Abstract: Field measurements in offshore areas have revealed that wind turbines are mainly exposed to large-amplitude and long-duration horizontal environmental loads, and those located in high-intensity areas are particularly susceptible to seismic activity during service life. However, it remains unclear how the initial horizontal loads affect the seismic behaviour of offshore wind turbines, particularly with respect to pile-soil interaction. To address this issue, this study employed the ZJU-400 centrifuge shaking table to conduct a series of centrifuge tests on a single rock-socketed pile in liquefiable saturated sands, with its prototype located in the offshore wind farm in Fujian waters. The experimental results demonstrate the bending moment and displacement responses of the pile subjected to the seismic loads in combination with initial horizontal loads. The proposed p-y model introduces a parameter related to excess pore water pressure to quantify its weakening effects on pile-soil interaction as observed in the centrifuge tests. When combined with the nonlinear Winkler foundation beam model, the proposed post-earthquake prediction model can effectively estimate the bending moment and displacement distribution of monopiles under initial lateral loading.

Key words: offshore wind turbines, initial lateral load effect, dynamic p-y curves, centrifuge shaking table