A special type of foundation that enables a structure to be supported by a layer of soil found at any depth below the ground surface. A pile foundation comprises two basic structural elements, the pile and the pile cap. A pile cap is a structural base, similar to a spread footing that supports a structural column, wall, or slab, except that it bears on a single pile or group of piles. A pile can be described as a structural stilt hammered into the ground. Each pile carries a portion of the pile cap load and transfers it to the soil in the vicinity of the pile tip, located at the bottom of the pile (see illustration).
The pile and pile cap configuration has provided the basic design solution to the difficult problem of obtaining deep foundation support below areas where poor soil conditions prevail. Poor soil conditions may be difficult to excavate through, and are incapable of supporting structural loads. They are typically characterized by the presence of a soft, compressible layer of clay, high ground-water levels, loosely filled soils, uncontrolled landfills, boulders, abandoned underground structures, and natural bodies of water. By supporting a structure on piles in lieu of spread footings, any adverse soil condition may be virtually bypassed, and adequate foundation support can be obtained at any depth, without the need to perform deep excavation, dewater, and install temporary sheeting and bracing.
Piles are available in a variety of sizes, shapes, and materials that enable a particular type of pile foundation to be viable both economically and structurally. Principal materials are timber, concrete, and steel.
Pile foundations are used to support marine structures and offshore platforms, since they are located over bodies of water. On land, pile foundations are used primarily in locations where poor soil conditions exist.
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