RESEARCH ON BEARING DEFORMATION OF SINGLE PILE UNDER VERTICAL FORCE-THERMAL LOAD-TORQUE LOADING PATH

The energy pile exhibits complex mechanical behavior, and there is relatively little research on the bearing deformation characteristics of the energy pile under multi-direction loads. To investigate the bearing characteristics of energy piles under vertical load, thermal load, and torque, the thermal load and torque were applied after preloading the vertical load to the pile top. By considering the effect of thermal load on the shaft resistance and boundary conditions of the pile, the pile displacement control equation is derived based on the load transfer method and boundary element method, and the analysis method of the bearing deformation characteristics of energy pile under vertical force → thermal load → torque loading path is proposed. The proposed method is in good agreement with the existing experiments and ABAQUS finite element results. The results show that thermal loading changes the load transfer characteristics of the monopile and affects the axial force and lateral frictional resistance distribution of the pile. Under the vertical force → thermal load → torque loading path, the additional load caused by the temperature change leads to the reduction of the monopile torsional resistance. Further parametric analysis shows that increasing the vertical load decreases the ultimate circumferential frictional resistance on the pile side, resulting in a 26.2% reduction (75%P_u, where P_u is the ultimate load) in the torsional resistance of the energy pile monopile. With the increase in the length-diameter ratio, the bearing capacity gradually increases, and thus the effect of thermal load can be offset by selecting a suitable length-diameter ratio. With the increase of temperature increment, the deformation increases gradually, and the deformation of the upper 0.6L is more significant, so the engineering pile foundation used as an energy pile needs to be reinforced on the upper part.