This paper reports a measure for easing spudcan-footprint interactions when a jack-up rig needs to be installed near existing jack-up footprints. Two novel spudcan shapes, skirted spudcan with four rectangular holes and 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 spudcan sliding towards 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 potential to ease spudcan-footprint interactions without any additional mechanical operations.

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The horizontal force and moment induced on a spudcan as it penetrates next to an existing seabed footprint have been identified as one of the key challenges in the offshore oil and gas industry. This paper assesses the potential of changing and then optimising the spudcan foundation shape to mitigate the spudcan-footprint interaction. Large-deformation finiteelement (LDFE) analyses are performed using the Coupled Eulerian-Lagrangian (CEL) approach with the simple elastic-perfectly plastic Tresca soil model modified to enable strain softening and to incorporate strain-rate dependency of the shear strength. The spudcan shape was optimised by parametric analyses varying the spudcan's skirt length, underside profile, and number of holes through the spudcan periphery. A spudcan with a flatter (or even concave) underside profile and with holes was shown to significantly reduce the induced horizontal force and moment during reinstallation next to an existing footprint. However, use of skirts has an adverse influence. Based on the results, an optimised spudcan shape is proposed.

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