell bo cut off below tho lowest 
 water line. V/hcn required concrete shall bo rammed down into the interspaces be- 
 tween t'e heads of the piles to a depth and thickness of not less than 12 in. and. 
 for one ft. in width outside of the piles. Y/hore ranging end cojpng timbors are 
 laid on piles for foundations, they shrll bo of hard wood not less than 6 ins. 
 thick, proporly joined together; their tops lr id below the Haves t water lino". 
 
 ' The San Francisco Law, 1910, section 43 reads:- "Timber piles shall b c 
 at 1: cist 7 ins. in diameter at tho small end and shall be cut off below standing 
 water lire. Titobor piles may be capped with concrete at least ]2 ins. thick or 
 with timber at least 12 ins. thick, drift bolted to aach pile; but all timber shall 
 be below standing water line. There shall be a clear distance of at ]c ast one ft. 
 between any part of adjacent piles. Timber -piles drive-n to rock or to refusal may 
 bo lorded not to ,oxcoed 500 Ib. per sq. in of middle sectional area. Timber piles 
 driven in- yielding arterial may be lorded not to oxcood 1 1/2 tons per inch of 
 diameter of middle section, but such piles six 11 be over 20 ft. long rnd none such 
 shall be lorded to exceed 25 tons". 
 
 PREPARING PItBS 
 
 I 
 
 Piles are prepared for driving by cutting or sawing the large ends square 
 id bringing the small ends to a blunt point with an axe, the length of tho bevel 
 
131 
 
 on the point being from 1 1/2 to 2 ft. Tho bark should be stripped for permanent 
 work.osppcially for piles below tho ground surface, and for piles which r.ro not 
 always undor water. In many cases the piles arc- not pointed but arc driven with 
 rounded or square ends. In softer silty material, whcro driving is easy, there is 
 no object in pointing thorn, rrid tho bearing power is probably greater without the 
 points. Blunt piles can bo driven in bettor alignment, especially in gravel or 
 hardpan, as points, striking obstacles tend to deflect the piles. Square ends will 
 cut or break through obstructions. Tho upper end should be champfcred for a few 
 inches, and a wrought iron band tightly fitted and driven into place with a light 
 blow. Sometimes the band is a little smaller than tho pile, and is ham nor od into 
 it by a light blow, either when the driving is commenced, or when the pile begins 
 to qD lit or broom. This method is apt to split off concentric layers in soft wood 
 especially if the ring is not placed at once. Tho rings should bo made of tho best 
 wrought iron, of carefully welded bands, 1/2" to 1" thick, and 2" to 4" wide. They 
 should bo placed at the beginning. If a ring breaks, the battered portion of the 
 pile should be cut off, and a now ring fitted at once. 
 
 An improvement upon the use of rings is the pile anvil or cap which 
 
 V 
 
 carries a recess of proper depth on its underside, and which the first blow of the 
 hr.nnier drives down upon the head of the pile, thus preventing any injury to it. The 
 anvil moves between the leads of the pile driver which act as guides. It canies 
 a short oak block on its top on which t he pile driver hamper falls. By these 
 
 arrangements the head of the pile is n ot only protected fro^. injury but it is also 
 
 ^ 
 
 perfectly guided. 
 
 DRIVING- PILES 
 
 The driving of piles is a matter which sjiould receive careful attention . 
 A hammer which is too light will accomplish little with its high falls except soft- 
 er ing the pile head in crse it is allowed to fall directly upon the latter; and 
 a very hervy hammer if used with an excessive fall may easily break the pile at 
 such a depth that the failure is not observed. A reasonably heavy hammer with a 
 comparatively sha t fall and rapid delivery will produce the best results. For 
 
:';;,*;;// : 
 
132 
 
 'heavy piles a hammer weighing 3600 Ibs. with a foil of 8 to 12 ft. will accomplish, 
 all that is necessary, but no pile ought to be used for which a 2500 Ib. hamner 
 is too heavy. A hervy hr.araer may quickly broom the end of 'c n :e pile, end in order 
 to prevent this the wrought iron ring or the anvil, already described, is put on 
 at the beginning of the operation of driving and then pulled off after the latter 
 is completed. Thus both .'/crooning and splitting of the head are avoided, 
 
 The usual form of pile driver, fig. 42, consists essentially of two 
 horizontal sticks of timber 10 ft. to 20 ft, or more in length, 3 ft. or 4 ft. 
 apart at the front and 6 to 20 ft. at the rear; two similar vertical sticks 20 to 
 50 ft. long and an inclined ladder connecting the rear ends of the horizontal 
 pieces to the tops of the verticals. A number of horizontal platforms are built 
 for convenience and bracing, connecting the inclined ladder with the verticals. 
 
 The hammer is of cast iron, sliding in leads, or vertical strips, 2" to 3" square, 
 
 / 
 
 spiked to the inside of the heavy uprights and faced with iron straps. An engine 
 or other hoisting apparatus is provided tc raise the ham:rter. In the commonest form 
 of pile dri-ver, the hanrner is permanently fastened to a wire rope passing over a 
 pulley at' the top of the lerds down through a snatch block to the drum of the 
 hoisting engine. \.Co- siderable energy is consumed in unwinding the drum as the 
 hamper falls. In another form the rope is attached to nippers fastened in a block 
 sliding in the leads. Fig. 43. The nippers are automatically released at any given 
 height by a 'tripping block fastened inside the leads, allowing the ham.ner to fall 
 freely, thus delivering a harder blow for the same fall than with the previous 
 form. But the nipper type is slower to operate, the height of the fall is not so 
 easily controlled; and there is danger of losing the hairier if 'the ground is very 
 soft, or if the pile springs out of the leads. The hoisting engine and boildr are 
 mounted on the pile driver frame at the rear, in order to counterbalance the weighjr 
 of the ham.ier and the supported pile. 
 
 Pile drivers may be moved on firm ground by wooden rollers, such as are 
 used by house movers. Pile drivers for railroad work are mounted complete on special 
 cars, the leads being hinged so thrt they may bs lowered to pass through bridges 
 
133 
 
 and tunnels. Of. Eng. tiev/s. Vol. 48, 1902, p. 363, For work ir water the entire 
 outfit is constructed on a barge, such as is described for ;.arl::ing test borings un- 
 der water, Fig. 6, Piles cm be driven more economically on water than on Irnd, 
 For driving inclined piles it is only necessary to hinge the le:ds at the bottom 
 with heavy bolts, and move the bottom of the ladder horizontally to secure ar.y 
 angle desired. Steam hoisting ermines are usually used, though for unir.roortc.nt 
 work or isolated situations, horse power, or even ^r.n power may be substituted. 
 
 PILE HAMMERS. 
 
 The hammer or ram of the pile d: iver usua.lly weighs from 2000 to 5000 
 Ib. Bothlighter aid hecvier v/eights than indicrted by th3s~ limits are occasionally 
 used, but the greater bulk of pile driving is done by hammers whose weights are 
 found b etween these limits. The fall of the hammer ranges from a few inches to 25 
 or 30 ft. A light hammer falling through a comparatively great height will frequent- 
 ly rebound and fail to accomplish much movement of the pile. A very hecvy hcm.fii- 
 f ailing through a very great height., may break the pile or crush its herd, cc.us.ing 
 a fibrous disintegration called "brooming", Ir order to prevent this brooming, a 
 wrought iron ring or collar, as previously described, should be placed over the 
 head of the pile while it is being driven. Generally speaking a hecvy temper , 
 falling through a small height, will yield by far the best results. For ordinary 
 engineering work a haa-.er weighing -'rom 2500 to 4000 Ib. felling from 10 to 25 
 ft. will give excellent results,. Lighter hammers are used fo:. sheet piling., end 
 heavier ones for massive reinforced corcre^e piles. 
 
 Steam hampers frequently -re employed for important -/or 1 :, especially 
 around cities. These hammers consist essentially of a stern cylinder from 2 to 5 
 ft. long, the piston rod of which carries a hervy weight. The hamner is lowered by 
 a rope to the top of the pile, sterm is conveyed to the piston through a flexible 
 tube and raises the weight through a distance equal to the stroke of the sn&chine, 
 when the steam is automatically cut off releasing the hammer. The stroke is much 
 shorter than that of the drop ha er, but the >B.lows crnbe delivered mud: more 
 rapidly/ While there isnot much energy in the individual blow, on account of the 
 
134. 
 
 shorter drop, the effectiveness of the successive blows rry be r.t least c.s greet, 
 because they do not give the v.aterir.l time enough to settle me", compact itself 
 around the piles. The cost of the apparatus is materially greater than that of the 
 drop hammer. 
 
 For a description and illustration of steam ha,.r:ers consult; "The 
 Goffer -Bern Process for Piers" by C..E, Fowler, 2nd ed. , 1905, pp. 52-56, figs. 
 32 and 34. ihe principle which is the same as that of steam forging hammers, was 
 first applied by Hasmyth to pile driving in 1845. Modern steam hampers are nr.de of 
 different weights:- "In the cr se of the Warrington-Nasrayth hr.ra.ner there r.re three 
 sizes, 550 Ib. for sheet pile work, 3800 Ibs. for medium pile work, and 4800 Ib. 
 for use on heavy work. The hamper is attached to the hoist rope but this is left 
 slack when the hammer is resting on t he head of the" pile; steam is turned on and 
 the ha..i7ier pounds automatically at the rate of 60 to 70 blows per minute until 
 the pile is driven. The bottom casting which rests on the pile is a bonnet which 
 3ncases the top r.nd prevents brooming or splitting". The Crrm-hasmyth hammer is 
 :ade in four sizes; 430, 2000, 3000 and 5500 Ib . ; "one of the peculiar features of 
 the Nasmyth invention v;as that of employing the pile itself as the support of the 
 sterm hammer parts of the apparatus while it was being driven, so that the pile 
 has the percussive force of the deadweight of the hammer as v* ell as the lively 
 lows to induce it to sink into the ground, One of the most ingenious contrivances 
 Df the pile driver was the use of s terra as a buffer in the upper part of the cy- 
 linder, which hr.d the effect of a recoil spring and greatly enhanced the effect of 
 
 \ 
 
 ohe downward blow". 
 
 Consult an interesting report made at the j.nnual Convention of the 
 Association of Railway Supts. of Bridges and Buildings, Lng. iiews, Vol. 52, p. 378, 
 >n the relative advantages and disadvantages of "steam hammers, or drop hammers for 
 
 ile drivers", for railway work. See also Eng. Eecord, Vol. 63., April 1, 1911, p. 369 ; 
 
 Tineiples of Prr.ctice for Pile Driving, 
 
 In En~. Lews, Vol. 46, p. 282, 1901, ilr. S, S.Thompson gives a description 
 nd illustration of a Uarrington steam pils driver used for driving piles for piers 
 
135. 
 of the New Cambridge Bridge, Boston, Llass. Some 15000 piTes were used in the ten 
 
 piers. A pile driver frr.me rising a bout 75 ft. out of the water was used. The pile 
 to be driven was hoisted and plr.ced ir. position, r.nd the hrmmer allowed to rest with 
 its full weight upon the pile, thus erasing it to senile through t he w ater and. nud. 
 Steam was then turned on, the hr.mer pounding r.utorn,'.tic:ll7 till the pile was driven 
 to the required depth. The weight of hammer was r bout 9800 Ib. , that of the striking 
 parts about 5000 Ib. It was a "gravity machine", that is, the steam lifted the 
 piston, then suddenly released it., allowing the w eight to fall 'by gravity onto the 
 pile. The required steam pressure was 90 to 100 Ib. per sq. in. The. hammer was 
 capable of giving from 60 to 70 blows per minute. In cr der to drive the piles oelow 
 
 \ 
 
 the surface of the water a follower of white oek, 14 ins. square and fro,: 25 to 
 35 ft. long v/as used. The followers were capped at each end with c ast iron. The 
 contractors drove considerably over 100 piles in 10 hours; as e. record days work 
 they drove 212 piles in a single day of 9 hours. 
 
 SIKSIK5 PILES BY "/Al'^R J3T . 
 
 In firm, compact naterial, where it is particularly undesirable to 
 injure the piles by nervy blows, recourse is often had to water get sinking, This 
 method is prrticularly effective in comprct sand, -.-here driving is vary difficult. 
 The pipe is attached to the sire of t^.e pile in a groove, or simply fastened to 
 the outside. It teiaiir* ces in a nos;le ne~ r the point of the pile, sometimes dis- 
 charging through an oblique hole exactly at the point. Uater is forced through 
 under pressure and removes or loosens the material immedic-.el;; in front of tl:e point 
 V/ater and mud co -B to the surface arounC. tl.e pile, entirely preventing tl-e skin 
 friction which commonly forms the chief resist* nee to4rl<vlvg. Boulders under 
 piles can be w.rried down by sinking a pipe to the bottom of the boulders and using 
 two water Jets. If the pile does not sink by its own weight, it .nc.y hrve weights 
 placed on top, or the sinking mr.y be aided by light blows from a hr.nrcer. If con- 
 venient, a few blows should be given after stopping the water jet. 'Then the vater 
 pipe is removed, the soil soon packs firmly r.nd the piles c a- .ot be sorted, even 
 with her-vy blows, The soil is rendered more comprct because it settles l:en -vet 
 
136. 
 
 This meti~vi is usually employed with screw piles end. is the only method of sinking 
 disc piles. It is ;lso used for certr.in forms 'of reinforced concrete piles. See 
 ^the later description of "Corrugrted Reinforced Concrete Piles". Rec: 11 the method 
 of sinking sheet piles for the U. S.iTaval Cor.ling Str.tion, Tiburon, California, 
 Chap, V, Figs. 40A,B,C. 
 
 BS/.T-ING POV/ER OF PILES. 
 
 1. Uhere priven to a Firm Bottom . Some piles, pr.rticulc.rly for build- 
 ings, oro driven through soft ovarlying strr.tr. to a firm material, such as rock' 
 or hardpan. These c.re supported laterally for their full lengths by the overlying 
 strata. If not injured by useless hamraring, their bearing paver is prr.cticr.lly 
 equal to the safe crusMgg strength of the timber. 
 
 2. V/here No Bottom is Reached. This is a common case in sv/amps or ' 
 marshes, or in loose silt or quicksand. Rr.ilrord trestles often exhibit the "out- 
 of-Sight" pile driving problem. See ling. Mews, Vol. 48, p. 442, 1902, for a des- 
 cription of construction work on the Southern Prcific Cutoff acres s the Great Salt 
 Lake., Utah. In many places it vas found that mud to r> d epth of at least 50 ft. 
 had accumulated. Piles 40 to 70 ft. long were driven and hervily braced for the 
 temporary t restles 'to support tveekg for the train loads of .material to b e dumped 
 to form the fills. Kev/ Orleans railroad cracks in ir/ 113: lr?st~nces. have presentee, the 
 same problem. The bearing power of pilesin these materials must becrlculated from 
 
 a c or si deration of the side friction and the direct bearing par.' er of the pile point/- 
 
 Let a = the cross sectional area of the pile at the point, 
 
 p = the direct bearing pov/er of the soil (zero to 6000 Ib. or more 
 
 per sq . ft. 
 s = the convex surface area in sq. ft. of the pile in the g round = 
 
 the average circumference x the d epth driven 
 f = the skin friction (100 to 600 Ib. or more per sq. ft.) 
 R = the safe load on the pile in Ibs. Then:- 
 R = pa + f s , . . ....... . ..... .......... (1) 
 
 Equation (1) gives a simple formula in -ahich the constants are as w 
 
 
 
 krown as those of many of the formulae in more common use. The constrnts usurlly cr.n 
 be determined in the field for the soil in any given case, notice that the San 
 Francisco Building Law, 1310, Sec/ 43, is firmed upon these general ideas but applie. 
 
137 
 to piles driven in nil c lasses of materials. Equr.tion 1 is the only formula t/hich 
 
 can be applied to piles sunk by thewrter jet or driven into --ery soft soil, v/here 
 
 . ~ 
 
 the penetration is excessive. For s"afe values of p and f consult the figures Givsn 
 in Chap. 2, Patton recommends for use v.lth equation 1:- 
 
 f = 100 Ib. per sq.ft. for the softest semifluid sojls 
 
 f = 200 Ib. per sq. ft. for compr.ct silt and. clay 
 
 f = 300 to 500 Ib. per sq. ft. for mixed earths \ ith cons id er able grit, 
 
 f = 400 to 600 Ib. per sq.ft. for cornp; ct sand and srnd rr.d gravel. 
 
 EKAIIPIE 
 
 Assume a pile railroad trestle in swamp a It; p =0, f = 150 Ib.' per sq. 
 ft. Assume the uniform dead plus live load from the superstructure - 6000 Ib. per 
 lineal ft. Select pile bents .of four piles e- ch., bents spr ced 14 ft. longitudin-y 
 
 ally. Er-ch pile carries R = 6000 x 14 = 21,000 Ib. By equation 1 the surface 
 
 4 
 required = s = R - pa = 21000= 140 sq. ft. If the pile averages 11 in. in diam- 
 
 f 150 
 
 eter, its convex surface = 2.88 sq. ft. per ft. of length. Therefore the 
 
 penetrrticn = 140/2.88 = 48.5 ft. The length probably would be specified as 50 ft. 
 
 If the piles were driven into compact clay, f = 200 Ib. per sq.ft.; 
 p = 5000 Ib. per sq. ft-, assume point diameter = 10 ins., then by equation 1 
 
 s = R - pa = 21000 - 5000 x 0.646J - 91.5 tfq. ft. The -penetration required = 
 
 f 200 
 
 91.5/2.88 = 31.7 ft. Probably the length would be spacified as 32 or 33 ft, 
 
 The value of f increases as the pile is driven deeper. Fro -a tects, the 
 skin friction may be assumed 300 to 500 Ib. per sq, ft. in driving piles 10 to 
 20 ft. into sti*fer materials, and 40 to 70 ft. into softer ;.irte rials. The skin 
 friction is small while the pile is being driven, prrticularly if the blows are 
 delivered in rapid succession. It rerches its nor.TK.l .'mount however in a few 
 
 hours after the driving has cersed. The direct berring pov.-er of the point is 
 
 foundations , 
 
 /auch greater than that ' f or ordinary sprerd '-* ' T because the soil is com- 
 pacted beneath the pile by the driving. Experiments shou thrt for building 
 foundations in compr.ct material, such as hard clay or sand, the direct be;rirg ' 
 power of the point maybe t rken from 40 to 100 Ib. per sc. in. . 
 
 3, Usual Pile Formula. In determining such a formula for the bearing 
 power of a pile, it will be necessary to observe the oenetrrtion ?er blow Curing 
 
I / 
 
 138 
 the latter portion of the period of driving. The final' pevetrr ticn is frecuentlj-. 
 
 crlled the "sat" of the pile. The energy of the falling hamrsr or r; m is consumed 
 
 first by the per.ar.nent crushing or brooming of the pile, and second., in over- 
 
 i 
 
 coming the resist, nee offered to its motion 'ay the ma'cerirl into r/hicli it is 
 driven. There rre other sources of consumption of energy, sue I: as tl.ie resistance 
 of the air, the resistance of friction offered by the lerds of t r e pile driver, 
 r.nd the resistance of the lope v/hich is attr-ched to the hammer in cruder to re- 
 cover it r.fter the blow is delivered, as well a s one or tv;o other sources of the 
 
 but 
 sane general,, indete rrni net e character. For the reason that these r.re indeterminate 
 
 and do not form a very rnaterirl portion of the actual energy jf the ram v they 
 may be neglected, The energy ersrte: 1 . in developing the Actual energ3>- of the 
 moving pile is also neglected b ecause it is restored. before the pile comes to 
 rest,, It is also supposed that the pile is driven under such ciroumstrnces a s to 
 accomplish the purpose of the operation., end- hence that no energy is wasted in 
 'che disturbance of the surrounding ..-rt:rial or in useless elastic work in the 
 flexure of the pile as r. column by rebounding hammer. 
 
 The piles used for building foundations are commonly driven into 
 comparatively co.npr.ct ovierirl. An attempt is rjr.de to judge of the ultimate or 
 safe bearing power of any given pile by mersuring the force of the blow delivered 
 and noting its effect in producing -penetration on ^he pile. The amount of work 
 V/li, delivered by the hamiier is equal to its weight \7 in Ibs. x the distance it 
 falls, h in feet. If no energy were wasted, this should equal the resistance E 
 of the pile :c the distance s the pile -.moves under the blow. Although there are 
 a number of other frctors these two terras are the principal ones in most prac- 
 
 X 
 
 tical formulae/ The effective work delivered by the hr.nner in ft. Ibs. is equal 
 to V/h less p. small amount consumed by friction on the guides, and against the 
 air, etc.; but these losses are so s.^ll that they cm be neglected. 
 
 If s = the penetration or set of the pile, then the mean resistance of 
 the -oile during the movement s must equal Wh/s. This would not be equal to the 
 final resistance of the pile R, however, bscruse of a static load Y/li/s, particularly 
 
139. 
 
 if aided by vibrations, would more a pile when the s arne average load delivered 
 by the hammer would not. The energy of the hamnBr blows may theoretically be 
 absorbed in five different ways:- 
 
 1. By brooming or mashing the pile either (a) at the head of (b) invis 
 ibly at the foot, or somewhere toward the middle; cf. Eng. L T ews, Vol. 48, p. 292, 
 1902, 
 
 2. By bouncing, and striking two or more light blows instead of one 
 heavy one. 
 
 3. By compressing elastically both the ~jile r.nd the hammer, and perhaps 
 the soil. 
 
 4y By overcoming the inertia of the pile end the strtic grip of the 
 earth. 
 
 5. By useful work in causing the pile to penetrrte against the earth's 
 resistance. 
 
 The consumption of energy to overcome friction 'of the guides, of the 
 air, the transfer of mechanical energy into her* are neglected, 
 
 la* The brooming of the head of the pile is a great source of loss of 
 energy, especially in careless driving.. It should be prevented or lessened by 
 using iron ringe, as previously described. The penetration s should rlwrys be 
 measured from a blow struck on fresh wood, obtained by tr inning or adzing the top 
 of the pile and after replacing the iron ring. 
 
 Ib. Brooming of t! e foot of the pile or at intermediate points car. 
 
 
 
 usurlly be detected by a skillful driver. It is often caused by useless hammer- 
 ing after the pila has prrctically stopped, or been driven to refusal. It always 
 neans a disintegration or destruction of the fibers of the wood and a consequent 
 loss in bearing power. The driving should be stopped before this occurs 
 
 2. Bouncing of the hammer neans that the pile has struck an obstacle, 
 nnd should not be driven furthei , or else that the hrm :er is too -light, or the 
 fall too great, or both. A heavier hammer or a shorter drop should be used to 
 secure the greatest efficiency. A slight bounce, as described in the following 
 paragraph is unavoidable, 
 
 3. Elastic Compression. At the instant of impact both the pile and the 
 hammer will be elastically compressed but most of the energy absorbed will be 
 given back as the ::>ile a nd the ham/ner move down in contact/ cr.usi ng the point to 
 travel faster than the herd and the hamner. If. the movement is short, so that 
 
140 
 sufficient time is not allowed for the pile and the hamper to e x;r, nd a f ter being 
 
 compressed, then when the point is brought to .a stop, the remnant of elastic 
 energy causes a slight upv/ard b ounce. The amount of energy absorbed in this way 
 is so small that it cm b e safely neglected. 
 
 Items 8 and 5 are the only ones which need be c onsidered if the work is 
 -properly done. The resistance to t he movement of the pile during the action of 
 one blow, will average Y/h/s, but will not be constant." Tha resistance will be 
 greatest at the instant the pile begins to move, because of the excess in the 
 coefficient of static friction., or of friction at low velocity over the friction 
 at relatively highjelocity, and also because of the settling of the earth around 
 and into irregularities of the pile since the last blow, was delivered. The re- 
 sistrnce will also be slightly greater as the pile comes to rest, because of the 
 increasing friction at low velocity. 
 
 For the greater part of the movement, s, the resistance will be approx- 
 imately uniform and less than the average Wh/s. This latter resistance will 
 represent most nearly the resistance to st: tic loads, particularly if vibrations 
 :re possible; hence, R will be less than Y/h/s and might be represented by a 
 fraction of the form R = Wh/a + x . (2) 
 
 Hence x is an amount to be assumed or determined by experiment. The 
 work diagram for a pile driven by a hammer is approximately of the form shown 
 in Fig. 44. The horizontal abscissae, like OD or JG represent the total (jnstan- 
 taneous ) resistance in pounds. The total work \7h delivered by the hammer, as 
 absorbed by the pile, is represented in the diagram by the area ODEFGJ. The 
 unif-orm resistance OB is the best measure of the future r esista.nce R of the pile. 
 It is required to determine Me resistance OB, in terms of known constants. 
 
 Construct the rectangiS OBCK whose area equals ODEFGJ = OBHSF + BDE + 
 FGH, as follows: Neglect the work FGH. Consider the decrersing excess resistance 
 BDE to the first inch of penetration, BE = 1 inch, and the initial excess BD = 3 
 times OB. This is purely an assumption but it can be considerably modified without 
 greatly affecting the results. Other assumptions, of the same nature can be ma.de 
 
141 
 with equal probability, but the fr.ct that they would not influence the final 
 
 results justifies in a mar sure the assumptions made r.bove. From fundamental 
 
 geometric principles the area of the triangle SDE = 3D :: BE = 3/2 OBo The rctual 
 
 2 ~ 
 area of the shaded figure BBME is assumed = 2/3 the r.rer. of the triangle BDE, or 
 
 numerically = OB. 
 
 To make the rectangle DECK - the area of the work diagram, make JHDK = 
 3DME - OB numerically, or make JK = unity. Then the area OBCX becomes Wh = 
 
 B (s + 1) and H = V/h/s + 1 ........ .;'.. .."(3) 
 
 If h is in ft., s in inches, B = 12 Wh/ s + 1 . (4) 
 
 If a safety factor of 6 is used, then the safe R = r is:- r = g Vfo ( .5) 
 
 8+1 
 
 Equation 5 is the so-called ''Engineering Liews" formula, deduced by 
 A.M.Wellington and first published together with elaborate discussions of fourteen 
 other formulae in the Engineering Isews, Vol.20, p. 511-512, Dec. 29, 1888. A fuller 
 discussion and amplification of the formula is given int:e Trans. Am. Soc. C,E. 
 Vol.27, pp. 99-129, Aug. and hov. 1892. 
 
 The Eng. .Hev/s formula is critized because it maJres x in equation 2 a 
 constant; that is, unity; v/hich of course is not correct for vr.rjdng soils or 
 weights of hr.ismers. Practically however if r is less than unity, the formula voul^- 
 give results for E greater thrn the co-.ipresEive strength of the timber, .us a 
 matter of fact if the penetration is less than 1", say 1/2", it usually means 
 merely that the pile is brooming rnc. that the point probably moves little if rt 
 all. If :: is made greater than unity, as already pointed out, it does not vitally 
 
 affect the results within reasonable limits. 
 \ 
 
 SPECIAL PILS FORMULAE 
 
 The amounts of the excesses shown by BD and HG in the figure depend 
 Almost or quite entirely on the character of the material into v/hich the pile is 
 driven, and it is impossible to assign either exact values to them or their 
 variations, Hor is it known whether there is any material portion of the irregular 
 line DlffiEG which is exactly parallel to OJ. Indeed the sh-;,->e r.nd the area of the 
 figure which is ecurl to the hr..:-:ier energy, V/h, depends essentially upon the 
 
\ 
 
142 
 character of the material and. the surface of the pile, Conse^uen^y, it is quite 
 
 impossible to assign the constant width OB to the rectangle which represents the 
 
 \ 
 
 hammer energy, and then call it the sustaining -capacity of the pile, The set s is 
 
 } 
 
 a matter of observation, but for the reasons that have just boen given x cannot 
 
 possibly be a constant and it is impossible to exactly deteraira its varirble 
 value. J.Foster Crowell writes for static loads x = 1 + n, raid, for dynamic or 
 
 vibratory loads x = 1 + n + n'. He would determine the value of n by observing the 
 
 , 
 penetration s 1 in inches under a blov/ of 40,000 ft. Ib. delivered to the pile and 
 
 then make n = I/2'(~a t . This standard fclow would 'be produced by a 2000 Ib. hcv.-...:er 
 falling 20 ft. or by a 3000 To. hammer falling 13 1/3 ft. He advises giving n 1 
 various values dependent upon the character of the lord v;bich the pile is to 
 carry. The following table gives the values n and n' indicated in his prper on 
 pile driving. See Trans. Am. Soc. C,E. Vol.27, 1892, p. 99. It is intended for 
 bearing loads only which always must be 3e ss than the crushing or column resistance 
 
 of the pile. , 
 
 TABLE BY J. FOSTER CRO'TELI. 
 
 
 s' inches.' 
 
 n =fs" T 
 
 2 
 
 i n' Classification 
 1 
 
 i 
 i 
 
 3.125 
 
 0.175 
 
 0.1 
 
 Large bldgs. to contain light machinery in motion 
 
 
 0.25 
 
 0.250 
 
 . 0.2 
 
 Long span bridge abutments for railv.r.ys 
 
 1 
 
 0.50 
 
 0.354 
 
 0.3 
 
 Long span bridge -abutments for highways 
 
 | 
 
 ;. 
 
