Experimental and numerical investigations on thermo-mechanical behaviours of energy pile group with different seepage parameters

The operational performance of energy pile (EP) group with seepage is strongly influenced by seepage parameters. In this paper, a model test system of 2 x 2 EP group with seepage is built to study the influences of seepage water level and seepage velocity on thermo-mechanical behaviour of EP group. Also, a numerical model of EP group considering seepage is developed to obtain the variations of thermo-mechanical behaviour of EP group under different seepage parameters. The findings demonstrate that an augmentation in seepage water level can enhance the heat exchange performance of EP group, but it also exacerbate the imbalance of mechanical properties between piles in the short term, in which the seepage only have a significant effect on the temperature of piles and soil below the seepage water level. Increasing seepage velocity and circulating flow rate can strengthen thermal performance of EP group and improve the equilibrium of pile axial force and displacement between the pile groups, but increasing seepage velocity also increases the imbalance of mechanical properties between the front and back rows of pile group. At the same time, compared to the circulating flow rate, the change in seepage velocity has a dominant impact on the thermo-mechanical characteristics of EP group. Moreover, when the seepage angle is within 0-45 degrees, increasing the seepage angle can effectively improve the heat transfer performance of EP group, and the temperature distribution of pile and soil is obviously different for different seepage angles, in which the mechanical properties of EP group have the best equilibrium when the seepage angle is 30 degrees for current simulation conditions.