Failure envelopes of large-diameter shallow buried bucket foundation in undrained saturated soft clay under combined loading conditions

As a towering building, the offshore wind turbine is often subjected to significant horizontal load. The large-diameter shallow bucket foundation is a new kind of foundation to adapt to the special load conditions of offshore in China. The classical approach for the bearing capacity is not able to evaluate the bearing capacity of large-diameter bucket foundation. The failure envelopes of large-diameter bucket foundation on soft soil ground without drainage conditions in V-H, V-M, H-M and V-H-M loading spaces are investigated by means of the finite element method. Some formulas are obtained to describe the failure envelopes in V-H and V-M loading spaces. It is shown that the failure envelopes in V-H and V-M spaces are symmetric, while the failure envelope in H-M space becomes more asymmetric with the increasing depth ratio. The vertical load V affects the shape of the failure envelope in V-H-M loading space. The asymmetry of the failure envelope around M-axial recedes with the increasing vertical load. According to the relationship between the actual combined loading and the computed failure envelopes, the stability of large-diameter shallow bucket foundation can be determined.