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. O O O,O O O O IQO O O O O O O O Q O O O O ^ 1 -4rt H . r E =4^1 o ooooooooo o 1 ooooooooooo ooooooooooi rrn I i 6 ooooooooo o' o ooooooooo o' 6656 060660600600000066 ooc lOOJO OOOOOOOOOO OO OO OOO OOOC 000 OOO ^Jl_ ^^ 4 p rv * > -r ^r,? "_t ~ ~ 14 DESIGN OF A RAILWAY BRIDGE PIER. ; _ _ DESIGN OF A RAILWAY BRIDGE PIER. 15 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 S \ I I ^ f I ..lAvyi 4-^-4. 'Vr'./T! a i \ ? 4- V, I ts t 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. BOORS FOR ENGINEERS Bridge Design and Construction Concrete Construction Contracting' Drafting and Lettering EartHworK Hydraulics Municipal Engineering' Railroads Roads and Pavements Structural Engineering Surveying Tunneling AMERICAN RAILROAD BRIDGES, by Theodore Cooper, C.E. $2.00. BRIDGE AND STRUCTURAL DESIGN, by W. Chase Thomson. $2.00. ENGINEERING STUDIES (Stone Arches, etc.), by C. E. Fowler, C.E. 12 parts, each $0.25. REINFORCED CONCRETE, by A. W. Buel and C. S. Hill. $5.00. CONCRETE BLOCKS, Manufacture and Use in Building Construction. $1.50. THE CEMENT WORKER'S HANDBOOK, by W. H. Baker. $0.50. ENGINEERING CONTRACTS AND SPECIFICATIONS, by J. B. Johnson. $3.00. SPECIFICATIONS AND CONTRACTS, by J. A. L. Waddell and John C. Wait. $1.00. COST DATA, by H. P. GILLETTE. $4.00. TEXT-BOOK ON PLAIN LETTERING, by H. S. Jacoby. $3.00. LETTERING FOR DRAFTSMEN, ENGINEERS AND STUDENTS, by C. W. Reinhardt. $1.00. TECHNIC OF MECHANICAL DRAFTING, by C. W. Reinhardt. $1.00. UNIVERSAL DICTIONARY OF MECHANICAL DRAWING, by G. H. Follows. $1.00. LINEAR DRAWING AND LETTERING, by J. C. L. Fish. $1.00. SHOP HINTS FOR STRUCTURAL DRAFTSMEN, by John C. Moses. $0.25. EARTHWORK AND ITS COST, by H. P. Gillette. $2.00. EARTH DAMS, by Burr Bassell. $1.00. EARTHWORK TABLES, by R. S. Henderson. $1.00. HYDRAULIC DIAGRAMS FOR THE DISCHARGE OF CONDUITS AND CANALS, by Charles Swan and Theodore Horton. $1.00. BRITISH SEWAGE WORKS, by M. N. Baker. $2.00. MANUAL OF AMERICAN WATER WORKS, by M. N. 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Stautter. $3.50. Full details of any of these books and other publications of the Engineering News Book Department, will be sent on request ; also information regarding any becks of a technical or general nature published by other houses. Engineering News Book Department 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 - --"- -^ I 't*.U --:-. - 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. .,. "^ & .. .-*-' LI . -^ rj r i -^ ,, , fcn-CA :; ' :i; 3S1? . rrr v*.c s" t " " u:: "' ! " : ' J ' " .^^--ut -- 1 ? ; ^-- ,, : .., . ., ^-jwii .^-* i - -. - , . r . . * " "> { ' ' ' J *' ~*" *" ** " ;v ' ' r . - . . - , ry;v '.-.- - 2- 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 *' V T,;.-, -.,-, -.,.. . *P| ^.-.Jdi/r ;..:; > : , . -f.y ; . ?ifi *<v ., j- ;..<, -K.C. , . - . i 7 ._ <" !.>". '-r . ; . " -^i '> " ' . - . '.,-.. .. ..' ?-;-- ----':.. .-.. _.- 1 -. - i ~ '- '' ' "'' ' '?? ' - ' 1.' ;' - . .' *. "* '" ** J " ft * ...frv^.V.:!^ ai-^*^CX>v/.lo --..-/<; *$ ft- " sf ,; ..i. -j\- ; '' " ; '- !' ~ C : ^'?