A foundation is that part of the structure that is in direct contact with the ground. It is that part of the structure that transmits the weight of the structure to the ground. The foundation is, therefore, a connecting link between the structure proper and the ground that supports it. Foundation transfers the load of the structure to the soil below on a large area. It prevents the differential settlement by evenly loading the substrata. Foundations are generally built of bricks, stones, concrete, steel, etc. The selection of the material and type of foundation depends upon the type of the structure above and the underlying soil.
Foundation design must take into account the effects of construction on the environment, such as pile driving vibration, pumping and discharge of groundwater, the disposal of waste materials and operation of heavy mechanical plants. Foundations must be durable to resist the attack of harmful substances.
A foundation is designed such that:
- The soil below does not fail in shear.
- The settlement is within a safe limit.
The pressure that the soil can safely withstand is known as the ‘allowable bearing pressure’.
Foundations may be broadly classified into two categories.
- Shallow foundation: A shallow foundation transmits the load to the strata at a shallow depth.
- Deep foundation: A deep foundation transmits the load at a considerable depth below the ground surface.