Deep Foundations

If the soil in the top layers near the ground does not have adequate bearing capacity it would be necessary to transfer the load to the lower strata. For buildings, this is achieved by means of piles. 

Pile Foundation 

Piles are long column-like members which transmit load of the structure through a weak material to an underlying hard strata. If the bearing stratum is hard and impenetrable like rock or hard dense gravel, a pile derives its strength mainly by bearing and is known as end bearing pile as shown. 

  Different Types &Piles (Based on Mode of Load transfer)

Piles driven in soil which increasingly becomes stiff with depth derive their bearing capacity from the friction along the surface of the pile and are known as friction piles as shown. Normally, in a pile, part of the load is carried by friction and part by end bearing. Piles can also be used to resist uplift pressures on structures as also to withstand lateral forces. Such piles are called anchor piles. A pile which is installed at an angle to the vertical is known as a batter or taker pile. 

Piles, particularly of timber have been  use from ancient times and can be considered as one of the earliest innovations in foundation engineering. However, it is only in the past few decades that appropriate methods have been evolved to analyse and design piles. 

Construction of pile foundation requires a careful choice of the type of pile and methodology of execution taking into consideration the soil strata, the level of subsoil water, the load characteristics of the structure, limitation of settlements and any other special requirements. The availability of materials and equipment and economic factors have also to be considered. 

Materials for Piles 

Piles can be of timber, steel or concrete. The earliest types of piles used were of timber while presently concrete piles are used to the maximum extent. Steel piles are expensive and rarely used.