Vertical dynamic response of energy pile under different load frequencies and thermal conditions

Currently, there is a considerable body of research focused on the thermo-mechanical behavior of energy piles under static loading; however, studies investigating the dynamic response of energy piles under cyclic loading remain limited. This study examines the dynamic response of single energy piles in sandy soil through model testing, analyzing changes in pile top displacement and cyclic stiffness characteristics. Additionally, a three-dimensional finite element model that accounts for the relevant behavior of the pile-soil contact surface under cyclic shear was developed and validated against the test results. Using this numerical model, the effects of the number of cycles, cyclic loading frequency, and temperature gradient on the vertical dynamic response of single energy piles were assessed. The findings indicate that as the number of cycles increases, the pile tip resistance appears to strengthen while the pile side resistance weakens, with the variation trend under heating conditions being more pronounced than that under cooling conditions. Furthermore, an increase in cyclic loading frequency leads to greater cumulative settlement of the energy pile, with the pile tip resistance showing an upward trend and the average pile side resistance a downward trend. Notably, the strengthening of pile tip resistance and the weakening of pile side resistance become less pronounced once a certain threshold is reached.