Finite element modeling of thermo-hydro-mechanical coupled processes in saturated and unsaturated frozen soils

In line with the sustainable development of northern Canada, extensive construction activities are taking place in local communities where the ground is composed of clay deposits. With a changing climate, the clay soil is expected to undergo more freeze-thaw cycles. This degradation poses a major threat to newly constructed infrastructure. Since soil is an essential part of the built environment, it is crucial to understand its behavior under freezing and thawing conditions. This thesis presents a comprehensive study on the mechanical and thermal-hydro-mechanical (THM) behaviors of frozen soils, focusing on both theoretical developments and practical applications. To achieve this, the research pays close attention to the interface between the compounds. It introduces a stiffness interface parameter to define complex interactions between clay-water composites and non-clay minerals at different temperatures. The key contribution of using this parameter includes developing a numerical homogenization model with the eXtended Finite Element Method (XFEM) to estimate the elastic properties of frozen clay soils. Subsequently, considering the interface between air-water capillary pressure and cryosuction, a two-dimensional THM finite element model was developed using the Finite Element Method (FEM) to analyze the coupled processes in unsaturated freezing soils by incorporating temperature-dependent properties and phase changes. Finally, the behavior of permafrost under the operation of Ground Source Heat Pump (GSHP) systems in thawing permafrost regions has been analyzed as part of a geo-energy and geological engineering project in the subarctic region of Umiujaq in northern Quebec. The study begins with an extensive literature review to establish the current state of knowledge and identify gaps in existing research. It then details the development and validation of numerical models, including their application to real-world scenarios. The findings highlight the importance of considering imperfect bonds between soil components, the complex interaction between air-water capillary pressure and cryosuction, the influence of phase change-induced strain, and the benefits and challenges of using GSHP systems in cold climates. Despite the significant advancements made, the research acknowledges several limitations, such as the need for more complex soil structure representations and broader validation efforts. Recommendations for future work emphasize enhancing model complexity, conducting long-term studies, and integrating field data to improve the accuracy and applicability of the models. Overall, this thesis advances the understanding of frozen soil mechanics and provides valuable tools for engineering applications in Arctic and subarctic regions. It contributes to the development of sustainable and resilient solutions for climate adaptation.

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