Response of energy pile-soil structure and pile group effect: An indoor similarity simulation study

Abstract

Energy pile has dual functions of coupled heat transfer and load-bearing. The research on its bearing characteristics has attracted much attention. This research is based on the indoor scale model test of energy pile to simulate the thermo-mechanical response of single pile and pile group of spiral energy pile under summer and winter conditions. The thermal response of the middle part of the energy pile is the largest. Under the action of circulating water, additional tension is generated in the pile section in winter and additional pressure is generated in summer. Through comparative analysis, it is proved that when multiple piles are operated simultaneously, the heat transfer efficiency is almost the same as that of single pile in the initial operation, and the heat transfer efficiency of single pile is reduced in the long-term operation, the temperature response of soil between pile and pile is higher, and the quasi-steady state time is shortened. The axial force distribution of single pile and multiple piles is compared and analyzed. The results show that in the service process of multiple piles, when the upper load is 0.8 Pu in winter, the axial force in the middle of the pile group is reduced by 0.73 kN compared with that of single pile. In summer, when the upper load is 0.8 Pu, for example, the circulating water temperature is 35 °C, 45 °C and 55 °C, and the maximum axial force in the middle of the pile increases by 0.5 kN, 0.79 kN and 0.8 kN respectively. It is proved that the pile group effect does exist when the energy pile group works, which will reduce the heat exchange efficiency of single pile, advance the quasi steady state time, increase the single pile axial force in summer, reduce the single pile axial force in winter, and even generate tension in the pile section. The energy pile group effect should be fully considered in the design and application of energy pile.