Abstract: Energy piles are a new energy-saving technology for buildings that combines load-bearing performance and heat exchange performance. Most studies on energy piles are carried out under free and unconstrained conditions or rigid constraints, such as pile-cap/raft systems. However, the thermo-mechanical response characteristics of energy piles under the relatively flexible constraint state of a composite foundation remain unclear. Field tests were conducted at the BeSTDR Infrastructue Hospital in Pingyu County, Henan Province, as an ultra-low energy consumption green building project to assess how cushion layers affect the thermo-mechanical response characteristics of prestressed high-strength concrete (PHC) energy piles. The development patterns of temperature and strain along pile body were measured, and the changes in constraint stress, thermal-induced side friction resistance, axial displacement, pile-soil stress ratio, and the response characteristics of the adjacent pile were preliminarily explored. The results show that under the experimental conditions, the constraint capacity at the pile top (0.133L) is approximately 65% due to the influence of the cushion layer. After 96 hours of heating, the region between 0.133L and 0.333L from the pile top exhibited minimal negative skin friction, with the maximum upward axial displacement at the pile top (0.133L) reaching about 0.14% of the pile diameter. After 120 hours of heating, the pile-soil stress ratio at 0.133L from the pile top nearly tripled.

Key words: prestressed high-strength concrete (PHC) pipe pile, energy pile, cushion layer, flexible constraint, thermo-mechanical response characteristics