Piles Moulded before Driving. The first type must be rein forced to permit of handling, and the reinforcement may be any of the forms used for reinforced concrete columns (see 1 485)4 Such piles may be driven with a drop hammer (1 751-54) or a water jet 757-59). In the former case, the pile is provided with a cast-iron point, and the top is provided with a cushioned head to prevent the crushing of the pile. If the pile is to be sunk by a water jet, either an iron pipe is set in the center of the concrete or a hole is moulded in the longitudinal center of the pile. One contractor makes longi tudinal grooves on the exterior surface of his piles to give an outlet for the water when sunk by means of a jet and also to increase the surface exposed to friction. In this country concrete piles are moulded in either a horizontal or a vertical position, although in Europe the latter seems to be the custom. The progress can be inspected better when moulded in a horizontal position; but when moulded in the vertical position, any laminations are perpendicular to the load. Vertical moulding is the more expensive, but only a little more with suitable facilities.
The Chenuweth concrete pile is made by plastering a woven wire net with cement mortar or concrete and rolling the combina tion about a mandrel to form a cylinder. The mortar is mixed rather dry, but the rolling squeezes out part of the water and secures an intimate contact between the mortar and the reinforcement, thus making a dense and strong pile.
Piles Moulded in Place. There are several forms of concrete piles that are moulded in place, the three best-known being the Simplex, the Raymond, and the Pedestal—all of which are patented.
The Simplex concrete pile is formed by driving a heavy steel tube, 16 inches in diameter, having at the bottom either (1) an "alligator tip" or (2) a cast-iron or concrete point. The for mer is an automatic bottom which keeps closed while the tube is being driven, but which opens and allows concrete to pass through when the tube is drawn up. After the tube has been driven to the desired depth, it is drawn up about 2 feet, concrete enough to fill about 3 feet of the tube is deposited in the bottom by means of a bottom-dump cylindrical bucket, and the concrete is tamped with a hammer dropped through the tube. The tube is then raised again, and the above operation is repeated until the top of the concrete reaches the desired height. This pile may be reinforced by dropping into the casing any unit system of reinforcing.
The advantages claimed for this form of pile are: 1. The cylin drical form gives a large bearing upon the harder substratum. 2. The ramming of the concrete forces part of it into the soil, which enlarges the hole and still further consolidates the soil, and also increases the friction between the concrete and the sides of the hole. The dis advantage urged against this form is that the more fluid portions of the concrete are liable to be lost in a porous stratum of soil. This objection is sometimes eliminated by inserting a casing of sheet iron inside of the driving tube for a part or all of the depth.
The Raymond concrete pile is formed and placed as follows: A tapering shell of sheet iron (usually No. 20) is placed upon a collapsible steel core, and the two are driven with an ordinary pile driver. After the shell and core are driven, the core is col lapsed and withdrawn; and then the shell is filled with concrete. The piles are made from 20 to 40 feet long, from 6 to 8 inches in diameter at the small end, and from 18 to 20 inches at the large end.
This pile may be reinforced by inserting reinforcement which is securely fastened together before being placed in the casing.
Notice that the taper is considerably greater than with wood piles, which the inventor claims is an advantage. An objection to this form of pile is that the thin shell is likely to be wholly or partially closed by the lateral pressure of the soil before it can be filled' with concrete.