Determination of the adequate thickness of granular subbase beneath foundations

Abstract EN

Where the native soils have poor structural qualities or are expansive, the soil investigation report may recommend importation of soils better suited to providing a sub base for structures.

This requires considering two soil layers in bearing capacity calculations.

Calculation of the ultimate bearing capacity of shallow footing on a two layered system of soil depends on the pattern of the failure surface that develops below the footing.

For a weak clay layer overlaid by a top dense sand layer, previous studies assumed that the failure surface is a punching shear failure through the upper sand layer and Prandtl's failure mode in the bottom weak clay layer.

In this paper, the bearing capacity of sub base layer underneath by a soft clay layer is investigated.

The properties of the sub base material are measured in the laboratory.

Design charts were obtained which can be used to select the suitable thickness of the sub base layer for a design allowable bearing capacity.