MEASUREMENT OF DENSITY AND WATER-CONTENT IN SOILS WITH X-RAY LINESCANAND X-RAY COMPUTED-TOMOGRAPHY

Potentials for using X-ray computed tomography for determining soil bu lk density and water content were investigated using Cecil sandy clay and Lakeland sand soils. Soils were moistened and samples were compact ed to several levels. These samples were sequentially dried and scanne d using tomography reconstructions as well as the linescan mode availa ble on a CT scanner. Mean X-ray absorption and pixel standard deviatio n data were collected for each soil sample at scanning in both modes. For each soil-mode combination, relationships between mean X-ray absor ption 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 w ater content and bulk density values for samples were determined for e ach corresponding mean absorption and pixel standard deviation measure ments 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 war pred icted to within 5%. In the linescan mode, density was usually predicte d to within 5%. Water content was not significant (P < 0.15%) thus a p rediction for water was not attempted in the linescan mode.