-": .;r o, -- -, . -* . ''-- OA 1 c, : v-^'3 ;ye">/--ov: ,f^ : .;-.:. . ... ii - - .i .; fi ft - 9 ! V% J-^S?T:;. fii.111 ..--, ... . J ' - --?-"." j. ' * ' . '- -- ? ' .,1 ' ,, .., : " ! "''' ; -" "" c :.1i ^ - Jv-'J * a--.-* : . ---, " J -^- :f -- :- i.- ./i . j : J"Z . -r- ..... : 7- a- O* V, " 1 3. 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 '" '-"! ** ' : - " -'-. ,' ,- ^ 7 '- ' 7 '- '" ' '":. i -- - - .. ' '-':-.'. A.- j-c;. CSSr.'T ..,;-. j- 4 ' "^ -' * ^ "^ ' .' ' - 5 : . ,.v> t .:: -.: ^ ..... .. . - * ... j_ r r , n . . , " ^ : '- .'-< M.. ' "' - - ..'.-; ' ': ' 'L ^ . -i. -. . . - svsw<4j:,. ^ ., ".ri-ors > > 7f . ^ . _- C ..- . -. ; "' -' L ~ " - t .- .;\. -, i! , 3 ' ' v " :i - ; 4. inexpensive and requires little equipment; therefore it may be advantageously 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 easily "by its own -Height but Is difficult to raise, especially in compact : "' JO A. -I:-' :. ..-.-': -/ih ' . --'. ' 5:: A ' "'-.i^ ,. v-o u^-.-j.! -- :.? -co ! ... . ':'. C .'^"j*c,^ '^ " "' :::;: ' ; -' J ' - :.-' 33 , V / -- i-^ ' -- ' - .'; ;>i? - : ',i^. '. .:ilvi/o^ ii.: 60 J : -.TOI.' J. 5. 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- :'f ' - K - .ii .. . .- " -T ' ' ' -0 . - . _ -- - -} --.- -/ - W--: ; -- A I C^. /.:." -cio 6. 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. V ^ .^ - '. Jli' ;v 2 or.-: r 8i 7. 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^ t .."*** *^ '-*" ' ** "--'* *- Jf ^m Li, J . itV i -. - -'^' / . I *^ /* ." . .' -"., . *" . . -fc -v'^nf^^ 7 '^f^ 5 !* -.'--. g : U3M??.j ..-^'' 3 .^?^^ J& ^^f v ^ ?*^ /s, n i- J i ....:. -., --..?ffJi,^il ....;-,',.; ! 4 .. .. v ,..-- } , ,. . : . ?* iin ...'.- " ".O'iiG i'. ',. ,".:". :c, : j ..3-q rfjPj? ^-^'i, _n'3 .,fc:. ? , u i ) 3jvlO acTr *i ,.. ;. tfjjw ai. Ipv-jj-f ;pJ.i", -hawo . - Jriw tti pJta sci? '-* : -- :- f -( .- rv,-.' ;-:; ~ AX /'-:. ?;;: 3 viie ,-i^r . !>'.'-- -^T- ; ^-t.~ t ^B-r.^-^'P-'*-^ S^-i.'i?Cf >; .. . 10? . SO-YiT'.'S Cfrtd' .TlCli .i p^>S!. SrfT,^^.I.-0. . ii.-".j.-.i a,--,rf''' .. ,. .. - a ... " I ' : 4.i J '- i l 9C i.J :C ,.? kr - ; 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 -J-iJ f'.'"- -> f'SG t.'.'tsi- ,'>V i^ 1 . t .E ... ' .lyr.r/oJ i. .. i. ...... s,riJOn ^:.iv;o $.i.y . -. ; .: . . jn % : a-., i: .'' ,X .,OSI tor. v .'-' .0''^ ^ . '. * 6?^^ "- * v .- '* L - ' - J - t ' f *' ' . lOl *,', , . ... ". ,- .*tiz ^4^ll^. : - - . . -.'^../i.j.rg . , - - - - 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#&: , 1 -"SJ'a ?ii . : ;;...~. ..-T-:.;:? ,si. r !. : --;r i I*;^5 [-. ;t v ^ ;; ^.^t . . .ev y ^ ; i "*v '' ! i r. .C f.,; i '-"""' T - ' fe v:i.-.; *-. -..--j^ >...KV : H;c^/ 3ri ;?** . .fi;.- ^ '-- i i^..: '" .' -. <-' ;. >.. .*:> ". "i'PV- : - -w^. v'^i-L. - -;lr:,-- ?^I^b4i ?* * r " j.ii ;' -'ii-.'. l - ne ' oioi-^r.- ..?* ^cs-'si'IJ i ^.v: ',:. ( 'L. . .: -t:';r^ fvr,--, ^f 1 c . . . . .- 'i ' J .,:'> ft 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.'. :.-' " '" '"--' :> .. 7 ..jn ; L'- : : 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 . ._li, .