Comparative Analyses on Thermo-Mechanical Characteristics of Energy Pile Group and Single Energy Pile

Three dimensional dynamic numerical simulations were conducted on thermal and mechanical responses of energy pile group and single energy pile to 72-hour continuous and intermittent heat rejection processes. The temperature of piles body, piles stress, additional temperature load, piles section displacement and lateral resistance of the piles were analyzed. Results show that the outlet water temperatures of the buried pipes are similar, but temperature differences of pile body between the pile group and the single pile are obvious, leading to a series of differences of mechanical responses between two pile types, such as pile body displacement and additional temperature stresses, etc. With mechanical force loaded on the top, the single pile exhibits greater stress than each pile in the pile group and the stress reaches the maximum in the lower part of the pile body. The additional temperature load is almost equal in the main part of the pile but varies dramatically near the pile tops and bottoms. With structure load exerted on the top, the settlements of the whole pile occur. But as time proceeds, the tops of the piles move upward and the bottoms move downward. The lateral resistance of the piles increases along the depth direction and reaches the maximum at the pile bottom. The outlet water temperature, pile temperature and displacement of energy piles fluctuate obviously under intermittent operational condition, and accumulative effect appears.