Objective  Aiming at the problems of high computational cost of nonlinear analysis and insufficient accuracy of code-based methods in the anti-overturning stability check of jack-up platforms with independent spud legs, this study aims to improve the relevant verification system and provide an accurate and efficient calculation method for engineering design.

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

Results It is confirmed that the spud leg motion is characterized by "overall translation + rotation around the rotation center". During the overturning process, the relative vertical distance from the rotation center to the mud surface has small dispersion and can be approximately constant. Compared with the CCS code method, the relative error of the proposed method is reduced by about 10%, which is closer to the accurate value of 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 spudcan) is reasonable. It can provide a reliable engineering reference for the anti-overturning stability check of jack-up platforms.