 0.75 
 
 0.433 
 
 0.4 
 
 Bldgs. to contain heavy machinery in motion 
 
 
 : 1.00 
 
 0.500 
 
 0.45 
 
 Short span bridge abutments and railway trestles 
 
 
 ; 1.25 
 
 0.559 
 
 0.5 
 
 .Short span b ridge abutments and railway trestles 
 
 i 
 
 ' 1.50 
 
 0.613 
 
 0.55 : Bldgs. subject to extraneous vibration 
 
 ! 
 
 ; i. 75 
 
 0.66S 
 
 0.6 
 
 Foundations for machinery 
 
 
 3.00 
 
 0.707 
 
 0.7 
 
 Elevator towers in ordinary cases 
 
 { 
 
 <a.25 
 
 0.750 
 
 0,75 
 
 Bridge )Lers exposed to current vibrations 
 
 < 
 | 
 
 '2.50 
 
 0.791 
 
 0.8 
 
 Light houses exposed to ordinary wave action 
 
 
 2.75 
 
 0.830 
 
 0.9 Foundations for turntables 
 
 r 
 t 
 
 5.00 
 
 0.866 
 
 0.95 | Foundations for pivot bridges 
 
 ' 
 
 5.25 
 
 0,900 
 
 1.00 
 
 Chimney stacks exposed, to winds 
 
 ; 
 
 -.50 
 
 0.936 
 
 ' 
 
 
 ; i.75 
 
 0.965 
 
 I 
 
 
 ,.00 
 
 1.000 
 
 
 
 Using a safety f-ctor of 6 as before, the modification of the mg, Lews 
 
 ormula, eq . 5 becomes for static loads: R = 2 Wh ^. ............ (6) 
 
 s+l+n 
 nd for dynamic and vibratory loads, R = 2 V/h ,..... ...... (7) 
 
 s+l+n+n 1 
 In all the preceding formulae 
 
 R = the safe sustaining weight of pile in pounds, 
 
143 
 
 W = weight of hammer in Ibs. 
 
 h = height of fc.ll ir ft. 
 
 s = mean penetration of pile in ins. under the Ir.st blows of hammer. 
 
 The other two pile formulae which hive been most used in engineering 
 prr.ctice in this country are the following: 
 
 Sr.nder's formula: R = 1,2 fTh , (vfcere f = 1/8 to 1/3) , , . , , . . . . . (8) 
 
 s 3 
 
 Trautwine's formula: R (in tons) = 0.023 fUyffi (where f =1_ to 1 . . . . (9) 
 
 s + 1 3 12 
 
 R (in Ibs.) = 52 f \l3tfT . ...;........ (10) 
 
 s -f- 1 
 
 In r.ll cases h is the height in ft. of the fall of the hammer and. s is 
 the mean penetration in ins. uncer the last blows. These and all other pile for- 
 mulae are to b e used only for piles driven into earth or similar mrterial, and are 
 not to b e applied when they give loads greater than the column resistance of the 
 pile -in case it is to project in an unsupported manner above the material into 
 which it is driven, or when the results exceed the crushing strength of the timber - 
 SPECIFIED LOADS FOE PILES, DETAILS, G-ZMEH^L BK4ARKS 
 
 The loads which may be imposed safely upon piles will depend upon the 
 
 ) 
 
 character of the material which they penetrate, the thorougliness -^vith which they 
 have been driven, the size of 4 <*ie pile, the unbraced length of the pile projecting 
 above the material in which it is driven, and. the kind af timber. Evidently the 
 permissible lords plrc3d upon piles rlways /.vast be less than the crushing strength 
 of the timber, and they can be specified only as indicated by experience in the 
 bast practice. TJie building laws of New York City permit a load of 20 tons per 
 ~ypile only, while those of Chicago permit or.cn pile to carry a Icr. d of 26 tons; the 
 ton in crchcrso being 2000 Ib. The piles undor some ftcw York City buildings arc 
 probably the sr.irll:st that can bo found in structural practice, tho length iB S'omc 
 casos being 20 ft. or loss, and the diameter of th . butt not more than 10 ins. 
 Pilos of this character carrying such loads -re not allowed in thr; best engineering 
 practice although th?y arj permitted by municiprl regulations under budldings 
 In good engineering practice piles for such loads would not be permitted with butts 
 less than 12 to 14 ins. and with points not loss than 6 ins. Those srnr 11 b uilc.ing 
 Piles w-cll driven to what is ordii'.r.rily termed "refusal" mr.j perhaps c-Trj'' 2C tons 
 
^ 144 
 
 but they should not bo allowed to carry more. 
 
 It should bo strtcd in this connection that foundation piles for build- 
 ings do not project r.bovo the .r. tcrial in which they crodrivon and hone o they may 
 proporly cr,rry comparatively high loads. \7nila 40,000 Ib. is certainly -11 thr.t 
 the very small pilos frequently used in Hew York City ought to carry., 25 to 30 tons 
 is not too much to place upon^ a pile v;ith a poir.t of 6 to ins. rnc. r butt of 12 
 to 16 ins. as frequent tosts and experience have shovn. The number of piles rc- 
 quir6d under any building cm then bo determined at ore c by dividing the tot.~l 
 lo.-d to be carried by the specified load of 40,000 Ibs. in i-.-ew York, or 50,000 Ib, 
 in Chicago, or such value from 40,000 to 60,000 as the specifications of the en- 
 gineer may permit, v;hen not necessarily restricted by municipal lav;. 
 
 If piles are wo 11 driven flush with the surface of the rnrtor'ir.l which 
 they penetrate, actual test shows that they may carry without settlement as much 
 as 50 to 75 tons (2000 lb.). There are numerous instances in which loads on piles 
 under structures which do n ot settle run from 30 to 50 tons. If ;nuch unbraced 
 length of the pile projects abovj the material in which it is driver., the load 
 which it is to carry must be corrcspondigly docror.socl. It is difficult if not im- 
 practicable to express any quantitative relation between that unbraced length rnd 
 the dccrerso in load. There rre numerous inst.-ncos of bridge falsework in which 
 loads of 15 tons have been safely crrriec. on piles projecting 20 ft. above the 
 surface of the surrounding material, the piles themselves ranging from 14 to 16 
 
 ins. in diameter at the butt. It is probrbl^r safe practice to limit the loading of 
 
 / 
 
 r pile of frir size and well driven, which projects 15 to 20 ft. a'^ovo tl.e sur- 
 rounding material, to 15 tons per pilo and to 10 to 12 tons when tLe length of the 
 unbraced portion is 25 to 30 ft. The limitrtion of loads in &uch cases however 
 should bo determined by the judgment of the- engineer in viev of the circurnst-nces 
 which nry bo found in each case. It can only be said in generrl t or.r.s that if the 
 pilos rre in rivers vhc-rc the curr nts mr^ bo strong, more c: ution .:iust bo exorcised 
 not to overload piles with consider,'. bio unbraced length tlv n in still water. 
 
 In t>& C-SG of v .ildinj; found.rtions . it is very cs^eptirl tl-.rt .settlement 
 
145 
 should bo reduced to an absolute hiiniraum, and. if a sr.r.ll ~^our.t is unrroiclable, 
 
 that it should bo uniform. H,nco when piles ar? used for sue:? purposes they should 
 be driven to some hard arc" 1 , unyielding str -;un: ':ich i^-di" tcly overlies bc.f.roc:.-; , 
 or which has r. thickness of at least 12 -co 15 it. If piles .'re driver directly to 
 bodrock they mus t bo surrounded by r. ;:r.tvirir.l sufficiertly stiff to prevent any 
 lateral motion of their upper pr.rts. There is danger in such conditions of tho piles 
 swinging over lr.torr.lly or pivoting on the rigid supports r.t tho points. It is 
 bettor therefore unless tho possibility of lateral .notion is c ertr.inly r. voided, to 
 drive into a stiff .natorial to prr.cticrl refusr.l rather tirn to solid rock. 
 
 '.'/lion piles r.rc driven t IrrouGh some clnssos of m:.torir,l is v.'ill bo 
 r_cessr.ry to fit to their points iron or stool shoes, Cf. Fi^s.45. Those shoes ;.rc 
 isur,lly of hr.rd or chilled cast iron, although str.ps of \vrou j'ht iron bent to fit 
 around the points and spiked to the latter hrve &O;TD times been v.soc".. The cast iron 
 sho.js or points are made in a number of different patterns. They r.ro securec. to tho 
 bluntly dressed ends of the pilos by either straps or a single contr.-.l dov/ol. They 
 usually woi^h from 25 to 40 Ib. Shoes v/oi shins 28 to 30 Ib. hr.vo been found very 
 satisfrctory in pile driving through riprrp -re 1 , submerged sticks of timber, Fiss. 
 45 A, B, C, D. exhibit shoes of strap iron; 45 2, F, 3, arc oxrniples of cast iron; 
 consult "Dor Grundbau" by Strukcl, Plato 12, Figss 15-22. Figures 45 E, I, J 
 illustrate recent cast iron 3ioos for piles. The plus shoes, Fijs. 45 E,I, arc- 
 attached to the pile tip by four straps as shov.n, spiked to the pile. They arc 
 made of a variety of dimensions and vvoishts froai 14 to 212 Ibs. The sheet shoe, 
 Fig.45J, is intended for coffer dam work or for v;ide Squared piles and is ; rdc in 
 weights from 17 to 142 Ibs., sec horvy sheet piling. Fig. 38 of theso notes, The 
 points of both plug and shoot shoes, Fig. 45 H.I,J are chilled and the .-netrl cast 
 around the straps. 
 
 Shod piles may without dif f iculty b o driven through stone filled crib 
 v/ork either new or old or through any similar .,r. ss of nrterirl provided trie broken 
 stones are not more than a bout 18 or 20 ins. in their greatest dimensions. Pile 
 foundations have been successfully constructed for hcrvy retaining and bulkhe-d 
 
146 
 
 walls for the foundations of v/hich it has been nccess/ry to drivo shod pilos 
 ;: rough, "stor.s filler, crib v,oric 25 ft. in depth .' irplaco ovor mud and s ilt at Icr.st 
 50 ft. in depth b~lov; the bottom of the crib vcrl:. Indeed, thore have boor, instances 
 vhere unshod piles hr.vo been driven through submerged solid timber platforms. It 
 ill however be fourd impr: cticr.blo to drive even shod piles through masses of 
 boulders of cons id e-^able size. 
 
 In driving piles through groat d c-pths of soft material, particularly 
 if there bo masses in it relatively hard, it is nocossrry co orercise great ore- 
 caution lest the points of the piles wander. Piles suitr.blo to such conditions 
 must be vary lon^ r.nd their grcr.t loni'ths v.lll prevent t) on from bcin very stiff. 
 The points r.re therefore easily dofloctod fro.n their proper directions if t?j.c-3 r moot 
 oblicuoly/a harder portion of the .material than thr.t \/hich surrounds it. On the 
 other hand, if piles are being driven in very hard end r'-sistant ,:E.teri&.l, tlere is 
 danger of too hard driving. After a pile he. s been brought fir.nly to what is called 
 refusal it is '.verse than useless to continue hammering it. The continued jlovvs 
 of the hazier v/ill be very likeljr to brea 1 : the pile at a knot or other weal<: place. 
 Consult articles on pile driving, Eng. i>;ev/s, B51.49, 1902, pp. 292, 294. 
 PREPAMTION OP PILE !PO?S - CAPPING OF PILES 
 
 
 
 Piles should be cut off at a level belov; the permanent water line and 
 sufficiently far below to permit any timber grillage or other platform to be 
 permanently vet, so that It may be durable for an indefinite length of time. After 
 having been cut off, the piles are. capped usually by 10 31 12 in. or 12 :: 12 i 
 timbers. The capping timbers may 'preferably be of yellow pine or orko In the T'est 
 they mcy be Oregon pine, sometimes redwood s ticks ere used. Eedv-ood is weak relati e- 
 ly in strength but lias the advantage of high durability cgainst' decay. Hie greet 
 weight of timber platforms and of their superincumbent lords is usually sufficient 
 to hold the capping sticks in piece upon the piles, particularly where concrete is 
 rammed in the spaces betv/een timbers of each layer. Sometimes as an added pre- 
 caution, the capping s tic":s and grillr e timbers are drift bolted to- each other and 
 to the heeds of the pile^o Ck.rs shoul . "je- a::ercised not to injure t>s pile heeds 
 
147. 
 
 The grillage timbers above the caps are to be placed in one or tws continuous 
 layers of 10 x 12 ins. or 13 x 12 ins. sticks at ri 3 ht ar.gles to each other, as 
 shown in Fig.24. Each alternate stick in the upper layer, if there are tvo, may 
 be omitted, and the resulting space filled with concrete. On t!,e top of this grill- 
 age is to be placed the concrete or o'cher footins of the foundation wall of the 
 
 building. 
 
 If the material surrounding the piles is very soft it is sometin-.es ad- 
 visable to excavate it from 2 to 4 or 6 ft. b*10* their tops and fill the resulting 
 space with concrete solidly rammed in among and around the heads of the ?iL 
 Should the material at the bottom of this excavated volume be very soft, it wi. 
 be necessary to fill in 10 or 12 ins. of sand or place a layer of boards on which 
 to start the concrete mass. By this d evice the tops of the piles will be firmly 
 collcred and held in their relative positions, thus adding to th* general .stiff- 
 ness of the foundation, as shown in -Figs. 39 and 40A. The b reat advantage of cap- 
 ping piles tot* a layoff coraraio is tet'S it does not require the piles to bo 
 aligned carefully or to b e cut off at cxrctly the same level. This is particularly 
 true where the concrete is reinforced as in footings, Fig. 30, 
 
 . Where it is necessary to sav/ off pile heads, under water, the best 
 results can be obtained by a circular sav: mounted on a vertical shaft supported 
 upon a movable frame, the frame sliding up and dovn between t he leads of an ordin- 
 ary pile driver, Fig.46. See also Fowler, Ordinary Foundations, Fi :3 .35, P .57. The 
 saw is operated by machinery preferably by an electric motor, installed upon the 
 pile driving scow or upon a temporary platform. For a complete description of 
 apparatus similar t'o the above, see Eng. Hevs,Vol.46, 1901, P .282. The work is 
 sometimes done by hand with an "alligator" sav, which consists of a steel blade 
 similar to a large cross cut saw, mounted on a rigid wooden fra,e and swung back and 
 forth from above. In the best work, divers occasionally are employed. In tidal water 
 great care must be exercised if it is necessary to have the tops cut off at 
 elevation. The position of the piles under water is sometimes *k* by a slight 
 wooden frame called a "spider". 
 
: t 
 
148 
 Although t>e positions in which the piles r.ro to b a driven are 
 
 specified and precisely indicated on plans, it usually is not possible to maintain 
 such accuracy when they are driven,, The plan of an actual foundation when ready 
 for capping may lose all s ambiance to the plan on paper but usually it will not 
 be difficult to draw the pile heads sufficiently into lines to be properly capped 
 
 c.nd with the specified number of piles within t>,s outline of the foundation. 
 
 i 
 
 PIgES I IT SOFT .-G-BOUMP 
 
 In alluvial or filled land or swamps it is frequently impossible to 
 drive piles to a solid bottom. In such cases reliance is placed wholly upon skin 
 friction. Piles can sometimes be pulled down by a block and tackle, pushed down , 
 by the deadweight of a hammer, or driven by a few very light blows. Nevertheless 
 after the. mud has had time to settle for 24 hours or longer, a large bearing- 
 resistance maybe developed. In these cases serious settlement may occur, especial- 
 ly if the super-structure is subject to shocks or vibrations fro.-.i moving loads, 
 Such piles are usually driven from 30 to 60 ft. or more into the soft material 
 There are many sites for railway and other structures which will not permit a pile 
 to be driven to a solid bearing. Goal docks have been built on the banks of the 
 Hudson River at Hoboken, 1J,J, , railway trestles have been constructed along the 
 northern shores of the C-ulf of Mexico, anc. along the alluvial banks of rivers, on 
 Tile foundations in which the piles have reached no solid stratum. The recent 
 "ork on the Lucin Cutoff, Salt Lake, for the So. Pacific Railro?d has been mentioned 
 in an earlier paragraph. 
 
 On account of this possibility of serious settlement, piles for 
 
 building foundations should always be driven to a firm bearing. If it is impossible 
 to reach firm bearing, very high or heavy buildings should be prohibited. If piles 
 support a superstructure a considerable distance above ground, or if they are 
 driven through very loose material to solid rode, there is denser of the structure 
 swinging over laterally under heavy loads, hence structures built in this manner 
 should be solidly brrcsd laterally. To give increased lateral stability., piles fre- 
 :.itly are driven on a b.rcter. This recuires c specirl for/.! of pile driver. Batter 
 
149 
 piles are used principally for railroad trestle work, where the outside piles of 
 
 each b ent are sloped downward rnd outward. Sometimes a ro-, of Tiles is driven on a 
 batter around the outside of a building or pier founletion to increase the resist- 
 ance to lateral stresses which might arise from earthquakes ox blors from moving 
 ships or drift. This method was adopted for the pile foundations for the Great 
 Western Power Company's paver ststion along the Oakland Estuary, primarily it is 
 stated to provide stability cgainst earthquake shocks. 
 
 Occasionally when a pile is driven point downward, as is the usual case, 
 wet sand, quicksand or saturated silt may force the pile out nearly as fast as it 
 is driven. Relief from this difficulty may sometimes be found liy sharpening the 
 butt end of the pile and driving it with the point up. The larger end of the pile 
 is then in the sand and will hold it in place. 
 
 In the Effort to reach firm bottom at great depths piles are some tines 
 spliced. This may be done by saving off the ends s quare, ua ng a dowel bolt 2 ft. 
 long, 1" to 2" in diameter, driven in slightly smaller holes an equal distance 
 into each pile. In order to give lateral stiffness, it is better to use, in 
 addition, iron straps called "fish plates", bolted or spiked on the outside. 
 
 It will seldom be advisable to drive piles of proper size less than 
 about 2'6" betweem centers, and if they are large 3' will be the limiting minimum. 
 If they are too close together it may be difficult to get them down to the desired 
 penetration without causing others already driven about them to rise. 
 
 Reference has been melde to the use of piles as a meens to examine a 
 foundation site for t he purpose of ascertaining its bearing cape city ( See these 
 notes, Chap. I ). 
 
 EFFECT pi? L 
 
 On The 
 BEARING PO r; ER ~CF TIMBER PILES. 
 
 Study the report by L. Wagoner and W.H. Heuer, 1908, which describes a 
 plan for the development of San Francisco Harbor, its comnerce and docks; particular- 
 ly the articles on piers and piling., pp. 34-39. Here are described tests for pile 
 bearing capacity made in New York City, 1902, to determine the actual bearing paver 
 
*fcte>a 
 
 ,:,:..: id 
 
 . 
 
 . 
 
 - .. 
 
 .' Oviil 
 
 ;,' :.- : 
 
 <'*'-- . .1. '-' 
 
 
 
 ,-. . .- i -s* j'l . - M 
 ' - ; '' :;;j J ' 
 
 : v : ' '' ; 
 
 |gj j 7U " 
 
 LfTfjj ^ 
 
 jt .^i, 
 
150 
 
 of wooden piles in soil practically identical in character to that along the San 
 Francisco water front. Twenty piles were tested, 79 to 85 ft. long; 14- to 22" 
 butt diameter; 5" to 10" point. Each pile was driven in water about 23 ft. deep; 
 the penetration in mud varying betv/en 45 and 52 ft. 
 
 Careful records were kept, 1. of dspth of penetrctiov into niud from own 
 weight; 2. additional penetration due to weight of 5300 Ib. ha.nner; 3. penetration 
 due to each blow from ha rimer falling 10 ft. with penetretionobtained at the end o' 
 every 5 consecutive blows; 4. final penetration due to each blow in the lest 5 
 blows. Piles were arranged in three groups of four piles eechand one group of 
 8 piles. On each group a platform was built loaded gradually with increasing 
 weights for 27 days, and then allowed t o re.aain another 27 days, noting subsidence 
 and conditions of collapse or other destruction. 
 
 On the 20 piles referred to, 12 were legged by bolting end spiking to 
 each pile 4 pieces of 5" x 6" timber 30 ft. long; the lov;er ends of these timbers 
 being 5 ft. above the pile point. Four had bolted to the.n 2 pieces 5" x 6" and 
 2 pieces 4" x 10", ecch 30 ft. long. The remaining 4 piles had no lagging. 
 
 The object in lagging was to determine if possible the increased Iced 
 such piles would sustain d ue to their increased"-" sectional and superficial areas. 
 
 Due to their own v/ eight the piles penetrated mud 3 to 15 ft., average 
 11 ft. The hammer caused an additional average penetration of 7.5 ft. At the 
 tenth blow the average penetration of unlagged piles wcs 32 ft,, of legged piles 
 only 17 ft. The unlagged piles reouired an avenge of 16 blows to 3 et full pene- 
 tration of about 49 ft.; the legged piles required an average of 63.7 blov;s, of 
 10 ft. fall, to obtain about the same penetration. The Isst five blows caused un- 
 lagged piles to penetrate 3 ft. or 0.6 ft. per blow, while legged piles sanjfc 1.2 
 
 * 
 
 ft. total, or an average of 0.24 ft. per blow. The final tests on loeding plat- 
 forms showed that unlrgged piles sustained each a weight of 18.7 tons; the legged 
 piles supported 28 to 34.6 tons each. All platforms settled somewhat in the 27 days 
 ile loaded; the maximum subsidence of any one pile being 1 -11/16", 
 
 These Kev/ York experiments incUcete thrt the legged piles in the 30 
 
151 
 lowest ft. of their lengths, presented about double the superficial area of 
 
 unlagged piles to frictional resistance and sustained nearly twice as much weight. 
 The cost of the lagging added about 30 percent to the cost of the driven pile v/hile 
 producing about double the bearing capacity. 
 
 It. is questionable whether lagged piles should be recommended, due to 
 their cost and the uncertainly of securing a lasting bond between the pile and 
 its lagging, 
 
 Recently piles, both wrapped v/ith metal fabric and without it, have been 
 covered with cement mortar by cement gun. If in this way the cement mortar can be 
 made to permanently adhere, not only should the pile be protected bpt increased 
 in bearing capacity. 
 
 When using single piles for piers and docks and where additional expense 
 is justified, the most satisfactory nethod for increasi ng bearing capacity and 
 lateral stiffness is to use the so-called cylinder pile described in later para- 
 graphs, Figs. 49 and 49A. 
 
 See the .Wagoner and Heuer report, page 39. for illustrations of a proposed 
 method for sinking lagged piles, reinforced at their upper ends by a protectirg 
 timber cylinder filled v.lth concrete and reinforcement. 
 
 SCRLV7 PILES 
 
 Screw piles usually are lade entirely of metal, though wooden stems 
 occasionally may be used. A common form consists essentially of a hollow iron 
 shaft 3" to 8" in diameter, whitJhrmay be made in sections. At the lower end ofthe 
 shaft are one or two turns of a cast iron screw blade, similar to an ?uger, the 
 blade being 1 1/2 to 4 or even 6 ft. in diameter, weighing frora 600 to 4000 Ib. 
 The blade or screw should be fastened s ecurely to the s fiaf t by s et screws, pins 
 or bolts. Screw piles are sunk by turning them, usually by hand, with long levers, 
 ropes or a worm gear working in a large toothed wheel fastened to a shaft. They 
 may be driven in almost any formation, though herd dry sand is the most difficult 
 to penetrate. Care should be exercised to keep the shaft verticr.l and to prevent 
 twisting it off. Sinking nay b e greatly helped by :he use of the water jet, which 
 
152 
 is easily operated at the point of the screw blade, water being supplied through 
 
 the hollow shaft of the pile. 
 
 Screw piles have been used more extensively in Europe than in the U.S 
 One of their peculiarities is the development of a high resistance to pulling, as 
 well as to b earing. This property renders them especially valuable for marine work 
 such as for lighthouse foundations or beacons. As no driving is necessary, they 
 are usaful where the shock from a pile driver would be undesirable, a s in the 
 bottom of foundations cons'tructed close to existing heavy structures. They may be 
 useful in certain specil c sses, because of the possibility of sinking them with 
 less headroom than that needed for ordinary pile drivers. A good illustration is 
 their use for some foundations in New York subways and tunnels. See Patton's 
 Fourdations, pp. 497-500. Large screw piles have been used to some extent for 
 founding bridge piers in southern swamps. 
 
 Fig. 47 shows the base of screw piles driven by hydraulic screwing 
 machine into rock chalk. Cf. Eng. Hews, Vol. 44, 1900, p.' 90; Proc. Inst. C.E. 
 of Gt. Britain, Vol.139, p. 302. The piles were screwed into the hard chalk to 
 depths between 10 and 15 ft. and into softer chalk 15 to 36 ft. The piles were 
 built of segmentral iron 3/4" thick, 9" inside diameter, 10.5 ins; - diameter, 
 outside the barrel, and 16 1/4" across the flanges. The lower part or shank was 
 of solid forged iron, 8" diameter with the end swelled and turned to fit the 
 inside of the segment iron, and having a collar upon which the latter rested, the 
 connections being made by throe stoel riv&ts. The lower end of the shank was made 
 to fit the socket of a 4 ft, cast steel screw blade of 6 ins. pitch of thread. The 
 length of the solid shank was between 10 and 20 ft. and that of the whole pile 
 varied between 30 and 57 ft. The references give a full description of the hy- 
 draulic machinery and the pioblems encountered in sinking the piles. 
 
 In an article by .T.\7. Barber, Proc. Inst. C.E. of &. Britain, Vol. 138, 
 p. 344, entitled "Victoria Bridge over the Dee of Queens'farj-y, England" is given a 
 description of screw pile foundations for the piers of a movable bridge. The t.vo 
 piers are formed of clusters of screw piles each cluster consisting of 10-6 :1 dia^ 
 
153 = 
 
 solid steel piles fitted with mushroom screws, 3 ft. diameter and screwed to 
 depths of about 18 ft. into the river bed, which is a fine sane, extending to a 
 depth of probably 100 ft. Fig. 48, cf. Eng. Eews, Vol.43 1900, p. 46, sha's the 
 pile screw to have dished flangc-s and an Increasing pi tch irwards. T'.e dishing 
 of the flange considerably strengthens the screv; and incr-f.ses its bearing power, 
 while the graduated pitch enables it to enter with less slip than usual, and. to 
 clear itself better then the ordinary flat flanje screv: of regulai ;>itch. Ec-Cl'. 
 pile res tested with 30 tons deadload for 3 days end ths greatest settle;n3nt 
 observed was 3/8 ins. 
 
 In Eng. Mews., Vol.50, 1903, pp. 331-358, is given a description of tl:.e 
 Pennsylvania Railroad tunnel under the Hudson Kiver, at tier/ York City. This 
 reference and Fig. 48A illustrate a hervy screv/ pile foundation for the tube 
 tunnel, Cf. also Trcns. An. Soc.'CoL., Vols. 68-69, 1910. 
 
