Selection of type of foundation for a house or building depends upon two factors, i.e. Nature of soil and Load from the structure. The performance of foundation is based on interface between the loadings from the structure and the supporting ground or strata. The nature and conditions of each of these varies, so the selection of appropriate foundation becomes necessary for these variations depending on the circumstances.
Selection of foundation based on Nature of Soil:
The nature of soil is the important aspect in determining the type of suitable foundation. The soil on which the house or building will rest should be stable, level and of uniform composition, but in some situations it may be otherwise.
Following are criteria for selecting suitable foundation based on soil condition:
- Where the soil close to the surface is capable of supporting load of the structure, shallow foundations can be provided.
- Where the soil close to surface is not capable of supporting structural loads, hard strata is searched for, and in some cases, it may be very deep, like in case of multi-storey buildings, where loads are very high. So, deep foundations are suitable for such cases.
- Field up ground have low bearing capacity, so deep foundation is required at that place, whereas uniform stable ground needs relatively shallow foundation.
- Level of the ground also affects selection of foundation. If the ground is not level, and has gradient then step foundation may be preferred.
Selection of foundation based on Loads from the Structure:
The type and magnitude of loads from the structure depends on the form and type of house or building to be constructed.
Following are criteria for selecting suitable foundation based on condition of loading:
- In case of low rise building with large span, the extent of loading is relatively modest, shallow foundation can be provided.
- High-rise building with short span has high loads. Therefore, deep foundation is required in such cases.
- In case of framed structure multi-storey building, where loads are concentrated at the point of application, the use of pads and piles are common.