Field test on thermal response characteristics of an energy pile in underground row piles

Abstract

Underground row piles are usually used in excavation of underground structures and abandoned after structural construction. The heat exchanger tubes embedded in the underground row piles can be severed as energy piles, which can exchange shallow geothermal energy. The construction process of the energy pile in the underground row piles was introduced. Compared with the traditional single energy pile, there is a special characteristic of the energy pile in underground row piles: piles are linked as a whole by the top beam at the top of the row pile. Field tests on the thermal response and thermo-mechanical characteristics of the energy pile in underground row piles were performed. The stable input power of 2.07 kW. The distribution of temperature, strain, and stress of pile body along depth were measured and discussed. It shows that the measured comprehensive thermal conductivity coefficient of soil is 3.72W/(m×K). In the thermo-mechanical analysis after heating, due to the end restrains by the top beam and toe in stiff rock, the rate of thermal stress to temperature change at the top and toe are -0.101 MPa/℃ (34% of fully restrain) and -0.061 MPa/℃ (20% of fully restrain).