Study on the thermo-mechanical response of a single energy pile in pile groups

In this paper, a simple calculation method is proposed to capture the thermo-mechanical response of a single energy pile in pile groups. The temperature variation mechanism of energy pile groups is captured based on the numerical simulation results. An exponential function is established to describe the relationship between radial temperature variation and radial distance, and a polyline function is proposed to simulate the relationship between axial temperature variation and depth. Considering the expansion and contraction of energy pile groups, the expression of radial and axial temperature stress is proposed by using equivalent pier method. The calculation method of unit skin friction and axial stress of a single energy pile in pile groups are proposed according to the temperature variation effect and pile group effect. Comparisons between the present calculation and three cases are made to verify the reliability of this calculation method. The research results show that the influence range of temperature diffusion is approximately within 5 times pile diameter. When the temperature rises by 26.3 degrees C, due to the thermo-mechanical loads, the unit skin friction near the pile top decreases by 55 %, while the unit skin friction near the pile end increases by 4 times. When the temperature drops by 13.7 degrees C, due to the thermo-mechanical loads, the unit skin friction near the pile top increases by 30 %, while the unit skin friction near the pile end decreases significantly. Comparing with the axial stress caused by mechanical load, the axial stress decreases by 18 % during the cooling condition (e.g., temperature variation Delta T(r) = -10 degrees C) at the middle point of the pile, while the axial stress increases by 4 times during heating condition (e.g., temperature variation Delta T(r) = +21 degrees C). The stability and durability of superstructure are significantly affected by temperature variation and mechanical load, which should be considered in the design of energy pile groups.