Analysis of the effect of multiple thermal-cold cycles on the bearing performance of phase change energy piles

As a famous underground heat transfer structure, energy piles have been widely used in geothermal energy development. However, the effect of the cyclic temperature field on the ultimate load capacity of a single pile is substantial. In this study, model piles were poured using a phase change energy storage concrete based on Gum Arabic with polyethylene glycol 600. An indoor modeling test was designed to compare the phase change energy pile (GPEP) with the traditional energy pile (TEP). The ultimate bearing capacity of a single pile is obtained through theoretical formulas and static load tests to compare the bearing performance superiority of GPEP over TEP comprehensively. The response mechanism of GPEP to temperature changes was determined by evaluating the temperature change of the pile body, shear strength, water content of the soil facing the pile, thermally induced frictional resistance, and pressure exerted by the soil facing the pile. The results indicate that the single piles of GPEP increased the ultimate bearing capacity by 13.04 % (theoretical formula) and 13.70 % (static load test) compared to TEP. Due to the energy storage properties, phase change materials effectively restrict the temperature-drag response of energy piles. This study serves as a valuable reference for the practical engineering implementation of GPEP.