A hypoplastic macroelement model for offshore wind turbine large-diameter monopiles in sand

At present, the numerical analysis of the monopile foundation of an offshore wind turbine subject to complex environmental loads is a major challenge in engineering design. Based on the concept of the macroelement model, this paper proposes a straightforward, speedy, and accurate numerical tool. Firstly, the numerical limit analysis method is employed to investigate the three-dimensional failure envelope surface of a large-diameter monopile in sand, and the analytical formula of the three-dimensional failure envelope surface is obtained. Then, using the three-dimensional failure envelope and combining the basic principles of the hypoplastic theory, a hypoplastic macro-element of a large diameter monopile foundation in sand is proposed. The performance of the macroelement model is calibrated by comparing it to centrifuge test results of a small-diameter pile and three-dimensional finite element results of a large-diameter monopile under cyclic loading. Finally, the macroelement model is used to analyze the performance of the OWT large-diameter monopile foundation under wind and wave loads. The results indicate that the macro-element model can precisely reproduce the performance of large-diameter monopile foundations under cyclic loading, and can effectively and accurately solve the complex pile-soil interaction problem of OWT large diameter monopiles under cyclic loading.