On load-bearing and soil-reacting characteristics of hybrid pile-bucket foundations subjected to static horizontal loading

The hybrid pile-bucket foundation is an innovative alternative to monopile foundation when used to support offshore wind turbines (OWTs). To understand the load transfer mechanism of the hybrid foundation when loaded horizontally, reduced-scale model tests and numerical modelling were performed to investigated loading/deformation characteristics of the pile-bucket foundation structure and stress-reacting features of the soil surrounding the foundation. Both the pore water pressure (PWP) of the soil and strains of the pile and bucket are recorded from the model test. Furthermore, the pile/bucket load sharing ratio, contours of plastic strain, and excess PWP of the soil are obtained and analyzed via numerical modelling of the model test. The results show that the horizontal load is mostly carried by the bucket, and the overturning moment is mostly resisted by the pile. Compared to the monopile foundation, the soil of the hybrid foundation shows smaller PWP increase and less principle-stress rotation, implying a lower rate of stiffness and strength degradation of the hybrid foundation when subjected to cyclic loadings.