The Constructor


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Bearing capacity of cohesive soils

The ultimate bearing capacity of saturated cohesive soils (clay and silt) with low permeability is most critical immediately after construction, before the excess porewater pressure has had time to dissipate i.e. undrained conditions. As time proceeds, consolidation occurs, the soil becomes stiffer and has more strength.

Therefore design of foundations on fine grained soils should be in terms of undrained or total stress. Skempton (1951) suggested for an undrained saturated clay (= 0o), the basic Terzaghi equation should be used, but with values of Nc related to the shape and depth of the foundation;

Since when = 0o, Nq = 1 and

Terzaghi becomes

And in net terms

Values of Nc can be found from the chart (Skempton, 1951) below:

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