Abstract: Energy pile is an innovate technology which can simultaneously support building load and acquire geothermal energy. In the practical use, expansion or contraction of the piles induced by thermal load will be restrained by the upper structure and bearing layer of pile bottom. Thus, the pile stress and displacement will be significantly influenced. However, there are only few studies focusing on this issue. Based on model test and numerical simulation methods, the thermal stress and displacement of two types of heat exchange piles (U-shaped and W-shaped) under different pile head and pile tip restraints were analyzed. Furthermore, the position of null point influenced by the pile head stiffness restraint and pile tip soil stiffness restraint were evaluated. The results show that as the pile head load stiffness restraint increased, the null point moved upwards, and the thermal stress decreased with the increasing of depth. As the pile tip soil stiffness restraint increased, the null point moved downwards, and the thermal stress increased with the increasing of depth. Compared with the case with no load, the null point will move upward with a working load.

Key words: foundation, energy pile, thermo-mechanical behavior, model test, numerical simulations