Capacities of tetrapod bucket foundations in clay under combined horizontal-moment loading

Tetrapod bucket foundations are known for being suitable foundations for offshore wind turbines in water having a depth of 20-50m. The rigid connection among the four individual foundations leads to increase in rotational stiffness of whole foundation system. Thus, these structures are effective in resisting large amounts of horizontal and moment loads arising from wind and waves. In this study, undrained bearing capacities of tetrapod bucket foundations subjected to varying uniaxial and combined horizontal-moment loadings are evaluated. 3D numerical models are developed to explore the effect of reduced shear strength at soil-foundation interface, spacing and embedment of the buckets in clay with linearly increasing shear strength with depth. Combined load bearing capacities are represented as failure envelopes. Finally, an expression is presented for estimating combined horizontal moment bearing capacity.