Combined loading of skirted foundations

The response of skirted offshore foundations to combined vertical (V), moment (M) and horizontal (H) loading has been studied using two-dimensional finite-element analysis and upper-bound plasticity analysis assuming the soil to be undrained. New information has been gained about the shape of the yield locus and the soil deformation mechanisms occurring at yield from the finite-element analysis. The shape of the yield locus was found to be similar to that predicted by previous workers in V-M and VH space but differed significantly in M-H space. This behaviour is explained using upper-bound plasticity mechanisms suggested by the soil deformation mechanisms calculated in the finite element analysis. This procedure is then used to give a good approximation to the shape of the yield locus and thus may form the basis for future design methods. Additionally, a simplifying transformation is suggested for the yield locus in H-M space based on plasticity analysis, which allows use of simple mathematical expressions to form a design envelope.