 DISK PIL5S 
 
 Disk piles are similar to s drev: piles but have flat or conical disks 
 instead of screv/ blades at the bottom. 2hey must be sunk entirely by \vater jet = 
 Their uses are very similar to those of s crew piles. In soils in which they ^y be 
 readily sunk, the3^ are cheaper than screw piles, e.nd equally efficient. The l:aft 
 may be aade of s ections of screv.- pipe 4." to 9" in diaroeter, similar to hecvy r/eter 
 pipe, or any convenient odd lengths. If the sinking is stopped by obstructions . 
 such as stiff clay pockets, it can usually be started ar;ain by lifting up the pile 
 6" to 1 ft. and dropping it suddenly, keeping the water jet going :TE rnv/>dle,Disk 
 piles were, extensively and successfully used for the foundations of ths Coney 
 Islcncl Pleasure Pier; consult Trans. Am. Soc. C,L. , Vol. 8, pp. 227-237. Both screw 
 and disk piles are used for moderate depots, ordinarily from 15 to 30 ft. 
 
 PROT3XTEI! PILES. 
 
 For dock and trestle work pile foundations usiis.llyaie of short life, 
 r /herever piles project above low tide their tops are subjected to severe dec: -in^ 
 agencies of air and water. Alternate v;etting ?nd d.xying groatl^ 7 shortens t" e 
 timber's life. Moreover, particularly in v/cr.a ->;aters such piles when unprotected 
 
',15. 
 
154 
 may be exposed to destructive boring by sea worms (teredo navalis and limnaria 
 
 terebrans), which feed on timber. 
 
 In recent years the r e inf orced concrete pile has made its appearance to 
 Replace v/ood because it is not subject to the same destructive agencies. Where 
 wooden piles are used they now frequently are protected by enclosing envelopes 
 of metal or concrete, Bhese envelopes reaching only to cl epths a f ev; feet below 
 low tide, But in many locations it is not feasible to use either reinforced 
 concrete piling or to protect with metal or concrete the exposed tops of v/ood en 
 piles. Where timber must be used without mechanicl protection it should be treated 
 by chemical means to toughen it against decay and to shield it as far a 3 possible 
 from sea worms, 
 
 CHEMICAL PBESERVi-TIBES FOB TIMBER. 
 
 Since 1830 the chemical treatment of timber to increase its lasting 
 qualities has been much studied by chemists and engineers. The great advances in 
 chemistry, particularly the investigations of coal and tar products, have made 
 substantial strides possible. The development of railroads requiring great 
 quantities of v.x>oden ties has made the study of timber preservation imperative. 
 It is for railroad ties and for foundation piles, particularly those exposed in 
 docks and trestles, that a study of chemiccl timber preservatives is demanded. 
 While there are many substances which have been advertised as timber 
 preservatives their are only four compounds that deserve particular mention: 
 
 1. corrosive sublimate (kysnizing) 
 
 2. sulphate of copper 
 
 3. coal tar oil, or creosote (creosoting) 
 
 4. chloride of zinc ( bur netti zing) . 
 
 Of these four antissptics creosote is the most extensively used. 
 
 To apply chemicals to timber, many schemes of treatment or processes 
 have been advanced and many have failed commercially. The differences in processes 
 lie chiefly in the moi e of injection of the chemical. We may mention four methods 
 of injection:- 1. steeping the wood for several days in the chemical selected; 2. 
 vital suction of chemicals by the growing tree; 3. forcing solutions through 
 freshly cut logs by hydraulic pressure in the open air. 4. forcing solutions by 
 
j >. 
 
155 
 hydraulic pressure applied in a closed vessel containing the wood. The first 
 
 method is still employed in kyanizing; the second and third have been abandoned, 
 the fourth gradually modified and improved is no\: the most universally used for 
 creosoting, Consult Apo. F, the Preservation of \7ood, Jolmson's I-Iaterials of Con- 
 struction, ed. 1909, p. 776, Creosoting is the best of all preserve tives , v .hen \vell 
 c'one, it is t: e only method effective against sea v/orms ; but creosoting is the 
 most expensive treatment. In general practice 8 to 10 Ibs. of creosote is injected 
 par cubic foot of timber, v;here the timber is exposed merely to. the v:eather. For 
 tisiber exposed to tsea v. r orms usurlly 10 to 20 Ib. per cu.ft. of timber is used. 
 
 Wood should 1 , not be cut after creosote treatment. Such cutting removes 
 t: e outer protection v/hich is the most effective. Titober to be creosoted should 
 be first frr.med, notched-, etc. The amount of creosote absorbed depends upon the 
 density of the v. ; ood. The greatest effects therefore sre obtained v.ith less dense 
 v.'oods. Creosote improves cheaper open grained \7oods more tlan the more expensive 
 hard varieties, a fortunate condition. Timber and railway ties properly creosoted 
 v;ill last from 8 to 20 years, piles exposed to sea.v.orms from 10 to 20 years for 
 good work and hig> quality creosote, 
 
 Consult "Experiments on the Strength of Treated Timber 1 , by v .'.X,Katt., 
 U.S.Dept. Agriculture, Forest Service Circular 39. The conclusions reached, page 
 21, are: 
 
 1. A hi-gl. degree of steam is injurious to wood. The degree of steaming 
 v/hich produces harm depends upon the quality and seasoning 1 of the timber, a Iso 
 upon the steam pressure anc. duration of its application. The limit of safety for 
 loblolly pine is a bout 50 Ib. for 4 hrs. or 20 Ib. for 6 hrs. 
 
 2. Zinc chloride does not v/eaken v/nod under static loading. Bat there 
 ere inflections that the v/ood becomes brittle under impact. 
 
 3. The -Dresence of creosote itself does not weaker timber. It tends 
 ho\ve ir er to retard seasoning. 
 
 C, S. Smith, in a paper entitled "Preservation of Piling ligcinst ukrine 
 
 Wood 
 ^Borers", U.S.Dept. Agr, , Forest Service Circular 128, enumerates different methods 
 
 for orotecting exposed portionsof pile, see pp. 3 - 11. Ee enumerates:- 1. external 
 coatings; 2. baric left or. t: e pile; 5. thin planks over the pile surface; 4. flat 
 headed nails forming c cor.tiruout covering, 5. hot paints, tars, asphalts. , etc. 
 
156 
 applied alone or with fabrics; 6. metallic feheetings of copper or zinc or 
 
 sections of iron pipe; 7. cement casings with or without spacing between the pile 
 and casing; 8. earthenware pipes with cement joints encloa. r.g the pile; 9. pre- 
 servative t reatmants. To leave bark on the pile is e protection against marine 
 borers as Ions s.e the bark remains intact; but bark encoureges the breeding of 
 inocctc, and. growth of fungi. It ruickly deteriorates rnd is re^c.ily dislodged by 
 blows. To be effective en external coating must be absolutely intcct, covering 
 the whole exposed surfr.ee of the wood. External mechanicd coatings or she? things 
 are expensive. They ircres.se the life of the -aile only to the extent of their own 
 life. Metal casings are costly and at first efficient but resdily corrode. Mr. 
 Smith concludes that denser timbers should never be treated chemically for 
 piling because of the difficulty of securing a satisfactory penetration of -;he 
 oil; that timbers of open grain like loblolly pine are easily penetrated end 
 embody all the characteristics of an ideal pile timber. 
 
 Consult "Wood Preservation in the U,S, , 1909" by <", F.Sherfesee, U,S, 
 
 "* 
 
 Dept. Agr, 7 Forest Service Bulletin 78, p. 25. The author argues:- The average 
 life of piles in the U.S., untreated, is 3 1/2 years. He estimates thr.t if all 
 the piles were tree ted their average life v.ould be 21 1/2 years. Assuming 
 4,000,000 e::posed piles in use, the annual replacement for all piles untreated 
 would be 1,140,000; for all piles treated, 190,000. Such & status would give an 
 annual decrease of 950,000 piles needed, or cfcout 159,600,000 ffit. board measure- 
 For the above figures he estimates the average pile to be 40 ft, long and. to 
 contain 168 ft. board measure. These figures are certainly suggestive. Assuming 
 piles untreated to c ost $0.20 per lineal ft., the srving in pile timber alone 
 vould be 0.20 x 40 x 950,000 = $7,600,000, In addition therewould be a further' 
 saving of cost for driving, cost for altering or rep Ice ing other parts of 
 structures rne.de necessc.r3? by the remove 1 and replacement of piles, the cost of 
 delays and interruption of business. Th?se are strong arguments in fcvor of 
 reinforced conciete piles wherever 'their use is justifiable. 
 
 Consult a discussion upon "Tentative Specifications for Creosoted 
 
. r 
 
 ',-', " 
 
167 
 Douglas Fir Piling and Lumber for Use in Marine Structures", and "Notes en 
 
 Creosote Oil Specifications", published in the Second Annual Progress Report 
 by the San Francisco Bay ilarine Piling Survey, January 15,1322, pp. 58-72. On 
 page 64 is given the following proposed specification for creosoto oil:- 
 
 "The oil shall be a distillate of coal-gas or colce-oven tar. It shall 
 comply with the following requirements: - 
 
 1. It shall not contain more than 3$ water, 
 
 2. It shall not contain more than 0.5$ of .latter insoluble in benzol , 
 
 3. The specific gravity of the oil at 38 C C co ipa red with vater at 
 15.5*C shall be not less than (D.045. 
 
 4. The oil shall contain from 5 to 10$ tar acids. 
 
 5. The oil shell contain not less than 10$ naphthalene. 
 
 6. The distillate based on water-free oil s:.^all be within the 
 following limits: 
 
 Up to 210*0 not more than 5% 
 
 Up to 235 P C not moie than 25$ 
 
 Up to 315C not less than 45$ nor more than 75$ 
 
 Up to 355 C C not less than 70$ nor more than 90$. 
 
 7. The specific gravityof t:.e fraction between 235'C and 315'C 
 shall be not less than 1.03 at 38*0 compared with water at 15.5'C 
 
 i The specific gravity of the fraction between 315"C ai'd 355 C C 
 shall be not less than 1.09 at 38 C C compared with water at 15.5*0. 
 
 8. The residue above 355 P C shall have a float-test of not more 
 than 50 seconds at 70C. 
 
 9. The oil shs.ll yield not more than 2$ colce residue, 
 
 10. The foregoing tests shall b e .7E.de in cccordance v/ith the 
 standard methods of the American r ;ood Preservers' Association, v/ith the 
 exception of those for tar colds rud naphthalene, s,s specified in clauses 
 4 and 5, which shall be made in accordance v/ith the methods of the Amer- 
 ican Railv/ay Engineering Association. B 
 
 The student is urged to 'examine recent reports and transactions of the 
 Wood Preservers ard Railway Association just Mentioned; also those of the 
 National Association of Railroad Jj -'ie Producers. 
 
 PROTECTED PILE PLATERS 
 
 In San Francisco Bay for docks and rc.ilway moles , it h s been frequent 
 practice to drive piles singly or in clusters of 2, 3 or more, protecting their 
 tops bove the mud line by coffer dcms of timber or metal, filling the annule.r 
 space between Ike piles end coffer den with concrete, plain or reinforced v/ith 
 fabrics or rods. Fig. 49 represents a typical design used in Sc.n Francisco for 
 
 
 
 wharves. The piles take all of the losd. In the case shown there are 3 piles, 
 sawed off at different, levels, to give . better bond with the coffer dsrn con- 
 crete, After the piles rre usced, wooden, steve cylinders, ba.nded, sre driven or 
 v.'ater jetted to propei depths beneath t he mud line. The cylinders are tlen sealed 
 
158 
 
 at the bottom, p.-mped out, and concrete deposited. Expanded metals o.r bars are 
 introduced as reinforcement. The reinforcement is placed at a sufficient dis- 
 tance from the concrete surface to be thoroughly protected. For t he v.ork shown 
 in Fig. 49 the r einforcement was placed 4" from the outer surface of the concrete. 
 In the course of time t he timber cofferdam is destroyed by t he Teredo and. by 
 decay, leaving the armoured concrete as a protection to the piles. 
 
 A considerable number of cylinders of this type were sunk in 1908 for 
 the passenger and freight slip, \7estern Pacific Eailroed, Oakland mole, California 
 Thegrecter part of the dock rests upon ordinary unarmoured piles, some of which 
 wer creosoted. The cylinder piles v/ere used to support the buildings and other 
 heavy s tructures for the freight slip and its machinery. There were 4 wooden 
 steve cylinders 6 ft. outer dicmeter, 15 cylinders 4 ft. outer diameter, both 
 sizes 5.6 ft. long. The timber fo *he wooden stave cylinders was made of 
 Oregon pine sticks 4 1/4" by 4 1/4", sized radially to 4" and beveled to give 
 tight joints. The 4 ft. cylinders hed 45 staves with bands every 2 ft.;2 bands 
 were pieced at the lower end or cutting edge and one band e.s a finish at the 
 top, at the elevation at which the cylinder was sawed to level. 
 
 Obviously this type of construction is applicable to the protection of 
 one, two, or any number of pileso In some cases steel shells have been used 
 instead of wooden ones. The steel shell has some advantages in driving, but 
 only with difficulty can it be c ut off at the pjroper elevation at the top. 
 Steel shells will resist the teredo but eventually would corrode and rust 
 away, leaving the interior concrete to protect the piles. Therefore this concrete 
 should be stiffened with an embedded envelope of mesh reinforcement, distinct 
 from the outer shell. 
 
 Steel shells or wooden stave cylinders similar to the above may be 
 driven or water jettsd to refusal to considerable d epths , ercavated end then 
 filled with concrete reinforced as desired. The upper portions of the shell 
 
 eventually whether of- metal or wood will be destroyed. V/hen such structures 
 
 no ordinary timber piles within them, as in Fig. 49, we get the transition to one 
 
 . 
 
'."fl-. 
 
159 
 to one form of reinforced concrete pile, na/nely, that form in which the 
 
 envelope or form is driven to be subsequently filled with concrete deposited in 
 place. Within the last ten years we have ssen the transition carried farther to 
 piles molded of reinforced concrete, fthich after proper aging, are transported 
 to t he foundation site and driven just like wooden piles. 
 
 PROT2CT5D CYLINDER PI IE 
 (Howard C. Holmes, Patent IMP. 920061) 
 
 This pile is illustrated by Fig.49A. It was first used in San Francisco 
 for docks built in 1912-13. For proposed bulkheads in South San Francisco Harbor 
 Projects, 1913, such piles were recommended; the cylinders projecting 10 ft. 
 above mean low v.ster, extending down 20 ft. from mean low water to mud bottom, 
 with 15 ft. more penetration into mud, making the tctal length of cylinder 45 
 ft. The untreated enclosed pile is cut off at mean low water level end has a 
 total length of 60 to 70 ft. 
 
 Around fcach pile is sunk a wooden cylinder 26" inside diameter. The 
 cylinder is built of 3" staves hopped with bands and otherwise constructed simi- 
 lar to the larger cylinders already described in Fig. 49. At the cylinder bottom 
 is provided a cutting edge. The cylinder is driven by an ordinary pile driver 
 using an enlarged cap or driving heed which like e hat or plug fits '^ e to P f 
 the cylinder. If driving is not easy the water jet is employed. A rope gasket 
 between the cutting edge and wooden pile makes a reasonably water tight joint, 
 TVhen the cylinder is fully driven it is pumped out, the concrete is deposited 
 in the dry and not until the interior has been inspected. Usually reinforcement 
 similar to thst of a building column is introduced. Such piles can be built to 
 make a monolithic i .ass with the reinforced concrete girders, beams and floor 
 slabs of z dock or bulkhead. Or if the dock floor is to be of timber and 
 structural steel, or all of timber, the superstructure can in any case be firmly 
 anchored. Eventually the wooden stave cylinder decays, but the reinforced 
 concrete remains to protect the pile. 
 
 A 70 ft. creosotod pile at San Francisco in 1913 cost about 48 cents 
 per lineal ft. or a total of 033.60. The driving cost was $4 - $5. per pile, 
 
160. 
 making a total cost for pile in place 38.60, or 55 cants per lineal ft: 
 
 Under similar conditions the cost of- an untreated 60 ft. pile protected 
 by v.o oden cylinder was:- for a 60 ft. untreated pile at 15 cents per lineal ft. 
 $9.00; $4.00 for driving, making a total of $13. in place. A- 45 ft. cylinder- 
 with concrete reinforcement complete as in fig.49A cost $1.50 per lineal ft., 
 or $67.50 total. The combined cost then of pile and protecting cylinder was 
 
 $80.50. 
 
 In other words a 60 ft. untreated pile protected by a cylinder cost 
 
 
 about $80. ; while' a 70 ft. creosoted pile t not otherwise protedted cost $38.60, 
 
 under the seme conditions for San Francisco harbor work. The cylinder piles then 
 were twice as expensive. 
 
 But t'e cylinder piles have about double the bearing capacity which 
 . for dock work enables the piles to carry double floor loads for the same floor 
 framing. . Their use might justify a larger spacing of cylinders under the dock. 
 !Dn general however the great merit of protected piles, like fig..49A, is their 
 durability, their increased bearing capacity and their lateral .stiffness against 
 thrust of flowing earth or surging ships. 
 
 Cluster piles like Fig. 49 stand as types between wooden pile construction 
 on the one hand and the he: vier forms of deep foundations on the other. From this 
 view point the coffer dam for a bridge pier may be considered a huge cylinder 
 of complex construction to withstand temporary loads and stresses, within whose 
 enclosing spcce many wooden piles or reinforced concrete piles may be driven; 
 or within which concrete may be deposited below water and masonry laic 1 in tl~e 
 dry. From the coffer dam it is only another step to t he pneumatic pile, to 
 the pneumatic caisson and to the huge piers sunk by deep well dredging to the 
 greatest depths yet reached by foundrtion science. 
 
 ADDITION! FJLFgiLlJCES 
 
 1. Pilos and Pile Driving; by A. L.L Wellington.; 1833 . 
 
 2o ;. treatise on ..lasonry Construction, by 1. 0, Baker, 10th ed. , 1909; 
 C>3, ,CV "n. 367-404, 
 
,. 
 
 
 . 
 
 
 It: 
 
 
 
161. 
 
 3. Der Grundbau; by M.Strukel, 1906, p. Ill; plates 12-18 
 
 4. A High Powered Locomotive Pile Driver, Carrying its own Turntable; 
 Eng. Kev7s, Vol.62, Nov. 18, 1909, p, 538. 
 
 5. Protecting Piles Against the Teredo Havalis on the Louisville r.nd 
 ueshville R,3, , by R.ltontfork, Tians. #31. Soc. C.E. Vol.31, 1394, p. 221 
 
 60 Concrete Shell Casings for Protecting Wooden Piles -against the 
 Teredo; Eng. News, Vol. 63, Jan. 1910, p. 30. 
 
 7. Supporting Power of Piles, by E.P.G-oodrich; Trans. Am. Soc. C.E. 
 Vol.48, 1902, p. 180. 
 
 8. Pile Driving Formulas, their Construction and Factors of Safety; 
 by C.H.Haswell; Trer.s. Am. Soc. C.E. , Vol.42, 1899, p. 267 
 
 9. On the I-Ias.nyth Pile Driver; by D.J.v.Mttemore, Trans. Am. Soc. C.E. 
 Vol.12, 1883, p. 441 
 
 10. Uniform Practice in Pile Driving; by J.F.Crowell, Trans. Am. Soc. 
 C.E,, Vol.27, 1892, p. 99; Discussion, pp. 129,589. 
 
 11. Specifications of Am. Railway Eng. end Maintenance of Way Assoc. ; 
 Eng. News, Vol.51, 1904, p. 264. 
 
 12. Test Loads of Piles Driven with a Steam Hammer at San FrancJsco; 
 Results Compared with Formulas for Bearing Power, by J.J.Y/elsh, Eng. fiev/s, 
 Vol.52, 1904, p. 497,503. 
 
 13. Pile Foundations for Buildings; International Correspondence School 
 Structural Engineering Course, Chapter on Heavy Foundations, pp. 51 -63, 
 
 14. The Relation of lion-Pressure Process of Wood Preservation to 
 Pressure Processes, by V, F, Sherfesee, Eng. Sews.Uarch 4, 1909, Vol. 61, p. 230 , 
 
 15 The Fractional Distillation of Coal-Tar Creosote, by A. L. Dean and 
 E,Bateman, U-S.Dept. Agr. , 'Forest Service Circular 80. 
 
 16. The Open Tank: Method for the Treatment of Timbers, by C.G. Crawford, 
 U,S,Dept. Agr,, Forest Service 'Circular 101. 
 
 17. The Analysis and Grading of Creosotes; by A.L.Dean and ,Bateman, 
 U,S,Dept. Agr,, Forest Service Circular 112. 
 
 18. The Lstiration of ..ioisture in Creosoted v .'ood, by A,L.Dean,' U' S.Dept, 
 Agr., Forest Service Circular 134, 
 
 19. The Efficiency and Cost of Conciete for the Preservation of Piles 
 Exposed in Sea Titter, by C>G,Korton, ic.t. Assoc. Cement Users, paper read at 
 Annual Meeting, Jan. 21-25 ; 1910. 
 
 20. Soft Ground Foundations, Panama-Pacific International Exposition, 
 Eng. :.]Kews,Vol.72, 1914, p. 250 
 
 PROBLEMS - Bearing Piles 
 
 1. A R,R. trestle is founded in a sv.'arap on 6 pile bents, spcced 12 ft. 
 Assign as the nax. possible load on one bent a dead load of 900 Ib. per lineal 
 ft., plus twice the :&.?.. possible live load from "Cooper's E3P' 1 loading. 
 Assume a frictional r esistarc e of 200 Ib. per sq.ft., and a direct bearing par/ er 
 of 2000 Ib, per sq.ft. If piles crnbe se-cured 14" in diameter at the butt and 
 10" at the point, hoi.' far should they be driven below the surface? 
 
 2. A corrugater reinforced concrete pile was sunk with water jet in 
 fine, compact sand. The pile tet^^crBfi^fection with diameter {mersurod parallel 
 to thoooldoo') of 16 inc. at the butt and 11 inc. at the point, tapering uniformly 
 for its full length of 36 it. The corrugations were 3" oernicircle-c extending 
 
 the full length of the pile. Compute the bearing power, accoming frictional 
 resistance on' th; cido of the pile at 500 Ib. and <fir:ct bearing power at the 
 point at 8000 Ib. per sq.ft. Soc Fig. 56. 
 
 3. If the total p;netration of a pile was 7.5 inches for the ]a st 5 
 blows of a 3000 Ib. he.rn.-nor, falling freely from a point 18 ft. above the top 
 of the pile, compute the safe load by Eng. Mows formula, Piles 40 ft. long, 
 average diameter 11 ins . 
 
162 
 
 4. It is rocuirod to drive piles with a 2700 lb. hamper till the safe 
 bearing power computed by 713. Sows Formula is 50,000 lb. V/hat should be tho 
 average penetration during tho last 5 blows if the average droo of hanmor is 
 20 ft. 
 
 5, A steam hammer weighing 4000 lb. striking 55 blows -3 or .nin. with a 
 stroke of 40 ins. drives the last 3 ft. of a rcinforcod concrete pile in 2 min. 
 10 see. Coi-iputD the safo bearing power of the pile by Eng.Kcws formula using 
 
 a value for x of 0.1 instead of 1.0, as for the drop hEawoy, 
 
 6. Compute the ultimate bearing power of the pile mentioned in prob. 3 
 by Rankino's formula (Civ. Ens., pp. 602-606) 
 
 + 4 E S x - 2 ESx , v;hero 
 i2 i 
 
 W = weight of ram in tons 
 
 h = height of fall in ft. 
 
 x = penetration of pile per blow in ft. 
 
 P = greatest load that the pile will bcrr in tons 
 
 S = area of cross section of pile in sc. ft, 
 
 1 = length of pile in ft. 
 
 E = modulus of elasticity in tons per sq.ft. 
 
 7 Co.7iputo the safe bearing power of the pile of prob. 3 from Major 
 Sander's formula P = 77h/8x. I^otction same as in prob. 6. 
 
 8. Compute tho ultimate bearing power of the pile of prob. 3 from 
 Trautwine's empirical formula 
 
 V/Y h . 
 
 P = 52 Y/ Y h . Notation same as in prob. 6. 
 1 + 12x 
 
 whi ch 
 
 9. Y/hat will b o the safe bearing value of a timber pilo A under the last 
 
 blow of a 1 1/2 ton hamper has a penetration of 3/4 in. the fall of the hammer 
 being 12 ft.? 
 
 10. A pile driven t hrough stiff clay has a penetration of 2 ins. under 
 the last blow of a haanor weighing 1000 lb. and falling through a distance of 
 
 14 ft. V/hat will be -the allowr.blo bearing value of the pile? 
 
 11. The last 5 blows of a 4000 lb. hammer falling 12' 6" drive a pile 
 . total of 4". With a factor of safety of 5 what load may bo carried, by Eng. 
 ricws, Saunder'^bnd Trautwine's formulas? If the pile is spruce, whet minimum 
 butt diameter is necessary so thct the safety factor shall bo 10 against 
 crushing of'-the head? 
 
 12. If the s tandard penetration s 1 of J.Foster Crowoll's formula is 
 observed to be 3/4" and tho foundation supports a bridge pier exposed to slight 
 vibration from water currents c.nd trains, determine tho supporting power of the 
 pile of prob, 11 by Crowoll's formula. 
 
 13. A cylindric coffer dem 6 ft. outfcido diameter is drive-n around a 
 cluster of 3 piles into soft mud. See fig. 49. It consists of Oregon pine staves 
 4" thick with metal be.nds on the outsir'c- but without bracing within. If tho 
 .-.iud acts similar to hydrostatic pressure end there is safety against ellipticcl 
 collapse- , what hoop compression in lb. per so. in. is produced at a depth of 
 
 15 ft. if the interior is cxcavcted and ua'cer pumped out? Would the timber be 
 safo agrinst crushing? 
 
163 
 
 CHAPTER -7 
 
 COECBETE AgD REINFORCED . COITCBETE PILES . 
 Their Advantages and Disadvantages. 
 
 The rapid decrease in tho available timber supply, combined with improved 
 and more economical methods for producing Portland cement has led during the last 
 docade to a widely incf%sed substitution of concrete for timber in all classes of 
 engineering structures. The concrete pile represents one of tho many used to which 
 concrete has been put successfully as a substitute for rood. In Europe, Hennobique 
 cast piles appeared as early as 1896. The first patents in the U.S. v/ore taken 
 out about 1901. Hn the short time 'since then concrete piles have grown rapidly 
 in favor and now in numerous instances are replacing timber piles for tho support 
 of l:.oevy structures in wet or marshy locations. In ggnoral, concrete piles can be 
 used uno.oi all conditions where timber piles arc applicable. Perhaps the most 
 marked advantage of concrete over timber is that the former is equally durable 
 i:- wot or dry soil. Tir.bcr piles decay rapidly if subjected to alternate wot and 
 dry conditions. The lowering of tho ground v.ater l:vcl around pilo foundations 
 constructed in cities is a common result of the construction of tunnels, subways 
 or pipe sewers. ' oodcn pil_s :ust be cut off below t: c lowest point to which the 
 water level may reach, a requirement often attended with considerable uncertainty 
 In many cases tho ground water level is so low that if wooden piles are used, 
 extensive concrete filling must bo placed above the- piles, requiring expensive 
 excavations. Concrete piles, on the other hand, may extend up to the superstructure 
 or ground surface and cm be bonded monolithicslly to concrete or reinforced 
 concrete capping, especially when the reinforcement is pieced to .rake tho parts 
 of the structuic continuous. 
 
