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Last edited 30 Apr 2018
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics to support them. Very broadly, foundations can be categorised as shallow foundations or deep foundations.
Pile foundations are a type of deep foundation, formed by long, slender, columnar elements typically made from steel or reinforced concrete, or sometimes timber. A foundation is described as 'piled' when its depth is more than three times its breadth.
Pile foundations are principally used to transfer the loads from superstructures, through weak, compressible strata or water onto stronger, more compact, less compressible and stiffer soil or rock at depth. They are typically used for large structures, and in situations where soil may be subject to excessive settlement.
End-bearing piles develop most of their load-bearing capacity at the toe of the pile, bearing on a hard layer of rock or very dense soil and gravel. The pile transmits the load through soft, compressible strata directly onto firm strata. This type of pile therefore acts in the same way as a column.
This is as opposed to friction piles (or floating piles) which develop most of their load-bearing capacity by shear stresses along the sides of the pile, and are suitable where harder layers are too deep to reach economically. The pile transmits the load to the surrounding soil by adhesion or friction between the surface of the pile and the soil. In this case, the whole surface of the pile works to transfer load to the soil.
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