Points to be considered to find out the depth of foundation
The depth of foundation is set on the basis of several factors. The estimation of foundation depth is dependent on various factors like type of soil, ground water table, loads from structure, bearing strength of soil and other factors.
The following general factors are considered as most vital do find out the depth of foundation:
1. Load delivered from structure to the foundation
2. Bearing strength of soil
3. Depth of water level underneath the ground surface
4. Types of soil and depth of layers for layered soil
5. Depth of nearby foundation
The lowest depth of foundation should be selected to ensure that the soil contains the necessary safe bearing strength as supposed in the design
Before calculating the depth of foundation, it is recommended to perform soil investigation prior to determine the depth of foundation.
From soil investigation report, the depth of foundation can be obtained on the basis of the type of structure, soil properties, depth of water table as well as all other variable that should be taken into consideration.
Soil investigation report provides The bearing strength of soil at various levels and at various locations.
If the soil investigation report is unavailable, the depth of foundation should be chosen so that it is not influenced by swelling and shrinking of soil because of seasonal changes. Depth of foundation is also influenced by the depth of water table to check and cleanse under the ground.
To build up foundation adjacent to the prevailing foundation, take proper precaution so that pressure bulbs of foundations are not overlapped if the depth of new foundation is to be kept under the depth of prevailing foundation.
The foundation should not be compacted at shallow depth in view of the frost action in cold countries.