Lateral response of monopiles with different stiffness under local scour

Local scour significantly threatens the life-cycle safety of offshore monopiles. While extensive research has been conducted on the bearing capacity of scoured piles, the lateral response mechanisms and their evolution across piles with different stiffness levels (flexible, semi-rigid, and rigid) remain insufficiently understood. This paper systematically investigates the effects of local scour on the lateral response of piles under both serviceability limit state and ultimate limit state, using finite element analysis. The results show that scour depth considerably reduces lateral capacity, with rigid piles being the most susceptible. Scour also shifts the maximum bending moment downward and alters the distribution of soil resistance along the pile. The contributions of different soil reaction components, including lateral soil reaction, distributed moment, base shear, and base moment, are quantified, with their load-sharing ratios varying systematically with pile stiffness. A multi-spring modeling framework integrating all soil reaction components is formulated using hyperbolic tangent functions to capture these stiffness-dependent responses. Validation against experimental and numerical results confirms the model’s accuracy in simulating the lateral response of monopiles under scour.