Description of Piles

The Pedestal concrete pile is formed by driving together into the ground a cylindrical casing and a core 2 or 3 feet longer than the casing; and then the core is removed, concrete to the depth of 2 or 3 feet is deposited in the bottom of the casing, the core is driven into the casing, which compresses the concrete and forces it out into the soil below the casing. Concrete is added and rammed successively until the projecting part of the pile has any desired diameter, usually 2 or 3 feet; and then the casing is filled to the top with concrete, and finally the casing is withdrawn.

Concrete piles, both bearing and sheet, have been used to a considerable extent in Europe for foundations, wharves, quay walls, etc.; and are rapidly coming into use, particularly bearing piles, in this country.

Cost of Concrete Piles. The following is the cost of making and placing 172 Raymond concrete piles in Massachusetts in 1906, exclusive of interest,' general expense, and the cost of moving the plant. The minimum length was 14 ft., the maximum 37 ft., and the average 20 ft. The piles were driven until the penetration produced by eight or ten blows was 1 inch.* Concrete vs. Wood Piles. Of course, when exposed to the air, or in sea-water infested with marine borers, concrete is much more durable than wood. In some cases concrete tops have been placed upon wooden piles to prevent the decay of the wood above the water line or to prevent the attack of sea worms above the ground line. Concrete piles cost more than wooden ones (see the next paragraph), and on account of their size will support a greater load, it being claimed that usually one concrete pile will support as much load as two or three wooden ones; but it is not always wise or possible to decrease the number of piles and proportionally increase the load on each. Concrete piles are superior to wooden ones for foundation work in that they need not be cut off below the water's surface, and hence the more expensive masonry structure need not start as low with concrete piles as with wooden ones.

The following exhibit shows the actual cost in 1904 of the con crete-pile foundations for the physics building of the United States Naval Academy at Annapolis, Md., and also the estimated cost of an equivalent wood-pile foundation.

Sheet piles are piles with square edges driven successively edge to edge to form a vertical sheet for the purpose of preventing the soil from flowing into the foundation pit or of guarding a foundation against the undermining action of the water. Formerly

sheet piles were always of wood, but re cently both steel and concrete have been used.

Wood Sheet Piles.

Ordinarily wood sheet piles are simply thick planks, sharp ened and driven edge to edge. Sometimes a thinner plank is driven outside of the thick one to cover the joint and prevent leakage; and sometimes two rows of thick planks are driven. Sheet piles should be sharpened wholly, or at least mainly, from one side, and the long edge should be placed next to the pile already driven, to cause the piles to crowd together and make comparatively close joints.

Formerly, when greater strength was required than one or two thicknesses of plank, heavy sawed timbers were employed as sheet piles, wooden blocks or iron lugs being fastened on the edges to assist in guiding them into position, or a tongue and groove was formed by nailing two strips on the edges of one side of the pile and one strip in the middle of the other edge; but now the Wakefield pile is usually employed when a wood pile is used and when greater strength is required than is afforded by a single plank.

The Wakefield pile, the patent on which has expired, consists of three planks bolted or spiked together so as to form a tongue on one edge and a corresponding groove on the other. Fig. 85 shows a cross section of the Wakefield pile. The planks are usually 10 or 12 inches wide, and 10 to 16 feet long.

Steel Sheet Piles.

Steel sheet piles were first used in 1902 at Chicago; but already a considerable number of forms have been pat ented. They may be divided into two general classes, viz.: those built up from standard structural shapes, and those consisting of special shapes. Fig. 86, shows several of each class. There are several other forms of the same general character as the Last one in Fig. 86; but they are not in as general use. One patent consists of a clip to be riveted at intervals to I-beams, whereby a wall may be built by driv ing I-beams base to base; and a somewhat similar form consists of two separate locking devices one of which is placed on the bottom of the I-beam to be driven and one on the top of the I-beam already driven. However, the interlocking steel piles are usually preferred as making a tighter wall.