Influence of Pile Diameter on Lateral Load Behavior and Failure Mechanisms of Large-Diameter Monopiles

Increasing monopile diameter significantly alters lateral load response, and traditional design methods have already demonstrated limitations, while the influence mechanism of the diameter effect is still not in consensus. Using the three-dimensional finite element simulation, which is validated against centrifuge test results, the influence mechanism of the diameter effect is analyzed, and the related failure modes are also examined. It is found that the lateral bearing capacity of the monopile increases significantly with increasing pile diameter. The interaction of the soil plug and soil around the pile can enhance the nonlinear characteristics of the lateral load-displacement response. As the pile diameter increases, the deformation response of the pile evolves from flexible through semi-rigid to rigid behavior, and distinct failure modes are also developed. With the increase of pile diameter, the depth range of the wedge failure zone for flexible piles increases gradually, whereas for rigid piles, the depth range remains essentially unchanged, but the radius of the rotational failure zone significantly expands. The depth range of the full flow failure zone of semi-rigid piles progressively shrinks with the reduction in pile bending deformation. Failure modes can significantly affect the initial stiffness of the p-y curve. The initial stiffness exhibits the dependence on the pile diameter, embedment depth, and failure mode simultaneously.