 The concrete pile costs more per lineal ft. than the timber pile, but in 
 many cases may scv_ the cost of other items of construction, such as excavation 
 to permanent water levels, additional depths of piers, footings or grille. jo , the 
 
 cost of much sheathing, purnpin;,', bad: filling. In such examples the work is 
 simpler, less in amount, and maybe done in a shorter period of time. Thus, in tho 
 
164 
 
 final result it may bo cheaper to use the more costly concrete vc. the timber 
 pile. The ideal location for a concrete pile foundation is in filled areas or 
 soft deposits ovcrlyirg more substantial strata below them and v/hcre a varying 
 v/ater level is at considerable distance bolow the surface of the ground. 
 
 Concrete piles are particularly advantageous for exposed marine work 
 because exempt from the attac'-.s of marine worins but they arc not necessarily 
 immune from the detrimental effects ofifeoashorc moisture conditions, vfliere hard 
 
 ( 
 
 driving has been necessary in order to place timber piles in position, engineers 
 have entertained doubts regarding the final bearing value of the pile; that is, 
 its real ability to support the load imposed on it, owing to the fact that many 
 piles driven under these conditions and removed later, have been found to be seri- 
 ously damaged by being telescoped or buckled. Timber piles are injured more fre- 
 quently in driving than is generally supposed, but comparatively few are over re- 
 moved, so that the integrity of the foundation is largely a matter of conjecture. 
 Concrete piles, if properly reinforced, r.ill stand more driving than timber ones. 
 All evidence would indicate that they arc relatively uninjured by hard driving. 
 Concrete piles can -be raac!e larger and longer than timber piles; therefore they 
 can support grcc.tor loads, They cs.n be proportioned to carry the particular loads 
 which they are intended to bear. Each concrete pile can be made to satisfy the 
 specifications. It is difficult to select tirnbor so that every stick will b e of 
 the proper size and requisite straightness. The use of larger piljs permits heavier 
 loading. This is conducive to speed in foundation construction by permitting 
 fewer piles. Concrete also possesses special advantages for forming heavy mono- 
 lithic water tight sheet piling in place. 
 
 Tho cl-iof '.disadvantages to tho use of concrete are a higher cost per 
 pile then timber and a grerter difficulty ir driving, owing particularly to tho 
 use of larger sizes. Doubts also have been expressed as to tho . porms.noncy of form, 
 in seme types molded in plrce, due to possible distortions effected while tho 
 
 vrcon concrete is setting. 
 
 From the above arguiuant it ,mst not be concluded ths.t concrete piles will 
 
165 
 
 eventually lately replace timber ones. Thore arc special locrtions for v/hich 
 
 COIL rote is the logic::.! typo. But for the greet , ; ass of pile foundrtion work, 
 ti inter still will be employed, for example for docks, trestles, railway v/ork on 
 .vsrshes; false work over vet or e.nd for light buildings. Timber piles properly 
 protected by coatings (including concrete shells) or chemicals, always v/ill have 
 
 their uses. 
 
 CLASS FICATIOK * CONCRETE PILES. 
 
 There are two general classes of concrete or reinforced concrete piles 
 in .coravion use:- 1. piles which are molded or constructed in place in the soil; 
 2. piles vliich are cast or molded soparrtely and then driven like timber piles 
 after the concrete has sufficiently hrrdc-ned. They may bo driven \i th a hammer or 
 water jotted into piece. The second class is most usual; of simple square section, 
 reinforced. 
 
 Of the first class there arc a number of patented schemes. Those deser- 
 ving special mention are the Raymond, Simplex, Clark and Abbott piles. Any of 
 these for vis :.iay be either plain or reinforced concrete. For t he second class may 
 be enumerated Kennobique and corrugated piles , also a now form proposed by Cole. 
 
 1. PILES MOLDED IK PUCE 
 
 Raymond Piles. Raymond piles wore invented in 1901. Fig. 50. They arc 
 formed by driving a light steel conical shell into the ground.; the shell is left 
 in place and the space filled wit!: concrete. There are two distinct typos: 
 
 1. Those driven with a namr.ior into firm soil 
 
 2. Those sunk with a water jet in looser soil 
 
 For the hammer driven piles, a patented driving shell is used, Fig. 50, 
 which consists of a hocvy .somcvrhat cora:>lic^tod tapering stool core, fig.50A, fitting 
 inside a light shell, Fig.50B, so arranged that when the pile is driven the core 
 mey be collapsed, withdrawn and used for the next pile. The light steel shell is 
 left in the ground and is stiff ^nough to retain the form of the hole until it is 
 filled with concrete, Fig.SOC. The core is fitted to an oak driving block, Fig.50A, 
 sliding i:. leads and is driven like an ordinary timber pile. The shell or mold 
 usually is made of No. 20 rolK steel, in sections 8 ft. long, with an overlap. 
 

 t.:-'-: 
 
 
 - .- : . .. . 
 
 *-. ..*,-. 
 
 . 
 
 
 
166, 
 Ono of the advantages of the system is that the shells may bo formed at the 
 
 site, of sheet steel, if desired. If reinforcement is required for column strength 
 a center rod 1 1/2 ins. in diameter and 3 - 3/4 in. side rods symmetrically placed 
 near the outside of the shell are used. The concrete usually is a 1-2-4 mixture 
 thoroughly rammc c". . The piles are :.iade in lengths from 20 to 40 ft. , top diameters 
 18 and 20 ins. , point diameters 6 and 8 ins. The conical form aids in compressing 
 the soil; it is claimed to give a greater bearing paver, '.".lion the piles are driven 
 to bedrock a special core 13 ins.' in -diameter at the bottom and 20 ins. at the 
 top is used. Twenty ft. pile lengths are recommended for ordinary soils because 
 t'-joir taper is greater and the bearing pov;er per ft. of length is assumed to be 
 STGcter than for longer piles. 
 
 The second form of Raymond pile, Fig. SOD, is adapted for use in sand, 
 quicksand, silt, or soft earth, easily loosened v/ith a \vatorjot. The shell is 
 .iade in 8 ft. sections, nost<ad,\vith rings on the upper outside and lover inside, 
 of each section. Each section as it sinks drav/s the next section after it. A cast 
 iron shoo is used vith a 3/4 inch nozzle at the point. A 2 1/2 in. pipe connected 
 vith the nozzle is held in place in the axis of the pile by spreaders at each 
 joi./c. Each section as it sinks is filled v.ith-.v ell rammed concrete. The 2 1/2 
 in. pipe is left in plac., other r oinforcemcnt is added v;Iicn needed. 
 
 Tho groat advantage claimed for the Raymond pile is that a form for 
 every pile insures the corr:ct shape, prevents the washing out of cement in quick- 
 sand or saturated soil, and prevents the distortion of t he cross section or diam- 
 eter by unequal earth pressure on ^een concrete. The promoters claim an increased 
 -bearing pov/er on account ::f the conical shape; the advantage is borne out by 
 theoretical analysis, assuming homogeneous soil throughout the length of the 
 
 pile, but in the case most often met in practice the point of the pile is driven 
 
 comparatively 
 into < firm sub-strata vhile the pile is surrounded by loose material 
 
 at the butt. In such cases, obviously, a pile of uniform or increasing diameter 
 dov/nv;ard vould be ^referable. 
 
167 
 
 SIIJPLEX PILES 
 
 The Simplex system, Fig. 51, consists in driving to a firm bearing a 
 
 from 
 heavy, metal form, Fig.51A, with a hollow circular cross section, uniform top to 
 
 bottom. Concrete then is introduced and the form v.i thdrawn in stages while the 
 concrete is rammed. The concrete fills the space previously occupied by the form. 
 On account of the ramming, its section usually is larger than that of the form, 
 the liquid concrete being forced outv/ard into the irregularities of the soil. An 
 "alligator" driving point, Fig.51A, which closes while driving and opens when the 
 form is pulled, allows the concrete to be forced out into the soil; when the re- 
 quired depth is reached enough concrete is lowered in a special bucket, Fig. 51B, 
 of capacity to fill 3 ft. of the form. The shell is then pulled upward 2 ft., the 
 concrete rammed with a heavy drop hammer, and the operation repeated. One of the 
 ordinary forms of heavy pile driver is used, but must be fitted with a powerful 
 hoisting tacfele, as forces as high as 100 tons have been required to pull the 
 shell. For working under water, Fig.510, a second thin shell is sunk into the mud 
 outside of the driving form, which subsequently rets as a form for that portion 
 of the concrete pile extending through t he water. \Vhen the surrounding material 
 is quicksand or saturated soil, which tends to fill the void formed oy the driving 
 shell, a second light shell of ho. 20 or 22 sheet steel may be slipped inside 
 the driving form before filling and left as a permanent fore for the concrete. 
 
 In place of the "alligator" point, a cast concrete point 2 or 5 ft. long, or a 
 
 * 
 
 cast iron or steel projectile shaped point is frequently used and left in place. 
 
 Simplex piles may be reinforced with vertical rods, Fig.51C, but more frequently 
 they are stiffened with interior cylinders of expanded metal or wire cloth. There 
 is apparently no limit to the dength, as driving pipe may Ira added in sections 
 .nd the forms driven through much harder soils than is possible for wooden piles, 
 'he principal advantage claimed is increased carrying power due to the side friction 
 eveloped in ramming the concrete, and to a full or increased diameter, giving 
 .arge bearing -.power nea.r the bottom and at the point. The heevy rr.mming expands 
 " e concrete into the surrounding earth, firmly compacting it and cementing the 
 
.- ' V. 
 
168 
 the pile to the adjacent sand or gravel. Tje piles as actually constructed are 
 
 apt to be so mevhat irregular in cross section. If constructed in soil v.hich is 
 not homogeneous, the irregular pressure on the green concrete may seriously injure 
 the piles by deforcing and decreasing the cross section in a v/ay which isfsxtremely 
 difficult to detect. See Eng. News, Vol. 69, p. 416. 
 
 CLARX PILES. 
 
 For the Clark pile the process consists essentially of an open-ended 
 cylinder nade in convenient sections and driven to the desired depth. It is 
 fitted v/ith inside couplings to diminish the driving friction. It usually is 
 driven v.lth a sterm ha.rner, freruently assisted by a v/aterjet. A v/aterjet is 
 alv.sys used to wash the inside of the cylinder clean. When a satisfactory depth 
 is resched by charging the v/aterjet velves, cement grout is injected at the bot- 
 tom of the cylinder and fills it by displacing the lighter v/ater. The cement 
 grout spreads out to some extent at the bottom, giving an increased bearing area, 
 Rods may be used for reinforcement. Cf. Concrete and Reinforced Concrete, by 
 K, A. Reid, Bd.1907, p. 442. 
 
 ABBOTT PILES, Fig. 52. 
 
 This employe a novel method of constructing concrete piles, to v.hich 
 additional stmngth and stability are obtained by producing an enlarged foot or 
 base at the lov;er end of the ^ile. It is a cast-in-place pile, somev/hat like the 
 Simplex, tl^e apparatus necessrry fo form the pile consisting of a casing and a 
 core. The casing is a steel pipe, Figc. 52A, B, 16 ins. in diameter, 3/8 in. 
 thick. The core is a smaller and longer pipe, v/ith a cast steel point and an 
 enlarged cast steel head. The core fits inside the caning, -its enlarged head en- 
 gaging the top of the casing, itt lover end projecting some 4 or 5 ft. below the 
 lov/er end. In the head of the core there is an oak driving block which receives 
 the blovo of the hammer. The core is fitted into the casing and both are driven 
 in the ground to the de:,irecl depth, an indicated in Fig.52A. 
 
 The core is then pulled out and a charge of concrete is dropped to the 
 ottom of the casing, as in Fig.52B, The core (or rammer, as it nov.- becomes) is 
 
'-I 
 
 .-.t . 
 
169 
 lov/ered into the casing and d riven through this charge of concrete, pushing it 
 
 to either side, as shown in Fig .520. This operation of placing charges of concrete 
 and ramming them is continued until a large bulb or foot of the desired size io 
 formed, fig. 52D. If the coil just below the foot is somev/hat harder than above it 
 the foot may flatten out on the bottom to some extent. After the foot has been 
 formed, the casing is filled to the top v/ith wet concrete and then pulled out, 
 leaving a concrete column 16 ins. in diameter, resting on a spread base or ped- 
 estal,- This column may be reinforced with steel rods if greater strength is 
 desired in that part of the pile. 
 
 It is evident that this pile v.'ill carry a considerably greater load 
 under given conditions than a straight pile without the foot. It has all the 
 frictional area along the stem that the straight pile hac, and also some around 
 the circumference of the foot. In addition to this friction, it has the bearing 
 value of the projected area of the foot on the firm soil at the lov;er end of the 
 pile. This soil has been compressed and compacted by the r aiming of the concrete 
 during the formation of the foot, and therefore is capable of bearing a greater 
 load than it \vae before the driving of the pile. Experiments have been cade with 
 this pile in a number of different kinds of soil, and it has been found that the 
 shape taken by the foot is, in all caces, roughly spherical, Fi.52D. Of. a dis- 
 cussion by E, Abbott, Trans. A.r,. Soc. C,E, , Vol.65, 1909, p. 507. 
 
 Many engineers have constructed concrete piles, disregarding the numer- 
 ous patents, merely sinking sheet iron casing by ordinary well drilling methods ., 
 filling the casing -with veil rammed concrete, reinforced as desired. Special 
 champ ferine; ms.cl-.ine8. fittec ? . v/ith a toggle arrangement have been used in moderately 
 firm soil to /ne.lre an enlarged space at the foot of a pile, which can be immediately 
 "illed v/ith concrete. Cf. Ta lor & Thompson, Fig. 208, p. 653, ec 1 ... 1909. This gives 
 :. footing of roughly spherical she.pe, similar to that described for the Abbott 
 .iile. Such e. footing con b e re.r.dily made from 2 1/2 to "6 ft. in diameter. 
 
170 
 2. PILES liOLDED AMD THEN DRIVER. 
 
 Most engineers nor; prefer to use concrete piles v/hich are molded separate- 
 ly and then driven, like timber piles. Made-in-place piles are liable to serious 
 defects caused by percolating water or unequal coil pressure, defects which it is 
 impossible to detect. Piles v/hich are molded, allowed to harden, then driven, can 
 be inspected and their quality accurately determined, as little injury is liable 
 to result from even the hardest driving. There are many patented varieties of the 
 molded type, differing from erch other in shape, cross section and method of re- 
 inforcement. All molded piles are reinforced v;ith iron or steel to stand, the 
 rough handling to which they are subjected in transportation from the molding yard 
 to the site and while they a re being placed in the leads and driven. The driving 
 strains are very great. It is thought fcy many that a pile v.lth reinforcement should 
 not be subjected to the impact of a hammer. Mcny piles have been driven, hovever 
 subsequently pulled and red- iven, without showing any injurious effect. Driving 
 caps are constructed with a hard wood driving heed and a cushion of hemp, sand, 
 sawdust or rubber. Cf. Fig. 53. Heavy hammers should be used in driving. For the 
 best results the hammer should weigh 1 1/2 to 2 times asmuch as the pile. Steam 
 hammers weighing 5000 Ib. or more ere chiefly used. V/here soil c ondit ions are 
 favorable, water ets are helpful, either alone or in combination with driving. 
 
 The earliest forms of molded piles are all of rectilinear cross sections 
 such as tire square, rectangle or triangle, because of the greater simplicity of 
 the forms. Piles may be cast either horizontally or vertically, though the latter 
 gives the better results. If piles are erst vertically they are better able to 
 resist t:~e shocks of driving and possess a higher compressive strength, b ecause 
 the layers of concrete are normal to the stress, If the forms are built complete 
 for a long pile molded vertically, it is difficult to ram the concrete into tl:e 
 narrow space. To overcome this difficulty, the forms may be built in sections as 
 the concrete is laid, or three sides of a rectangular form may be built complete 
 and the fourth side added as the concrete is poured. Piles now are rr.rely ccst 
 in the vertical position. It is possible to effect considerable saving in forms 
 
C'JC. 
 
171 
 by using the horizontal system of pouring, as the upper portion or lid of the 
 
 form for square or polygonal cross sections can be omitted, entirely, v/hile the 
 side pieces can be removed after 24 hours and used again. Hollow speces frequently 
 are left in cast piles in order to lighttm them ^7itho^t greatly decreasing their 
 
 strength. 
 
 HEMBBIQUL PILES 
 
 Hennebique piles introduced in 1896 were the first reinforced concrete 
 piles Gf.Eng. News, Vol.51, 1904, p,233. They are usually square in section with 
 verticrl rods. The rods are wired together near the corners. Sometimes additional 
 rods are used at the middle of the sides. See Fig.54A. The lower end of the pile 
 is protected with a pyrenidal cast iron shoe. The reinforcing rods are bent to- 
 gether at the point, welded and fastened to the metal shoe. The piles frequently 
 are iiE.de hollow, sometimes with a jet pipe imbedded in the middle and left in 
 place as additional reinforcement. Provision for jetting .nay be made in the lower 
 end by the insertion of a piece of wrought iron pipe about 3 ft. long, bent in 
 such a manner as to extend from ths center of tl'e point to the outside of the pile 
 just above the shoe, whore an outside connection can b e rncde, and later removed, 
 saving a considerable length of pipe. Hennebique piles occasionally have been 
 .-.ic.de of triangular cross section v.lth three verticrl reinforcing rods. Fig-54B. 
 
 CORRUGATED PILES 
 
 The corrugated pile is usually octagonal in cross section, Fig. 56, 
 is tapering in shape, 16 ins. in diameter sit the butt and 11 ins* at the tip. 
 Each of the faces of tl e octagon contains a semicircular longitudinal corrugation 
 2 1/2 to 3 ins. in diameter, running for almost the entire length. The pile is 
 hollow, r/ith a core 4 ins. in diameter at the top, 2 ins. at the bottom, which is : 
 used for jetting purposes. The core is made by the use of a tapering, collapsible 
 mold, thus obtaining an opening for the water jet at small expense. After the pile 
 :.r s been placed, this opening can be filled with fine concrete or cement mortar 
 t:..us Baking e solid pile. The piles are molded horizontally, the forms being 
 striroed sfter 24 to 48 hours, The piles arc- kept wet for et least ten days before 
 

 . 
 
 - 
 
1 7 
 
 J I r^ 
 
 driving. They are reinforced throughout with Clinton welded wire fabric. The 
 piles may be sunk under favorable conditions by the water jet alone. It is common 
 however to employ a heavy steam hammer striking with a light fell on a special 
 cushion cap, used either simultaneously with a water jet or at 3e ast to secuie a 
 final firm bearing. For an illustration, cf. Reid, Concrete end Reinforced Con- 
 crete, ec".. 1907, p. 453o It is claimed for this pile that as the corrugations in- 
 crease its convex area, its bearing capacity is correspondihgly increased, on 
 account of the grester surface exposed for frictional resistance. The corrugations 
 also r.ssict -naterially in the escape of water, making it easier to jet the pile 
 
 into position. 
 
 COLE PILE, Fifi* 54C 
 
 Another type, circular in cross section, is formed in an entirely dif- 
 ferent manner., in that it is not molded or cast but is rolled mechanically into 
 shape. Cf. an article by H.J.Cole, Trans. Am. Soc. C,E. , Vol.65, p. 482, A sheet 
 of ordinary' wire fabric, to- 16 gauge, 1/2 inch mesh, of the length required to 
 make the pile, is attached to the rod which s erves as the winding core and later 
 as a part of tha r einforcement of the pile. JThe other edge of the sheet is 
 c.ttached to a movable platform v/hich is pulled tov;rrd the core as it is wound up 
 On this sheet is placed the other reinforcement ; and the whole is covered with 
 e li.ysr of fine concrete. The .TES is then v.ound up like r jelly roll, fastened 
 with vire ties ever-/ 6 inches, end <nore frequently where needed. In some of the 
 later oiles, the method of fastening the outer edge of the wire cloth lias been 
 changed by omitting the wire ties and substituting a rivet with its end upset so 
 ">at it is slightly larger in diameter then the mesh of the cloth. These rivets 
 are inserted in the outer ed^-e of blie cloth with this upset end upward, and as the 
 pile is rolled up, t?iey are forced into the raeshes of the fabric in the body of 
 v-e pile, thus tying or rather buttoning it together. The platform on which the 
 pile is ,'uoi" 1 ed is incline:"! so that, without any lifting, the completed pile is 
 rolled therefrom to thG car, v . ; hic;i is? to carry it to the seasoning yard. The plat- 
 form of ';". e csr is also inclined and when "ci-e car has reached- the yard, the pile 
 is rolled to its place on skies,. B} 7 this method no large plant s except the rolling 
 
G .?.? i:'f r -i3^<;' 
 
 ..in--: 
 
 -.. : -'jjK ;v;y if 
 
 -" ' 
 
 - f li- 
 
 :;J; :oi; 
 
 . . 
 
 'v.'WC irfj :vi Oi'il' 
 
 ''? i-fv'.' T. icnoiJj 
 
173 
 device is regi ired to handle the pile during its foirativa stage. V/ben thess 
 
 piles are to be driven into place, a driving head is used and when jetted, a 
 wrought iron jetting pips forns the winding core. Pilesof this kind, 61 ft. long, 
 have been dciven and pulled out for eEaminatioa , found to be intact and redriven. 
 Like other piles of this class, the;? have stood very severe treatment. In one 
 instance an attempt was made to destroy a pile by over -driving; later the pile 
 was pulled up and the only ,pp5-,rent injur}- v.'as the rushing ox brooming of the 
 upper 2 ft. This type has been used in the foundations of soae of the '.stations 
 of the Brighton Beach Eailroad, in Brooklyn, K,Y, , in filled ground. It has also 
 been used in other places throughout the United States. 
 
 SPECIFICATIONS - R5IMFQBCED COHCBETE PILES. 
 Specifications, Reinforced Concrete Piles, San Francisco Building Law, 
 
 1910, sec. 43:- "Reinforced Concrete piles may be built in place or driven after 
 building b3^ water jet or by hammer if the head is protected from injuries. The 
 ratio of length to least cross sectional dimensions at the center shall not 
 exceed 25. Reinforced concrete piles shall not be loaded to exceed 350 Ib. per 
 sq.in. of concrete at middle section.. There shall be a clear space of at leest 
 one foot between any parts of adjacent piles". 
 
 The San Francisco Ordinance further stetes:- "Reinforced concrete piles 
 shall b e buil'c in accordance with the provisions for the construction of rein- 
 forced concrete in Class 3 buildings, as far as such provisions apply". Clearly 
 
 direct conpressive or column bending stresses should not exceed safe values. Bond 
 between concrete and stesl should not be severed by driving. A rich mixture of 
 concrete should be specified of proportions at lor.st 1 cement, 2 sand, 4 broken 
 stone, the stone to pcss a 3/4 in. ring. The concrete as used should be wet, par- 
 ticularly for piles molded in place, It should be well rammed. In Hew York City 
 where J>iles with large steel areas in their cross sections have been used, the 
 building department has allowed a higher bearing feclue than for plain concrete 
 piles, viz=, 350 Ib. ~oer sq. in. on the concrete in compression and 4200 Ib. per 
 sc , in. on the steel. To prohibit corrosion the reinforcement should be well 
 covered with concrete at lerst 3 to 4 ins. i*o allowance in bearing capacity should 
 be .nai'e for exterior steal shells since their life is doubtful. 
 
 The usual -Dile formulas for o ear ins capacity as developed for timber 
 

 ., 
 : :.. ...-.;. .a: '. 
 
 * -. . 
 
174 
 piles do not give satisfactory results for concrete types For concrete piles 
 
 jetted to place the hammer formulas do not apply at all. In such cases equation 
 1, Chapter 6, may apply. To demonstrate carding capacity the method at present 
 adopted in the United States is to actually losd the concrete pile v4 th a test 
 load applied upon a platform. Pig iron commonly produces the load. Double the 
 guaranteed load must not produce settlement. 
 
 For concrete piles sunk by hammer driving alone, a formula talcing into 
 account the weight of the piles givts reasonable results. Equation 1 represents 
 
 Hitter's formula: 
 
 R = hj W 2 . ) + w + Q (1) 
 
 s W+Q 
 
 in which R * the resistance, in Ibs. to further penetration, W = the weight of the 
 hamner in Ibs.; Q = the weight of the pile in Ibs-, h = freight of hammer fall- : 
 in ins., s = the penetration of the pile in ins-by the last blow. 
 
 Consult the Shird Annual -Progress Report of the Sail Francis CO Bay 
 Marine Piling Survey; Feb. 1923; J>p 16-32, for a discussion of Concrete in Marine 
 Structures. This article gives specifications for manufacturing and driving r : 
 concrete piles with timel^r re^nerlrs upon the necessary protection t imbedded steel 
 particularly in "ocean" exposmre , for 'example, piles under ocean piers. The fol- 
 lowing paragraphs give a few excerpts :- 
 
 "Reinforced concrete .piles ahi-11 b e composed of one-to-five concrete* 
 Each pile as it is cast shell be dated and no piles shall be handled until at 
 least 40 days after, being cast. The driving shall be done with a steam hammer 
 having a striking part weighing 5000 Ib. and a normal stroke of 36 ins. Rein- 
 forcement bars shall be placad at least, three times the bar dimension from any 
 exposed surface and at least five times the bar dimension from adjacent parallel 
 bars. If specified to be picked at less than the above minimum depth and spacing, 
 letal reinforcement in that pa tion of the structure above high tide and directly 
 ex rosed to seawater spray and air shall be galvanized. Spacing from exterior 
 surfaces shall b e maintained by wiring to preccst mortar blocks; interior spacing 
 by wires or steel chains approved by the Engineer". 
 
 The materials, theijr proportions and manipulation are fully described 
 and specified. Ths student will profit by a full reading of the reference. The 
 problem of durability in marine concrete construction is anclyzed. Structures are 
 broadly classified as "simple" or "composite" in regard to type; and exposure is 
 roughly judged as "harbor' 1 ov :I ocean" exposure in regerc 1 . to the intensity of 
 
-.-,(' 
 
175 
 
 disintegrating conditions. 
 
 t 
 
 "Simple" structures are understood as including homogeneous concrete 
 structures greater than 12 ins. in minimum section and having no steel, wood or 
 other structural material imbadded at less than 6 ins. from the surface." 
 
 "Composite concrete structures are understood as including structures 
 having ;-ie:cbers 'of reinforcing steel, structural steel or wood, embedded at less 
 than 6 ins. from the exposed sur faces" , 
 
 "Harbor c-xposnrc is understood to refer to structures located in pro 
 tooted harbors where the members are only occasionally exposed to seawater spray 
 and arc- well brrcc-d and" anchored against impects. Ocean exposure refers to 
 structures located in the ocean and opposed to continual spray from surfaand hecvy 
 inspect of waves." 
 
 Thus for some cases galvanized reir.forcing steel is reconmendod, the 
 steel to be uniformly covered with a spelter coating of 2 1/2 oz, of spelter per 
 sq< ft, of surface area. Painting with asphalt of exposed surfaces of concrete 
 also is prescribed; part icularlyly for "harbor" exposure. 
 
 PROJECTION OF EMBEDDED STEEL AND WOOD. 
 
 "The principal cause for the disintegration ofcomposite structures 
 composed. of concrete and reinforcing or structural steel is the rusting of the 
 embedded steel under the accelerated corrosive action of t:e sea water. This 
 rustjSng takes piece above mean tide elevation, in that portion of the structure 
 exposed to both sea water moisture and air. The e.ction is increased by the use 
 of porous concrete and by the formation of fine cracks under impact end t ension 
 ^iclr assist the penetration of moisture and air. It is retarded and prevented by 
 t/..e use of dense, impervious concrete and by the sealing of c racks to prevent or 
 retcrd penetration. The action varies widel3' with the nature of exposure, 'i>oing 
 v?ry rapid in "ocean" structures which are repeatedly bathed with spray, and 
 comparatively slow in "harbor" structures which are infrequently wet directly by 
 spray. The damage consists in splitting and cracking of the protective coating 
 as the embedded steel expands on rusting. The forde of expansion increases with 
 the size of bars end their concentration, and for this reason the spacing and 
 depth of protective coating is made dependent on the size of bar. Because the 
 cracking destroys adhosion between the steel and concrete, mcchanicrl bond bars 
 are preferable to plain bars. Embedded structure! steelmay be protected by giving 
 a heavy coat of paint, so that the salt moisture cannot come in contact with the 
 Steel, but this decreases the bond. It is possible that a system of painting 
 reinforcing steel which will not seriously reduce the bond may be developed , but 
 v/ith present experience galvanizing is recommended. The protective costing for 
 painted structural steel and timber should be reinforced against impacts with a 
 g?lvanized wire mesh, 
 
 Reir.forcod structures having a "harbor" exposure begin to show cracks 
 
. ''- "" 
 
 ? ir . 
 
