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The Applicability of Dual Gamma Scanning to Freezing Soils and the Problem of Stratification¹

ABSTRACT

The attenuation of a dual energy gamma beam provides a powerful technique for studying the swelling phenomenon associated with soil freezing. However, the development of a stratified system due to the formation of a discrete ice lens in the same plane as the gamma beam requires special attention. Erroneous results are obtained when attenuation equations which are developed for homogeneous mixtures are applied to stratified media. The calculated dry bulk densities are then always lower than the averaged actual dry bulk densities and sometimes even negative. The calculated water contents are then always higher than the averaged actual water contents and sometimes in excess of 1 g/cm³. Stratification may also occur during the shrinking of unfrozen soil when cracks form in the same plane as the gamma beam. The equation describing the attenuation of a gamma beam in a stratified medium is formulated. A technical modification in the scanning procedure is suggested in order to solve the appropriate equations and to locate the interface.

¹ Contribution from the Dep. of Land Resource Science, Univ. of Guelph, Guelph, Ontario, NIG 2W1. Presented at the meetings of the American Society of Agronomy (Div. S-1), Houston, Dec. 1976. The authors acknowledge financial support from the National Research Council of Canada and the Inland Waters Directorate of Environment Canada.

² Graduate student, professional associate, associate professor, and postdoctoral research associate, respectively.

Received for publication June 6, 1978. Accepted for publication July 31, 1978.