209. Concrete and Reinforced-Concrete Piles. A recent devel opment of the use of concrete and re inforced concrete is to construct piles of this material. A reinforced -concrete pile foundation does not materially dif fer in construction from a timber pile foundation. The piles are driven and capped with con crete ready for the superstructure in the usual manner. In comparing this type of piles with timber piles, they have the advantage of being equally durable in a wet or dry soil, and the disadvantage of being more expensive in first cost. Sometimes their use will effect a saving in the total cost of the foundation by obviating the necessity of cutting the piles off below the water line. The depth of the excavation and the volume of masonry may be greatly reduced, as shown in Fig. 54. In this figure is shown a comparison of the relative amount of excavation which would be necessary, and also of the concrete which would be required for the piles, thus indicating the economy which is possible in the items of excavation and concrete. There is also shown a possible economy in the number of piles required, since concrete piles can readily be made of any desired diameter, while there is a practical limitation of the diameter of wooden piles. Therefore a less number of concrete piles will furnish the same resistance as a larger number of wooden piles. In Fig. 54 it is assumed that the three concrete piles not only take the place of the four wooden piles in the width of the foundation, but there will also be a corresponding reduction in the number of piles in a direction perpendicular to the section shown. The extent of these advantages depends very greatly on the level of the ground-water line. When this level is considerably below the surface of the ground, the excavation and the amount of concrete required in order that the timber grillage and the tops of the piles shall always be below the water line will be correspondingly great, and the possible economy of concrete piles will also be correspondingly The pile and cap being of the same material, they readily bond together and form a monolithic structure. Reinforced-concrete piles can he driven in almost any soil that a timber pile can penetrate, and they are driven in the same manner as the timber piles. A com bination of the hammer and water-jet has been found to be the most successful manner of driving them. The hammer should be heavy and drop a short distance with rapid blows, rather than using a light hammer dropping a greater distance. For protection while being driven, a hollow, cast-iron cap filled with sand is placed on the head of the pile.
Concrete and reinforced-concrete piles may be classified under two headings: (a) those where the piles are formed, hardened, and driven very much the same as any pile is driven; (b) those where a hole is made in the ground, into which concrete is rammed and left to harden.
Reinforced-concrete piles which have been formed on the ground are designed as columns with vertical reinforcement connected at intervals with horizontal bands. These piles are usually made square or triangular in section, and a steel or cast-iron point is used.
Fig. 55 shows the cross-section of a corrugated pile used in the foundations of the buildings for the Simmons Hardware Company, Sioux City, Iowa, and for John J. Latteman, Brooklyn, N. Y. The pile tapers from 16 inches at the large end to 11 inches at the small end. The reinforcement consists of Clinton electrically-welded fabric, the size being approximately -;-inch wires longitudinally, and wires, 12 inches on centers, for the bands. The hole in the center is inches at the top, and tapers to 2 inches at the bottom.
The piles were driven by means of a water jet and hammer. The jet extended through the opening in the pile, and protruded three inches below the bottom of the pile. The pressure of the water was sufficient to dig a hole and carry the loosened soil up the corru gations, and the weight of the hammer drove the pile down. When the pile was nearly in place, the jet was removed, and the hammer was used to force the pile until it was solid. The cap was made as shown in Fig. 56; and in driving the pile, a hammer weighing 2,500 pounds was dropped 25 feet, 20 to 30 times, without injury to the head.
210. Concrete Pile. The Raymond concrete pile (Fig. 57) is constructed in place. A collapsible steel pile core is encased in a thin, closely fitting, sheet-steel shell. The core and shell are driven to the required depth by means of a pile-driver. The core is so con structed that when the driving . is finished, it is collapsed and withdrawn, leaving the shell in the ground, which acts as a mould for the concrete. When the core is withdrawn, the shell is filled with concrete, which is tamped during the filling proc ess. These piles are usually
18 inches to 20 inches in diam eter at the top, and 6 inches to 8 inches at the point. When it is desirable, the pile can be made larger at the small end. The sheet steel used for these piles is usually No. 20 gauge. When it is desirable to reinforce these piles, the bars are inserted in the shell after the core has been withdrawn and before the concrete is placed.
211. Simplex Concrete Pile. The different methods for pro ducing the Simplex pile cover the two general classifications of concrete piles—namely, those moulded in place, and those moulded above ground and driven with a pile-driver. Fig. 58 shows the standard methods of pro ducing the Simplex pile. In Fig. 58, A shows a cast-iron point which has been driven and im bedded in the ground, the con crete deposited, and the form partially withdrawn; while B shows the alligator point driving form. The only difference be tween the two forms shown in this figure, is that the alligator point is withdrawn and _the cast iron point remains in the ground. The concrete in either type is compacted by its own weight. As the form is removed, the con crete comes in contact with the soil and is bonded with it. A danger in using this type of pile is that, if a stream of water is encountered, the cement may be washed out of the concrete before it has a chance to set.
A shell pile and a moulded and driven pile are also produced by the same company which manufactures the Simplex, and are 'worn _ mendPd for use under certain conditions. Any of these types of piles can be reinforced with steel. This company has driven piles 20 inches in diameter and 75 feet long.
212. Steel Piles. In excavating for the foundation of a 16 story building at 14th Street and 5th Avenue, New York, a pocket of quicksand was discovered with a depth of about 14 feet below the bottom of the general excavation. A wall column of the building to be constructed was located at this point, with its center only 15 inches from the party line. The estimated load to be supported by this column was about 500 tons. It was finally decided to adopt steel piles which would afford the required carrying capacity in a small, compact cluster, and would transfer the load as well as the other foundations to the solid rock. These piles, 5 in number, were en very close to an existing wall and without ing it. Each pile was about 15 feet long, and was made with an outer shell consisting of a steel pipe 5 inch thick and 12 inches inside diameter, filled with Portland cement concrete, reinforced with four vertical steel bars 2 inches in diameter. This gave a total sectional area of 27.2 square inches of steel, with an lowed load of 6,000 pounds per square inch, and 100.5 square inches of concrete on which a unit-stress of 500 pounds was allowed. This utilizes the bearing strength of the external shell, and enables the concrete filling to be loaded to the maximum permitted by the New York Building Laws. The tubes and bars have an even bearing on hard bed-rock, to which the former were sunk by the use of a special air hammer and an inside hydraulic jet. The upper ends of the steel tubes and reinforcing bars were cut off after the piles were driven. The work was done with care, and a direct contact was secured between them and the finished lower surfaces of the cast-iron caps, without the intervention of steel shims.* 213. Grillage. A pile supports a load coming on an area of the foundation which is approximately proportional to the spacing be tween the piles. This area, of course, is several tittles the area of the top of the pile. It is therefore necessary to cap at least a group of the piles with a platform or grillage which not only will support any portion of the load located between the piles, but which also will tend to prevent a concentration of load on one pile and will distribute the load more or less uniformly over all the piles. Sometimes such a platform is made of heavy timbers, especially if timber is cheap; but this should never be clone unless the grillage will be always under water; and even under such conditions the increasing cost of timber usually makes it preferable to construct the grillage of concrete. A concrete grillage is usually laid with its lower surface a foot or two below the tops of the piles. The piles are thus firmly anchored together at their tops. The thickness of the grillage is roughly pro portional to the load per square foot to be carried. No close calcula tions are possible; a thickness of from 2 to 5 feet is usually made. When reinforced-concrete structures are supported on piles or other concentrated points of support, the heads of the piles are usually connected by reinforced-concrete beams, which will be described in Part III.