Closed-Form Solution for the Ultimate Bearing Capacity of Large-Diameter Rigid Piles in Sand Based on Two-Wedge and Rotational Failure Mechanisms

Large-diameter rigid piles with a low embedded depth-to-diameter ratio have been predominantly utilized in offshore wind turbines. A reliable way to evaluate the lateral bearing capacity of rigid piles in sandy seabeds is crucial for ensuring pile stability. However, existing research provides limited insights into this aspect. This study deals with the estimation of ultimate bearing capacity for rigid piles based on the limit equilibrium method that employs meniscus–conical double-wedge and rotational failure sphere models. The proposed 3D model encapsulating the double-failure mechanism more accurately represents the soil failure morphology surrounding rigid piles under the ultimate limit state. The upper double-failure wedge is composed of a passive wedge at the pile front side and an active wedge at the pile rear side, with failure bottom angles determined using rigorous Mohr’s circle analysis. Based on force and moment equilibrium equations within the pile–soil system framework, the limit equilibrium solution is derived. The reliability of this solution is validated through comparisons with documented results from model tests, centrifugal tests, DEM, and FEM. Meanwhile, the effects of embedded depth, pile diameter, and load eccentricity on pile bearing capacity, wedge failure, and the rotational failure mechanism are thoroughly investigated, aiming to provide valuable references for engineering design.