Inferred Winkler model for stiffness of suction caisson foundation under combined loading in non-homogeneous and layered soil

With the development of offshore wind turbines in deep water, suction caisson foundations jointly used with jackets have become a promising foundation type for those constructed in windfarms covered with soft soil. Reasonable prediction of the stiffness of suction caisson has a significant influence on analyzing both static and dynamic response of supported structures. Distributed spring-based Winkler models have been successfully constructed to evaluate the stiffness of pile and caisson foundations under vertical and lateral loading. However, the counterparts for suction caisson under general loading conditions (i.e., combined vertical, horizontal, and moment loading, V–H–M) are relatively under-developed, despite the latter representing one of the most fundamental working scenarios of the foundation. The goal of this work is to establish a simplified Winkler model capable of calculating stiffness of suction caisson foundation under combined loading (V–H–M) in non-homogeneous and layered soil. This purpose is achieved via the concept of “Inferred Winkler model.” In particular, we construct a special model structure that accounts for the distinct influences of foundation embedment and non-uniform distribution of soil reactions, while maintaining theoretical consistency with well-established Winkler models for pile and shallow foundations. Specific relationships and expressions in the above model are then inferred from finite element analysis (FEA). The performance of the proposed model is evaluated against FEA regarding both foundation response and soil reaction distributions under combined loadings in homogeneous, non-homogeneous and layered elastic soil. Reasonable agreement between the calculation results suggests that the proposed model is reliable for foundation stiffness assessments and has a much lower computational cost compared to FEA.