Thermally induced mechanical interactions of energy pile groups subjected to cyclic nonsymmetrical thermal loading

Abstract

Prior to this study, the long-term thermally-induced mechanical interactions of cyclic nonsymmetrical thermally loaded energy pile groups in soft clay have not been systematically elucidated, particularly with a limited understanding of the interactions among operating and non-operating energy piles, soil, and caps. Observing such a challenge, this paper presents a three-dimensional (3D) thermomechanical finite-element model (FEM), which considers the thermal-dependent behavior at the pile-soil interface and is validated using typical centrifuge tests reported in the literature. Special attention is given to the influence of soil-pile thermal expansion coefficient ratio, pile-soil stiffness ratio, and slab-soil stiffness ratio on the abovementioned interaction. The results indicate that a larger soil-pile thermal expansion coefficient ratio intensifies the interaction between energy piles and the surrounding soil, causing cyclic variations in thermally mobilized friction. With increasing pile-soil stiffness ratios, the differential thermomechanical responses among different piles within a group are enhanced because the toe and shaft resistances mobilized by the cap through nonoperating energy piles are weakened in the interaction process among energy piles, nonoperating energy piles, and the cap. Moreover, the increase in the slab-soil stiffness ratio exacerbates this interaction, strengthening the integrity of the pile groups.