What is "pile cap"

Pile \Pile\, n. [AS. p[=i]l arrow, stake, L. pilum javelin; but cf. also L. pila pillar.]

1. A large stake, or piece of timber, pointed and driven into the earth, as at the bottom of a river, or in a harbor where the ground is soft, for the support of a building, a pier, or other superstructure, or to form a cofferdam, etc.

   Note: Tubular iron piles are now much used.

2. [Cf. F. pile.] (Her.) One of the ordinaries or subordinaries having the form of a wedge, usually placed palewise, with the broadest end uppermost.

   Pile bridge, a bridge of which the roadway is supported on piles.

   Pile cap, a beam resting upon and connecting the heads of piles.

   Pile driver, or Pile engine, an apparatus for driving down piles, consisting usually of a high frame, with suitable appliances for raising to a height (by animal or steam power, the explosion of gunpowder, etc.) a heavy mass of iron, which falls upon the pile.

   Pile dwelling. See Lake dwelling, under Lake.

   Pile plank (Hydraul. Eng.), a thick plank used as a pile in sheet piling. See Sheet piling, under Piling.

   Pneumatic pile. See under Pneumatic.

   Screw pile, one with a screw at the lower end, and sunk by rotation aided by pressure.

A pile cap is a thick concrete mat that rests on concrete or timber piles that have been driven into soft or unstable ground to provide a suitable stable foundation. It usually forms part of the foundation of a building, typically a multi-story building, structure or support base for heavy equipment. The cast concrete pile cap distributes the load of the building into the piles. A similar structure to a pile cap is a "raft", which is a concrete foundation floor resting directly onto soft soil which may be liable to subsidence.