Three-dimensional finite element analysis of stress and deformation characteristics of energy piles under inclined loads

The three-dimensional finite element simulation for energy piles with thermo-mechanical coupling effects is implemented by optimizing the pile-soil material parameters, boundary conditions, steps and grid types, etc. In this analysis, the stress and deformation characteristics of energy piles under inclined loads are investigated based on the existing experimental and numerical results. Further, the modelling method is validated by comparing the settlements at pile head from this study and those from the model tests and two-dimensional numerical simulations. Finally, the laws of settlements at pile head, frictions at pile side, lateral displacements and bending moments are explored through the variation of three main influence factors: vertical loads, lateral loads and temperature differences, and the corresponding suggestions for engineering design of energy piles are proposed. The results show that when the temperature difference ΔT>0℃, the thermal expansion will appear and the vertical displacement atop the pile is even upward. However, with the increase of vertical loads, the settlement-load curves will gradually tend to the curve when ΔT=0℃. Besides, the frictions at pile side are negative on the upper and middle parts of piles, and are positive on the lower part of piles. The lateral displacements and bending moments when ΔT>0℃ are both greater than those when ΔT=0℃. When ΔT<0℃, the frictions at pile side are positive on the upper and middle parts of piles, and are negative on the lower part of piles. The lateral displacements at top of the pile when ΔT>0℃ are greater than those when ΔT=0℃, the reason is different from that when ΔT>0℃, and the bending moments are less than those when ΔT=0℃.