Numerical investigation of novel spudcan shapes for easing spudcan-footprint interactions

This paper reports a measure for easing spudcan-footprint interactions when a jack-up rig needs to be installed near existing jackup footprints. Two novel spudcan shapes, a skirted spudcan with four rectangular holes and a skirted spudcan with six circular holes and sloped bottom profile, were investigated using 3D large deformation finite-element (LDFE) analyses. The LDFE analyses were performed using the coupled Eulerian-Lagrangian (CEL) approach in the commercial finite-element package ABAQUS. After displaying the validity of the analyses against existing LDFE results and centrifuge test data, the efficiencies of the novel spudcans were studied against a generic spudcan shape, including the effects of spudcan offset distance from the footprint and the footprint depth. Both soft and stiff seabed strength profiles were considered, with the undrained shear strength increasing with depth. The potential of the spudcan sliding toward the footprint center during installation was evaluated based on the resultant _maximum horizontal force (H_max) and moment (M_max) acting on the different spudcans. It is found that, between the two novel spudcans, the spudcan with six holes and sloped bottom profile is more effective at reducing H_max and M_max. Any reduction in the resultant horizontal force on the spudcan can generate a large reduction of the moment at the top of a long jack-up leg. The results from this study indicate that the novel spudcan with circular holes and sloped bottom profile has the potential to ease spudcan-footprint interactions without any additional mechanical operations.