Effects of thermal loading conditions on the thermo-mechanical response of energy pile at different depths

Abstract

This paper investigates the thermo-mechanical response of a full-scale energy pile under different thermal loading conditions at a field site in Liyang City, Jiangsu Province. The results show that a 1 °C increase in inlet temperature during heating led to a rise from 0.33 °C to 0.74 °C in pile temperature, while a 1 °C decrease during cooling caused a drop of 0.65 °C to 2.10 °C. Additionally, the ratio of the pile temperature change to the theoretical maximum pile temperature change remained consistent across different inlet temperatures, indicating a fixed temperature response sensitivity of the pile to inlet temperature variations. The most significant temperature change occurred in the middle part of the pile, where the thermal strain was minimal due to the greatest soil and structural constraints, leading to the highest thermal stress. In contrast, the smallest temperature change and thermal stress were observed at the bottom of the pile. Besides, the average compressive stress under the intermittent heating operation was 37.9 % lower than under the continuous heating operation, while the average tensile stress under intermittent cooling decreased by 63.3 %. By providing different field data on the thermo-mechanical behavior of the energy pile under various thermal loading conditions, this study is beneficial for the design and operation of energy pile systems.