Abstract
Huge offshore gravity structures such as deep-sea oil platforms are often equipped with a skirt system underneath their bases. When such foundations of substantial size with deep skirts are to be placed on soft clay deposits, it becomes important to take account of the influence of a non-homogeneous strength profile in bearing capacity calculations. In this study, plasticity theory was used to evaluate the influence of linearly increasing undrained shear strength with depth on the bearing capacity of shallow foundations, under both plane strain and axisymmetric conditions. Based on the results of computations, a simple method is proposed to calculate bearing capacity using a set of charts, which introduces the effect of increasing strength consistently into the framework of conventional bearing capacity theory. A series of centrifuge experiments was also conducted for circular models founded on clay beds. With a limited number of test cases, the experimental results have proved the validity of the proposed method. Furthermore, the failure observed in the model clay beds was due to punching shear; the mechanism of which was confined to shallow depths to avoid shearing of the clay quickly strangthening with depth.
