In-Situ Thermomechanical Response Test of an Energy Pile Under Temperature Loading

Abstract

The energy pile is a building energy-saving technology that uses shallow geothermal energy. It has the advantages of higher heat-transfer efficiency and lower land requirements than a traditional ground source heat pump system. The thermomechanical response characteristics of an energy pile under cooling and heating conditions were studied. An in-situ test of the cast-in-place energy pile was used to carry out the cooling, recovery, and heating stages. Based on analysis of the stress–strain distribution characteristics and the variation law of shaft friction under the conditions of temperature load and pile restraint, the results showed that the strain distribution of the cross section at a given depth in the pile was uniform and that there was no obvious eccentric stress in the vertical pile loading. The thermally induced axial stress had a linear relationship with temperature change, and the soil around the pile and the constraint conditions at the top or toe of the pile have an impact on the location of the maximum thermally induced load. According to calculations at a ± 10 °C temperature difference, the maximum stress can reach 1.79 MPa during cooling and 1.46 MPa during heating. The variation of unit temperature in each depth range causes shaft friction to become more uniform, and shaft friction increases almost linearly with temperature.