Soil Exploration Depth
Exploration, in general, should be carried out to the depth to which the increase in pressure due to structural load is likely to lead to perceptible settlement or shear failure of the foundation. This depth is known as depth of exploration, Which depends on the following factors.
- Structure type
- load on structure
- Foundation shape and size
- Loaded Areas Position
- Soil Profile and its Properties
The depth of exploration at the beginning of the work may be decided as per the thumb rule given below, which may require modification as the investigation proceeds.
Rule of thumb for determining depth of exploration
- The depth of exploration should be one and a half times to two times the estimated width of the base (lower dimension) from the base level, single or combined, from the base level of the foundation.
- In the case of weak soils, exploration should be continued to a depth at which the load can be carried by the stratum without excessive settlement or shear failure.
- Isolated outstretched leg or a raft: one and a half times the width.
- Adjacent footing with clear spacing of less than twice the width: one and a half times the length
- Pile foundation: 10 to 30 meters, or more, or at least one and a half times the width of the structure
- Retaining Wall Base: One and a half times the width of the base or one and a half times the exposed height of the wall face, whichever is greater.
- For floating basement the depth of construction should be equal to the depth of construction.
- In any case, the depth to which the weathering process affects the soil should be considered as the minimum depth for the exploration of sites and taken as 1.5 m. In case of black cotton soil, the minimum depth of exploration is 3.5 m.