^,si- ^ i- ' "i- -'> iV- - " ; "- ^-- i c e '" ' ' - - ' -'- : 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 ^ . ,-j ^:; v ! - : .-v..:vo rii - .' crW^ Jbno . . . j (< "J .%-v -;_-.. . - ' , r .- 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" ..'-. - ; - . - > so .v. v ' ' ' -..: ; - , .. . - ' I >"^- c '* : " : >v - ::i .' : - i '-' c - '-- -"ft" -,;."" I- ^" ' ' ' ' ..-. -'-"' '"' .. . : - - ; . : - .;..- - 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 , " '" -' ' .". ' ' ' - t " i -^- . * :--'- :, . -,. -. ... ^' ' ~ 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- - . ' \ :! ,- . . : itiZT&tife'ffiig "fezi ' : ~ ( l'- : ;',- ' ' .. "S5 : rreB':J' ttl ".^tL^V v 'j rri ! 'jT%rc/'"a- - > : ' '"; C ;'::'.'' ' ' - ' -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 *>r=, c. J. ' .:*;.' .; ' '--= uO L. r '.'' ?it -I , : . ;.': ri ^- ih-'r; :: .i - '" t ' : JV ,r;.V ,a.. .10 v"? -u~ ^?v . u.iv 'fi --.cr C-".'i : :v ; .^ ,'iiTT.. 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. ..,; v.'i-y.. : ^'" '- ' ^'" ^ btr ; .'. ; *"' >.o /". : ~' 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 : . , i ' -. . . , ' ' : -I -.;... : . -"- .f .-; :> - r - ' ' : ' '" ' t !( .4v>? . ' '- : i-' l .'% ::'^' : '''. ' . . ; . ' -- . i i*}^ . -..: : l" ..' - r 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 :J. -u:.- -., .. n ': :.v.-yf. ',-}-:... .', y-I'/l-i^ ...:,; ' -:';.. - 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 A' ''-' -' > J'.': ; '": " r. jiir ; ;'..: ., J ':. -Jc.eS r. o3 . 3:.'.: >-/ : ;:-,-. ;. , .. . r3 f".?'--"-^ ;'' ; - -"^ ' .._J^. ..-.(' ;.- . 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 ..-.: :-i,~r,f .s* fjo - . : .'- ;' * 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 i :.# - - .; ...a :.;:,* ' . -'.: 1 .i> t ICi1 . " 'f: ',3; .-.st/'.yi ... ;:.;'T .:.; . . v : ?.'< ; <:- ifa^. ,,v:.; .^. - : ' . " ->' c..- v ..; 3J -S *'b :" : ' - '. .-?''' .' '- I fr. ';:.' '--.u.!.? ; --:.* ; .; >',:.. .-3,.,-i i ;' : , -. ; - :t , : ' " : Mnf-.::'i: <*!* ''.' ' : .:"A?<; "-' | -:: tt ;fl ; , . _ , '(". '' ';'-'. : -1 .':'[ ''.'I;' ;r . -.< -.- *' ' ' "' ' ;r ;"''/:!.:;'. - : "Tis . '4 r - . .? "~l : \ . ; ^ - : f 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 ,.? -.1 ' n . I at- - : v 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, -I. . . tl t ~ * * .__.... ... - ~. ... . . ... Tf. J ". ' '> ; :. ' ' i -I V 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. . /S.V '* .' !'': ^ : T 5 r,i- li '- '"-' ? i " ' : ." . .i.i -: : - '.:. .. - ;':.. ;.' c : : ;r -..-. 'r^^:; C &i ' -' : M '^- . ;: ' : '-'- .:>;- -^;- .-..., v"^ - : ' ! - I v; . ; . .. . -- ,_-.. : . :; ; .. :.. " : ''IH'Vi<;'! .. w ' _ i i . : - 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 ~> .. -. .,./ V ','-- ; -' V ';.. - V:C " : ' r -- ^^ -O;;- - " ' ~ 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. " v ^"^ /U P/f* TO e /r BfD/rocK /j '' tr/ , 1 ,3 } . LOC/IT/O/V of TEST .. 8-6" :$ fJM . / T A /. /o.ez LOCATION OF /QUO/TO f?/UM, P/LE.S s C/)L it r^ ~? 5:^ / \ f PIL.E g Jane/ , S/hcj jAcr of Ao/e 2/f. 0?