PILES, ill hydraulic architecture, are beams of timber, or stakes of wood, driven firmly into the ground, for various purposes ; as, for forming a foundation for buildings, piers of bridges, &c., iu which cases they are driven quite down into the ground, or are cut off level with its surfiice, w;th view of obtaining a solid bearing for the weight of the intended superstructure.
Amsterdmn, and some other cities, are wholly built upon piles. The stoppage of the breach in the banks of the Thames at Dagenham, was by dovetail piles ; that is, by piles mortised into each other by a dovetail joint.
Piles are not employed for foundations, unless the ground is suspected to be unsound, or when the weight to be borne is exceedingly groat. They make the foundation solid, by reaching deep into the earth. down to a more substantial stratum than that of the surface. Indeed, the mimeo. of fixing the piles, by driving them by repeated blows of a powerful machine till they will go nu tiarther, ensures that they come to a good bearing.
Piles are also used for making the faces of wharfs, banks of rivers, piers for the sea, &c. For these purposes they are driven iu rows, but only a sufficient depth in the earth to make them stand firm, and support the planking or framing which is fixed against them. These piles are usually driven rather in an inclined position. Fur temporary defence against the water, in laying the foundation of bridges, &c., piles are always required ; they are employed in different ways to form an enclosure, or water-tight wall, called a cotler-dam, round the area where the work is to be laid, and from which space the water is drawn by pumps. This is the most difficult of all kinds of piling ; because it must stand a great height above the ground, have sufficient strength to resist the pressure of water, and be perfectly close and tight. In navigable rivers detached piles are driven, and very firmly fixed, to mark the enclosures where barges are to lie, and to fender off others from them, as well as to moor them to.
Piles are in general formed of square timber, tapering if the tree happens to be so, cut to a sharp point at one end, and shod with iron to enter the ground. The other end is bound by a strong iron hoop, to prevent the pile-head from splitting by the violence of the blows which drive it down. When they are to be driven quite below ground, small trees, if sufficiently straight, may be used without squaring ; but fur coffe•-dams, square piles are always used, except for tilling up a row between such square piles. When they are
Cu touch each other, flat ones, called pile planks, are used ; they are three or four inches thick, according to the depth of water, and have grooves formed in their adjacent edges, to receive tongues or slips of wood, which make the joints quite tight. This method is termed sheet-piling. To enclose an area for a coffer-dam, two rows, or walls of piles, are usually driven one within the other, at a distance usually equal to the depth of water where they are driven; or, if' the current is rapid, once and a half. The space between these is filled with clay, so as to form a mound or rampart of that material, defended on the outside and inside by wooden walls of piles. To make these walls, large square piles are first driven, at a distance of ten or twelve feet asunder, in the line of the intended range of the dam ; horizontal tie-beams are then extended from one pile to the next, on the inside, and some times on the outside also, each tie being notched into the piles, so that its outer edge is in a line with the inside of the groove for the plank-piles, which are to be driven down to till up the spaces between the piles, and will be guided by these ties to stand exactly vertical, and in a straight line. The first plank-piles are fixed adjacent to the main piles, and thus they are continued from both ends of the interval, till the planks meet in the centre, where the last plank is inserted, and, being formed rather it makes all the rest tight. The pile planks are cut inclined, or wedge-like, on one side only, to form the point, by which means the point is in the line of one of the edges of the plank. When a plank pile is to be driven adjacent to another, this edge is applied to the one already fixed, and then, as it is driN'en, the inclined or wedge-like edge entering the ground, causes the pile to approach, and press very close to its neighbour; and it is chiefly by this means they are made to fit The fillets are made by spiking a ledge or ruler of wood first upon the edge of one plank, and a groove of corresponding depth and width is ploughed in the edge of the adjacent plank to receive it.