| Summary: | This paper focuses on the simulation of the coupled heat transfer and water flow in unsaturated soil layers surrounding a solitary energy pile undergoing heating and cooling cycles typical of a field-scale energy pile. The results indicate that heating leads to drying of the soil surrounding the energy pile, which has been shown in previous studies to result in an increase in axial capacity. During cooling, the degree of saturation was observed to recover to the value present before the start of heating initially, however, it will not recover in the following years. Which will lead to a cumulative effect after several cycles of heating and cooling. Heating and cooling cycles lead to an overall reduction in the thermal conductivity of the subsurface, reducing the heat transfer from the energy pile but also leading to greater storage of heat in the subsurface surrounding the pile.
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