Pneu-mat′ic pile.
（Hydraulic Engineering.) a. A hollow iron cylinder or tube closed at its upper end, with the exception of an aperture, through which passes a pipe connecting the pile with a receiver. The receiver communicates with an airpump, and by exhausting the air when the pile is in position over the spot where it is to be sunk, it is caused to penetrate the bottom; the mud, sand, or other deposits through which it passes being withdrawn and discharged into the receiver, while the pile is forced down by atmospheric pressure. This method was patented by Dr. L. H. Potts in 1843, and through its means piles were secured in the hard bottom of the Goodwin Sands, off the coast of Kent, England, after passing through 75 feet of sand. The pile is filled with concrete, and the inventor also proposed the injection of chemical solutions at its foot to consolidate the sand and form a firmer foundation. b. A caisson with a means of excluding water, so that excavations may be carried on in the submerged end. It was first used in France. A mode of sinking cylinders for foundations by means of compressed air, as shown at Fig. 3850, was adopted to meet difficulties incident to building a bridge over the Medway at Rochester, England. It was at first intended to sink the hollow cast-iron piles for the piers by means of the exhaustive process, but the remains of an old timber bridge imbedded in the mud of the river rendered this impossible This foundation cylinder is composed of several sections, as a b c, bolted together through interior flanges; the edge of the bottom section is beveled, that it may more readily penetrate the ground. The top may be either dome-shaped or flat, and strengthened by interior transverse ribs or braces. d is a siphon through which water is discharged by the pressure of the condensed air; e f, air-locks through which the workmen enter and return and supplies are introduced; g, a platform for the hoisting apparatus, which removes excavated material. The cylinder has a supply-pipe and valve for introducing compressed air, a safety-valve, pressure-gage, and a large escape-valve for discharging the compressed air suddenly when required. The operation of sinking is as follows: a sufficient number of sections being bolted together to reach the bottom are placed in position, and, the air being allowed to escape, the cylinder sinks until bottom is reached; air is then forced in, and workmen are sent down who excavate the material beneath to as great a depth as possible; this is removed by the hoisting apparatus and passed out through the air-locks. When this is effected the workmen withdraw, the escape valve is opened, and the water rushes in, filling the cylinder, and allowing it to sink still farther, the closed top is removed, and another section added and secured to the one beneath, when the top is replaced, air is again forced in, and the operation proceeded with as before. It is obvious that the weight of the cylinder must be adequate to resist the upward pressure of the condensed air, or that it must be sufficiently loaded to enable it to do so. When sunk to a sufficient depth it is filled with grouting, concrete, or beton. See air-lock; caisson, where the operations of sinking the piers of the East River Bridge, N. Y., and those of the Mississippi Bridge at St. Louis, are described.
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| Pneumatic pump. |
