Poromechanical analysis of regional frozen ground responses under heat exchanger operations

The permafrost of the Northern Hemisphere is under threat of degradation due to increasing global temperatures resulting from climate change. Thawing permafrost exhibits lower strength and increased permeability, leading to soil instability and subsidence beneath structures. To mitigate the effects of permafrost thaw, heat extraction is utilized to cool the frozen soil bodies. Ground heat exchangers (GHEs) are geo-structures that exchange heat with the ground and can be used for heat extraction. In this work, thermo-hydro-mechanical modeling is employed to simulate the state of a saturated soil body during freezing and thawing in Umiujaq, Quebec, Canada. An initially frozen soil body is analyzed under seasonal temperature variations and GHE operations. The pore pressure development and ground deformation are well quantified. It is shown that GHE operations can effectively mitigate the risks associated with talik formation, with group-GHE formations being more effective in this regard. Additionally, it is demonstrated that group-GHE operations are effective in mitigating excessive thawing settlement. Furthermore, the shortcomings of single-GHE operations, such as limited radius of effect and differential settlement, can be improved by group-GHE formations through a confinement effect.