FOUNDATION (ante), the artificial structure on which the remainder of an edifice rests. The body of the foundation is the masonry or timber-work used ; the bed, the prepared surface on which the body rests. The bed may be a leveled surface of rock, sand, or earth, consolidated by beating or by driving piles into it; if the tops of the piles are bound together by a flooring of timbers—called a grillage—this flooring is deemed the bed of the foundation. Rock is the best foundation, but its bearing power should be tested, and its upper surface should be made normal to the direction of the pressure. To avoid expeuse, the bearing surface may be left in steps, but the steps should be filled with well fitted masonry, that there may not be undue settlement upon the filled side, in case the lowest step should be much lower than the highest. Great care should be taken to apportion the load to the supporting power of the foundation; if the latter be found inadequate, the area of the foundation should be increased until the weight distributed to each unit of surface shall be brought within the proper maximum.
Engineering science has been severely tested by demands for sure foundations in places where the soil and substrata are by nature yielding, or exposed to the insidious action of running water, or where both evils are united.
Except upon solid rock, settlement cannot be avoided. It is enough for the safety of the structure if the settlement can be made uniform in all its parts. In some cases, an "area" is made, as under the new capitol at Albany, N. Y. The earth was removed to a proper depth under the whole structure, and the level surface exposed was thor oughly beaten. The surface was then covered with 6 in. of concrete of broken stone and cement, thoroughly grouted; layer after layer was formed, until sufficient thick ness was made, and fin:4V the concrete was covered with broad foundation stones, placed so near to each other that the concrete could not rise between the blocks. On this platform the building is erected. If the subsoil be tolerably firm, small blocks will probably find a continuous bearing surface better than large ones, unless care is taken to dress both level; but beds of concrete may be laid, upon which broad stones may be floated before the concrete sets, and perfect contact may be secured. If the ground
contain springs of water, the water must be kept from washing out the concrete before it has come to harden. Drains may be made to some point in the work, whence the water may be removed by pumping, or sheet-piling may surround the area, in the manner of a coffer-dam. In England, the foundations of the Rochester bridge were laid in large cylinders filled with masonry; the tide water entered the cylinder, and washed out the concrete; when the tide was out a piece of stout canvas impervious to water was laid in the bottom of the cylinder, the concrete placed upon it, and the water A yielding soil is frequently consolidated by driving into it timbers called piles. These are trunks of trees, cut as long as may be, sharpened at the smaller end and driven into ground by blows from a heavy iron ram raised and let fall by machinery. A very effective steam pile-driver lately used has the ram joined to the piston of a steam-cylinder; the weight of both ram and cylinder rests on the pile, and the action is so rapid that, after the pile is once started into -the earth, it is scarcely allowed to stop until it comes to its final bearing. If piles are driven at distances of, say, 4 ft. between centers, into ground previously loose, the ground must be greatly compressed to make room for so great masses of timber, which also serves to bind the whole mass together. If, fiddler,' the tops the piles are cut to a COnmon plane, and cross timbers are securely bolted to the heads of the piles, a very secure platform is constructed upon which great weights properly distributed will sink equably, if at all. Sometimes, after the tops of the piles have been cut to the required level, the earth is removed for 2 or 3 ft. and the space is filled with concrete, the grillage being placed above the concrete.