Analysis of Energy Piles Under Cyclic Axial Loads and Impact of Loading Amplitudes

This paper presents a study on model tests of single energy piles subjected to cyclic axial loads in sand and the development and validation of a 3D thermo-mechanical finite element model. The model accurately simulated the behavior of the pile-soil interface under cyclic shear loads. A subsequent parametric analysis examined the effects of the number of loading cycles and the loading amplitude on the vertical dynamic response characteristics of energy piles. The results showed that under heating conditions, the maximum variation in compressive thermal stress in the energy pile gradually decreased, with its location shifting upward along the pile shaft. A critical cyclic amplitude ratio was identified: below this threshold, the rate of increase in pile tip resistance continuously increased while the average pile side resistance weakened progressively. The presence of a static load accelerated the weakening of the average pile side resistance to some extent. As the number of loading cycles increased, the settlement rate of the energy pile gradually degraded. The cumulative settlement rate at the pile top increased with the cyclic amplitude ratio, peaking before slightly declining. In comparison, the static load ratio had a relatively minor influence on cumulative settlement.