SELECTION CRITERIA FOR BUILDING FOUNDATIONS.
Selection criteria for foundation for buildings depend on two factors, i.e. factors related to ground (soil) conditions and factors related to loads 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 circumstances.
Selection of Foundation based on Ground Conditions:
The ground or soil condition is necessary for determining the type of suitable foundation. The soil on which the industrial, commercial or residential building rests may 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 soil close to the surface is capable of supporting structure loads, shallow foundations can be provided.
- Where the ground 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 foundation selection. If the ground is not levelled, and has gradient then step foundation may be preferred.
Selection of foundation based on Loads from Building:
The loading condition i.e. type and magnitude of loads, depends on the form and type of building to be constructed. In case of low rise building with large span, the extent of loading is relatively modest, so shallow foundation is preferred in this case. While high-rise building with short span has high loads. Therefore, deep foundation is required in such cases. Deep foundation is provided because ground at greater depth are highly compacted.
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. Where, loads of the buildings are uniformly distributed, like from masonry claddings, the piles are not needed.