Nondimensional parametric method for studying lateral cyclic response of offshore monopiles in sand

Abstract

A monopile is the most widely used foundation type for offshore wind turbines. Long-term cyclic loading from wind and waves creates an accumulated displacement and changes in the stiffness, which are critical in the serviceability limit state. Design codes present little information in this regard. A series of model tests were conducted to further explore cyclic response of a stiff pile in drained sand subjected to 10,000 cycles. The improved nondimensional groups were applied to interpret the resulting data. The test results show that the accumulated residual displacement and cyclic stiffness increased with the number of cycles, depending on the load characteristics and sand densities. On this basis, two explicit models for predicting the accumulated residual displacement and unloading stiffness due to cyclic lateral loading were developed in a nondimensional form. The application of the improved models for laboratory tests and field-scale piles was also demonstrated.