A multi-spring framework for the lateral bearing characteristics of pile-bucket foundation in clay

As a promising supporting structure for larger offshore wind turbines, the pile-bucket foundation has been successfully deployed in several wind farms in China. However, there is currently no existing design guidelines for its lateral bearing capacity and existing studies adopted the conventional p - y framework that only captures the distributed lateral resistance. Considering the necessity of capturing all the resistance components, an extension of the four-spring model for large diameter monopile is proposed to predict the lateral bearing response of the pile-bucket foundation. A series of finite element simulations are conducted to investigate the lateral bearing mechanism of the pile-bucket foundation under varying foundation size, load parameters and soil parameters. Numerical results indicate that the supplement of bucket alters the bearing mechanism of the monopile and the lateral soil resistance is primarily governed by the pile and bucket diameters. Then a hyperbolic p - y model is constructed by dividing the pile-bucket foundation into reinforced section and non-reinforcement section, and modifying the initial stiffness and ultimate lateral resistance. On the basis of the modified p - y model, M f - θ f (distributed moment) spring, M b - θ b (base moment) spring and Q b - y b (base shear force) spring are introduced and the parameters are calibrated. The moment contribution ratio for each spring of the pile-bucket foundation is calculated and compared: p - y spring > M b - θ b spring > M f - θ f spring > Q b - y b spring. With increasing bucket size, the contribution of p - y spring and M f - θ f spring decrease and the influence of base spring becomes more pronounced. The proposed multi-spring model is expected to provide new perspectives for the design methodology of pile-bucket foundations.