Abstract: In order to study the thermal characteristics of pre-bored grouted planted energy pile groups in saturated clay foundation under different operation modes, a self-designed model test system is used to examine the thermal response of single pile and pile group. By embedding sensing test elements, data on pile top displacement, pile stress, pile and surrounding soil temperatures, horizontal soil pressure, and pore water pressure are collected. Findings show that the heated pile influences adjacent unheated piles through thermal diffusion, leading to increased pile body temperature and top displacement. Moreover, the overall heat transfer efficiency of energy pile groups is lower than that of single piles. The absolute displacement change at the pile top in energy pile groups is greater under cooling conditions than under heating conditions, necessitating safety considerations. The group effect results in larger pile top displacements and lower additional thermal stresses in energy pile groups compared to single piles. Furthermore, as the number of energy piles in a group increases, the thermal characteristics become more pronounced, accompanied by greater variations in horizontal soil pressure and pore water pressure around the piles.

Key words: pre-bored grouted planted energy pile, the additional thermal stress, model test, thermo-mechanical coupling, bearing characteristic