Failure Envelopes of Tripod Pile Foundation Under Combined Load in Non-homogeneous Clay

Tripod pile foundations are an alternative foundation for offshore wind turbines. Three-dimensional finite element limit analyses are carried out to determine the bearing capacities of tripod pile foundations in non-homogeneous clay under combined vertical (V), horizontal (H) and bending moment (M) load. The undrained shear strength of the clay is considered to increase linearly with depth. Three-dimensional failure envelopes in V-H-M loading space are established through a simplified loading strategy considering the reality of the loading condition. The obtained results are finally presented in terms of normalized and dimensionless capacity factors. Moreover, the effects of length-to-diameter ratios (L/D), spacing-to-diameter ratios (s/D) for the tripod piles, and the gradient of undrained strength in terms of soil depth (k) on failure envelopes are further discussed. Several failure mechanisms are identified to be associated with different load combinations.