Objective  This study addresses the challenges associated with high computational cost in nonlinear analysis and the insufficient accuracy of code-based methods for the anti-capsizing stability check of Jack-up platforms with independent spud legs. The aim is to enhance the existing verification system and provide an accurate, efficient calculation method for engineering design.

Methods Taking a Jack-up platform without a spudcan as the research object, a finite element model of the soil-spud leg was developed using the Arbitrary Lagrangian−Eulerian (ALE) method. The capsizing moment was simulated by applying a bending moment at the top of the spud leg. The variation in spud leg displacement, rotation angle, and the relative vertical distance from the rotation center to the mud surface were analyzed. The generality of the laws was verified by varying the spud penetration depth (8 m−15 m) and soil parameters. The results of the proposed method, the China Classification Society (CCS) code method, and the nonlinear pipe-soil analysis were compared, using an actual platform case for validation.

Results It is confirmed that the motion of the spud leg is characterized by "overall translation + rotation around the rotation center". During the capsizing process, the relative vertical distance from the rotation center to the mud surface has small dispersion and can be considered approximately constant. Compared with the CCS code method, the relative error of the proposed method is reduced by approximately 10%, bringing the results closer to the accurate values obtained from the nonlinear pipe-soil analysis.

Conclusions The proposed method balances computational accuracy and efficiency, and the proposed selection standard for the moment arm hinge point (60% of the spud penetration depth can be adopted for platforms without a spudcan) is reasonable. It can provide a reliable engineering reference for the anti-capsizing stability assessment of Jack-up platforms.