Characterization of Coupled Electromagnetic, Thermal, Hydraulic, and Mechanical Properties of Frozen Soils
Advisor: Professor Tugce Baser
Abstract
This research focuses on the investigation of the coupled electromagnetic, thermal, hydraulic, and mechanical properties of frozen geomaterials subjected to thermal gradients. Accelerated subsurface warming in the cold regions exacerbates the temporal and spatial evolution of frozen ground properties, and this necessitates the accurate characterization of frozen geomaterials. Existing studies often focus on isolated external effects, such as thermal conductivity or mechanical strength under frozen conditions at constant temperatures, without considering the complex interdependencies between these properties. Therefore, the main objective of this research is to investigate the thermal, electromagnetic and hydraulic properties of frozen soils subjected to the thermal gradients and their impact on the mechanical properties. Laboratory experiments were conducted using capacitance sensors and Electrical Impedance Spectroscopy to characterize the effect of initial degree of saturation, initial dry density, temperature, and applied frequency on the bulk electromagnetic properties, specifically dielectric constant and electrical conductivity, of sand, silt, and clay. The measured dielectric permittivity values were used to calibrate the physics-based models for estimating the water content and ice content of soils at different temperatures below 0°C. The estimated water contents were plotted against temperature to generate soil freezing curves. A series of laboratory experiments were performed to characterize the thermal properties of soils during the freezing and thawing process and a new methodology for measuring ice content during freezing and thawing was introduced. The latent heat during the phase change of water was quantified and used to predict the ice content. The results from the latent heat calculations were consistent with ice contents estimated from the capacitance experiments. Direct simple shear tests were performed at temperatures below 0°C on soil samples having initial degrees of saturation identical to the soil samples prepared for previous experiments.
This approach of having similar initial degrees of saturation enabled a detailed evaluation of how ice content, as indicated by the soil freezing curves, influences the shear strength of frozen soils. The results from this study demonstrated the significant impact of initial degree of saturation, temperature, and soil type on the thermal, hydraulic, electromagnetic, and mechanical properties of frozen soils. An increase in the initial degree of saturation resulted in a higher dielectric permittivity, electrical conductivity, latent heat, ice content, and the shear strength at temperatures below 0°C. A decrease in the temperature initiated the phase change that results in decreasing dielectric permittivity, electrical conductivity and significant increase in the shear strength. A further decrease in the temperature continued to increase the shear strength of frozen soil due to the changes in mechanical properties of ice. For the same initial water contents, the clay and silt soils exhibited lower ice contents and shear strengths compared to the sand.
The outcomes of this research will significantly advance the understanding of how the coupled effects of thermal gradients, initial degree of saturation, and soil type influence the electromagnetic, thermal, hydraulic, and mechanical properties of frozen soils. By providing a detailed characterization of these interdependencies, more accurate predictions of soil behavior under changing environmental conditions can be achieved. These insights are crucial for optimizing the design and adaptation strategies for infrastructure in permafrost regions. The results from this research contribute to long-term sustainability by enhancing the ability to assess and mitigate the impact of global warming on frozen soil stability, ultimately supporting more resilient infrastructure development in the Arctic and similar cold regions.