/0*r jt/rfoce . -cf- >*v Of= TST 3 re. LEGEND. K/- .. rj E: <Jonab (jren C/ffy x -i . 6vftbm ; 'ef-Jn/e. .-v ON LT j i a/ ram e fa TEST H*LL OF FIGURE. 4 F. in '!. ^m ilG. /* General f>lar) and profile of Hudsorj fftver- af" /proposed crossing of- Calsrti/l flqueducf , Show'mo wash borirtys, exploration shafts and horizontal e,ore hcr-injs f~~IG / F^/ar? and Drofiie of ^for-m H>n<f Cross'ina -showma results of cor-e borin 9. >l XI > Timber &rillaqc on 24- or JO'-/'- fT r?f of off} nvcr/e ffpril . _L __ _ __Y_ 1 ^. * * ! . J SECTION ON LINE JK. 8.333 49 fat FOUNMT/ON Or I I J / I I I I/ I I /- I I l!/l J, I .ll \ ' v \ I f\l H I l\ E B 7.2' 5.'0' X \ .0' \ x 5. 0' 0' slope o parabola of cohesion K 110 = 1.10 100 A - A' = 4K cos = 4.4 y. 0.832 = 3.67 .'. A'y = 1-.835 Prelini's Method for Properly Stepped / Slopes and Slope of Equal Stability i =^54l' \ \ \ \J - Figure 36A K -lac ft. :..~-.^ [_ ^ ' -x^^^l _ ^-,^1: * I i i . il .. x ft * LU ' * * i "~~ > ,_ i > J.. ^4 t -- -I Idealized Section of Earth Cut and Timbering. Figure 36B TOP iJ L 4 -I - -u 4O 8 r/ LE. DEPOT, > ' t ' t : - \? ' Typical ConsTrucTion San atofl S3 Concrete Jb &O7. Jroa &oruf_ of )n\/try Cajo F~/G C E i/o/ 6S 1 ' ' I ' i ' i U-.U.i-lJ " >" 1 ' 'i i 'i 12 .%"</ l f - Pro ten J7bf?r. -TOT Ji'afo'rrp * ~ 1, tl : B U I J Li U U L| -5 r' 1 1 | ' ' - ' * I , 2 - , * ^ j _ ^ . KE5T H/tKLEtf . 0/er/e 4. A: ;<: .*':'*. ': . L I 1 I il nn < s/*,,z ._-- - ; I w ' CROSS V- '!_ '' ' & t .-- - v - ^^vr ^ : i 4 f ' VS. . HI9WHHK3S HBB^H f - ^ Jepf. 7, /3f3,f/>. /J$ -Zoo i ^j ^^ o < t " Sock surface *//S/S/^/7?/^7rrsr- Fig. . ._ . *. . : ' ' '': '" '' ? . ...*.. .. n S ^ O xl ,.l - ' ( ' N/\ catena \e> used n Dam , .-., ton ' -< tv o WorKVu t j.H ' ' -i ., v, l 6 5- 1 1 4 ' ft i*J t j - 85 173 TIT l.fal I C-CCUO II 5iO 5"OCOC 3 C. gOOOC -btV ^-^JOO 10 5oo -L . rVI af-eria 13 used in Dam Material fluthont-y and Fir f. ! e. DpeaficOrav. Weight Ibaum - Vlanirrium 1 S>trer-i<g1--i T O ^ ; :'i 268 I - - T I78TJH -*= ' * ' 166? 10 - '5C-' '18 __ ' , : . 1 800 . ! . -. i - - i *C4 - ' i 5<-.. : it-*"- I16f i -V l "*- i si i <!, h ' ' ITO.| tfecco I IB . 3ft8 -iS 00 -0 O w e* t I , , hi> i j '' " o_r 5 \? Z4 8 I 4-0' ' " i | -if | 101 Or ' ' -TeJ 1.11. J.fcS . i-T.8 ' .'_! OZ. . ;>' "*L l.-i_ o._ll -' *-OI I 6 1-1 g 8- ieV o i iM .to ! il-T ' i-c I ' ' < C/iSf /RON v ft J<f. /nc/i \ jy 6 //*. Z 8 //v Z /so /o 8 4o ' Jg 14.4 ! -7^<? 2-f.,? V^ Z#^ ^^^ JZ.4 1 SCO 360 /so /a. 8 ZOff 144 85 I I IS / 130 /'/ 90 I JIO f'/A ;> /A 4So i 7s /A J 4 so I ft /'/i 460 1 7* t'/t 400 288 I BO Z 4 SO 324 ZOO 2'/4 I 7 /g /7* 70 I 7 /g /'/z 160 I fr /'/i 780 J'J* -78 I ft 8 60 /% 99o / 2 96o /SO . /0.8 ZOO 144 9S l/g % i ft / 7 /g f ft /oio /3o I'/i fy 7 /g / 7 /g /'/i "4 /6o i/> $*JJ\J 7 /g //i' 1/60 / fo 2 fa / / / , V '280 400 28.8 26o z <^ 324 290 ' 3 /08 /3o I'/g Z'/t '720 /'A '420 / /% ?% - fOK. J4 //Y t-/ 7'- ZSO /8.0 Z8S Joo 2/6 34S 3S-0 2S2 400 46o 3 / 3Z4 S/S 36.0 SJS /%2 ;/+ 3/4 / J /+ r r 7- UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped belowi ENGINEERING LIBRARY FEB 1 LD 21-100m-9,'48(B399sl6)476 v r YE 789480 UNIVERSITY OF CALIFORNIA LIBRARY