Centrifuge Modeling of Cyclic Lateral Behaviors of a Tetrapod Piled Jacket Foundation for Offshore Wind Turbines in Sand

摘要

A program of centrifuge model tests conducted on the cyclic lateral behavior of a tetrapod piled jacket (TPJ) foundation for offshore wind turbines (OWTs) in medium dense sand was reported. The key parameters investigated were the lateral loading direction, cyclic load amplitude, and cyclic loading type (i.e., one- or two-way loading) in terms of the overall response of the TPJ and the more detailed pile-soil interaction. Under small- and moderate-amplitude loads, that is, 20% and 40% of lateral bearing capacity, respectively, loading along the diagonal direction had a more pronounced impact on increasing the accumulative displacement and unloading stiffness of the foundation than along the orthogonal direction. Both suggest less favorable conditions for the former regarding the serviceability of OWTs. Throughout the loading, a progressive transfer of the lateral load carried by the upwind piles to the downwind ones was identified and a degradation factor model was derived based on cyclic p-y curves to assess the cyclic lateral pile-soil interactions of TPJ foundations in preliminary design. The complementary two-way loading test showed less hysteresis and degradation behavior of the soil than the one-way test, and hence limited accumulative displacement of the TPJ despite the load being applied in an asymmetrical form. Thus, the degradation model developed in the scenario of one-way loading is considered conservative.