EXPERIMENTAL AND NUMERICAL ANALYSES OF COUPLED THERMO-HYDRO-MECHANICAL BEHAVIOR IN UNSATURATED SOIL UNDER ONE-DIMENSIONAL HEAT TRANSFER

Abstract

**Please note that the full text is embargoed until 08/01/2024** Comprehension of the behavior of unsaturated soil in response to thermal gradients, moisture gradients, and deformation is important in geotechnics. Thermal gradients control fluid density and viscosity and moisture gradients alter thermal properties of unsaturated soil. Similarly, thermal gradients affect the thermal strain of unsaturated soil and changes in porosity influence hydraulic properties of the soil. Thus, thermal, hydraulic, and mechanical properties of unsaturated soil interact with and influence each other; the combination of these interactions form a mechanism called coupled thermo-hydro-mechanical (THM) processes. Although the study of the behavior of coupled THM processes is essential in predicting the performance of geo-structures, complex and lengthy field-scale and laboratory experiments, as well as limitations in existing numerical models of coupled THM processes impede a thorough evaluation of this behavior. Therefore, this study aims to provide a comprehensive evaluation of coupled TH and THM processes of unsaturated soil experimentally and numerically. A series of soil heating tests were performed to examine the coupled THM and TH processes, and experiments were conducted in different modified soil testing devices of different sizes and configuration, and they equipped with measuring devices will measure key soil properties; i.e. temperature, thermal conductivity, volumetric water content, matric suction, and heat flux. Two soil samples soil samples were tested under various moisture content and temperature conditions. Additionally, an improved mathematical framework was implemented in a multiphysics simulation software to predict the coupling behavior of THM processes. The study also assesses thermal contact resistance at the soil-structure interface under varying moisture content and density levels using experimental and numerical approaches in a closed-system column testing apparatus. Results show that increasing moisture levels lead to higher temperature differences and reduced thermal contact resistance. Dense soils exhibit higher heat transfer, and loose soils show a correlation between thermal contact resistance and moisture content. Then, this study evaluates the impact of a grout in ground heat exchangers, revealing its effect on heat transfer and suggesting improvements for design. The study also analyzes how moisture migration in soil varies with initial moisture content, affecting hydraulic, thermal, and mechanical properties. Finally, the influence of gravity on moisture migration is examined through heating tests on silty sand with a thermal gradient, considering different initial moisture contents.