Load transfer mechanism of O-cell method for offshore foundation considering nonlinear pile-soil interface response

The O-cell test is widely used for bearing capacity evaluation of offshore pile foundations, but accurate determination of the conversion coefficient γ1—which links O-cell results to conventional static load test outcomes, remains a key challenge. In this study, a nonlinear soft/hardening unified model considering the initial shear stress is established, and the finite element numerical model considering the nonlinear characteristics of the pile-soil interface is established by compiling the FRIC subroutine. The stress-strain relationship in the process of O-cell test is simulated, and the influence of pile parameters and load cell position on the conversion coefficient is discussed. Based on the fitting results Page 2 of 2 of the γ1-d curve by the extended Classical Freundlich model, a simplified judgment method for the position of the equilibrium point is proposed. The results show that γ1 is primarily governed by the slenderness ratio L/D, increasing with L/D and decreasing with pile diameter when L is fixed. The proposed model and findings provide a theoretical basis for optimizing load cell placement and improving the accuracy of bearing capacity conversion in O-cell tests for large-diameter offshore piles.