X-ray computed tomography of frozen soil

Abstract

X-ray tomography (CT scanning) is widely used by the health community to obtain three-dimensional images of the human anatomy. Its strength lies in its being a non-destructive technique that can investigate the internal structure of the human body and other materials, including soil. The research to be presented builds on extensive CT investigation of the structure of intact natural soil cores, using a CT unit specially designed for investigation of soil materials. With the design of an appropriate temperature control system, the CT unit has been modified so that the structure of intact frozen soil samples can be investigated. This research investigates the changes in structure and the redistribution of water to form ice lenses in saturated samples of an Aurora silt loam frost-susceptible soil that were thoroughly mixed to produce an initially homogeneous material, and of a Honeywood silt loam that was deliberately contaminated with motor oil. The soils were subjected to relatively rapid, downward freezing, with access to water at their base. Preliminary results indicate that CT can produce excellent images (even without digital filtering) of the ice lens distribution within a frozen silt loam soil, the consolidation of soil between the ice lenses, and the effects of hydrocarbon contamination. Ice lenses of less than 1 mm thickness can be detected. Image analysis techniques used to improve image quality in medical CT analysis and in remote sensing are being investigated.