GEOTHERMAL ENERGY PILE-SOIL INTERACTION UNDER MECHANICAL LOADING AND THERMAL CYCLES

Harvesting shallow geothermal energy for heating and cooling building spaces in winter and summer is considered environmentally friendly and renewable. Recently, geothermal energy piles have been used as heat exchanger elements in ground source heat pump systems to exchange heat with the ground underneath buildings for heating and cooling purposes. However, imposing thermal cycles on such piles may result in possible adverse effects on their structural and geotechnical performance. A comprehensive understanding of the behavior of geothermal energy piles is therefore vital for the successful applications of such systems. This paper aims to investigate the interaction between the soil and geothermal energy pile subjected to a combination of mechanical loading and thermal cycles. Coupled thermo-hydro-mechanical (THM) finite element analyses were carried out on a hypothetical geothermal energy pile using climatic and geological conditions in Winnipeg, Manitoba, Canada. Numerical results were presented in this paper in terms of pile head displacements, strains, and stresses developed in the pile, as well as shaft friction and effective radial stresses along the pile-soil interface. The effects of heating and cooling on the ultimate geotechnical pile capacity were also presented. Based on the numerical results, it was found that the thermo-mechanical loads have considerable effects on the geothermal energy pile responses.