Functions of foundation, deep foundation types

Functions of foundation

1. Transfers the building load safely to the soil, within the bearing capacity.
2. Spreads the load over a large area to reduce the pressure.
3. Keeps settlement uniform and within limits.
4. Gives a firm, level base for the structure.
5. Resists lateral loads, sliding and overturning (wind, earthquake, earth pressure).
6. Gives stability against uplift (tall structures) and soil movement, such as shrinkage or swelling.
7. Protects the building from the effects of ground moisture, frost and chemicals.

Types of deep foundation

1. Pile foundation: Long slender members driven or bored into the ground.
   • End-bearing piles transmit load to a hard stratum.
   • Friction piles transfer load by skin friction.
   • By material: timber, RCC (precast or cast-in-situ), steel; by installation: driven or bored.
   • A pile cap joins the pile group under a column.
2. Pier foundation: Large diameter vertical cylinder or column of masonry or concrete, used for heavy loads on firm strata at moderate depth.
3. Well (caisson) foundation: A hollow cylinder or box (brick, concrete) sunk through soil by dredging inside, then plugged with concrete; used for bridge piers under water.
4. Under-reamed piles: Piles with bulbs at the lower end, for expansive soil.
5. Drilled shafts (bored piles): Large concrete shaft drilled in the ground.

 pile cap [=======]      pier    well
   | | |                 | |     |  |
   | | |                 | |     |__|
 =hard layer=         =hard=   sunk