Centrifuge model tests on bearing capacity and deformation of sand layer overlying clay

A series of centrifuge model loading tests on dense sand overlying soft clay was carried out to investigate its bearing capacity and associated deformation including the failure mechanism. The effects of the thickness of sand, the strength of underlying clay and the width, shape and embedment of footings on the bearing behavior of the sand were studied. It was found that the bearing capacity increases with increasing sand thickness-footing width ratio until it reaches that of uniform sand, which can be considered as the upper limit of the bearing capacity of the layered soil. The bearing capacity also increases linearly with both the strength of the clay and the overburden pressure at the footing base. For cases with bearing capacity smaller than that for uniform sand, punching shear takes place, where a truncated cone shaped sand block between the footing base and the clay surface penetrates into the clay. The side angle of the sand block to the vertical increases with increasing sand thickness-footing width ratio and overburden pressure, and decreasing clay strength. It was confirmed that this variation of the angle should be taken into account in the bearing capacity calculation.