Abstract: To explore the bearing characteristics of single pile under the combined action of torque (T) and vertical load (V) on the pile top in clay foundation, vertical load was applied after preloading the torque to pile top. Based on the results of laboratory model tests and combined with the boundary element method, a reasonable assumption was made for the vertical ultimate friction resistance of pile side under the T→V loading path. The nonlinear solution of single pile under the T→V loading path was obtained by MATLAB programming, and then the bearing capacity envelope was plotted. To facilitate its application in engineering design, the expression of the failure envelops for the bearing capacity of single pile under the T→V loading path was obtained by fitting the experimental data. The results show that the vertical bearing capacity decreases with the increase of torque on single pile, and the T-V combination effect becomes more obvious when the torque load exceeds one third of the limit value. Both the bearing capacity and the deforming resistance of single pile are strengthened with the increase of length-diameter ratio, and the deformation of pile shaft mainly occurs in the range of 0~0.6L. Therefore, the reinforcement of shallow foundation can effectively reduce the deformation. The vertical ultimate bearing capacity of single pile improved with the increase of elastic modulus of pile shaft under the T→V loading path. Nevertheless, the vertical ultimate bearing capacity was only increased by 26.74% when the elastic modulus of single pile increased by 10 times. Therefore, it is not advisable to improve the ultimate bearing capacity of pile-soil system by increasing the concrete grade.

Key words: T→V loading path, single pile, model test, boundary element method, bearing characteristics