Thermally-induced long-term behavior of energy piles under inclined load in saturated clay

Thermally-induced long-term behaviors, such as the ratcheting phenomenon, have been observed in vertically and horizontally loaded energy piles under thermal cycling. However, whether this phenomenon occurs in inclined loaded piles and the underlying mechanisms remain unclear, especially considering the combined effect of horizontal and vertical loads on pile–soil interaction. This study employed laboratory model tests and numerical simulations to investigate the long-term behavior of the energy pile under an inclined load in saturated clay. The experiment involved constant vertical loading of 100 N, 15 thermal cycles with temperature changes of ±3.5 °C, and various horizontal loads (35, 71, and 109 N, corresponding to horizontal displacements of 4%, 7%, and 12% of pile diameter, respectively). Due to the scale effect, all acquired data have been normalized to facilitate better use in the qualitative thermomechanical analysis of energy piles. Measurements and simulations demonstrated that the ratcheting phenomenon is evident in inclined loaded energy piles. Cyclic thermal loading caused irreversible vertical and horizontal displacements of the pile head, with an accumulation rate decreasing as thermal cycles increased. The analysis suggests that the ratcheting phenomenon may be induced by variations in load transfer caused by the energy pile–soil interaction under long-term thermal operations. These findings provide valuable insights into the long-term performance and design considerations for energy piles subjected to inclined loads.