When it becomes impossible to provide the suitable surface foundation for a structure; the use of pile foundations becomes necessary, this situation arose from either the soil condition or the order of bottom layers, the nature of the loads transferred to the soil or the nature of the site and operational conditions
Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like bridges and dams
The main components of the foundation are the pile cap and the piles. Piles are long and slender members which transfer the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity. The main types of materials used for piles are Wood, steel and concrete. Piles made from these materials are driven, drilled or jacked into the ground and connected to pile caps. Depending upon type of soil, pile material and load transmitting characteristic piles are classified accordingly.
Pile foundations have been used as load carrying and load transferring systems for many years. In the early days Timber piles were driven in to the ground by hand or holes were dug and filled with sand and stones. Steel piles have been used since 1800 and concrete piles since about 1900.
The industrial revolution brought about important changes to pile driving system through the invention of steam and diesel driven machines. More recently, the growing need for housing and construction has forced authorities and development agencies to exploit lands with poor soil characteristics. This has led to the development and improved piles and pile driving systems. Today there are many advanced techniques of pile installation.
Function of piles:
As other types of foundations, the purpose of pile foundations is:
- To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined
- To install loose cohesion less soil through displacement and vibration.
- To control the settlements; which can be accompanied by surface foundations.
- To increase the factor of safety for heavy loads buildings
A structure can be founded on piles if the soil immediately beneath its base does not have adequate bearing capacity. If the results of site investigation show that the shallow soil is unstable and weak or if the magnitude of the estimated settlement is not acceptable a pile foundation may become considered. Further, a cost estimate may indicate that a pile foundation may be cheaper than any other compared ground improvement costs.
In the cases of heavy constructions, it is likely that the bearing capacity of the shallow soil will not be satisfactory, and the construction should be built on Piles can also be used in normal ground conditions to resist horizontal loads. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.