Behavior of cyclically loaded monopile foundations for offshore wind turbines in heterogeneous sands

This paper presents a probabilistic assessment of the long term performance of monopile foundations for offshore wind turbines in dense sand with spatially varying stiffness. Response of the monopile foundation to long term cyclic loading is simulated by coupling a three-dimensional finite element pile–soil model with a stiffness degradation material model. With the implementation of random field model of sand stiffness variability, this study provides a discussion on the probabilistic effects in the long term response of the pile–soil system. The probabilistic response is evaluated with respect to the serviceability and ultimate limit states of monopile foundations in the Monte Carlo framework for a set of monopile embedment lengths and lateral loading cycles. The statistics associated with the monopile displacements, rotations and bending moments demonstrate the influence of the monopile embedment length and the number of lateral loading cycles on the long term probabilistic response of monopile foundations. The estimated probabilities of exceeding the limit states revealed the serviceability limit state as being dominant in this study and indicated the importance of the installation tolerance on the long term response of monopile foundations.