Numerical investigation of spudcan-footprint interaction in non-uniform clays

The re-installation of jack-up rigs near an existing footprint left by the previous installation can be problematic due to the development of horizontal and moment loads on the spudcan footing and hence on the rigs. This paper reports large deformation finite element results of spudcan-footprint interaction in non-uniform clay deposits. The performance of the numerical model was verified by simulations of existing centrifuge tests. A detailed parametric study was carried out varying influential factors including the initial spudcan penetration depth to form the footprint, spudcan diameters, soil sensitivity, undrained shear strength profile and the offset distance between spudcan and footprint centres. The effects of these factors on the development of the vertical, horizontal and moment loads are quantified, and the peak magnitudes of the induced horizontal and moment loads at different offset distances are then compared. It is found through the numerical analyses that the critical offset distance, which maximises the peak horizontal and moment loads on the spudcan, ranges between 0.5 and 0.75 times the diameter of the spudcan used for the formation of the footprint. By contrast, an offset distance of 1.5-2.0 times the diameter of the larger spudcan of those used for initial penetration and re-installation is able to result in a minimal influence of the footprint on the re-installation.