When the upper layer of ground on which the construction is to be done is of weak soil, then the load of the structure needs to be transferred to the deeper layer earth. Pile foundation carries the load of the structure and transfers in to the strong soil or rocks beneath.
Pile foundation is more suitable when the structure has very heavy concentrated load or in case of high rise buildings. This foundation is capable of taking more load as compared to spread foundation.
Based on load transfer criteria, Pile foundation has following types:
1. End Bearing Piles
This type of piles take the load of the structure all the way downwards to the strong layer of soil, hence the name End-bearing Piles. Here piles act more like columns, bypassing the weaker layer and transferring the load to stronger layer. The bottom of the pile rests at the intersection of weak and strong layer.
2. Friction Piles
Friction Piles are shorter in length as compared to end bearing piles. They work on the principle of skin friction. The entire surface of the pile, cylindrical in shape, transfers the load of the structure along the length of the pile through friction to the soil. Hence the load is distributed throughout rather than being concentrated at the bottom.
Based on method of installation, Pile foundation is classified as:
1. Driven or Displacement Piles
The piles are pre-cast before being installed in the foundation. They are installed by jacking, hammering and screwing into the ground.
2. Bored or Replacement Piles
The hole is bored into the ground first, and then the piles are formed as reinforced concrete.
Based on the type of material used, Pile foundation can be as follows:
- Timber Piles
- Concrete Piles
- Steel Piles
- Composite Piles