Optimization design of spudcan structure for mitigating spudcan-footprint interaction

In order to ease spudcan-footprint interactions during jack-up rigs penetrating in the vicinity of an existing seabed footprint, three new spudcan shapes, a six-hole lotus-shaped spudcan, a flat-bottomed spudcan, and a concave-shaped spudcan were proposed and analyzed comparatively to carry out an optimizing study of the spudcan structure. Firstly, large-deformation finite element (LDFE) was performed using the Coupled Eulerian-Lagrangian (CEL) method with the idealized elastic-plastic Tresca model to analyze differences between the innovative spudcan shapes and the traditional one in interaction mechanism of spudcan-soil during spudcan penetrating next to an existing footprint with an eccentricity of 0.5D, as well as the horizontal range of plastic deformation of the disturbed soil, the inclination angle of spudcan and the offset of the pile leg. Then FEM method and the method of specification were used to evaluate the bearing capacities of different spudcan structures. Finally, the risk of puncturing was assessed during different spudcans penetrating in the layered soil. The results show that the six-hole lotus-shaped spudcan, flat-bottom spudcan, and concave-shaped spudcan can mitigate the horizontal sliding force and peak bending moment at the top of the pile leg compared with those of traditional spindle-shaped piles obviously, which are reduced by 32.59%, 22.47%, 28.18%, and 26.32%, 12.88%, 18.02%, respectively. It can be seen that all the new spudcan structures can ease the adverse consequences of the spudcan-footprint interactions effectively. Among them, the six-hole lotus-shaped one works best, and the concave-shaped one is slightly less but simpler and easier to produce. Besides, considering the impact of the spudcan penetrating on the adjacent jacket platform, the six-hole lotus-shaped spudcan structure is a priority due to the least horizontal range of soil disturbance. In view of the risk of puncturing when spudcans penetrate into the layered soil or discontinuously, the flat-bottomed spudcan is a priority due to the least possibility of puncturing when the same stable load is applied and the spudcan is penetrated into the same depth.