Using an NMR Device to Determine Unfrozen Water Content in Frozen Soil

Abstract

The overall goal of our research project is to study the unfrozen water mass and mobility in frozen soils. During this project, frozen samples of standard clays with different adsorbed cations will be analyzed to determine their surface potential, micro-fabric, and how they interact with unfrozen water. The amount of unfrozen water content at sub-freezing temperatures is measured using a nuclear magnetic resonance (NMR) device. Before using the NMR to test the unfrozen water content, we developed a system to control and stabilize the temperature of the soil sample during the test. We determined that the optimal sample length detected by the NMR is 3.5 cm. Nine duplicate silt samples each with a different moisture content were prepared and tested using the NMR. The result demonstrated a linear relationship between the moisture content of the silt samples and the corresponding NMR signal intensities, thus validating the NMR approach. Future test will be conducted on frozen cation-exchanged clay samples to determine their unfrozen water contents as a function of temperature.