In this paper, a deep tripod-bucket foundation with a height-diameter ratio of 2:1 is proposed. The three-dimensional finite element model considering the interaction between the tripod-bucket foundation and soil is established in ABAQUS. The ultimate bearing capacities Hult, Vult and Mult of foundation in homogeneous clay seabed under pure horizontal load (H), vertical load (V) and moment load (M) are calculated. Furthermore, the loading performance of the foundation under combined load conditions was studied with fixed displacement ratio method. Considering the tripod-bucket foundation can withstand upward and downward loads, the combined bearing capacities under vertical upward (V+) and vertical downward (V−) load conditions are involved in this study. Results show that H and M in V+-H and V+-M load space decrease gradually with the increase of V+. In V−-H load space, H increases with the increase of V−, then keeps constant, and then gradually decreases. In V−-M load space, M increases with the increase of V−, then decreases gradually. In V-H-M load space, the H-M envelope is unsymmetrical about M axis. Under different V levels the shape and range of each H-M envelope are different. Finally, the dimensionless standard envelope of the deep tripod-bucket foundation is analyzed, and the failure mode of soil around the monopile is studied.
As a towering structure, the offshore wind turbine (OWT) needs to bear huge horizontal loads (H) and moment loads (M) as well as vertical loads (V) due to the effect of wind, wave and current, leading to vertical displacements (w), horizontal displacements (u) and rotations (θ) of the foundation. This loading mode is called the combined loading mode (Salencon and Pecker, 1995). Under combined loading conditions, the ultimate bearing capacity of bucket foundation cannot be calculated accurately by the classical bearing capacity calculation formula, so numerical modeling is generally adopted for analysis and calculation (R Liu et al., 2014).
