Responses of model monopile to cyclic lateral loadings in clay

Abstract

Large diameter monopiles are usually used as the foundation of offshore wind turbines. Monopile foundations are subjected to laterally cyclic marine environmental loadings which tends to accumulate displacements and rotation of the monopile. To preliminarily evaluate the cyclic responses of monopile in marine clay, 1g model tests have been conducted to combine with reported centrifuge tests to efficiently illustrate the behavior. This study investigates the laterally monotonic and cyclic responses of the model pile embedded in kaolin clay. As expected, obvious differences are observed between results of the 1g model tests and the centrifuge tests owing to the effect of stress levels, but important quantitative relations between results of these two types are revealed: two equations closely related to cyclic loading magnitude ratio ζb with same cyclic loading symmetry ratio ζc, could be qualitatively obtained to predict the pile responses in centrifuge tests by using the result of 1g model tests. The normalized unloading stiffness of model pile in 1g test is less than that of obtained from centrifuge tests with the same ζb values. This result not only highlights that it is necessary to account for the stress level of soil to understand cyclic lateral responses of monopile foundations, but also reveals that it is possible to qualitatively insight responses of monopile through 1g model tests.