 ". - ^v 
 
 "' 
 
 - -'' ' .'JL'~ ' 
 
 '-ocii.', ;?vi- 
 
 ^.X'. jr 
 
176 
 
 in the moi e vulnerable locations in from five to ten years. Many have been in 
 service for from 10 to 15 years without serious frilure resulting from the 
 cracking, Painting the exposed surfaces with. asphalt, as specified, and main- 
 taining the .costing when it deterio^tes will prolong the life of these structures 
 indefinitely and make them comparable .to high class structure 1 steel construction 
 .which is raaintcinec" in a similar way by inspection and painting," 
 
 The student is referred to the following articles dealing with concrete 
 structures exposed to sea water. - 
 
 Reinforced Concrete Huniciprl Pier at Santa Conies-, California.; by *, K, 
 
 r /"arner; Eng. Hero.. Vol.62, Dec. 9,1909, p. 633. 
 
 2. Ocean Pier to be Scrapped because of Concrete Disintegration; Err:, iiews, 
 Vol. 84, March 25,1920, p. 621, 
 
 3. Deterioration of Structures of Timber, Metcl end Concrete Exposed to 
 Action of Sea "water; Committee Report, Institution of Civil Engineers of St. 
 Britain, 1920. 
 
 4. Effect of Sea Y/ater on Concrete Structures; by C.E.Y/.Dodwell; Canadian 
 Engineer, Vol.39 ; Aug. 26, 1920, p.279; comment by T , K, Thomps on , p. 359. 
 
 5. Articles on the Effect of Sea Water on Concrete, by P,,J.?/igg and L.R. 
 Ferguson.; Engineering News-Record, Vol.79, pp. 531, 532, 641, 674, 689, 837, 
 794, 1212, 
 
 6. Action of the Salts in Alkali and Sea Water on Cements; Technologic ?&p. 
 Bureau of Standards, No. 12, by Bates, Phillips and Wigg; 1912. 
 
 7. Tests on the Absorptive and Permeable Properties of Portland Cement 
 Mortars and' Concretes Together with Tests of Dempproofing and Waterproofing 
 .Compounds and Materials, U.S. Bureau of Standards, Tech. Paper No. 3, by Wigg and 
 Bates, 1911. 
 
 8. The Use of Wood and Concrete in Structures Standing in &9a Water, by 
 E, S. Taft, Trans. Internat. Eng, Congress, Sen Francisco, 1915, Vol.X, p. 321. 
 
 9. Concrete Test Specimens in Seawatar at Charleston i.avy Yard.; Errv. Record, 
 Vol.64, Aug. 19 ,1911, p. 229, 
 
 10. A Four-Year Test of ts Effect of Seswater on Concrete; Ens. News, Vol. 70, 
 Nov. 20, 19 13, p. 1093. 
 
 11. Action of Seawater or. Concrete; Results of Six-Year Pesos of 23 Molded 
 Piles of Various Mictures Sub erged '.in Boston Harbor anc? Withdrawn Periodically 
 for Examination; Eng. Rec. Vol.69, March 21,1914, p. 344, 
 
 12. How to i'lake Concrete Resist Action of Seawater; Eng. Record, Vol.73, 
 May 27,1916, p. 702. 
 
 13. The Application of the Perforating Process in the Preservative Treatment 
 of Wood with a Special Reference to Douglas Fir, by ;:,,M, Blfke, Journal of the 
 Boston Society of Civil Engineers, Vol.7, No. 4, April 1920 p. 99. 
 
 14. Preservation of Piling Against Iferine \7ood Borers; S-C, Smith; U, S.Dept, 
 Agr , Fforest Service Circular 123, Jan. 23. 1908. 
 
 15. Recommend Concrete for Oces.n Structures at New York; Err,-. News- Record, 
 Vol.86, June 15,1321, p.. 052. 
 
 IB. More Observations of Effect of Sea Water on Concrete; Eng. iiews -Record, 
 Vol.86, Jan. 20, 1921, p. 121. 
 
 17. Deterioration of Structures in Sea Water-, Second Interim Report-, Com. of 
 Inst. of C, E. of Gt. Britain ,1922. 
 
 18. Concrete Piles; E, J.Cole, Trsns. Am. boc. C.E. , Vol.65,p.4&7, 1903. 
 
 19. Concrete and Reinforced Concrete Construction, R,^.Reid, Ed.. 1907 , p. 428-464. 
 
 20. Concrete, Plain and Reinforced, Tailor & Thompson, ed. 1909 ,p, 650-656, 
 
 21. Reinforced Concrete, Buel & Hill, ed. 1906, p. 162-174. 
 
 22. Construction and Use of Concrete-Steel Piles in Foundation Work.. Sng, 
 Fev/s,Vol.51,p.233, Ivlarch 10,1904, 
 
?:*&. ".."", 
 
 C .' "" 
 
177 
 
 23. References to articles on concrete piles, Eng.li'ev/s, Vol.54, p. 594, 
 Vol. 62, p. 684-5, Vol.63, p. 30, 411; Ens- Record, Vol. 60 ,p, 656, Vol.61, y. 218, 
 
 24. Soine Experiences v/ith Concrete Piles in Chicago; J, K.Jensen; En~.uews, 
 Vol.69 ,p.4$6. 
 
 25. Hair forced Concrete Piles on t::e Chicago, Hock Island and Pacific F.,R. , 
 Eng. Record, Vol.67, p. 606. 
 
 PROBLBLiS 
 
 1. Describe concisely the essential features of the following types 
 of concrete piles:- (a) corrugated, (b) Simplex, (c) Raymond, (d) Kennebicue, 
 (e) Cole, (f) Pedestclo Give c.s far cs possible your idea of their relative 
 advantages and disadvantcnjes, 
 
 2o A concre'ce pile 48 ft. lon^, square section., 20 ins. side or butt 
 tapering to 10 ins. r.t point, is driven by a 5000 Ib. ha/.ner felling 15 ft. 
 per blow, Un'"sr the last five blov;s the pile penetrates a total of 2 3/4 ins, 
 Fird the prob.ble resistance to further driving by Hitter's fornula. Cf. Trans. 
 A:-i. Soc. C.Eo, Vol.65, p. 470. 
 
178 
 
 PART II 
 
 FOUMDATIOKS UICDER HATER 
 See Also Chapter 3, 
 
 The subjects discussed are: 
 
 Chapter 8 Concrete Deposited Under T/ater 
 Chapter 9 The Coffer Dam 
 Chapter 10 Open Caisson;- 
 Chapter 11 Pneunr.tic Caisson 
 Chapter 12 Deep V/ell Dredging 
 
 CHAPTER 8 
 CONCRETE DEPOSITED UNDER V.'ATSR 
 
 The construction of foundations by any of these methods frequently is 
 facilitated if not made possible by the deposition of concrete in mass under 
 water. It has often been contended 1 , by engineers that such deposition v;ill not 
 yield reliable results, particularly in sea water. The objections are mainly 
 based upon the difficulty experienced in depositing concrete under v/ater without 
 w.ashin~ the cement out of the mass, thus leavin : an inert residue of sand or 
 ;;ravel and broken stone in place of a continuous volume of sound masonry. 
 Ample experience however in connection with successful s tructures has demon- 
 strated the feet that concrete ;.i.y be deposited under v/ater so as to set in a 
 hard and ei'durin^ mass with satisfactory resisting capacity, 
 
 Tliere are a number of conditions requisite for such results end they 
 ere v/ith care practicable of attainment. They are as follov/s:- 
 
 1. The space within which the concrete is to be deposited must be so 
 completely enclosed that the water shall be entirely without current, 
 
 2. A rich Portland cement concrete, not leaner than one cement, two 
 sand and four b roken s tone . 
 
 3. A properly designed bucket, preferably cubicrl in shape, v/ith a 
 tripping bottom so arranged to b e alv/eys under control and permit the concrete 
 
 to escne in one .nass v/ith the least possible disturbance. The bucket used shoulc', 
 be the largest which the dimensions of the work will peroit, preferably in no 
 case to hole less than one cubic yard and as much more as practicable. The ton 
 
II i'-i.-l'j 
 
 <.r.C. so'i 
 
 ri.'i.,,,' ."io-'-^a 
 
 ^ ' c 
 
 ; '- ->.',: '.-}-, 
 
179 
 
 of the bucket may well be protected by a perforated <?over which should be 
 raised before the bottom is tripped. Fig. 57. 
 
 4. The bucket must be lowered uniformly and not too rapidly in a ver- 
 tical direction only and be held for a moment just at the surface of the water 
 to enable any air held in the voids of the concrete to escapfc. 
 
 5. The concrete must be thoroughly mixad v;et so t s to reduce the voids 
 with their enclosed air to a minimum. 
 
 6. When the volume of the work is considerable, the concrete must be 
 deposited in uniform layers with their surfaces inclined downv/ard to a central 
 point, from which the laite.nce is to be removed carefully by a hand pump if 
 necessary. 
 
 7. The process of deposition must be carried on continuously from the 
 beginning to its completion. 
 
 8. The bucket must be tripped only when it rests solidly on the concrete 
 already in place, so that the concrete being deposited shall have absolutely 
 
 no free fall , whatever through the water. 
 
 Large masses of concrete have been deposited where these conditions 
 have been scrupulously maintained with most excellent results, \7hen the water 
 lias been pumped out of the cofferdam enclosure the general naass has been found 
 to be practically all that could be desired. There will usually be a few s oft 
 pockets of laitance b$rt too few and small in size to exercise any influence 
 upon the carrying capacity of the whole ;nass. 
 
 Under circumstances in which it is necessary to deposit concrete by 
 allowing it to fall through the water or in a current, it is necessary to use 
 bags of canvas, cheesecloth or other similar loose fabrics, so that washing of 
 the concrete will be prevented to any material extent, at the same time giving 
 the cement opportunity to find its way through the fabric of the bags.. The 
 latter will then be well c emented together where they lie one on anothei . Paper 
 bags are also sometimes successfully used. After the bags are in place the water 
 
:', ..-. ."v:- . ::.. :- '. < 
 . y -l &''. ' , "i .', .. '.-.: :.<-.:. : 
 
 r1 >; . - f (.--! 
 
 'rt '.' ;,- !T 
 
 *.;.<WW: : 
 
 -r. . a 
 
 ! io 
 '..' s J'Jf i 
 
 T-; 
 
180 
 
 * 
 
 scales away enough of the paper to enable the contents of the bags to unite into 
 a coherent mass; that is, such a result will follow if the ba-s are properly 
 handled, and if the paper is of the proper texture. When ba^s are used they may 
 hold 1/4 to 1/2 a cubic foot er.ch, and they should not be more than 2/3 filled 
 in order that they may to some aster. t mould themselves into each other and form 
 as nearly as possible a solid mass. 
 
 Concrete has been deposited under water in different ways: 
 
 1. 3y usin~ ba^s of paper or canvas; En;:. Hews, Vol. 28, p. 379. 
 
 2. Through adjustable chutes, (tremie concrete) 
 
 3. V/ith tripping buckets 
 
 4. Depositing i -> molds under water; Ln{j. Nev/s,Vol.53,p.232. 
 
 Examples of (Joftcrete Deposited Under Y/ater 
 
 1. Concrete Deposited by Chute* In En;;.. Eews, Vol.39, p. 181, there is 
 a description of concrete deposited under seawater for the Charlestown bridge 
 piers, Boston, I.Iass. Consult also the third annual report of the Boston Transit 
 Commission. The concrete piers rest on pile clusters. The contract required al- 
 ternate ranges of bearing piles to be cut off at different ^rcdes. The first, 
 third and fifth rows were cut off 18 inches above the bottom of the excavation; 
 tl:s second-, fourt?-., sixth, etc. were cut off 10 ft. below low v;ater; these latter 
 rowsnot being cut until s 6 ft. layer of concrete had been deposited over the 
 bottom of the excavation. The lowr-level piles were driven, then cut off by a 
 circular saw, before the hi-vh level piles were plr.ced. Before the hi'jh level 
 piles were cut a cofferdam of Wake field triple lap sheet piling was constructed 
 around the proposed pier; this cofferdam consisting of 2 in. spruce planks bolted 
 or nailed together. Perusal of the r eferences will explain variations in the 
 design of cofferdams for different piers. Clay and stone, were dumped outside 
 the dams to fill that part of the excavation. 
 
 These cofferdams formed a mole 1 , or box for tl-e deposit of concrete upon 
 and about the piles. The concrete -.lasses extended 5=39 ft. below mean low water 
 the top foot in depth of the concrete laid after the coffer dam hc.d been 
 d out. The concrete was made of 1 -part English Portland cement, 2 parts 
 
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191 
 
 clean sharp said, and 5 parts gravel dredged from the harbor. The concrete was 
 mixed in a continuous mixing .nachine with inclined su:is. 
 
 The concrete was deposited under water through a cliute or tube 14 ins. 
 In diameter at the bottom, 11 ins. at the neck, v/ith a hppper r.t the top to 
 receive the concrete. The tube was mr.de in removable sections with outside 
 flrnges to adapt it to different depths. It vr.s suspended by a differentir.l 
 hoist from r. true!: moving laterally mounted on p. frame which could travel the 
 length of the pier, 
 
 In operation the foot of the chute rested on the bottom. The concrete 
 was dumped into the hopper. The chute was then slov/ly raised ~nd the concrete 
 allowed to run out in a conical heap vhils the loss of concrete in the tube wr.s 
 mrde good by dumping in more concrete r.t the top. Thus., as the t ruck moved on 
 the traveler a ridge of concrete wr,s. deposited across the pier, the chute being 
 r.lwr.ys kept full, or nc-rrly so, by dumping in .nore concrete at the top. 
 
 Uhen a ridge was finished the traveler wr.s moved and another ridge 
 built.- '""'en the v/hole ,-rer. of the foundrtion hr.d been covered c. nev; Dr. yer \vr.s 
 deposited on it r.s soon r.s the first .hr.d sufficiently hardened. It was thought 
 thr.t the best r suits v/ere secured v/ith Ir.yers 2 1/2 ft. thick, though some 
 courses v/ere Ir id 6 ft. in thickness, if the br.nlc v;r.s too hie"."- or uneven, or the 
 chute moved or rr.ised too Quickly, the clT.rge of concrete wr.slost and the water 
 rose inside the chute to the level of thr.t outside. In these cr.ses the concrete 
 first dropped in wr.s liable to v/r.sl". so that separation of the s and. from the 
 cement followed, The s'.me condition resulted when the work was stopped, since 
 the concrete v/ould otherwise set in the chute. It usually took about one cubic 
 yard of concrete to replace the water in the chute, which amount wr.s in danger 
 of giving badly washed concrete = AS the inspector grined experience, accidentrl 
 losses of the charge became infrequent. After an intermission work was commenced 
 near the center line of the pier so that any bad concrete would be surrounded by 
 good. A canvas piston was devided to keep a first charge from dropping too 
 rapidly tLroujh the water. Its cost was considerable anc" its use abandoned. 
 
ff ; 
 
 J'.\f . 
 
 ; . . . 
 
182 
 
 The chute seemed to work best when the concrete was mixed not quite moist 
 enough to be -plastic. If mixed too wet the charge was liable to be lost and if 
 very dry, there was a tendency to choke the chute. An excess of grrvel permitted 
 the outside water to tforce its way in at the bottom and an excess of sand tended 
 to check the flow of concrete. 
 
 TRH.IIE CONCRETE 
 
 In tae past decade tremie concrete has been more and more frequently used 
 as distinguished from concrete deposited in mass by bucket.; for example, in tunnel 
 vork. The Detroit tunnels, consisting of units of structural steel shells sunk in 
 o-^en excavation were covered on bottom, sides and. top with a concrete mass. See- 
 Trans. AIVI. Soc. C.E. , Vol.74, p. 288, Plate 43 and Fig.7. The proposed tunnels 
 under the Estuary at Y/ebster St., Oakland, California, are tentatively designed to 
 consist of units of reinforced concrete shells about 200 ft. Ion;; each, to be 
 'oulkheaded, floated to place and sunk in open excavation. After joints between the 
 sections have been sealed inside and out, the tube is to be covered where necessary 
 with masses of concrete probably to be deposited by trsTue. 
 
 The processes of deposi tin^ concrete by tremie have been gradually improved 
 so that now the objections to this method are not so serious as heretofore, when 
 cornpE. red with the deposition of concrete by bucket. 
 
 Reference has alrerdy been :.iade to the Third Annual Progress Report, San 
 Francisco Bay Marine Piling Survey; the articles on "Concrete in I/Ir.rine Structures" * 
 p, 16-32. Article 8 from Section C, ;1 The Manipulation of Concrete" reads as 
 follows:- 
 
 "Concreting Under Y.ater. Concrete shall not be deposited in sea water or under 
 the sea water unless authorized by the Engineer. Y.Tien placed in sea water, concrete 
 shall be discharged through a water ti^ht tremie into prepared pockets of such 
 capacity that each can be completed without interruption of the flow of concrete, 
 The treraie pipe shall be. of sufficient size to permit the free flow of the plastic 
 concrete, and the arrangement shall be such that the t.emis can be readily raised 
 or lowered without interruption of the flow from r hopper or .-ixer until the pocket 
 is completed. The size of pipe, dimensions of pockets and capacity of hopper and 
 mixer shall be determined by the Zirjinesr and will d epend upon the depth of water 
 and- the size of dimensions of the pockets to be filled. In operating, the top of the 
 tremie pipe shall be plugged with hay or straw to be forced ahead of the charge of 
 concrete. \\fter the charge is strrted, the flow of concrete into the t remie shall 
 be carried on continuously v.lthout interruption until the pocket is completed. 
 
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183 
 
 lower end of the treraie pipe shall be kept embedded in the concrete to 
 such a depth that -water c annot be forced back into the pipe through the plastic 
 concrete . 
 
 Tremie concrete shall be proportioned at least one part cement to four parts 
 aggregate. The consistency of the concrete shall be mushy so that it will flow 
 readily without s eparation". 
 
 2. Concrete Deposited by Bucket. A description of methods used for de- 
 positing concrete in seowater for the pivot pier of the Karlem Ship Canal 
 Drawbridge, New York City, /jiven in the next chapter on coffer dam construction. 
 See figures 57, 58, 59. In this method a bucket with tripping bottom was employed; 
 sea also Engineering News, Vol.31, p. 349. 
 
 In Engineering News, Vol.42, p. 405, Mr. J. F. O'Rourke describes a 
 bucket which was used for placing concrete underwater, constructing foundations, 
 City Island Bridge, New York City. These piers are of concrete faced with li ie- 
 stone ashlar and granite copings in their visible portions. They rest upon rock 
 bottom in depths of s eawater averaging 20 to 30 ft. below mean high water. The 
 nonmal tide range rs 8 ft. Between City Island and the mainland is a tidrl strait 
 of considerable current velocity. There was little surface material over the 
 rock bottom except bouldors. Tho pier concrete was deposited in wocden coffer 
 dans similar in construction to fig. 38. The O'Rourke bucket is an improvement 
 on fig. 57; for an illustration see Taylor & Thompson, Concrete: Plain and 
 Reinforced, p. 306. The bucket is rectangular with a V-shrped bottom consisting 
 of two flap doors similar to those in fig. 57; but there r.ro two other desirable 
 features:- 1. the lower edge has a timber frame which Gives r. vide bcr.rinc; when 
 the bucket rests on the soft deposited concrete, which prevents its sinking into 
 and cutting the concrete. Between the cutting edge end the hinges of the- flap 
 doors two sides of the bucket box cue open, allowing er.sy flow of wr.ter in r.ncl 
 out of the bucket bottom as the flap doors open or close, thus giving the least 
 eddy disturbance as concrete is dropped; 2. at the to~o the bucket has flap doors 
 which are closed when the concrete is b eing deposited; they also reduce the 
 action of currents or eddies, The top and bottom flap doors rre operated auto- 
 matically. The obvious advantage of this bucket for depositing concrete under 
 water is that it does not let the material fall through the water and that it 
 
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184 
 operates to shut out water from the concrete charge until the concrete is finally 
 
 in position. 
 
 MiSSES,' Bhere concrete is deposited in water there should be no stream 
 or tidal current and no local churning or eddying of thev.-ater through careless 
 depositing of concrete. Still v/cter is produced by proper designs of coffer dams 
 or sheet piling enclosures. Local churning or eddying is reduced to a minimum 
 through the use of bags, chutes or buckets for depositing concrete. Even with the 
 greatest precaution the concrete will be somowhr.t disturbed, forming laitance. 
 When concrete is deposited under water carelessly much laitance is formed. 
 
 A number of piers built in San Francisco Harbor about 1904 or earlier 
 rest upon cluster piles whose heads are protected by reinforced concrete deposited 
 in cylinlric v;ood stave coffer dams, see fig. 49. In later years many of these 
 piers have been inspected and in some cases the cluster piles were found to have 
 highly defective concrete tops. Uherever the stave coffer dams were driven, 
 sealed at the bottom, pumped free of water and dredged of soft material, so that 
 the concrete could be deposited around the pile heads in the dry, the work is 
 found upon inspection to b e scvrird'and first class. Bat where the core ret e was 
 
 iff* 
 
 deposited into such cylinders without first pumping out the water ., it apper.rs 
 thr.t it was practically impossible to produce first class concrete work. The 
 presence of expanded metal or other reinforcing material within the cylinders 
 together with the presence of the pile heeds crusel too much disturbance of the 
 concrete as it was dropped through the water, separating the cement fnari the sand 
 and aggregate, producing grert mrsses of inert soapy Rdr.terir.lsbr Ir.itarsce. As the 
 wood stave cylinders decayed the concrete was found di sintegrrted and ciumbled 
 away lerving the wood pi'..es bare and the dock floor un -supported. 
 
 YThere concrete is deposited in still water rn coffc-.r dams , like fi'js. r 
 38, 39, 59, rind 65, it is well to plr.ce the concrete in layers with tha top 
 surface sloping from the outside tov/rrd the center of the p-'.er or cofi'pr dan 
 enclosure so thrt lu:.ritaacG v;hich forms may flow or be swept toward th<? center 
 ard be i amoved rt irrcervals. 
 
185 
 
 Laitance is decomposed cement formed in the presence of an excess of 
 water. The word is of French origin but quite generally adopted in the United 
 States and England for the light colored powdery substance which is held in 
 suspension by water when cement or concrete is deposited below the surface. ?/hen 
 ever concrete is Irid under water, the water is likely to b e clouded by what 
 appears to be particles of c ement floating up from the mass which is being laid. 
 A similar formation tends to cc cur on the surface of concrete laid in the dry' 
 with a large excess of water. Laitance has nerrly the same chemical composition 
 except for loss on ignition as normal Portland cement, but consists ir. rgely 'of 
 amorphous material of an isotropic nature. It has almost no setting properties. 
 Therefore when concrete or mortar is laid under water- or with a large excess of 
 water a portion of the cement is tendered incaprble of setting and the strength 
 of the concrete mass is consequently reduced in proportion. Where concrete is 
 laid under water or vith large excess of water in mining there should be 
 specified a higher percentage of c em'ent tl-an usual, about one-sixth more. A 
 lean mixture is more serious^ injured by an excels of T - r ter than a rich one. 
 For further study of Ir.itance consult Taylor arid ^'.-lo.'-.ipscr.. Concrete: Plain and 
 Reinforced, pp. 2c, 303, 384. 
 
 Additional References: Placing concrete oru er v-.-.sr, Engineering Sews, 
 Vol. 24, p. 548, p. 575; Vol. ol, p. 131; Vol.. 35, p. 127; Vol. 43, p. 26; 
 Vol. 46,, p. 275; Vol. 50, p. 25V; Vol. 62, p. 58'5, T.-r;lor Chomps on, Concrete 
 Plain and Reinforced, edition 1909, pp. 301-2 
 
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186 
 
 CHAPTER (9 
 
 COFFER DAMS 
 
 Pivot p ier, Karlem Shi]2. Cartal Bridge. The application of the coffer 
 dam process for constructing foundations on a hard or rode bottom is well illus- 
 trated in Fig. 59. The plan there shown was used to construct the draw-sprn pier 
 of the Harlem Ship Canal Bridge situatec 1 at the north end of Manhattan Island in 
 New York City. It is typical of a successful treatment upon rock bottom in con- 
 siderable depth of water where very strong tidal currents were found at certain 
 stages of the tide- 
 
 The greater portion of the foundation bed lies on the roughly levelled 
 rock bottom of the canrl, but a portion on the east sice reaches over the natural 
 slope of the rock surface. The canal is a rectangular prism cut mainly through- 
 rock in the vicinity of the bridge. The entire foundrtion bed was covered with 
 mud and silt which l:ad flowed over the rock to a depth o f 3 to 5 ft, The mud and 
 silt were cleaned off by dredging before the timber work of the coffer dam ras 
 floated into place, 
 
 Two concentric thirteen sided polygonal walls of timber, strongly braced 
 (Fig. 59) 4 ft. 6 in. apart, were built in the water with the bottoms shaped to 
 fit t--e rock foundation bed rs closely as possible. In thiscr.se the rock bed had 
 very little solid material or debris upon it ; and. that little wrs dredged off as 
 thoroughly as practicable. Hrd there been deep mud, srnd or other material over 
 the rock bottom, it first would have been carefully cleaned away by dredging or 
 -other means. As shown in the plans, the lower portions of the timber v.r-lls were 
 constructed of 12 in, by 12 in. sticks and the upper portion of 8 in. by 12 in. 
 and 6 in. by 12 in. timber. The 1 1/2 in. bolts runvjin" through the timber walls 
 and the timber struts between them, held the two frc ,ies rigidly at the proper 
 distance apart. Almost any sound timber will serve for such temporary construction. 
 
 After the polygonal structure wr.s completed it was towed to its proper 
 position r.nd secured accurately in place by suitable timber platforms rnd braces 
 about it. Temporary flooring was then plrced r.t a number of points on its top for 
 
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187 
 
 the puipose of receiving sufficient loads of stone to sink it. 3y these means it 
 was accurately and solidly sunk to the foundation bed. 
 
 After it was sunk to place the laver edges of the timber walls were 
 carefully examined by the aid of a diver and other appropriate means in order 
 to locate any openings that might exist under the' bottom of the dam due to im- 
 perfect fitting. The greatest of these openings was only a few inches in height. 
 All the openings were then closed by depositing caa^as bags each containing 
 about 5/4 cu. ft. of concrete in them under the inner shell and similar bags of 
 sand under the outer shell. After the deposition of the bags of concrete under 
 the inner shell a few buckets of concrete were deposited en masse over them 
 immediately inside of the enclosure. These operations completely closed all 
 openings between the foundation bed and the exterior waters of the canal and also 
 prevented from flowing inwards under the inner shell any clayey material and 
 gravel which might otherwise have found its way from the annular space between 
 the two walls of the dam to the central enclosure. The bags of cement raid s and 
 were carefully deposited, a diver being sent dorm to arrrnge their positions to 
 completely fill the openings between the coffer dam shell and the rock. 
 
 The annular space was then filled up to the ale vet ion of high water with 
 a mixture of dry or loam and gravel. I-.'o particular care was taken to attain any 
 special mixture. The gravel mr.y have baen from 1/3 to 1/2 of the vhole mass, This 
 material was simply dumped into the wrter contrir.od ?.n t^e annular volume thus 
 puddling itself as it settled to the bottom. A gravel mixture such as that de- 
 scribed is probably as good as anything that can '.50 used for the purpose. Pure 
 clay is not well adapted, to such v,ork . If a cuvre.-t of wrter however snail finds 
 its way through a bank of thrt ;rf terial, it will grr dually and continuously wash 
 the passage larger until serious damrge and possibly the failure of the con- 
 struction takes place, The gravelly mixture of dry or dry rrd lorm, not less 
 than 1/5 being a gravel, net too coarse, makss r 'very solid end resistant dam. 
 If r small current finds its w.y through at any point, the gravel vlll quickly 
 'o into the passage ard obstruct it so that it is not apt to grow Irrger c.nd 
 
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186 
 frequently fills itself. 
 
