Thermomechanical response of energy piles in dry sand under monotonic cooling with varying end-support conditions

Energy piles serve as load -bearing foundations that facilitate sustainable heat exchange with shallow geothermal energy by integrating geothermal heat exchangers (GHEs). Nonetheless, the thermal loading introduces the potential for expansion and contraction in energy piles, which can impact the soil -pile interaction. Since the majority of the experimental research on energy piles only considered the heating load, investigating the thermomechanical response and bearing capacity of energy piles under cooling and different end -support conditions remains an area that requires more elaboration. To address this, two series of experiments were performed on a concrete energy pile using 1 g physical modeling in dry sand with a relative density of 48 %. The tests were conducted on semi -floating energy piles (SFPs) and end -bearing energy piles (EBPs) under monotonic cooling while varying the average pile temperatures (a total of 6 tests). The results indicated that the EBP's behavior under cooling load was similar to SFP's. The bearing capacity alterations of the pile were calculated by determining the maximum thermomechanical stress induced in each of the conducted tests. The experimental results revealed that the bearing capacity of SFP was more significantly affected during a cooling load than EBP. Specifically, under identical mechanical loading conditions, the maximum reduction of the bearing capacity of SFP and EBP was found to be 13.4 % and 5.5 %, respectively. This phenomenon can be attributed to the distinction in load transfer mechanisms between the two foundation types, where a decrease in frictional shaft resistance had a more noticeable impact on reducing the bearing capacity of SFP compared to EBP. A comparative analysis was also conducted among settlement, axial stresses, and mobilized shaft friction values induced by various loading types.