Research on offshore wind turbine support structures under seismic soil liquefaction

This study uses a two-stage finite element method to analyze offshore wind turbine (OWT) support structures under soil liquefaction during earthquakes. First, a three-dimensional cuboid u-p analysis with the soil cap yield criterion provides time-history soil accelerations and pore water pressure ratios. The second stage models the OWT support structure using traditional finite element methods, incorporating seismic displacement fields into p-y, t-z, and q-z nonlinear springs, with excess pore water pressure ratios reducing their stiffness. Numerical simulations were performed on 10, 15, and 20 MW OWT structures, yielding key insights. Ground accelerations near the soil surface cause frequent soil liquefaction, effectively mitigating seismic forces on the OWT foundation. When pile length is sufficient, the analysis with the u-p model requires less steel than traditional methods without considering soil liquefaction. Moreover, the reduction in sandy soil stiffness extends into deeper layers, making settlement a critical concern during soil liquefaction. Analysis accounting for soil liquefaction consistently reports greater settlements than traditional approaches. Consequently, the critical factor for deep pile OWT support structures with regard to soil liquefaction is foundation settlement rather than the design of the steel structure section.