Numerical Study on the Bearing Mechanism of Hybrid Monopile-Bucket Foundations for Offshore Wind Turbines

Various hybrid foundations have been proposed to improve the lateral performance of monopiles for supporting offshore wind turbines. Among them, the hybrid monopile-bucket foundation which consists of a traditional monopile and a wide-shallow bucket has received more and more attention. The existing reported studies on the lateral bearing responses of the hybrid monopile-bucket foundation are extremely limited. This study aims to gain deep insights into its bearing mechanism through validated three-dimension numerical models. Based on the computed results, the soil failure mechanism around the hybrid foundation and the lateral force/moment-bearing characteristics between the components (the pile and the shallow bucket) of the hybrid foundation is revealed. It is found that the load and moment sharing ratios of the monopile decrease with the increase in Dbucket/ Dpile ratio, indicating the monopile of the hybrid foundation will afford less external lateral force and moment when the Dbucket/ Dpile ratio increases. Considering the practical values of Dbucket/ Dpile, the percentage of lateral force afforded by the monopile of the hybrid foundation is in the range of 5%–30%. This reveals the external lateral force is mainly carried by the bucket while not the pile. On the other hand, the percentage of lateral force afforded by the pile of the hybrid foundation varies between 70%–85%, indicating the pile of the hybrid foundation resists most of the external moment. The numerical results presented in this study are expected to provide design references for practical applications of the hybrid foundations.