Measurement of Density and Water Content in Soils with X-ray Linescan and X-ray Computed Tomography

Abstract

Potentials for using X-ray computed tomography for determining soil bulk density and water content were investigated using Cecil sandy clay and Lakeland sand soils. Soils were moistened and samples were compacted to several levels. These samples were sequentially dried and scanned using tomography reconstructions as well as the linescan mode available on a CT scanner. Mean X-ray absorption and pixel standard deviation data were collected for each soil sample at scanning in both modes. For each soil-mode combination, relationships between mean X-ray absorption and soil bulk density and water content were determined as were relations between pixel standard deviation and soil density and water content. The experiment was then repeated to provide validation data. In the tomographic reconstruction mode with validation data, optimal water content and bulk density values for samples were determined for each corresponding mean absorption and pixel standard deviation measurements which minimized the error sum of squares. Density was predicted in both soils to within 2%. Predicted water content was within 50% of observed values. Using known values of density, water content was predicted to within 5%. In the linescan mode, density was usually predicted to within 5%. Water content was not significant (P < 0.15%) thus a prediction for water was not attempted in the linescan mode.