Pseudo static finite element analysis of bearing capacity of suction anchor subjected to cyclic loads in soft clay

A pseudo-static elasto-plastic finite element method is proposed to evaluate the bearing capacity of suction anchors subjected to a combination of average and cyclic loads in soft clay using the undrained cyclic strength. The octahedral shear stress of soil elements associated with the average mooring load is first determined by elasto-plastic finite element calculations using the undrained static strength of soft clay for the method. The undrained cyclic strength of soil elements associated with the specified number of cycles to failure is further determined based on the octahedral shear stress. The load-displacement curve at the mooring point along the loading direction is then determined by the elasto-plastic finite element calculations using the undrained cyclic strength. The cyclic bearing capacity of anchors is finally determined based on the curve and the displacement criterion to failure. The effects of the average mooring load on the undrained cyclic strength and the bearing capacity of suction anchors subjected to a combination of average and cyclic loads are considered. In order to show the validity of the method, model tests on cyclic bearing capacity of suction anchors with different diameters, aspect ratios, average loads, frictional factors, loading directions and failure modes are conducted. The test results are predicted using the pseudo-static elasto-plastic finite element method. The predicted results are less than the test ones. The average difference is not over 10%. Variations of the normalized cyclic bearing capacity with the number of cycles to failure only depend on the normalized average loads. The effects of load directions, anchor diameters and frictional factors of outer wall on the normalized cyclic bearing capacity can be neglected. If the normalized average load is 0.5 and the number of cycles to failure is 1000, the cyclic bearing capacities are about 75% and 80% of the static bearing capacity respectively for the vertical failure and the lateral failure, which are in