 Before the coffer dam was thus completed, openings each 4 in. in diam. 
 extending from the enclosure to the exterior of the cr.nal were i7T.de at an eleva- 
 tion not higher than mer.n low water in order that the water surface might rise 
 ard fall in the enclosure with that exterior to it. If this were not done, the 
 rise and fall of the tide would force currents undernerth the dam in and out of 
 the enclosure, in consequence of the unbalanced head which would result from 
 varying stages of the tide. 
 
 After the dam VE.S completed the concrete mass immediately overlying the 
 foundation bed, as shown in Fig. 59, was deposited in place. This deposition vies 
 Made observing all the precautions described in Chapter 8. The concrete mixture 
 consisted of 1 Portland cement, 2 sand and 4 broken^stone. The 'bucket used con- 
 tained 1 cu. yd. and is shown in Fig. 57. It was tripped in the manner illustrated 
 after resting solidly on the bottom at any desired place. Its arrangement was 
 such that the concrete slid out of it with the least possible amount of wash. The 
 depth at mean high water was 24 ft. and the layer of concrete about -9 ft. thick. 
 Herce the weight of concrete was not sufficient to completely overcome any tend- 
 ency to flo\tation produced by the water being forced underneath the concrete 
 ard along the foundrtion bed when the enclosure was pumped out. Enough of the 
 blocks of limestone which were to be used in tho face masonry of the pier vcrc 
 then lowered upon the concrete to rrakc it certain that the latter could not rise 
 after the completion of the pumping. Throughout the deposition of the concrete 
 which was carried on continuously night ard day from beginning to completion-, 
 the upper surface was". inclined towards the center so that any laitanco which 
 might be formed would flow to that depressed point. 
 
 Before proceeding with the deposition of concrete within the coffer dam 
 an annular surface on the foundrtion bed 8 ft. wide extending around its entire 
 circumference just inside the dam was cleaned of dirt ard loose material by a 
 scraper, Fig-58, to enable a closo bond to be formed bctwe:n concrete rr_d bedrock. 
 The screper was worked by ropes running over blocks held at suitable points 
 

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around the dan and running to a hoisting engine, 'art it was ^idec^ by fend, The 
 
 or 
 
 loose material was thus cleaned from the annuls surface and scrapec in tcwrrd 
 the pier center where it v^s filled into buckets by divers r.nd removed. The 
 bond between the concrete to be deposited and the bedroc!: was by this merns 
 secured throughout a surface at least 8 ft. wide around the circumference of- 
 the pier brse, Tfee central portion of the bed was clerned but with less care. 
 After the concrete had been allowed to set r.early 5 weelcs the hole; 
 passages through which the tidal v,rter hr.s been rllowed ingress and egress were 
 closed and the water pumped out, The dam proved to be perfectly tight aid satis- 
 factory in every way. Some laitance kad settled rt the central depression as well 
 as at a few other points, and while there were a few spots of soft material the 
 mass of concrete on the whole was found to be of excellent character and the 
 remainder of the pier was built upon it within the coffer dam in the dry. After 
 the completion of the masonry the upper portion of the dam was removed do van to 
 ar_ elevrtion a little below mean low water; its lower portions were allowed, to 
 re.r.ain in place, serving to protect the footing courses of the pier. One of the 
 dangers to be guarded against in the construction of such a foundation is the 
 possible v.rshing of tie lower portion of the concrete by rny cm rent -which may 
 find its way und.er the dam. All points of access should be effectually ard 
 absolutely cut off, as is done by the coffer dam when completed in the proper, man - 
 
 ne r , 
 
 The plan, T?ig.59, shows the main features of the construction of the 
 
 pier above the concrete footing. There are seen to Th>e two concentric tiers of the 
 dressed stone, the outer one forming the face masonry. The her rt ing is that part 
 of the pier inside of the two tiers of dressed stone end is of concrete Ko. 5> 
 which in this case means 1 cement, 5 sand ard 5 broken stone. The material is dis- 
 tributed in this irr.nner for the reason that the track on too of the pier which 
 carries the entire weight of the superstructure of the draw span would rest im- 
 mediately over the concentric tiers of dresr-ed stone. The hearting of concrete 
 ivios. 3 carries very little load and consequently .lay be less ric,h in csaent than 
 that used in the footing course. The central block of concrete too. 2, I cement, 
 
190 
 
 2 sand and 4 broken stone , carries the pedestal block (shown on the plan) which 
 supports the heavy central casting about which the superstructure turns. The 
 4 inch pipe which is shown ranning from the central portion of the upper surfcce 
 down through the masonry to a point outside drains the top of the pier after the 
 track of the draw span is in place. In present day practice it is not uncommon 
 to build the pier entirely of concrete, Ashlar face stones are now used mainly 
 for appearance. 
 
 The anchor bolts which hold the center casting in place on the top of 
 the pedestal block run down into the concrete about 4 ft. These bolts are frcm 
 1 1/2 to 2 1/2 ins. in dirrn. and may be built in the masonry with proper anchor 
 plates at their lower ends, or they may have split lower ends with w edges r.nd 
 ragged sides. They may be 8 to 12 in number according to the size of the central 
 casting. They should nave sufficient resistance to hold the center casting rigidly 
 in place so that there nay be absolutely no motion while the bridge is turned. 
 
 VARIATIONS OF THE COFFER fi!.M PROCESS 
 
 Fig. 59 exhibits a typicrl example of hervy coffer drin construction for 
 "bridge pier work. Coffer dams of lighter construction are often used: see Figs. 
 38 and 39. These diagrams show pier construction for Karlern Rifcer Highway Bridges, 
 Hew York City. These piers were sunk in marshes along the itiver banks where the 
 ground water level rose near to the top of the excavr.tion- The piers shown by 
 Bigs. 38 and 39 were built about 1895. During the past two decades (1903-1925) 
 some of the lighter coffer drm work has been constructed of structural steel sheet 
 piling rather than wood. Consult Eng. wews, Vol.60, p. 394, for a description of 
 large steel sheet pile coffer drms\for a ship lock at Buffalo, Hew York. The .nasonry 
 sea walls of these locks were built inside long lengths of sheet pile coffer dams 
 subdivided into pockets by cross walls' of steel sheet piling. Laclcawanna Inter- 
 locking sheet piles were used; see Fig.40, group 2, 
 
 Any cylindric caisson, whether of wood staves, as for pile clusters 
 under docks, fig. 49, or of sheet steel shells when driven ir. river beds, employs 
 cofier dam principle of construction when the caisson or tube is driven, or 
 
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191 
 
 water jetted to refusal, excavated, pumped out, ani then filled with concrete. 
 Sometimes such cylinder using wood or metal shells are first sunk by the pneu- 
 matic process and in early days {the middle of the last century) were sunk by 
 the so-called vacuum process. Having reached their proper depths, the pneumatic 
 cylinders after sealing at the cutting edge become coffer dams for the remainder 
 of the 'work. 
 
 PIVOT PjER, SEVENTH AVE. SWING BRIDGE, NEW YORK CITY. 
 
 In Fig. 65 is shown a pivot draw span pier for one of the. New York City 
 bridges. The type of construct! or. in general is somewhat si nilar to that. of 
 Fig. 59. But the structure while being sunk, instead of -being a coffer dam, is in 
 the first instance an annular pneumatic caisson. After .reaching rock rnd when the 
 work ing- chamber is sealed with concrete, the structure properly becomes a coffer 
 dam shell -to be excavated in the interior and filled with concrete and masonry 
 just like the work of Fig. 59. 
 
 The term "coffer dam" is often used for the detachable wood box which 
 during construction fits upon the higher levels of a deep pier. Such coffer darns 
 are detachable timber box-like frames which extend usually from the mud line or 
 river or bry bott cm to above mean high water. Within this box. the upper part of. 
 the pier, lighthouse or water intake, is built in the dry, after which the coffer 
 dam is removed. Below the mud lire or water bottom the foundation extends to rock 
 or other suitrb'le foundation bed, usually of crib work construction. See Eng. 
 ^ews, Vol.37, p. 331; also Fig. 64 for illustrations of these special detachable 
 coffer dams. Consult also "The Design of a Railway Bridge Pier" by C^Derleth.Jr. 
 plate 7. See also Baker, Treatise on Mr.sonry Construction, Fig. 93, p. 434.; and 
 Patton, Practical Treatise on Foundations, 
 
 DUMBARTON BRIDGE FOUNDATIONS. 
 
 The recent construction of piers for the Dumber ton bridge, San Francisco 
 Bay, exhibits a special application of the coffer dam process, See Trans. An.' 
 Soc. C-E, , Vol.76, p. 1572. These piers consist of steel shells filled with con- 
 crete and rest on pile clusters. To protect the piles r.r: piers against erosion, 
 
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192 
 
 the pile clusters extend upward into the steel shells, vhich are of circular 
 
 plan; the largest shell being 40 ft. in diameter; the smallest 18 ft. Because of 
 the swift tidal currents these shells had to be held in place by. a structural 
 steel framing very similar to the framing of a gas holder. The steel shell cor- 
 responds to the gas holder tank but was slid into place in sections outside its 
 frame; one section of shell after mother being added' as the work proceeded from 
 the bottom upward. Concrete v^.s deposited inside these shells in still water. The 
 steel frame and first sections of shell were weighted and jetted to piece after 
 about 10 ft. of mud and sand tod been dredged frcm the pier site with an orange 
 peel bucket. For the largest pier the frame and shell were placed and the dredging 
 and pile driving done from false vork built upon eight clusters of piles driven 
 to forma hollow square, 48 ft. on a side, enclosing tiie pier space. After the 
 first sections of pier shell were in place about their guide frame the ground 
 within was further excavated, the center portion being dredged about 5 ft. Deeper 
 than at the outside which just about offset the uplift of ground due to driving 
 the outside row of piles first and working towards the center with succeeding 
 piles. Concrete was deposited in any section of the shell to within 7 ft. of its 
 top, this being the highest level to vhich the concrete could be placed with out 
 disturbance from the tidal currents passing over the top of the section. A bottom 
 dump bucket was used raving a capacity of 18 ca.ft. A diver wcs continuously 
 
 employed. 
 
 ADPITIOHAL REFERENCES 
 
 1. Harlera Ship Canal Bridge; V/.H.Burr, Proc. Inst. C.E. of Gt. Britain, 
 Vol.130, p. 220. 
 
 2. See Indices, Engineering wev/s, 1890 to date, heading "Coffer Dams". 
 
 3. Ordinary Foundations; C.E. Fowler 
 
 4. Proposed Coffer Dam for Raising the Battleship ;,!aine, Eng.Eews, 
 Vol. 52, p. 520. 
 
 5. The Forth Bridge; report by P.Phillips 
 
 6. The Chicago Ship Building Co.'s New Dry Dock; Eng. Hews, Vol. 34, p. 50 
 
 7. New Type of Thin Wall Coffer Dam; Eng. News-Record ..Vol. 83, p. 817, 191S. 
 
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193 
 
 CHAPTER 10 
 OPEN CAISSONS 
 
 If an open caisson is to be employed, the foundation bed must be leveled 
 with a fair degree of accuracy to receive the caisson in its true position. In 
 such cases it is good procedure to build a bottomless box with its lower edges 
 shaped to fit the river bed or other bottom as closely as practicable. The sides 
 of this bottomless box should be carried up well tov/nrd the surfr.ce of. the water 
 or perhaps completely to that surface, so that 'all current at the botton of the 
 box may be entirely destroyed. After the box has beer, sunk by loading upon plat- 
 forms at its top stone or other heavy material,' the open places under its lower 
 edges must be closed. This can be done very satisfactorily by depositing bags of 
 concrete around the interior of the box and either bags of concrete or bags of 
 sand around the exterior edges. A bank of -gravel or rip rap of suitable size, or 
 a combination of th.3 two, should be deposited about ube outside of the box; the 
 latter in the meantime being held securely in position by such platforms, cribs, 
 anchors or piling as the current may rake necessary. The bottom of the enclosure 
 thus formed must then be cleaned most crrofully and thoroughly of all clay, nad, 
 sand or other fine or soft material or denri^, by dredging, scraping or similar 
 methods, in vjhich operations divars are frequently employee:. This cleaning is 
 imperative for a good bond between t he foundation bed and the footing course. 
 Concrete may then be deposited under water frcn properly designed buckets in the 
 inside of the box on the prepared foundation "bed. 'The upper surface of this con- 
 crete footing should be truly horizontal raid usurlly the aass need not be more 
 than two to three feet in depth at its shallowest point. The upper surface of the 
 concrete can be mr.de horizontal v.hen it is being deposited by placing either small 
 scantlings of timber or light railroad rails horizontally across the box along 
 its narrowest dimensions so that upper SIT faces may be 2 to 3 ft. above the 
 highest point of the bottom. The concrete should be deposited in uniform layers 
 until the too of the freshly deposited mass is a little above the upper surfaces 
 
';. ~ 
 
194 
 of the scant lings or mils; tfce letter being 6 to 8 ft. apart. If a lighter 
 
 railroad rail or other similar bar of metal be swept along the tops of the scant- 
 lings the upper projections of the concrete will b e smoothly leveled off and 
 most or all of the depressions in it will be filled. If any depressions wfcicfc re 
 not filled be found, additional concrete can be deposited at such points whether 
 before or after the. leveling rr.il is swept over it. In using this leveling rr.il, 
 particular care should be taken to disturb the concrete only so much as may be 
 necessary to level it. 
 
 The concrete footing mass will thus be located at the bottom of a well 
 of absolutely still water and it should be allowed to set from 2 tor 3 to 4 or 5 
 weeks before a load is placed upon it. At the end of that period of time it should 
 be carefully tested by the end of an iron rod or pipe at all points of its surface 
 to discover whether it has hardened in a satisfactory manner. If it has not, all 
 soft portions should be carefully excavated, by a diver if necessary, and the 
 resulting depressions filled with rich mo roar or concrete in suitably sized bags 
 so that a satisfactorily hard, continuous bed may be afforded for the reception 
 of the open caisson. This type of bottomless box is shown in Fig. 60. The sides 
 are seen extending up to mean low water and down to the rock bottom enclosing the 
 mass of concrete 3 ft. thick-. For a distance of 6 ft. from the bottom the 
 sides of the box are made of 4 in. by 12 in. planks, and above that elevation of 
 2 in. planks. The vertical pieces to which the plank sides are bolted or spiked 
 are 4 in. by 8 in. in section and about 4 ft. rprrt, 
 
 PIER III, KkRLEM SHI? CA1&L BRIDGE, ME7 YORK. 
 
 ThS open caisson shown in both horizontal an?, vertical section in Fig. 60 
 was built on two layers of 12 in. by 12 in. timbers laid solidly at right angles 
 to each other, with a 6 in. by 12 in. caulked platform above them. This solid 
 timber bottom is built either on shore and launched or else in the water. The 
 6 in. by 12 in. plank sides are then built around the edges of this solid timber 
 platform, but ore not bolted or spiked to it.. Those sides are simply held down 
 on the platform by the 1 1/2 in, rods running from the 10 in. by 10 in. 
 
195 
 
 cap pieces down to the upper layer of 12 in. by 12 in. sticks. Horizontal recesses 
 are cut into the latter timber in which butts for the rods are placed. The rods 
 may therefore be entered in the holes provided for them and screwed in the nuts, 
 
 * 
 
 thus giving them a firm hold to the bottom of the caisson. When the upper nuts 
 are screwed down onto the cr.p piece the sides of the caisson are drawn so tight 
 on the caulked platform that the joint between the sides and bottom of the caisson 
 may be made water tight. Eye-bolts and hooks are sometimes used to hold the sides 
 of the caisson in place and other devices are also employed. After the caisson is 
 thus constructed either partially or wholly, One side of the bottomless box already 
 described is removed down far enough to permit the open caisson to be floated 
 into place immediately over the concrete bottom. The masonry of the pier is then 
 started on the caulked platform of the caisson, the whole gradually sinking as 
 the masonry is laid in place. V/hile this sinking is/progressing, the caisson must 
 of course be held rigidly in its proper position by requisite platforms and braces 
 so that when the sinking is completed it shall rest accurately on the concrete 
 bed. If water leaks into the caisson to any material extent, it must be pumped 
 out. As the caisson sinks, its sides are braced either against the completed 
 masonry or against each other, so as to resist the increasing lateral pressure 
 of the water. 
 
 A reference to Fig. 60 which represents the bottomless box and caisson 
 actually used in the construction of the Harlem Ship Canal Bridge, New York 
 City, will make clear the various steps of tiiis process of pier building as well 
 as the methods of framing ard the dimensions of timber suitable for the Con- 
 struction. After the pier is completed, the nuts on the upper ends of the rods 
 holding the sides of the caisson in place are loosened and the rods themselves 
 are unscrewed from the nuts in the upper layer of platform timbers. These oper- 
 ations release the sides of the caisson and allow them to be removed. The sides 
 of the bottomless box are then cut off or otherwise removed down to or below 
 mean low water. The remainder of the box is frequently left in place. 
 
 If the construction is in sea water so that marine borers may destroy 
 
.-. 1 .- -::, 
 
 ; v ".: '1 , 
 
196 
 
 he timber, it will be best to deposit more gravel or rip rap or both around 
 the bottom of the pier until the timber of the permanent part of the fbunlation 
 is covered, as those animals work only in water. As the plans show, there must 
 be a minimum clearance betv/een the caisson and the enclosed masonry of a foot 
 to 18 ins. at the bottom of the pier. 
 
 OPEN CAISSON SUPPORTED ON Hjg_S 
 
 The same aethod of build ire a. pier within an open caisson is also fre- 
 quently employed where the bottom is soft enough to permit the use of piles. See 
 Fig.GOA. Under such circumstances piles are driven in as regular order as pos- 
 sible over the entire foundation site, with centers rbout 3 ft. apart. The piles 
 are cut off at such distance below mean low water as will insure all timber be- 
 ing always under water or at least saturated. The machine for cutting off the 
 piles under water consists simply of a vertical shaft fitted with a pulley and 
 frequently held between the leads of a pile driver v.'ith a circular saw attached 
 to its lower end. The pulley on the vertical shaft is belted back to and rotated 
 by an engine on the scow, after the saw is set at the proper elevation, it is 
 put in motion and moved about so as to cut off all the piles at a uniform ele- 
 vation. In tidal waters the elevation of fee saw must be adjusted to the varying 
 stages of the tide. The open caisson constructed as already described is then 
 floated into place over the pile foundation and properly braced and gilded as 
 it sinks. The construction of the masonry within the caisson causes it to sink 
 gradually until it rests as nearly un--~r>mly as possible on tha tops of the 
 piles, instead of on the concrete foundation bed in tlie previous instance. 
 
 Before the caisson is brought into position over the piles the latter 
 should be carefully inspected or tested so as to determine v.hebhe~ the tops are 
 all at the same elevation. If the piles Ir.ve not been truly cut of f a* en* 
 elevation, it nay be feasible and satisfactory to place on the tops of t^ose 
 that are low partially filled bags of corcrete. Or, as is sornetirne.-; C one . v.l.in 
 
 t. - 
 
 mattresses of corcrete may be placed on the tops of^ number or all ol tl:o pilss, 
 
. - 
 
 
if the caisson or other imposed load can be brought do\vn on the concrete before 
 the latter is set. The imposition of heavy loads upon fresh concrete thus placed 
 v.lll compress it over the tops of the piles to such extent at each point as the 
 depressed elevation of the top of the pile may reouire. This method of leveling 
 the tops of piles that are irregularly cut off, if performed with due cr.re .and 
 judgment, v.'ill be productive of satisfactory results, Obviously the method 
 is ruite impracticable if the load cannot be imposed before the concrete is set, 
 
 In all these cases of gradual sinkirg of a caisson by the increasing 
 .'nr.ss of ;^r.sonry v/ithin it, careful computations should be made to determine 
 v/hr.t the depth of submersion will be at different stages of the work. This in- 
 formation is needed for the sr.fe regulation and control of the sinking caisson 
 and its load. In all cases the sides of the caisson must have joints caulked 
 
 ith oakum or other similar nrterial, preferably from the outside, in order 
 that the enclosure may 'be as nearly xr.ter tight as possible. 
 
 This method of founding piers is very economical \vherever' it may be 
 applied. It is not adapted to great depths of water although its rair;e of 
 application is sufficiently v/ide to include :viany structures 
 
 ADDITI Qli'. L REFERENCES 
 
 1. Caisson Used in Founding the Swr. \Vall at San Francisco, by 
 Randall Hunt; Eng. Hev/s, Vol.24, p. 96. 
 
 2. Reinforced Concrete Caissons, Their Development and Use for Break - 
 V/aters, Piers and Revetments; by W.y,Judson., Eng. Lev/s,Vol.62,p.34 ; Western 
 Society of Engineers, Hay 19, 1909. 
 
198 
 CHAPTER U 
 
 PNEUMATIC CAISSONS 
 
 A pneumatic caisson is a box or compartment opening downward. Its side 
 and top ere sealed to prevent escape either of r.ir or water. The box is sunk or 
 made to penetrate in water or water-bearing /naterials. During the process of sink- 
 ing water is expelled or displaced from the box or caisson chamber by means of 
 compressed air. This enables men to 30 into the chrmber to excavate material under 
 the cutting edges or in other v:ays facilitate the removal of -naterial and sinking 
 of the structure . 
 
 The foundation proper is bailt immediately upon the working chrmber, For 
 .r.rge and deep piers the foundation produces its own necessary sinking weight. 
 Mrcller caissons such as are used under buildings must often be additionally 
 weighted xvith pig iron or .rcsonry. 
 
 For the passage of men and viaterials vertical shafts extend from the 
 caisson roof to elevations above the permanent water level. Somewhere in each 
 shaft there is an air lock. In modern work the air lock is always at the top of 
 s:aft above the permanent water level. 
 
 The caisson men (often termed "sand hogs") dig out the material viiich 
 
 
 
 consists generally of mud, srnd, .gravel, loose stories, boulders and the like, They 
 dig especially from under the cutting edges. Blasting is someti:nes resortsd to. 
 Specially designed buckets, mud and srnd pumps, and other excavating machinery are 
 frequently used to lift the major part of the vr.terial which is token out' through 
 the material shafts or by pipes, is dumped into scows ani carried av.r.y. 
 
 As the excavation proceeds the caisson and structure above it gradually 
 sink until the cutting edges reach bedrock or other suitable foundation stratum. 
 
 ~ 
 
 The deeper the foundation .bed below the water surface the hi^ier must be the 
 air pressure in the caisson. The grerter the air pressure the more serious is the 
 inconvenience ard finally the danger to the workmen. Thus, the process cannot be 
 used for depths grer ter 'ohan about 120 ft, "below water surface. Indeed, for depths 
 greater than 100 ft. the most important problem is the care and handling of the met 
 

 
 1 . 
 
199 
 
 At this place a general comment mi;;ht be made as to the fitness of 
 different processes for driving -.piers to depths below vr.ter, 
 
 The processes describee! in Chapters 9 to 12 inclusive usur.lly may carry 
 structures to the following depths: 
 
 Coffer dam 40 ft. to 45 ft. 
 
 Open Caisson 40 ft. -to 45 ft. 
 
 Pneumatic 100 ft. to 120 ft. 
 
 Deep well dredging 175 ft. to 200 ft. 
 
 HISTORY OF THE PKEUMATIC PROCESS 
 
 The ider. and possibilities of this process h-ve long been known to engin- 
 eers. The first conception dates from 1647. In 1779 Coulomb presented to the 
 Paris Acr.demy of Science r. prper explaining hov: to execute excavations under wa'ie* 1 , 
 His proposed apprratus was very similar to that now in general use. 
 
 Two processes for utilizing a difference of air pressure for sinking 
 
 * 
 
 foundrtions under water /x-y be recognized: 
 
 1. The Vacuum prccess 
 
 2. The Plenum "xrcoess 
 
 a. the pneumatic pile 
 
 b. the pneumatic caisson 
 
 Pj^yijmc PILES. 
 
 The earliest piles sunk either lay the vacuum or plenum processes were of 
 .-natal; either wrought or erst iron. Such cylinders were usually composed of 
 sections from 6 to 10 ft. long and 2 to 8 ft. in diameter, bolted togetJuer by in- 
 side flanges; see Baker, Art. 863, p. 429, ed. 1909. 
 
 VACUUM PROCESS 
 
 The vacuum process consists in exhausting the air from a caisson (usually 
 cylindric in form) from which cylinder the .material hrs been considerably excavated 
 so that the air pressure from without acting on the cylinder top mr.y force the 
 structure downward By exhausting the air within the pile, water flows into the 
 working chrmber, under the cutting edge, thus loosening the soil and causing the 
 cylinder to sink. The process has only been used for piles sunk through mud or 
 sard. The method is now obsolete. The vacuum should be obtained suddenly so that 
 
. t 
 
200 
 the atmospheric pressure may give the effect of a. blow. Cylinders hr.ve bean 
 
 sunk by this method 5 or 6 ft. by r. single exhaustion. See firmer, Art. 859 , p. 428. 
 
 PLENII! PROCESS 
 
 / 
 
 The plenum process in 3 ts ma:n fertures has already been described in 
 the introductory paragraphs of this chr.pter. It cr.n be applied in sinking foun- 
 dations through all clr.sses of soils. The smaller cr.issons in form are pneumatic 
 piles about 6 to 8 ft. in diameter, s imilatr in general appearance to those tlrt 
 were used in early days for the vacuum process, it present they are common for 
 building foundations or for small bridge piers. They may be of structural steel 
 or of wood stave construction. See references to Building Foundations; particularly 
 Ens. Kews, Vol.40, p. 363, for wood caissons; and En*> News, Vol.30 , p. 458, for 
 metal designs. Lately sane caissons nave been built in part or vhole of reinforced 
 concrete, see Eng. Record, Vol.62, p. 556. 
 
 Pneumatic caissons of large sizes are generally rectangular or polygonal 
 in plan. Most building caissons where not circular are rectangular, of sizes about 
 8 ft. by 16 ft. to 12 fit. by 24 ft. Sometimes, as for pivot piers, caissons are 
 polygonal and. annular, Fig. 65. The great Forth Bridge caissons are circular in 
 plan, Fig. 66; those of the St. Louis bridge are irregular hexagons. Both the Forth 
 and St. Louis caissons are steel. In the last thirty years fc/e greater number of 
 large caissons sunk for bridge pier work hr.ve been of v/ood construction, see 
 Fig. 64; also Eng. iiews.Vol. 65, p. 320; Vol.61, p. 63; Vol.63, p. 9; Vol.62 , p. 546, 
 In the last ten years many caissons, particularly snail ones for buildings, which 
 formerly might have been constnucted of wood, are nov/ being built of structural 
 steel or of a combination of wood and steel, or even of reinforced concrete. 
 
 Wood cais.sons like Fig. 64 will never be altogether superceded by struct- 
 ural steel designs or by reinforced concrete. The selection of type is mainly a 
 matter of dead weight, V/here great piers are sunk to depths below water level, as 
 in the case of the Memphis Bridge, anc. rest upon sand, clay or hardpan at depths 
 of 90 to 100 ft., safe abnormal pressures must not be exceeded. Therefore the 
 pier must have considerable plan and relrtively light weight per cu. ft. of volume. 
 
. 
 
 
 
201 
 This condition cannot be obtained through the design of a structural steel 
 
 caisson filled with concrete, whose weight must obviously be not less than 150 
 Ib. per cu.ft. On the other hand a caisson half of whose volurre or more is timber 
 and the rest concrete ani metal can have a dead weight averaging 100 Ib. per cu. 
 ft. or less. 
 
