Design of spiral coil PHC energy pile considering effective borehole thermal resistance and groundwater advection effects

This study presents experimental and numerical research results in determining an effective borehole thermal resistance of a spiral coil energy pile. A precast high-strength concrete (PHC) energy pile with a spiral coil GHE was installed and thermal response test was carried out to evaluate the thermal behavior of the energy pile and to validate the effective borehole thermal resistance. Besides, parametric studies using a numerical analysis were carried out to suggest a multiple regression equation for the effective borehole thermal resistance of spiral coil energy piles. The adjusted coefficient of determination (adjR2) of the regression equation was 92.4%, which was also verified by comparison with experimental results. Furthermore, using current analytical models, this paper examined the effect of groundwater advection on the long-term ground temperatures. In the long-term period operation, groundwater advection attenuates the average temperature rise in the ground compared to the case with the absence of groundwater advection, and this phenomenon ultimately causes a decrease of the temperature penalty value. The temperature penalty value, considering the effect of groundwater advection, was calculated and compared for various groundwater advection velocity values in different pile arrays.