Simulation of thermo-mechanical performance of pile geothermal heat exchanger (PGHE) considering temperature-depend interface behavior

Pile geothermal heat exchanger (PGHE) has attracted great interests in recent years, but some new challenges have emerged with its application, especially in understanding its thermo-mechanical behaviors. In this paper, based on the experimental data from a modified direct shear test, a finite element simulation model is developed to investigate the thermo-mechanical behavior of PGHE. The simulation model has been verified by an in-suit test. The influence of interface behavior, thermal loads, and soil properties on the PGHE's thermo-mechanical behavior has been investigated. The results show that the changes in contact force and friction coefficient has to be considered in a comprehensive way in estimating the influence of thermal load on the bearing capacity of PGHE. Compared with the results without thermal loads, bearing capacity of PGHE shows a decreasing ratio of 8.7%, and an increasing ratio of heating is found to be 13.2%. In addition, the simulation results suggest that without head load imposed, at a certain depth, the axial stress has a linear relationship with the change of temperature, but when a head load is imposed, the linear relationship is only separately valid in each temperature region (heating or cooling). The thermo-mechanical performance of PGHE should be fully considered during the design stage, and this paper has the certain actual reference significance to engineering applications.