 The greatest developments in caisson work have been made recently (1) 
 in the care with which the vorkraen are treated, (2) in the design of men and 
 material shafts, and (3) in the construction and operation of air locks. In the 
 Brooklyn Bridge caissons, Fig.67, the two material shafts, 7 ft. in diameter., 
 which -project downward through the caisson roof, during the sinking, were sealed 
 at the bottom by a water trap. Such designs offer great danger fran possible 
 blow-outs. In the same pier the iir.n shafts were 3 ft. 6 in. in diameter with 
 air locks 7 ft. high by 6 ft. 6 in. in diameter, situated just above the caisson 
 roof. In modern work both types of sha ft would be condemned; the material shafts 
 because of the danger from blow-outs; the men shafts because the air locks are 
 far below the outer water level; 3D that in case of accident men could not reach 
 srfety but would be drowned. 
 
 "The first foundations sunk entirely by modern compressed air prxesses 
 were the pneumatic piles for a bridge at Rochester, England, put down 1 in 1Q51; 
 the cutting edgt reached a depth of 61 ft. The first pneumatic caisson proper was 
 employed about 1870 at Kehl, France, for a railroad bridge across the Rhine, The 
 first three pneumatic pile foundations in America were_ constructed in South 
 Carolina in 1856-60. The great St. LOUJ,S bridge caissons were put down in 1870 
 to depths of 109 ft. 8 1/2 ins., which depths have hardly been exceeded since". 
 Cf. Baker, Mrsonry Construction, ed. 1909, pp. 428-455. 
 
 CAISSON DESIGN AND OPERATION 
 
 The clear height within the working chrmber should be from 7 ft. 6 in. 
 to 9 ft., so that the men may have sufficient head roan for their work, but no 
 ercess. The roof of the caisson must be able to hold at lenst all that part of the 
 structure above it necessary to produce the sinking weight, neglecting the upward 
 
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 V:C " : ' r -- ^^ -O;;- - 
 
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 i^.;- 
 
 . :' 
 
 
202 
 
 air pressure in the caisson since at r.ny time a blow-out may occur. After the 
 foundation is completed the caisson chamber is filled v/ith concrete and the roof 
 rio longer must support a part of the s inking weight as a beam. The working stresses 
 in the roof material can therefore be taken high, especially for steel caissons. 
 The side plates or walls of the caisson carry considerable of the si nk ing weight 
 to the cutting edges and also ;.iust withstand the lateral pressure from the material 
 without. Brackets and stiff eners reinforce these sides to properly carry the 
 weights from the roof to th". cutting edge. Again, brackets and stiffening beams 
 or trusses, running horizontally between the brackets, and vertical struts, must 
 ireinforce the sides from being forced i invar d. V.'ith .great depths the pressure from 
 without upon the sides maybe enormous, especially if Icrge boulders are encounter- 
 ed, did glanced by the cutting edges. Too -great a precaution cannot be taken with 
 this part of the design. These stresses also are temporary and vanish with the 
 completion of the work. 
 
 The caisson chamber must be thoroughly caulked whether of wood or iron 
 to prevent Irrge losses of compressed rir. The men shafts should be so located 
 anc: b e of such numbers that in case of accident the workmen may readily get to 
 them. For safety the air locks should be high up in the shafts. The material shafts 
 should be so Disposed that the excavated caisson materials need not be handled 
 and carried too much in the v.orking chambers. Therefore for caissons of large 
 plan it is economy to have a number of material shafts. The tops of the man shafts 
 should always be above v/ater to avoid accidents to the workmen bolow, should the 
 coffer dam give way. The material shafts need not necessarily but preferably 
 should rise above water. All shafts are made in cylindrical sections bolted to- 
 gether through external flanges between which rubber bands or sane soft ar.d im- 
 pervious substance is placed to render the joints air tight. The men shafts are 
 usually 3 ft . 6 in. in internal diameter; the material shafts about 3 ft.; just 
 sufficient to give clearance to the buckets. Buckets are usually cylindrical, 
 
 about 2 ft. 6 in. base diameter, and 3 ft. to 4 ft. high. Air locks for men are 
 usually 4 ft. 6 in. by 7 ft. high with ordinary hinged doois at top and bottom. 
 
.T ' 
 
203 
 
 Air locks for material shafts are of patented types, or sized sufficient to pass 
 
 ' . 
 
 the buckets, with hinged doors below and with sliding doors above, generally 
 operated by compressed air. The sliding doorshust be designed to allow the buckets' 
 steel cable to pass through them without excessive loss of compressed a ir, All 
 locks should be at the shaft tops. As the structure sinks, additional sections 
 are bolted to the shafts, first removing and then again replacing the locks. After 
 rock bottom is reached and the caisson is filled with concrete as much of the 
 shafts as possible should be removed for future use in other work. Air locks are 
 always removed, 
 
 Sinking '.'/eight. The normal frictional resistance on the sides of pneumatic 
 caissons varies with the depth ard is usually found between 300 and 600 Ib. per 
 sq. ft. for depths of 50 to 90 ft. in sand, silt and 1 , mud; see Chapter 2, p. 48. 
 When boulders are encountered the resistance is greater. When much air escapes 
 under the cutting edges the resistance is less. The head of water outside of and 
 the compressed air pressure 'i thin the caisson produce, especially with great 
 depths , a considerable buoyant force v/hich can be rerdily con pa tec".. The sinking 
 weight at all stages of the work must be sufficient to overcome these resistant 
 forces of side friction and buoyancy together with the direct resistance at the 
 cutting edge. KJ::.'. .-. caisson is excavated under cutting edges and ready for the 
 next stage in the sinking, a sudden exhaustion of air gives the effect of a blow 
 to start the mass of the foundation downward. 
 
 Caisson Flotation. Caissons rre usually built upon the shorfc, then launch- 
 ed and towed to the foundation site, where they are accurately located, held in 
 position by cables, staging and piles, and the work of sinking commenced. It is 
 imperative therefore so to design the caisson and such pr.rts of the crib or 
 coffer drm immediately above it that when launched the structure shr.ll have a 
 stable flotation, 
 
 S ink i ng C a i s s on s . No caisson should be allowed 'to sink until a careful 
 
 examination is .rr.de to see that everything is raacVy. After excavations have been 
 ..ir.de under all parts of the cutting ec.ge, the men should be brought out of the 
 

204 
 caisson befcre sinking is begun. The power plmt should have ample capacity, 
 
 especially reserve compressors to supply in case of emergency large quantities of 
 air at a moment ' s 'no ti ce. Great care must be taken aid judgment exercised in 
 sinking caissons to bring them into or keep them in perfect alignment. The cutting 
 edge is a very important feature. It should be made strong enough either to cut 
 through an obstruction or lodge upon it. Should the edge fail, it may force the 
 caisson out of position and even ruin the v:ork. In bringing caissons into align- 
 ment similar principles of excavation are to be observed to those described later 
 for the deep well process. In pneumatic work this feature of excavation can be 
 more intelligently and certainly prosecuted. Consult Eng. toews ,Vol. 63, p. 9, for a 
 description of the sinking of the caissons for the I/lcKinley Bridge, St. Louis. 
 The same subject is treated further in Engineering-Contracting, Vol. 33, p. 77, 
 
 Excavating; Lifts and Pumps. Sard lifts, mud pumps, etc. operated by com- 
 pressed air and water are very efficient in caissons sunk through soft materials. 
 Sea the references in this chapter, but parti cularly the Reports of the Memphis 
 and St. Louis Bridges, ard the article describing the Havre de Grace Bridge 
 Caissons, where different styles of pumps are exhibited. 
 
 Physio lo icr.l Effects _of Conroressed Ai-.?L'' > I. ( L2?LiLIL s _ AIL Krnd li iy* \7oitemen. 
 To avoid as much rs possible the ill effects of the pneumrtic process on men when 
 working at great depths, observe the following: 
 
 1. Select only healthy men 
 
 2. Prevent sudd on changes of t anperature 
 
 3. Avoid candles and gas, and use only incandescent electric lamps. 
 Th&s prevents soot in the working chamber , w hi ch men would otherwise breathe into 
 their lungs. 
 
 4. In winter give shelter to the men when coming frcm the caisson. Under 
 high pressures they should bo released frcm the air locks with precaution so that 
 they are not subject to chill from sudden change in tenperature. 
 
 5. See that the men do not indulge in alcoholic .Liquor or violent exercise, 
 
 6. Rigorously police sanitary rules in large e.aiasors employing many men, 
 
 7. Shorten the working hours with greater depths, usi rg as lev.' as two 
 hour shifts for hinh heads of water pressure. 
 
 8. For great depths provide elevators in the men shafts. 
 
 9. In summer and with great depths the a is son 1 temperature is apt to be 
 high; proper refrigeration or cooling plant should be installed. 
 
 10. The air compressors :iust be able to supply the rnar'i^urn quantity of rir 
 required per minute in the crisson, and in addition that required for emergency 
 ard that for the operation of machines and to supply leakage. Otherwise there is 
 danger from blowouts rnd fro,n sudden chilling to the men in the chamber. 
 
205 
 For a more detailed discussion of this subject read fee following: 
 
 1. French Government Regulations for iVork tinder Compressed Air; Eng.News, 
 Vol. 62, p. 718 
 
 2. Caisson Disease and its Prevention; by H.Japp, Trans. Am. Soc.C,!!. 
 Vol.65, p. 1, 
 
 3. A Symposium on Caisson Disease, Eng. Kews, Vol.68,p.862. 
 
 4. Caisson Sickness, by Leonard Hill, published, by Longmans, Green & Co. 
 1912, 
 
 5. A Compressed Air Hospital; Eng. News, Vol. 23, p. 557, 
 
 CAISSON CONCRETE 
 
 Caisson concrete should be ric h and. fairly wet. Compressed air tends to 
 drive the water out of concrete. The best Portland cement should be used; a concrete 
 of 1 part cement, 2 parts sand, and 4 parts broken stone to pass a one inch ring 
 is now commonly prescribed. In fact broken stone to pass a 1/2 or 3/4 inch ring is 
 sometimes specified. Care should be taken in laying and ramming the concrete .near 
 the roof and corners of the working chambers. In large caissons it is often advis- 
 able to divide the working chambers by partitions into distinct compartments. This 
 reduces the tendency for serious accidents during sinking but separates the masses 
 of concrete . 
 
 The Caisson and a considerable portion of the foundation above it should 
 have vertical sif.cs From the cutting edge to the top of the roof of large steel 
 
 S 
 
 caissons the height measures about 12 ft.; for v/ooc. en caissons it is more, about 
 20 ft. A slight batter, perhaps 1 in 24 , may exist in the sides of the permanent 
 crib work above, but large batters aggravate the problem of aligimont and do not 
 seem to reduce materially the side friction. The sides of the caiason and crib 
 should be as smooth as possible and with steel designs, all rivots should be 
 
 
 
 countersunk' on the outside. 
 
 CRIB WOHK AIID OFFER DAM ^ 
 
 Crib work between the caisson roof and the river bottom, for bridge piers 
 may be constructed of hervy timbers, the spaces between the timbers being filled 
 v.'ith concrete. The crib ficminj should be designed to make the concrete act as a 
 solid ,-iass. L detcchable coffer darn with vertical sides is bolted to the crib work 
 and bracod laterally from within to withstrnc 1 the water pressure w ithout. The joint 
 
206 
 between the coffer dam and crib work must bo water tight. A layer of hemp raid 
 
 cotton has r.t times been used for this purpose. Inside ihe dry coffer dam t he 
 masonry is built. Below water the pier usually is entirely of concrete,Tabove 
 water it may have a cut stone froing v i'th a concrete Iierrt. After the pier or 
 structure is conplete above v/ater the coffer darn may be removed and used again 
 some where else, 
 
 i EAST JIIVEB 3EIDG-E 
 
 Fig. 63 shows one of the tower piers of Hie ivew East Eiver Suspension 
 Bridge, Sew York City. Fig. 64 gives a skeleton idea of its caisson and permanent 
 crib. Both caisson and crib are of timber work. The caisson is divided into three 
 
 
 
 compartments by too heavy partitions through which openings have been provided 
 for communication between the parts of the working chamber . The caisson proper 
 is 20 ft. in depth, the permanent crib 33 ft., and in this 53 ft. the foundation 
 has tertical sides. The main caisson and crib timbers are 12 in. by 12 in. The 
 sheathing consists of two layers of 3 inch plank. Diagonal 3 in. by 12 in. sticks 
 for so;ne distance above the wo iking chamber give beam strength to tbs caisson roof, 
 The cutting edge is shod with a 6 in. by 8 in. by 7/16 in. angle and .e vertical 
 edges of the c ai sc.v: end crib are protected v/ith 1 1/4 in. bant plates,, 
 
 ::.V-IITE AYE. &V/IPG BRIEGS, N3" YCH'" CITY 
 
 Fig. 65 shovs u" e foundation of the pivot pier o f the Seventh Avenue 
 Bridge across the Earlem River in Hew York City. The caisson is cylindrical on 
 the outside and octagonal on the inside. It is snnulax ere. has a clear herd room 
 within of 8 ft. The cutting edge and outside plates are of steel for a height of 
 15 IS, The side plates are reinforced by 1'2 in. channel struts e.ixl 12. horizontal 
 I-beams. The inner side of the caisson is of 12 in. by 12 in. yellow pine sticks 
 
 
 
 running vertically sheathed with 3 in. plank. The caisccsi roof is of 12 in. by 
 12 in. sticks sheathed with 3 in. plank. A trussing 7 ft. deep of 12 in. by 12 in. 
 pieces supports the roof. The removable coffer dam, a polygonal frame of sixteen 
 sides exists above the elevation - 11 ft,, from which level the rock fcced part 
 of the -3ier starts. Its framing is clearly inc'icrted in the plan. In the heert of 
 
the pier is found a cylindrical mass of concrete of 10 ft. 6 in. radius less rich 
 than the rest, it consists of one natural cement, 2 sand end. 5 broken stone to 
 pass a 2 inch ring. The caisson concrete consists of 1 Portland cement, 2 sand, 
 and 4 stone, to pass a 1/2 inch r ing. After the foundation reached rock tot ton 
 and the caisson was properly sealed with concrete, the interior octagonal mass 
 of soft '-aterial was removed. It was intended then to pump out the water from the 
 central veil but due to fissure? in the rock this was found to be impossible until 
 these passage v;ays for water from without were thoroughly filled with concrete and 
 grout. The lower 8 ft. of the well and also the outer portions of the rest of the 
 pier were . ; nde of concrete of 1 Portland cement, 2 sand ard 4 stone to pass a 
 1 inch ring. 
 
 An article on the Design of A Railway- Bridge Pier by C.Derleth,Jr. , 
 published as a reprint of the Engineering I^ews Publishing Co. 1907, is to be con- 
 sidered an appendix to this chapter. Therein are given the principles of design 
 for a masonry pier with wood coffer dam supported on crib work, tho crib work in 
 turn resting upon a rectangular caisson designed in structural steel. 
 
 ADDI TI OKAL RKL7REFCES 
 
 A. BUILDINGS. 
 
 1. Foundations for 'ftew York Municipal Building; by Li.Deutsch, School of 
 Ilines Quarterly., Nov. 1910, Vol.32; Eng. Mews , Vol. 63 , p. 24; Vol.64, p, F-24 
 
 2. Pneumatic Foundations for the Gillender Building, New York City; Eng 
 News, Vol.37, p. 13. 
 
 3. Manhattan Life Building, New York; Eng. Record, Jan. 20, lb 94., p.li2. 
 
 4. Hydraulic Caisson Foundations, Johnston Bldg. , Kew York; ^rgoRuoerd., 
 Vol.32, p. 117. 
 
 5. F.W. Skinner, The Development of Building Foundations; Eng. Scccrd, 
 Vol. 57, p. 412 
 
 6, T.K, Thompson , Underpinning the Cambridge Building; Trans. Am. S^c. 
 CoE. , Vol.67, p. 553. The Kew Singer Building Foundations, Trans, Am. 3oc . C.E, 
 Vol.63, p. 1, 
 
 7.. Pneurartic Foundations of the Emigrant Bank Bldg., Eng, Re<;jrd v Vol . 60 
 p . 528 . 
 
 8. The Substructure of the Bankers Trust Co. Bldg,, Eng. Record., Vol. 62 
 p. 677, 
 
 9. See also En;:. Record, Vol.65, p. 105; Vol. 66, p. 320, 
 
 10. Recent Developments in Pneuaratic Found rt ions for Buildings, by DA., 
 Usina, Trans. A.n. Soc. C,E, , Vol. 61, p. 211, 
 
 B, BRIDGES 
 
 11. Brooklyn Caisson, iJev; York arc. Brooklyn Bridge; Ehg. New?,, ir ol 8, 
 pp,. 182, 213, 224, 232, 
 
208. 
 
 12. Memphis Bridge, Mississippi River, Eng. Sews, Vol.27, p. 470; 
 Vol. 30, p 509; Report by G. S. Morrison, 
 
 13. C/U.n.^r Bridge Foundations; Eng. News, Vol.28, p. 222, 246, 
 
 14. Ti-e Construction of the South Main Pier of the Quebec Bridge, Eng, 
 Nev/s, Vol. 65, p. 3;>4. 
 
 15. Forth Bridge Report by ?. Phillips. 
 
 16. Report on the Washington Bridge, by W. R. Button. 
 
 17. Report on the St. Louis or Eades Bridge- 
 C. GENERAL 
 
 18. A Concrete Pneumatic Shaft at Tower, Minnesota Eng.Record,Vol.62, 
 p. 556- 
 
 19. Construction of Base of Baltimore Light in Chesepeake Bay, Eng. 
 Record, Vol. 57, p. 284. 
 
 20. A Deep Well Sunk "by Caisson; Eng. Record, Vol.61, p. 696. 
 
 21. Dam Foundation Placed by Suspended Pneumatic Caissons; Eng. News- 
 Kecord, Vol.SS, 1013 ,p, 108. 
 
 22. Revised Rules on Co/nprecsad Air Work in New York; Conference of 
 Engineers, Contractors, Workmen and State Departments adopts measures for safety 
 of men and work; Eng. News-Record, Vol.85, 1920, p. 1225. 
 
 23. Experiences in Pneunjati c Caisson Sinking in Mexico, Bridge Pier 
 Sunk 80 ft. with Green Labor; CaiP:;on Provided with Open Well for Dredging 
 Simultaneous with Pneumatic Work; Sng Hews -Record, Vol.87, 1921, p. 848, 
 
 24. Stresses in Caissons by C,E, Fowler; Ergineering-Contracting, Vol.86, 
 1921, p. 1552. 
 
 25. Foundation Problems in Srecting Standard Oil Bldg. , 30 Stories High, 
 Hew York City, by Ralph H. Chambers; adjoining nearby buildings underpinned down 
 through cuicksand, novel method of coffer darn construction; Eng. News-Record, 
 Vol.87, 1921, p. 732. 
 
209 
 
 CHAPTER 12 
 DEEP \VELL DREDGING 
 
 Constructing foundations by the deep well dredging method is one of the 
 oldest known. It finds wide application, and. it yields excellent results, in the 
 greatest depths yet reached. The foundation structure may be framed of timber or 
 iron, or steel, with the closed cells in either case filled with concrete, or if 
 the framing is of timber, they are sometimes filled with gravel. In most East 
 Indian practice the superstructure has been built of masonry (brick or concrete) 
 usually fitted however with an iron cutting edge. The open cells of the foundation 
 structure are used as diredgi-ng wells and they remain open until the foundation 
 bed is reached, Reinforced concrete types are now also coming into use. 
 POUGHKE2PSIE BRIDGE, Kgr.' YORK; TIMBER CRIB WELL 
 EAST OMAHA. BRIDGE, MISSOURI ?IVER; jgTAL_CAISSQH 
 
 Figures 61 and 62 present two caissons designed for the open dredging 
 process; the first shov.s a timber framed caisson used under one of the piers of 
 the Poughkeepsie Bridge, Hew York; the second a steel open caisson under the 
 central pier of the East Omaha Bridge across the Missouri River. As shov;n on the 
 plans the closed cells of the timber caisson were filled with gravel. As the steel 
 shells will corrode and disappear after a sufficient period of time, gravel fillin,; 
 should not be used for a steel caisson, but concrete must be employe-d as was done 
 at the East Omaha Bridge. The gravel and concrete fillings must be deposited in the 
 closed cells during the process of sinking, the weight being required in that 
 part of the process,. 
 
 An examination of the plans shows that the bottom of each caisson is 
 shaped or framed to cutting edges formed to leave dredging chambers with sloping 
 sides leading to open or dredging cells or wells above. These cutting edges do 
 not offer sufficient bearing surfe.ce to give material support to the caisson. 
 Herce as the dredges take out material from the dredging chamber, the imposed dead 
 weight of f-e caisson overcomes the friction of the -surrounding -aterial against 
 
210 
 
 its (Sides. As the caisson sirJcs, the inclined sides of the dredging chamber force 
 the .material towards the center of the chamber and this enables the dredge to 
 readily reach it. In the case of the timber caisson the wedge-like walls of the 
 chamber are usually, though not necessarily, framed of solid courses of 12 in. by 
 12 in. timber. Each course of timber is laid at right argies to those adjacent to 
 it and they are all thoroughly drift bolted and spiked into a solid mass. These 
 wedge like walls might be framed sufficiently strong by leaving interior spaces 
 to be filled \vith concrete. It is only necessary to design them in view of the 
 fact that they are the portions of the caisson vhich are most liable to damage by 
 coming in contact with boulders, sunken timber ot other obstacles whi c h may und er 
 certain conditions produce great pressure against them. It is therefore necess- 
 ary that they should be built of great resi sting power. The walls of the closed 
 cells, containing in this case 3 ravel, were framed in this particular instance 
 of two tiers of 12 in. by 12 in. sticks strongly drift bolted and spiked together. 
 During the progress of the work, these ti Tiber walls must be carried up sufficient- 
 ly high to be above water and the gravel filling must be put uniformly in all the 
 pockets so that uniform sinking may be aided. If the weight of the Structure 
 itself is not sufficient to overcome the side friction or the resistance offered 
 under the cutting edges temporary loading-; of pig iron or other heavy material may 
 be employed. Inasmuch as the entire foundation structure is continuously submerged 
 while sinking, caulking the joints between the timbers is not required. 
 
 The construction of the caisson is begun at the cutting edges; the upper 
 walls of the dredging chambers and wells being built up first. This part of the 
 v.ork is frequently done on shore. After a sufficient poition of the structure is 
 framed, it is launched and the remainder of the framing is done afloat. The 
 portion of the structure thus completed is then towed to the site, carefully held 
 in accurate position by Chinese or other anchors, piles, frs.vied platform or other 
 suitable means, and it is so secured until it has penetrated the bottom Ter enough 
 to be safely held by the surrounding material. 
 
 The -orocesses of constructing and sinking the steel caisson (circular in 
 
211 
 
 plan, fig, 62) are only so far different frcm those outlined for the timber caisson 
 as the cteracter of the material requires. The steel cylindrical snd c onical shells 
 which sta.Tt from or unite in the cutting edge are first carefully riveted together 
 on shore to a convenient height arc", then launched. I'M s portion of the caisson 
 may preferably be made v.i oh caulked joints around the dredging chamber, so t hat 
 there will be no troublesome leakage whan first set afloat. This portion of the 
 caisson may also be fitted with a false timber bottom if recessary so as to secure 
 great buojtancy. It will generally however be better to do without tMs feature 
 
 if practicable. After the lower portion of the caisson surrounding the dredging 
 
 % 
 
 chamber is floated, it is towed to the correct location and held there by precise- 
 ly the seme means described in connection with the timber caisson. It is then 
 sunk by filling the annular space between "ttie two concentric shells with c oncrete 
 which should be deposited in uniform layers 9 to 12 ins. thick and thoroughly 
 rammed. The two concentric s lie lls are then built up with the bracing between so 
 as to receive more concrete until a sufficient portion of the structure has been 
 completed to enable it to reach the bottom. The sides are always carried high 
 enough to be above water and care should always be taken to keep the water out 
 of the annular space so that the concrete may be laid in the dry. After the 
 
 
 
 cutting edge has reached the bottom the operation of dredging is begun. The in- 
 clined sides of the dredging chamber will force the material toward the center of 
 the dredging well as the caisson sinks, thus enabling the dredge to reach it. If 
 necessery this caisson mcy also be temporarily loaded in order to overcome the 
 skin friction which in the materiels usually penetrated is now faiily well known, 
 and it is not difficult in most cases so to (design caissons to ualce their own 
 . weight sufficient to produce the desired, sinking as 13- e dredging progresses. 
 
 By this process a rock bottom cannot in general be r eached. A rock surface 
 could not. be satisfactorily cleaned if a level portion of the rock should happen 
 to exist, although divers might be employed in depths of Vvater not too great for 
 their working. As a matter of fact little or no level rock surfe.ce exists under 
 
212 
 foundation structures. It isnot practicable to level or finish in steps the : .c . 
 
 bedrock that might exist below the dredging chambers of the caisson. It is there- 
 fore usual to sink the caisson into sane solid stratum of material, suchas sand, 
 gravel or hard clay or a mixture of those materials or of others having sufficient 
 resisting or bearing capacity to carry the imposed loading. At most sites where 
 thi^process can be applied it is seldom difficult to find such strata. Foundation 
 beds of this character ordinarily lie underneath softer materials suchas mud 
 or silt and it is imperative that the cutting edges of the caisson penetrate so 
 deeply into the bearing stratum that they can in no way be reached by the scouring 
 action of a v,ater current. It is very e ssential that this feature of any location 
 selected be most carefully and thoroughly considered for among other things, the 
 presence of piers will cause increased contraction of river section and will tend 
 to produce increased scour. In case the river bottom is of send or silt it may 
 be subject to comparatively large soil movements to considerable depths in the 
 riyer bed; as is constantly the case in sediment bearing rivers subject to floods. 
 In the application of open dredging to most conditions it is imperative to fafetyl 
 that the caisson be sunk a considerable distance below the lowest scour. 
 
 There are instances where the bearing stratum is of sand with mud and 
 silt above it in which the penetration into the sand has not been more than 8 to 
 10 ft. The stability secured by such a shallow depth of penetration is more or 
 less uncertain. Other cases exist in vhich the penetration into the sard is a s 
 ranch as 40 to 50 ft. In these latter instances there was very little .nud or silt 
 orer the sand . 
 
 After a suitable depth has been reached in the stratum which is consider- 
 ed to yield a satisfactory foundation bed, the dredging chamber and dredging wells 
 are filled with concrete. Inasmuch as the foundation bed will not be o f rock, a 
 very close boni between that bed and the concrete will not be secured. It is 
 however essential that as much soft material as possible shall be removed from th-- 
 dredging chamber so that the first layer of concrete deposited under water shall 
 suffer as little deterioration at its under surface as possible .- The deposition 
 
213 
 
 of this concrete through the water of the dredging chamber must be conducted wi 
 all ohe care vhich has already been prescribed for that work. It may be necessary 
 at some points to deposit a portion of the concrete in bags, but in general it will 
 only be necessary to deposit from as large buckets as the dimensions of the work 
 will permit, until all the dredging chambers and dredgingwwlls are filled. If the 
 caisson is framed of timber, it will be necessary to place a coffer dam at the top 
 of it in which the neat ,.:asonry of the pier will be started. This is a requisite 
 feature of construction for the reason that it is necessary to keep all pernarent 
 timber below the lowest low vater. The coffer dam will be framed on the top of 
 the permanent timber work of the caisson. Its sides will be of the same general 
 character aid may be held in place in the seme general way as the sides of the 
 open caissons described in Chapter 10; or the detachable coffer dams referred to in 
 Chapter 9. 
 
