How to Calculate the Allowable Bearing Capacity of Soils? Explained in 1-minute.

Soils have an ultimate bearing capacity (qu) which estimates the pressure they can take from a foundation before they fail (typically in some form of shear failure). However, foundation design is normally governed by allowable bearing capacities (qa) which are based on the need to limit the settlement of the soil. 

Clay Soils

In cohesive soils such as Clay, the Allowable Bearing Capacity can be estimated based on the undrained cohesive strength (Cu) of the soil:

Granular Soils

For Granular Soils like sand, silt and gravel, the Allowable Bearing Capacity can be calculated based on the N value. However, this depends on whether the soil is saturated with water or not:

※ What is the SPT N Value? Significance and Calculation Method

Chalk

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Rock

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