Evaluation of Coupled Interaction Effects Caused by the Long-Term Performance of Energy Piles in a Piled Raft Foundation

The results of a set of coupled thermo-hydro-mechanical (THM) finite element (FE) simulations are presented to evaluate the effect of long-term periodic temperature variations within a range of 10 ℃ applied to energy piles in a piled raft located on saturated stiff clay on the soil-pile-raft interaction. At shallow depths of the active pile, where the variation range is more significant than in other areas, the presence of the raft in direct contact with the soil causes the maximum thermal compressive stress to exceed approximately three-fourths of the axial mechanical stress, as well as the generation of tensile stress. Additionally, the stabilized additional settlement of the foundation was approximately one-sixth of the mechanical settlement, demonstrating the importance of evaluating the serviceability of the superstructure while considering additional stresses. However, it was observed that the variations in excess pore water pressure were not significant for the corresponding values considered. Furthermore, parametric studies revealed that variability in the thermal expansion coefficient and thermal conductivity of solid soil particles had a similar qualitative effect on the system's response, despite some quantitative differences. This implied that the effectiveness mechanisms governing the soil's temperature variations and thermal deformation potential were nearly identical, despite their distinct ability to alter the stress state.