If soil at or near the ground surface is not capable for supporting a structure i.e bearing capacity of soil is low, then deep foundations are required to transfer the loads to deeper and harder strata.
Necessity of Pile foundations:-
- when the soil having low bearing capacity.
- when the plane of the structure is irregular in load distribution.
- when water table level is high
- when there is a chance of soil erosion or scour.
- If there a chance of high volume change in rainy season like as volume change in black cotton soil or expensive soil.
Classification of Piles:-
Piles may be classified on the basis of function
End Bearing Pile:-
It is used to transfer superstructure’s load to a suitable strata of soil by end bearing.
This pile transfer load by means of skin friction.
This pile is used for compaction and for increasing density of loose granular soil for increasing bearing capacity of soil.
This pile is used in to anchor down the structure subject to uplift due to hydro static pressure.
It is used to provide anchorage against horizontal pull from sheet piling.
It is used to resists large horizontal and inclined loads.
Classification based on materials.
It is made tick pipe or rolled steel, H-section and these are driven into ground with their ends open or closed.
It is made of cement concrete. these are either pre cast or cast in situ.
It is made of timber and having low bearing capacity.
It is made of the lower portion of steel and the upper portion of cast in situ concrete.