Bearing behavior of a single pile in double-layered nonhomogeneous subsoil under V-T combined loads

To discuss the bearing behavior of a single pile under combined vertical load V and torque T in offshore double-layered nonhomogeneous subsoil, the shear modulus of each soil layer is assumed as an increasing distribution with the depth defined by a power function. Then, considering various loading sequences and the non-coordination deformation along the pile-soil interface, the governing equation for the pile shaft is first established by using the load transfer function and the shear displacement method. Subsequently, the analytical solutions are deduced to calculate the inner forces and deformations of the pile shaft under various bearing stages and loading sequences (V→T or T→V). Based on the results by the obtained solutions, the failure envelops for the bearing capacity of the pile shaft are plotted correspondingly. Through a comparative analysis of the results with the available achievements, the rationality of the proposed method is verified. Finally, a parameter analysis is carried out to discuss the influence laws by the key factors such as the slenderness ratio of pile shaft (L/D), loading sequences and constant coefficients determining the shear modulus distribution (m₁, m₂, n) of subsoil. The results show that the bearing capacity decreases with the increase of L/D and n. The main influence range of m₁ is z/L≤0.4 and the influence range of m₂ increases with the increase of T_t /T_ult under V→T loading path. The effect of m₁ can be ignored and the main influence range of m₂ is 0.6≤z/L≤1.0 under T→V loading path. To increase the value of torsion at the pile top will result in a decreasing vertical bearing capacity with a final zero value. Furthermore, the failure envelope under V→T loading path remains outside of that under T→V loading.