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
subbase for structures. This requires considering two soil layers in bearing capacity
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 subbase layer underneath by a soft clay layer is
investigated. The properties of the subbase material are measured in the laboratory.
Design charts were obtained which can be used to select the suitable thickness of the
subbase layer for a design allowable bearing capacity.