Abstract: A mobile jack-up rig is an important facility in offshore oil and gas development and often works in close proximity to a permanent jacket platform. Penetration of the spudcan could displace a large volume of soil and induce considerable loadings to the pile foundation of a nearby jacket, which may jeopardize the designated performance of the jacket platform. The aforementioned effect is more significant in cohesive soils where deeper penetration is expected. However, the currently available industry guideline and approaches have obvious limitations on this important issue. Therefore, a numerical approach is developed in this paper which has two steps to study the effects of the spudcan penetration on an adjacent jacket pile in cohesive soils: (1) computation of the lateral soil displacement induced by the spudcan penetration in a free field assuming the jacket is absent through the arbitrary Lagrangian Eulerian (ALE) numerical method, and (2) computation of the pile lateral loading induced by the aforementioned soil displacement based on the P-Y curves by the conventional beam-column method. Feasibility and reasonability of the approach are verified by calculated results against centrifugal experiment results published in the past. The paper reveals the deformation mode and flow mechanism of the soil in the free field, indicates the variation of additional loadings of the adjacent pile induced by spudcan penetration, and especially finds that the induced soil displacement is heavily dependent on soil deformation characteristics such as , and the induced pile loading is found to be not sensitive to the variation of within a reasonable range. Finally, the study discusses how to define the boundary condition at the pile head where the pile is connected to the upper structure, and whether the linear superposition law is appropriate for loadings induced by the spudcan penetration and the jacket.

Key words: mobile jack-up rig, spudcan penetration, soil displacement, P-Y curves, pile head constraint, cohesive soil