Effects of Soil Type on Axial and Radial Thermal Responses of Field-Scale Energy Piles

This paper presents a field test on the axial and radial thermal responses of friction-type energy piles embedded in clay under monotonic thermal loads (2.5 and $5.0\mathrm{kW}$). The inlet and outlet water temperature, pile temperature, and strain were monitored. The heat exchange efficiency and thermal response of the energy pile are discussed and analyzed. Further comparative analyses of friction-type energy piles embedded in compacted sand showed that the radial thermal stress of a pile is much lower than the axial thermal stress, which may not play a major role in soil–structure interaction. The axial thermal stress of an energy pile embedded in clay increases with increasing axial constraint. The constraint of the energy pile cannot be simply predicted through the shear strength of the sand. The influence of the radial thermal stress produced during the operation of the energy piles on the bearing capacity of the pile can be disregarded, especially in soft soil.