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Micro steel pipe pile was used for existing foundation reinforcement and renovation. An energy micro pile-raft foundation equipped with heat exchange tube was constructed in silty clay. The diameter and the length of the energy micro pile are 160 mm and 13.0 m, respectively. A series of in situ thermal performance tests were carried out by controlling cycle heating, in which the inlet and outlet water temperatures, flow rate, and thermomechanical properties of the energy micro pile were measured. Combined with a numerical simulation method, the thermomechanical stresses and displacement of the raft were also analyzed and discussed. The energy micro pile-raft foundation was also analyzed for different combinations of energy piles and nonenergy piles in the group. Results show that the micro pile-raft foundation can provide sufficient heat exchange compared with other types of ground heat exchangers. Differential settlement at both the pile top and tip were observed for the groups that contained both energy piles and nonenergy piles.

This paper presents the experimental results of small-scale model tests of an instrumented floating energy pile group in which the piles were embedded in dry medium-dense sand and subjected to the seasonal temperature pattern of the city of Nanjing in China. The study also included a model test to assess the effect of including nonthermal piles on the thermo-mechanical behaviour of the floating energy pile group. For comparison, a model test of a single floating energy pile embedded in the same soil and subjected to a similar temperature pattern was also conducted. The results show that the thermo-mechanical behaviour of an energy pile group is different from that of a single energy pile in terms of the thermally induced change in axial pile stress and the displacement of the pile top and tip. This difference in behaviour could be explained by the higher lateral confining pressure expected on a single pile than on a pile in a group due to pile interaction effects, which could lead to different end restraint boundary conditions. We conclude that the thermo-mechanical behaviour of an energy pile is controlled mainly by the end restraint boundary conditions.