Measurement of Soil Structure, Water Movement and Solute Transport Using ComputedTomography

摘要

Structured, heterogeneous porous media present series problems in predictingwater and contaminant movement. X-ray computed tomography (CT) applied to soil cores was found to be an effective tool for nondestructively characterizing small-scale heterogeneity and for measuring small-scale water and solute movement through soil. At a pixel scale of 0.7 x 0.7 mm, autocorrelation and partial autocorrelation functions suggest that soil bulk density is characterized by a first-order autoregressive system in undisturbed soil cores. At a pixel scale of 0.1 x 0.1 mm, macropore diameters can be estimated down to 0.5 mm with a mean error of 3%; errors decrease to less than 1% for diameters greater than 3.0 mm. Perimeter fractal and area fractal methods were used to characterize the spatial variability of soil bulk density using the large data sets produced by CT. Both methods produced unique fractal dimension relationships for forest, field and uniformly-packed soil cores. CT was used to quantify the effect of an artificially-created macropore in a uniformly-packed soil core on the infiltration wetting front. The distribution of solute breakthrough times within a soil core was computed from CT data collected during a solute breakthrough experiment. The data was used to produce a relative frequency distribution of velocities within the core.