 If the caisson is framed of steel, fig. 62, it may either be carried up 
 to high water or stopped at low water, or carried up continuously to the top of 
 the finished pier. In the latter ccse, the masonry of the pier up to the coping 
 course will be of concrete r.nd it will be advisable to have the surface finished 
 with cut stone at tih.e points where the bridge superstructure may rest. The dredging 
 wells and dredging chambers are filled with concrete deposited under water pre- 
 cisely as already described for the timber caissons. If the steel caisson be used, 
 it should be borne in mind that the iron or steel portion will eventually corrode 
 anl disappear, although many years may elapse before that operation is even 
 partially completed- It is essential therefore in designing the steelwork of the 
 caisson that the continuity of the concrete masses which form so large a portion 
 of the vhlurae be as little trenched upon as possible. It is not of serious moment 
 whether the plates and gngles or rods eventually corrode away if enduring masses 
 of continuous concrete so remain in place that they do not change their positions 
 in reference to e ech other. Vertical partitions running entirely or any materiel 
 distcnce across the pier should be avoided as their disappearance by corrosion 
 
-'?:.. ..".-c .- ... ,. 
 ^ '*..- 
 
 '-ii J--T;lf??*-iJ't6j ': o"T?T'.';'' - 
 r^ -_..^.-^:i;ii i .': ^ '.^oS'i V: ^^ - '- c 
 
 - - 
 '"' ' " .. i 
 
 -, / : ,.;.,, . y ..--,. 'i.-o^ JJ^I V C^ : J ^' f'Vls 
 
 -' - - --" ; ; -~ 
 
 . . .-:. . > :.ji,_^-. 
 
214 
 would tend to separate the masses of concrete. As the plans show in the present 
 
 instance the only interior partition of steel is the shell of the dredging well 
 which is concentric with tfee outer shell. The corrosion of the former therefore 
 would leave tho concrete of the centralwell a continuous mass. Only the bracing 
 angles and rods are found between the two c oncentric shells end they may entirely 
 corrode away still leaving concrete in the annular space practically continuous. 
 These considerations should govern all designs of stoel caissons whether fbr the 
 
 open dredging process or for any other method. 
 
 of 
 It would conduct to the durability of all timber caissons or, other 
 
 timber structures under water to use wooden tree nails or pins of suitable size 
 for timber framing, instead of iron or steel drift bolts or spikes aid they are 
 sometimes used for sub-aqueous timber work. In most instances however this pro- 
 
 t 
 
 cedure seems unnecessary, at an^/ rate it is not often followed. 
 
 In designing open caissons it is essential to the best dredging results 
 that the number and location of the dredging wells be most carefully considered. 
 In order that the caisson shall sink vertically it is imperative that It bo . 
 pOBdiblo to dredge at different points v.lthin the oxtorior limits of the cutting 
 edge. If tho material is harder under one portion of the caisson than under 
 another, it may be necessary to dredge tho hard portion ahead of the softer. Again 
 if one side of tho Crisson settles faster than the other, it will bo necessary to 
 dredge on the latter side ahead of the former until the error a motion is correct- 
 ed. Similarly other conditions mr.y arise under which it is advisable and fre- 
 quently absolutely necessary to correct an error of moti on by dredging in one 
 particular portion of tho cutting odgo area rather than another. Tho caisson 
 therefore should be so arrargod that this choice of the dredging points may bo 
 exercised as widely as possible. At the same time tho number of dredging wells 
 should bo reduced as far as the preceding considerations will permit. It is ovideu" 
 that the disposition of the dredging wells will bo affected by the shape of tho 
 caisson. In case of the circular caisson of Fig. 62 one largo circular well is the 
 be'st arrange. rent, whcrors in Fig. 61, a considerable number of wolls were wisely 
 
215 
 
 used. The inclination of -the sides of the dredging chamber should not.be too 
 
 great to the vertical in order that the niaterial in the chamber may offer as little 
 resistance to sinking as possible and that at the sane time the material may 
 readily be forced into reach of Hie dredging bucket. No definite \alue can be given 
 to that angle but it probably should seldom exceed 30 to 35 degrees. The pottion 
 of tl-.e plan of the caisson taken for the dredging wells will bo affected by the 
 amount of weight to be secured to overcome the fractional resistance of the sur- 
 rounding material. If the dredging veils take up most of the volume there will be 
 but little weight available for sinking. On the other hand, if they arc too small 
 the operations of the dredge will bo prejudiced. A careful br.lr.nco between these 
 services must be secured in view of the features of each case. 
 
 It has sometimes been thought advisable to batter materially the exterior 
 surfaces of these caissons. A little batterirg may be given to the upper portion 
 if desired, but at least the lower portions for a considerable distance above 
 the cutting ed~e should be cylindrical, that is, opposite sides should be parrllel 
 and vertical. If the batter of the sides coranencos at or near the cutting edge 
 the caisson will be held truly vertical in sinking only with great difficulty if 
 at all. Host serious trouble has arisen in some cases in conseruenco of such a 
 feature of design, There is probably very little decrease of resistance if any 
 secured by battering even the upper portion of the caisaon* Liuch more steadiness 
 and accuracy of sinking will be secured by making the cai ss m cylindrical in its 
 general form, anc? if any portion of the exterior surface is battered that portion 
 should begin at a considerable distance above the cutting edges, as shown in 
 
 Fig. 61. 
 
 The depths of penetration reached by this process up to the present time 
 
 have a ;vsxi:-aum (for bridge piers) of about 170 ft. to nearly 200 ft. below the 
 surface of 'the water. The abnormal pressure on the foundation beds when the latter 
 are sand have in some instances been as high as 11,400 Ib . per sq. ft. although 
 it is more corcmon to fine", the abnormal lords imposed on the foundation beds run- 
 ning from about 5000 Ib. to 8000 Ib. per sq. ft. without any deduction for skin 
 
216 
 
 friction, but with deduction for buoyancy for the foundation material in water. 
 
 Theoretically the open-well caisson can be sunk to any depth provided 
 suitable granular :r,aterial is encountered. Practically tl?.e depth is limited by 
 the weight required to overcome the skin friction on the sides of the caisson and 
 by obstructions offered to the cutting edge. The greatest depth -recorded for an 
 open-well caisson is for a mine shaft in Germany, which was sunk 256 feet. 
 
 In the Omaha foundation, Fig. 62, a system of 3 in. jet pipes 20 in 
 number opened into the dredging chamber ner,r the cutting edge, being reduced to 
 1 inch at that point. Those pipes, imbedded in the concrete, were cesried vertical- 
 ly o the top of the cylinder. At intervals of 10 ft. vertically a connection was 
 made fro :U eech pipe -through the outside shell to the exterior of the cylinder by 
 means of a 3/4 inch pipe. This system of water jets helped to reduce tho friction- 
 al rosiste.rce both for ths sides and cutting edgo and eidod in controlling the 
 descent of the caisson. See Eng. Record, Vol.30., jferch 3,1894, p. 218, 
 
 HAYJKESBUBY BRIDGE, MEW SOUTH TOi 
 
 The Hawkesfeury Bridge in Australia, Fig.62A, had its piers sunk by tho 
 deep well dredging process. These piers are rernrrkable for the depth of foundation. 
 The metal shells are 20 ft. wide and. 48 ft. long in plan between semicircular 
 ends. Each pier was provided with three dredging w el Is, each well 8 ft. in di?m= 
 The deepest pier rests on a bed of Ir.rcL gravel 126 ft. belov; the river bottom, 
 185 ft. below high vat or and 227 ft. below tho track of the bridge. See Eng. News 
 Vol. 15, 1886, pp. 98-100; also Baker's Masonry Construction, p. 425; rnd Fowler's 
 Ordinary Foundations, pp. 94-96. 
 
 COHCHETE CAIBSOF-SPILLVt.Y, C..L..VER.S ILM 
 SPRIHG VALLEY U..TER COIJRiJSY 
 
 On March 24,1918, the Calaveras darth dam fe.il ed. Cf. Eng. Sews-Record-, 
 Vol.80, pp.631, 679, 692., 704; Vol.81, p. 1158; Vol.82, p. 487, It was being cai- 
 structod chiefly by the sluicing method with some dry material dumped from cars 
 in the dovmstream fc.ce. 
 
217 
 Nearly the entire upstream slope of the partly finished dam was 
 
 completely displaced by being pushed outward and downward fir an its normal position 
 into the reservoir to a maximum distance of about 400 ft, 
 
 The top of the completed'. dsm , 25 ft. in width > was to have elevation 810, 
 or approximately 235 ft. above the bed of fee creek, elevation 575. The upstream 
 slope VB.S t o be 1 vertical to 3 horizontal and the downstream slope was 1 vertical 
 to 2 1/2 horizontal. The concrete storm water conduit of horseshoe shape, 19'6" 
 x 19*6", was built approximately along the line of the creek bed from the toe of 
 the dovzistream slope to the toe of the upstream slope, fitted \1 th temporary gates 
 at the upper end aid connected with a concrete outlet tower about 250 ft. high, , 
 that is, with the top of the tovr above high water in the finished reservoir. 
 Fig. 69 shovs roughTy the connection between the tower and the end of the horseshoe 
 conduit. 
 
 The tower was situated on 1he upstream toe of the dam. It rested on rock 
 at elevation 576; its reinforced concrete base vwas an octagon of 50 ft., diameter, 
 The base slab was 9 ft, thick. The cylindric tower shell began therefore at 
 elevation 585, with 4 ft. thickness of shell and 28 ft. outside diameter. The 
 shell tapered to a thickness of 12"' at the top at elevation 805 with an outside 
 diemeter of 12 ft. Both the base and shell were very heavily reinforced, like a 
 reinforced concrete chimney. The tov.'er was designed to withstand in addition to 
 other stresses, the effect of an earthquake acceleration of 6 ft. per sec. per sec. 
 
 The sliding earth at the time of the dam failure produced so great a 
 pressure that this concrete outlet tower was overthrown, the shell being ripped 
 from its base. It vsas moved far out into the lake. 
 
 At the time of the slipping the water in the reservoir stood at elevation 
 652. Fortunately the entrance to the horseshoe tunnel was clogged with debris 
 after the tower failed, so that v.ater ceased to escape. 
 
 It became immediately necessary to protect the injured dam from future 
 flood voters. Two precautionary measures were at once planned:- 1. a horseshoe 
 tunnel 8 ft. in diamo.ter was driven through the solid hillside to the west of the 
 
218 
 
 so that the reservoir might be drained to tho stream below the dam; 2. it was 
 decided to sink a shaft through the mass of material v.'hich had slipped from the dam 
 find--*!hich over lr. id the site of the overthrown outlet tower, 
 
 Fig. 69 exhibits this shaft which was essentially sunk by the dredging 
 process though little wr.ter was encountered since the structure was sunk after the 
 reservoir lir.d been drr.indd by the 8 ft. tunnel already mentioned. 
 
 The slipped material, after the dam failure, had a surface elevation of 
 about 655 t the outlet tower site. Therefore it vr.s necessary to penetrate ver- 
 tically through rbout 70 ft. of nr.terial to elewtion 585 at the base of the.fr Hen 
 tower. It vr.s doterminod to biild this sir. ft as a temporary structure rnd only to 
 
 olcvrtion 665' since for the present water could not safely bo impounded to greater 
 
 i 
 heights in tho reservoir because of tho wrecked condition of the dam. 
 
 It vas first necessary to excavate the ground to give a level space upon 
 which to build up the cutting edge for the caisson spillway shaft. The cutting 
 edge consisted of si;scl plates sot by bolts with pipe s leaves , shown in Fig. 69, 
 by "plan of shoe" anO. "section of driving shoe". The spree between the plates was 
 filled v.lth concrete. Jlio caisson shaft is a right cj .Under 16 ft. outside diam, , 
 concrete shell 2 ft. thick; with sufficient reinforcement both vertically and 
 horizontally to give 'iho structure toughness, not so much against lateral pressures 
 of earth or water , but to ir.r;urc sufficient strength, to the cylinder against 
 sinking strains. The sin, ft ras built in sections using a set cf stool forms 5 ft. 
 deep.. Those forms were us?d over and over again until tho entire shaft ws ccm- 
 
 . pleted. 
 
 Workmen excavated mate-rial frcm inside the shaft, which vr.s token out by 
 
 bucket and derrick hoist. J.s tho oxcavr.tion proceeded the shaft sr:nk under its 
 own weight. Ls it sank, additional units of its height were poured tc keep tho top 
 always above the ground surface. 
 
 Provision was made by pipes in tho concrete to allow of water lubrication 
 
 i 
 
 at the cutting edge. But little difficulty vr.s encountered in sinking tb c shaft. 
 
 7,'licn the cutting odgo reached olsvr.tior rjb:iut 585 sinking vr.s stopped rnd 
 
219 
 
 the shaft thoroughly sealed with concrete to form a \vater tight joint v/ith 
 concrete base of the old outlet tower. At the same time a ccmpleto connection 
 was made by excavation and tunneling between the new spillway shaft and the old 
 horseshoe tunnel. The details are sufficiently shown in Fig. 69; see "Slevation 
 and section through adit". 
 
 1. J.Newman; Notes on Cylinder Bridge Piers and the Uell System of 
 Foundations; published by Spon and Chamberlain. 
 
 2. Foundations, Abutments and Footings; Hool & Einne; article on 
 "Open Caissons" by J. C. Sanderson, pp. 114 - 122. 
 
 3. Open V/ell Piers and Subdivided \7arren Trusses of Bismarck, Man dm 
 Bridge; Eng. Kov/s-Record, Vol. 88, p. 180 = 
 
220 
 
 CHAPTER 13 
 DEEP FOUNDATION PRESSURES 
 
 The determination of pressures is a complex problem when investigating 
 horizontal joints at increasing d epths in deep foundation structures, such as 
 bridge piers aid high masonry dams. Distinction :nust be nr.do between absolute 
 
 
 
 pressure on the foundation bed and abnormal pressure on the seme; see these notes, 
 page 47. When a pier is submerged in water or granular nr.terial impregnated with 
 water, v;e must consider the effect of buoyancy. Water may introduce itself under 
 pressure at any joint or at the foundation bed.. In such cases the moment of 
 stability from gravity loads is considerably decreased. The determination of 
 buoyancy effects however is quite uncorta in sinc-e we must assume tho degree to 
 which water pressure may bo oxcrtod within aid under the masonry mass or at its 
 foundation bed. Consult Corthcll, Allowable Pressures on Deep Foundations; also 
 those notes, pp. 47-49. 
 
 In Chapter 4 pp. 58-66, the stresses on a horizontal joint have been 
 investigated and formulas written for stability against (l) sliding; (2) overturn- 
 ing; (3) vortical pressure or crushing. It can be shown hov.evcr by the general 
 theory of stress the -t the ;naximu:n effects do not necessarily occur on a horizontal 
 joint. There -re?.y bo at some point in the nasonry mass a .greater shear or pressure, 
 or even a tension, on a plane inclined to the horizon. Those observations apply 
 particularly to structures like high retaining walls, or bettor, high masonry 
 dams . which a re subject not only to gravity, buoyant and other vertical forces, 
 but also to groat horizontal thrusts from water or crrth or ice. Consult tho 
 following references: 
 
 1. Morrison and Broclie; Masonry Darn Design, Chap. 8, p. 169. 
 
 2. V7. C. Unwin, on the distribution of shearing stress in masonry 
 dams; Engineering, Vol. 79, pp. 414, 513, 593, 825. 
 
 3. Cta. Cain, Trans. A;i. Soc. C. E. , Vol. 64, p. 208. 
 
 4. L. W.Atchorly and K.Pearson, Or. Some Disregarded Points in the 
 Stability of .fesonry DT.^JS; Proceedings Inst. C.L. , Vol. 162 5 p. 456. 
 
 5. O.L-Brodie; ifc.sor.ry Dam FormuL-s; Columbia University, School of 
 Mines Quarterly, Vol. 29, p. 241. 
 
. - .-.-.- 
 
 i , . . S- i f - ' . ... * . 
 ... J L , . 
 
 : "" ; " "'"- 
 
221. 
 
 6. Stresses in Masonry Dams; Eng. Record, Vol.57, p. 162. 
 
 7. Experimental Investigations of the Stresses in Masonry Dems Subjected 
 to Water Pressure; by J.Y/.Ottley r.nd A.W. Brightmoro; Proceedings Inst. C.E. , 
 Vol. 172, p. 89. 
 
 8. Stresses in Dams; An Experimental Investigation by Moans of India 
 Rubber Models; by J . S.W i Is on and W.Gove; Proceedings Inst. C.E. , Vol.172, p. 107. 
 See also Engineering, Vol.80, p. 134. 
 
 9. Stresses in Masonry Dams; by E. P. Hill; Proceedings Inst. C .E. , Vol.172 
 p. 134. 
 
 10. Bligh; Dams and Weirs; Art. 22, p. 27; formulas for maximum stress. 
 
 In the following analysis, Fig. 68, only vertical loads are considered. 
 The forces W can be treated to include not merely dead, live aid buoyant forces 
 but also the effect of side friction as in the case of piles or cylinders; yet 
 because the masonry dam or pier under present consideration is relatively so 
 massive and large, it is on the side of safety to neglect the effect of side 
 friction by assuming that eventually the mass adjusts itself to its surroundings. 
 
 The analysis given does not involve the effect of lateral forces, such as 
 water thrust on dams ; earth thr us t agrinst retaining walls; arch or dome thrust 
 for abutments or buttresses; ice thrust against dras, bridge piers or water 
 intake towers; current pressure upon piers; or wind pressure on towers' and chim- 
 ne"S. The dynamic effect of wave action against dams is a special case which 
 might also bo iicntioned. Further, in retaining wall and abutment structures with 
 
 unequal lateral pressures on the two sides (as in the case of an arch bridge 
 
 \ 
 abutment which has arch thrust, water and earth pressure on one side and only 
 
 crrth pressure on the other) there might be considered the effect of abutting 
 power of earth on tho land or approc.ch side assisting to withstand the arch 
 thrust. But in conservative practice such a procedure would not be allowec"., 
 though its effect must contribute largely to the lateral stability of deep abut- 
 ments. 
 
 In Fig. 68 let tho pyramid of blocks represent a deep foundation, for 
 example, a bridge pier. AB is tho lovol of the pi or top; h its height above tho 
 mean water level CD. Let EF bo the water bottom. Let the material b etwocn the lovr.-. 
 EF and GH be mud, weighing m Ibs.'pcr 09. ft, Assume tho water weight f Ibs. per 
 cu.ft. Lot the material between the levels GK and JK be sand, of s Ibs. per cu.iv . 
 

 
 , ' >';', -,v 
 
 '. 
 
 
 
 - 
 
 i -/,. 
 
 JU .> j 
 
 : j" 
 
 . ,- 
 
 ! '.' " ' ' 
 
 
 
222 
 
 v/oight and aippose JK to be the rock surf re o or foundation bo: 1 . Lot W represent 
 tine total weight of superstructure resting upon the pier top or first block; ]_ 
 the total weight resting upon tlie second block and so on. Let hi, h, h 3 , etc. be 
 the heights of the several blocks beginning with the top. Let AI, Ag, A 3 , etc, be 
 the base areas, and ti, t2, ts, etc. the v.ldths of the same blocks respectively, 
 Let p be the allowable intensity of pressure at the br.se of the first block; 
 let w be the weight of its :rr.torial per cu.ft., and c a coefficient indicating 
 the relative dimensions of the plan; cti is tie block's width at right angles 
 to the plane of the diagram. Therefore AI = cti 2 , Lot p. bo the allowablc- 
 pressure intonfeity and v/i the weight per cu.ft. of the material of all remaining 
 blocks. Let c have tho s rmc significance for those blocks as for the first. Here 
 a distinction is made between PI and wi for tho foundation, and p and w for the 
 cap or coping. Usually P> Pi If the upper part of a pier were concrete and the 
 lower part of timber crib filled with concrete, then the two parts would have 
 different values for pi andv/i; the crib work taking lessor TCluos for each. 
 
 
 
 Again, tho vc. luo of c might be different for different blocks. Too much variation 
 has been avoided so that tho equations would express principles without 
 prolixity, 
 
 Tho load upon the base of tho first block then is:- 
 
 1/i/l = v7 + cti 2 hiw - cti 2 (iil-fr)f - (l) 
 
 Hero cti 2 (hi-h)f is the weight of displaced water; it rets only with its full 
 amount when water gets freely into the joint at the base of the block. Ehoorotical- 
 ly this quantity should be affected by a coefficient k depending upon the degree 
 of porosity of the joint; k would then vary between zero and unity. For high- 
 values of k the pressure v/ould be smaller in the pier but the lighter effective 
 weight would give less lateral stability against overturning agrinst horizontal 
 forces. This ;atter of buoyancy is of most importance for the joint at the rock 
 sur face . 
 
 In rccc-nt analyses for high masonry dams it is custo;ir ry to assume full 
 buoyant water -oressurc at the upstream edge of the joint, with an intensity of 
 

225 
 
 pressure decreasing line-ally to zoro at the downstream edge. In any case tho 
 distribution and cmount of such prossure from Ic-akage of wrter under the struc- 
 ture must depend upon assumption and that assumption must bo a matter of judg- 
 ment in erch particular design. It is now customary in great masonry structures 
 like darns to provide interior channels or galleries into v*uch to drain off 
 lerkage with the idea that such moans rill reduce to a minimum any buoyant, 
 action, Consult: 
 
 1. J. R. Freeman - Some Thoughts Suggested by tho Austin Dam Failure; 
 Eng. Hews, Vol.66, p. 462. 
 
 2. C. L.Har: ison - Provision for Uplift and Ice Pressure in Designing 
 Masonry Dams - Trans. Am. Soc. C.E. , Vol.75, p. 142, 
 
 3. F, P. Stearns,- ifcsonry Dams and Their Foundations; Eng. Record, Vol.64 
 p. 492. 
 
 4. E. Wogmann - Tho Design of Masonry Dams; Should Hydrostatic Pressure 
 Underneath and Ice Pressure be Included? Eng. News, Vol.66, p. 594. 
 
 In recent years much attention has been given to the study of therraal 
 Stresses in masonry structures. There is no doubt that some crumbling, rupture 
 or shearing may be due to this cruse as well as to the effect of ice pressure 
 from freezing w ate r which has found its way into a crack or fissure. Consult: 
 C S.G-owen, The Effect of Temper ature Chr nges on Masonry, Trans. Am. Soc. C,E, , 
 Vol. 61, p. 399, 
 
 The greatest allowable pressure upon the br.se of tho first block is 
 cti 2 p-, and this quantity must be equal to or greater than eq. (1). ^SSU-TB it 
 ecusi thereto, then, 
 
 ~i ~~~~ ' (2) 
 
 , i 
 if 
 
 PI * c(lii-h)f - 
 
 Equation (2) give?; the -v/alue of t^ and thus we also know A^ and the total weight 
 Alhlw of the first block. The lord upon the br.se of the second block is:- 
 
 W 2 = Wl + Ct2 2 h2 (w x -f) ^ ct 2 2 pl ........... . . ..... (3) 
 
 ct 2 pl is the greatest allowable pressure upon the joint Ag 
 
 In equation (1) it is assumed that water gets freely into the joint A^ 
 thus k = 1 for that joint. If buoyant action is only partial k lies between one 
 and zero. If no water enters joint A 1? k = 0. In general :- 
 Wl = \7 + cti 2 hiw - kcti 2 (hl-h)f, 
 
~ - 
 
 I -, 
 
 . ..'.-i .' 
 
224 
 
 In good masonry water cannot enter the joints freely rnd therefore the 
 tera containing I: is generally omitted, the assumption bein further on the 
 side of scfety, when only vertical forces v/ act. If there are horizontal thrusts 
 then lighter pressures on A give less moment of stability against overturning. 
 Similar rencrks . regarding k apply to lower joints. 
 
 From equation (S) neglecting the inequality :- 
 
 .-..-. (4) 
 
 Af 
 
 y 
 
 - ch 2 (v/i - f ) 
 In 1 ike nr.nner : 
 
 c Pl - chg (Y/! - f ) 
 where rigorously W 2 = Wl + ct 2 2 hg^i - kct 2 h2f . Similr.rly:- 
 
 *4 = W 3 ................. (6) 
 
 /I - 
 
 cp ] _ - ch 4 (v/i - f ) 
 
 It is r.ssvmed in equation (6) c.nd in \vhr.t follo\vs thct perfect buoyc.ncy 
 exists t]ixoughout the entire depth o-f the foundation. This is only true \vhen tlve 
 : ter c-n r.ct freely tlrou^i the mud rnd s^.ixL rnc 1 Ir.ve perfect access to r.ll 
 joints, In neither of its conditionc cr.n this assumption be flilly realized in 
 practice. Further in equation (6) f has been used instead of m because mud ^ 
 
 certainly cannot flov- into fee v.:a, onr y wher eas w~ter as already strted n.y. For 
 the regaining blocks f will be used instead of s. Asa in: - 
 
 t 5 = J Y/4. o .................. (7) 
 
 ] cpi - ch5 (vji - |) 
 
 The total pressure on the rock surface is : 5 = 5 + CtgShgwj - kctgShgf 
 If water gets freely into the bed joint, k = 1, and 
 
 W 6 - V/ 5 + ctG-^hsv/! - Ct 6 2 h5f 
 If no water gets in the rock bed joint k = and 
 
 W 6 = 175 -i- ct5 2 h 6 wi = W +^cthv/o 
 
 Where Tcthw equals the total \veight of H:.e pier, no water gettir^; into any joint. 
 The veight of the totrl cr. terial displrced above bedrock by the pier is:- 
 
225 
 
 M = c (ti 2 *(hi-h) + t2 2 h + tsh3 ] f + ct 4 2 h4m -t- c ^^hs + t6 2 ^6 \ s, 
 The abnormal pressure on rod: bottom is, vith no buoyr.nt reduction: - 
 
 P = Wg - M = W + Fcthw - M ' Ct 6 2pk ....... .......... (8) 
 
 P is the greatest allowable pressure intensity on bedrock. If p Q ^ pi, use p-^ 
 in equation (8). Neglecting tha inequality in equation (8): 
 
 t 6 =A' W -t-gcth-.v - M ....... .......... (9) 
 
 V cp 
 
 If buoyant action effects any or all joints proper reduction mud&t be 
 made in the effective v/ eights of the respective terms inctlro. of equation (S), 
 
 ABDITIOML BLFERMCES 
 
 1. H. L.Wiley, The Sinking of the Piers for the Grand Truck Pacific 
 Bridge at Fort Willion, Ontario, Canada; Trans. Am. Soc. C,E, , Vol.62, p. 
 
 2. O.LaBrodie, Mrsonry Drin Formulas; Columbia University School of Mines 
 Quarterly, Vol.29, p. 241; Vol.31, p. 145. 
 
 3. H, Chatley; Stresses in Masonry. 
 
 4. C.S>G-ov/en - The Changes at the New Croton Bam; Trans. Am. Soc. C.E, 
 Vol.56, p. 32. 
 
 5. Col. Harrison and S. H. Woodv/ard , Lake Cheesman Drm rnd Reservoir, 
 Trans. A;-n. Soc. C,E.-, Vol.53, p. 89 = 
 
 6. L.Jorgensen; Arch Dam Design; The Constpjit Angle Arch Dam; Eng. Hews, 
 Vol.68, p. 155; The Influence of Poisson's Batio on Stresses in Arch Dams, Eng. 
 Hews, Vol.68, p. 208. 
 
 7o H.LKDworth, G-eology of D?JII Trenches; Eng. lews, Vol.67, p. 476; 
 Asso. of Water Engineers of G-t. Britain, 1911. 
 
 8. G.YoWisner rnd E.T. Wheeler, Investigation of Stresses in High Masonry 
 Dams of Short Spans, Eng. Ee\vs, Vol.54, p. 141. 
 
" 
 
 
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in '!. ^m 
 
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 f~~IG / F^/ar? and Drofiie of ^for-m H>n<f Cross'ina -showma results 
 
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 24- 
 
 or JO'-/'- fT 
 
 r?f of off} 
 
 
 nvcr/e 
 
 ffpril 
 
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 __Y_ 
 
 1 ^. 
 
 * * 
 
 ! 
 

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 SECTION ON LINE JK. 
 
 8.333 
 
 
 49 fat 
 
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 0' 
 
 0' 
 
 slope o 
 
 parabola of 
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 K 110 = 1.10 
 100 
 
 A - A' = 
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 4.4 y. 0.832 
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 for 
 
 Properly Stepped 
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 Slope of Equal 
 Stability 
 
 i =^54l' 
 
 \ 
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r r 7- 
 

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