Analytical method for single pile under V-H-M combined loads in sand

The large-diameter monopiles of offshore wind turbines are always subjected to multiaxial loads. The design criteria for the vertical and lateral bearing behaviors of piles are designed independently, while lots of tests show that the vertical load has a remarkable influence on the lateral bearing capacity. The effect of the vertical load on the lateral behaviors of the large-diameter monopiles can be distinguished into three aspects: (1) the variation of the ultimate resistance p_u of p-y curve caused by vertical loads; (2) P- effect; (3) the resisting bending moment M_R generated by the uneven distribution of vertical skin friction. Based on the theory of passive wedge failure model as well as the influence of the ultimate soil resistance per unit length p_u caused by the vertical loads, the corrected p-y curves for sand are obtained respectively. Furthermore, an analysis method for the monopiles inserted in sand under combined loads, including the lateral load, vertical load and moment, is established, which is based on the elastic-foundation beam theory of the traditional lateral-loaded pile, taking the P- effect and M_R effect into considerations. Finally, it is proved that the theoretical results are feasible, applicable and reasonable by analyzing several project cases.