The monopile foundation of an offshore wind turbine will unavoidably suffer from long-term cyclic loading during its lifetime, due to impacts from waves and wind. In this chapter, a series of tests on a rigid model monopile, subjected to lateral cyclic loading, were carried out in Qiantang River silt to investigate the pile–soil interaction mechanism and accumulated deformation. The tests revealed that the accumulated displacement is closely related to the cyclic load ratio but has no obvious relationship with the relative density of the soil. In contrast, the unloading stiffness is independent of the cyclic ratio but is related to the relative density of the soil. The soil around the rigid monopile under cyclic loading undergoes a shearing stage during the first ten cycles, followed by the densification stage. The shearing stage dominates the cyclic responses of the rigid monopile, within which the total displacement in each cy...