Quantification of Different Types of Unfrozen Water Contents in Various Soils by Low-field Nuclear Magnetic Resonance

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4. Quantification of Different Types of Unfrozen Water Contents in Various Soils by Low-field Nuclear Magnetic Resonance

Due to the soil-water interactions, a certain amount of liquid water remains in soils at sub-freezing temperatures. The relationship between unfrozen water content and temperature, i.e., soil freezing characteristic curve (SFCC), governs the hydrologic and mechanical behaviors of soils. Theoretically, different types of water, e.g., adsorptive water and capillary water, have diverse freezing behaviors and different influences on the overall properties of freezing soil. In this study, low-field nuclear magnetic resonance (NMR) was utilized to measure the unfrozen water contents for soils with different particle sizes and dry densities. The NMR-measured SFCCs demonstrate the unfrozen water content is highly dependent on soil properties. The NMR tests show that the T₂ relaxation can be used to identify and quantify different types of soil water. T₂ distribution results also indicate that the steep drops of unfrozen water contents are mainly caused by supercooling, and the freezing of adsorbed water occurs gradually. A commonly used SFCC model is used to fit the measured data, and the fitting results show that the model without consideration of the different types of soil water is insufficient to accurately simulate SFCCs. This study reveals the roles of different types of soil water in the freezing process, providing a basis for a better understanding of the behaviors of freezing soil.

9th International Congress on Environmental Geotechnics (ICEG2023)

Advances in Testing and Material Characterization