Thermo-mechanical behavior of energy piles based on coupled THM model

The energy piles can underpin the superstructures and provide low-carbon, environmentally friendly and sustainable cooling/heating functions, leading to ever-growing attention received from the civil and energy industries. The thermo-hydro-mechanical (THM) coupling may significantly affect the interaction between the energy piles and the surrounding soils, and thus the load-bearing and deformation characteristics. In this study, the basic governing equations for full THM coupling are derived based on the standard mixture theory of porous media. The finite element method THM for and its implementation in COMSOL software are verified through comparisons with the analytical solutions to the saturated non-isothermal consolidation problem. Based on the THM coupled framework, a two-dimensional finite element model for the energy piles is further established considering the change of fluid properties with temperature and different pile-soil contact models, and the specific configuration and modeling procedures are described. The results indicate that the proposed model can predict the distribution and evolution of stresses, strains and displacements on the energy piles, and further capture the multi-physical behaviors associated with the piles and soils. This study highlights the importance of the consideration of THM coupling effects, which can provide a useful guidance for the multi-physical problems involved in the design, construction and utilization of the energy piles.