Estimating ice and unfrozen water in permafrost samples using industrial computed tomography scanning

ABSTRACT: The relations between unfrozen water content and temperature in permafrost soils are important in cold regions engineering because much of the geomechanical behavior of permafrost depends on ice content which can vary with temperature. X-ray computed tomography (CT) scanning is a method with applications in geoscience, soil science, and geotechnical engineering that has shown potential in permafrost research. In this study, we use an industrial CT scanner, as opposed to the more common medical CT scanners that have been previously used, to establish relations between the ice, sediment, and unfrozen water content of a clayey soil at -1, -3, -6, and -12 degC. High-resolution CT scans were compared with time-domain reflectometry (TDR) records of unfrozen water content. Image processing results showed 12.8% increase in the ice volume of the sample at colder temperatures accompanying a 14.5 % decrease in water content tracked by TDR. The expansion of ice lenses at colder temperatures was also visualized in CT images. The extracted changes from image processing and TDR records were more significant between lower temperatures due to more unfrozen water contents.