Effects of pile and soil properties on thermally induced mechanical responses of energy piles

Energy piles, having the dual roles of exploiting geothermal energy and providing structural stability, are creating large worldwide interest. This paper aims to provide knowledge on the potential effects of pile and soil properties on the thermally induced mechanical behavior of energy piles. It presents the results from in-situ experimental investigations conducted on an energy pile. Three-dimensional numerical models were developed and validated to evaluate the behavior of energy piles equipped with various U-pipe configurations from the viewpoint of energy efficiency and structural safety. The results indicated that although increasing the pipe length could improve the thermal exchange capabilities of energy piles, it introduced more significant mechanical effects on the piles, which should be considered during the design. Moreover, parametric studies were performed to explore the potential effects of the soil thermal expansion and elastic modulus on the thermomechanical response of energy piles. The comparative analysis showed that the soil thermal expansion after heating would reduce the thermal compressive stress induced in the energy piles. The soil thermal expansion effects were time-variable and became more significant with the operating time of the energy piles. The thermal stress increased and approached the theoretical maximum value as the soil elastic modulus increased.