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-dime nsional finite-element analysis and upper-bound plasticity analysis as suming the soil to be undrained. New information has been gained about the shape of the yield locus and the soil deformation mechanisms occu rring at yield from the finite-element analysis. The shape of the yiel d 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 beha viour is explained using upper-bound plasticity mechanisms suggested b y the soil deformation mechanisms calculated in the finite element ana lysis. 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 desig n methods. Additionally, a simplifying transformation is suggested for the yield locus in H-M space based on plasticity analysis, which allo ws use of simple mathematical expressions to form a design envelope.