Bearing capacity of 3D jack-up rig by skew- boundary condition with viscoplasticity element-by-element method

Traditional finite element methods (FEM) face significant computational challenges in analyzing large-scale 3D interaction problems due to the substantial size of global matrices. This paper proposes a 3D viscoplasticity element-by-element (meshfree) method combined with skew-boundary conditions as an efficient alternative. The method is applied to evaluate the bearing capacity of a 3D jack-up structure, comprising three legs, spudcans, and a hull, resting on homogeneous soils. The jack-up structure is modeled as a linear elastic system, while the soil adheres to the Mohr-Coulomb yield criterion. Verification of N_c for spudcan-soil interactions at various depths, including fully open cavity conditions, demonstrates logical agreement with existing solutions. One-leg simulations predict N_c values up to 16% higher than SNAME guidelines but remain lower than those from three-leg simulations, highlighting the conservatism of simplified models. Detailed plastic flow deformation analysis provides critical insights into soil-structure interactions. These findings have significant implications for offshore engineering, suggesting current SNAME guidelines may overestimate soil failure risks, leading to overly conservative designs. Our findings serve as a preliminary basis for questioning the conservativeness of these norms. The proposed method offers an efficient tool for complex soil-structure interaction analysis, improving predictive capabilities and advancing offshore structure engineering.