Model tests on thermal-mechanical behavior of single energy piles embedded in loess soils

The paper presents the results of laboratory model tests on energy piles embedded in loess. Under a 5 kN vertical mechanical load, the piles underwent four sequential heating–cooling cycles. Pile–soil temperature, settlement, and pile strain were then monitored under dry and saturated conditions, respectively. The results show that during the cooling phase, the average heat transfer is significantly higher under saturated conditions, while only a small difference is observed during the heating phase. Under saturated conditions, the heat transfer radius in loess is approximately 2~3 D , while it exceeds 3 D under dry conditions. The variation of the pile head mechanical load is closely related to the fluid temperature. Unlike the 2nd to 4th heating cycles, negative change rates were observed during the initial heating cycle under saturated conditions. Saturated conditions cause lower pile head mechanical load and settlement than dry conditions. After the heating cycle stabilizes under dry conditions, negative side friction is observed in the upper part of the pile (Z/L < 0.43), while positive friction occurs in the lower part, and the pattern is opposite during the cooling cycle. Under saturated conditions, negative side friction is consistently observed in the upper part of the pile throughout the thermal cycling.