Evaluation of combined horizontal-moment bearing capacities of tripod bucket foundations in undrained clay

• H–M envelopes of tripod bucket foundations were analyzed by 3D FE analysis.
• H–M envelopes increased as increasing S/D and L/D, decreased as increasing kD/sum.
• Normalized H–M envelopes were only influenced by L/D ratios.
• A design equation of the combined H–M capacity was developed.

A series of three-dimensional finite element analyses was conducted to evaluate the combined horizontal-moment bearing capacities of tripod bucket foundations for offshore wind turbines in undrained clay. The tripod bucket foundation consists of three single bucket foundations, which enhance the bearing capacities because of the effect of the interaction among individual buckets. A linear-elastic perfectly plastic model, which obeys the Tresca failure criterion, was used to simulate the stress–strain response of clay, in which Young׳s modulus and undrained shear strength were assumed to increase linearly with depth. The effects of bucket spacing, embedment depth, vertical load, and non-homogeneity of clay on the combined horizontal-moment capacities were analyzed. Finally, the design equation of the combined horizontal-moment capacities was developed as a function of the aspect ratios (skirt length/diameter) of the foundations.