Abstract: The early concrete hydration not only releases a large amount of heat but also causes the early deformation and constraint stress of the pile, which affects the bearing capacity of piles. However, there are few studies on the effect of formation temperature on the thermo-mechanical properties caused by the early concrete hydration, especially the pile group effect. Field tests were carried out to investigate the thermo-mechanical properties of 3×3 group piles influenced by early concrete hydration. The distributions of temperature and strain of piles along pile depth were measured. Moreover, the heat dissipation and additional stress of piles, and heat dissipation group effect influenced by formation temperature were discussed. Meanwhile, the thermo-mechanical properties of the single pile were also conducted for comparative analysis. The results show that the temperature superposition effect of pile group influenced by hydration heat is not very obvious. The dissipation rate of hydration heat in the constant temperature zone is relatively slower than that in the variable temperature zone. The residual stress of concrete is unevenly distributed along the pile depth, which has large values in the middle and small values at two edges. The maximum residual stress occurs at a depth of 0.6 times pile length.

Key words: pile foundation, group pile, concrete hydration, formation temperature, constraint stress