Numerical Investigation of the Thermo-Mechanical Response of Single Energy Pile

Geothermal piles are being used to serve dual-purpose: transfer the structural load to the ground and act as heat exchanger elements to harvest and reject heat from and to the ground. Thermal loading can change the mechanical performance and bearing capacity of the geothermal piles during heating and cooling cycles. Therefore, the thermo-mechanical responses of the geothermal piles should be comprehensively studied. In this paper, the thermo-mechanical performance of a geothermal pile was analyzed using a 3D finite difference model in FLAC. The energy pile tests performed at Lambeth College, London were simulated using the developed numerical model. Comparison of both thermal strain and thermo-mechanical strain along the depth of the geothermal pile during both heating and cooling cycles confirms that the numerical model can accurately simulate the thermo-mechanical performance of energy piles. The validated model have been used to study the effects of soil properties and thermal operation periods (both short-term, after 10 days, and long-term, after 2 months) on the response of the geothermal pile. Results showed that increasing the soil stiffness induces lower strains and higher stresses along the pile. Increasing soil elastic modulus by 10 times results in 5% reduction in the minimum axial strain in the geothermal pile. It is also important to note that the position of the null point depends on the stiffness of the soil and pile. Results indicated that the null point moves upward by increasing the soil stiffness.