Date on Master's Thesis/Doctoral Dissertation

12-2021

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, PhD

Committee Chair

Ghasemi-Fare, Omid

Committee Member

Rockaway, Thomas

Committee Member

McGinley, Willaim

Committee Member

Hadizadeh, Jafar

Committee Member

Berson, Robert

Author's Keywords

Thermo-hydro-mechanical; heat transfer; numerical modeling; phase change; porous media; soil

Abstract

Underground geo-structures and climate change can trigger coupled heat, moisture, and vapor flow in shallow and deep subsurface which is frequently referred to as non-isothermal multiphase flow. The coupled multiphasic flow in soil may induce volumetric shrinkage or expansion deformation depending on the thermo-hydraulic loading condition. In saturated porous media, temperature gradient and heat transfer may affect pore fluid pressure and/or pore fluid flow depending on thermal, mechanical, and hydraulic properties of the media and the saturating fluid. In vadose zones, the prediction of coupled nonisothermal multiphase flow in porous media has been the subject of many theoretical and experimental studies in the past half a century. In particular, the evaporation phenomenon from the shallow subsurface has been extensively studied based on the notion of phase change between liquid water and water vapor. Therefore, several Thermo-Hydro-Mechanical (THM) models have been developed to simulate the thermal and phase change processes in soil media. However, most studies in the past are based on rather simplified assumptions that disregard important coupled relationships of thermal, hydraulic, and mechanical properties and constitutive models of the soil media. The objective of this study is to propose a general theoretical framework that considers intrinsically coupled interactions in the soils and relaxes the long-lasting simplified assumptions. Five major hypotheses are made and several thermal, hydraulic, and mechanical constitutive models are developed to address phenomena such as thermal pressurization, thermally-induced pore fluid flow, evaporation, and drying-induced deformations. Each chapter deals with a unique hypothesis and boundary-value problem where the proposed model is tailored to answer some of the key observations in the experiment. The range of the problems considered in this study is broad from large-scale underground laboratory tests deep in geological systems to small-scale laboratory experiments. The proposed models are solved with the finite element numerical method and validated against experimental data. Interpretation of the data, discussions, parametric studies, and concluding remarks are key elements in each chapter. In chapters 2 and 3, it is found that considering temperature-dependent parameters in conjunction with the thermo-poroelastoplastic model further improves the results to better capture the thermal pressurization, especially during the cooling phase. The magnitude and sign of thermo-osmotic conductivity strongly depend on the temperature and microstructural properties of clays which cannot be ignored. Comparison of the numerical results with and without considering thermo-osmotic flow and thermal infiltration, confirms the importance of the thermo-osmosis phenomenon during thermal loading in clayey soils. Moreover, even a slight perturbation in porosity variation and temperature dependency of the thermal expansion coefficient of the fluid can greatly influence the thermal pressurization of pore fluid in very low permeable soils (e.g. clays), while variations of pore fluid density govern thermally-induced pore fluid flow in high permeable soils (e.g. sands and silty sands). Furthermore, for coarse soils such as sand and gravel (e.g., k ≥ 5×10-12 m2) and the soil temperature is in ranges of 20 to 55 °C, it is necessary to consider the thermally-induced pore fluid flow to model the heat transfer in the soil media. The results demonstrate that the Boussinesq approximation is a key assumption when dealing with heat-induced pore fluid flow in quasi-steady-state conditions. In chapters 4 and 5, numerical results indicate that the Non-Equilibrium Phase Change (NEPC) model has higher robustness in predicting the volumetric water content in the soil close to the soil-atmospheric boundary. However, NEPC and Equilibrium Phase Change (EPC) approaches to estimate the same temperature variations in the soil. In the case of precipitation (e.g., rainfall), the NEPC model predicts higher degrees of saturation in deeper soil in which the infiltrated water reaches 150 cm below the surface, while, in the EPC model, the infiltrated water barely reaches the 100 cm depth. The increase in moisture content close to the heat source facilitates the heat transfer in the medium and thus results in a 40% to 50% reduction in soil temperature close to the heat source. Results also confirm that the contribution of the film flow in overall mass flow in the medium is required for accurate modeling and cannot be ignored. In chapter 6, the developed model reasonably captures the anisotropic elasto-plastic shrinkage of the clayey soil during the transient drying process. Numerical results demonstrate that drying shrinkage results in a 30% porosity reduction. Approximately 82% of the total volumetric deformation is irrecoverable (i.e., plastic) and occurs in the first couple of hours of the drying process. Finally, the last section is devoted to sensitivity analysis of the THM behavior of Boom clay concerning its elastic and plastic strength. The parametric study shows approximately 10% more reduction in the final surface shrinkage when the difference between the slope of the drying-induced compression line and the swelling line (i.e., λ - k) is doubled.

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