Various geotechnical-related energy applications, such as geothermal piles, subject soils to temperature changes. Recorded temperature variations around thermo-active infrastructure and within the active layer of the permafrost reveal the cyclic and transient nature of these temperature changes. Previous studies on the thermo-mechanical behavior of soils did not consider the effect of the temperature change rate on such behavior. Since it is widely accepted nowadays that soil behavior is rate-dependent, evaluating soil behavior under more realistic, transient temperature changes is crucial. In this dissertation, a method to calibrate triaxial cells used to expose soil samples to transient thermal loads is developed. This calibration is critical to ensure reliable thermally induced pore water pressure measurements and estimates of thermally induced volumetric strains of tested specimens. Then, thermally induced water flow and pore pressure generation under partial drainage conditions are formulated to account for the effect of temperature change rate on the thermal consolidation of cohesive soils. The formulation is performed by coupling Darcy's law for water flow in porous media with existing relations estimating thermally induced fully-drained volumetric strains. The resulting partial differential equation—the thermal consolidation theory—is solved and validated against experimental results that used the calibration from the first task. Using this newly developed theory, it was found that temperature-dependent properties of the pore water and the soil's hydraulic conductivity have a significant role in thermal consolidation. Lastly, a microstructural analysis is performed to assess the evolution of the microstructure of a normally consolidated clay under a full thermal cycle consisting of a freezing (F), thawing (T), heating (H), and cooling (C) thermal path. This microstructural investigation aims to explain the observed macroscale responses of cohesive soils under such a thermal path. After each step along the considered thermal path, the microstructure evolution was assessed using measurements of the specific surface area and pore size distribution. In the end, the variations of specific surface areas and pore size distributions were used to explain the macro-scale thermo-mechanical behavior of cohesive soils. / Doctor of Philosophy / Temperature can impact the properties of the soil, such as strength and stiffness. Besides the alterations in the strength, temperature change can cause volume change in the ground. In cold regions such as Alaska, the soil is frozen all year (i.e., permafrost) or experiences freezing-thawing cycles throughout the year. Freezing strengthens the soil but causes expansion of its volume, destroying infrastructures, including roads, runways, and buildings. Also, geothermal energy applications that utilize the ground as a heat exchanger medium may increase or decrease the surrounding soil temperature. Increasing the ground temperature changes the strength of the soil and also causes settlements. Climate change is also aggravating the situation. The temperature rises due to climate change alters the temperature pattern worldwide. Furthermore, global warming exposes frozen grounds to longer thawing stages at higher temperatures, deteriorating the permafrost. Consequently, such thermal cycles make cold regions' infrastructures susceptible to damage. Measurements of the temperature variations in the ground show that they are cyclic in nature, with different rates, maximums, and minimums. Therefore, it is essential to study the thermal behavior of soils under cyclic thermal loads. For this purpose, a new method for accurately measuring soils' response to more realistic temperature changes is developed in this dissertation. Then a model is developed to predict thermally induced volume changes and water pressures that account for the rate of temperature change. The model is then used for a sensitivity analysis to study the most important parameters controlling the deformation induced by temperature changes. It was found that variations of pore water properties with temperature and the ability of the soil to retain or drain water are the two most critical parameters that control thermally induced deformation in soils. Finally, the microstructure evolution of cohesive soils with temperature is also investigated to explain the observed alterations in soil behavior with temperature. This microstructural assessment suggests that the microstructure of soils reacts to temperature by changing the pore size distribution, shape, and number of pores.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115711 |
| Date | 10 July 2023 |
| Creators | Zeinali, Seyed Morteza |
| Contributors | Civil and Environmental Engineering, Motaleb Abdelaziz, Sherif Lotfy Abdel, Brandon, Thomas L., Rodriguez-Marek, Adrian, Dove, Joseph E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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