Determination of pore networks and water content distributions from 3-D computed tomography images of a clay soil

Abstract

Knowledge of flow in porous media can be improved by analyzing three-dimensional (3-D) images of the water distribution in a soil. We report on such a study using computed tomography (CT) scanning of a clay soil sample first in dry conditions. Then, after an infiltration experiment, by scanning the sample again in wet conditions. We used test phantoms to determine the optimal scanning parameters to obtain images with a bimodal gray value distribution with high contrast and small standard deviation. We also determined the effect of slice thickness and reconstruction algorithm on the restoration and segmentation of the images. For a good 3-D representation of the pore space we scanned the slices adjacently at an axial resolution of 1 mm and a pixel size of 0.27 × 0.27 mm². The high contrast between air in the pores and the clay background allowed a global thresholding for the segmentation whereby the connectivity and topology of the pore networks is conserved. From the difference between the images of the dry sample and the wet sample we determined the water content distribution. We used the image data for measurements of the water distribution to study the relation between the structure of the pore networks and water flow.