Optimize characteristic value of SPT for seismic design of offshore wind turbines in liquefiable soils by stochastic models

Abstract

Dynamic numerical analyses on an offshore wind turbine (OWT) supported by a suction bucket foundation were performed to investigate the effects of soil spatial variability on the ground liquefaction and tilts of OWT, and to provide suggestions on selecting a representative percentile of the random distributions of a clean sand equivalent SPT blow count, (N1)60cs, for deterministic models. The material parameters of an elastoplastic constitutive model (Cyclic Mobility model) in the numerical model were derived from the (N1)60cs (spatial variability). Monte Carlo simulations were used to describe the seismic responses of the laterally loaded suction bucket foundation in spatially variable soil. Simulation results for deterministic models (uniform properties of soil) were compared to results for random models (spatially variable properties of soil). Tilts of OWT and liquefaction potential index of ground are chosen as criteria, and those obtained from the random models and deterministic models were compared to identify the representative (N1)60cs, based on the principle that the deterministic models produce reasonable consistency with the upper limit of the random model responses. The effects of site conditions, seismic conditions, and other factors were evaluated, and it is found that the coefficient of variation (COV), (N1)60cs, acceleration, and frequency have significant influence.