A comparison of optical and X-ray CT technique for void analysis in soil thin section

Abstract

The application of X-ray computed tomography (CT) in soil micromorphology has motivated researchers to quantify soil structure, particularly void space, for three dimensional analysis. The objective of this study was comparison of optical and a proposed CT method for void space determination, using a set of four thin section samples. The thin section samples were imaged for optical data using plain polarized, cross polarized and oblique incidental light. CT imaging used a 3D reconstruction to attain the average X-ray attenuation value of the thin section. After registering the two imagery types, an identical region of optical and CT imagery was extracted for analysis. Optical and CT imagery was classified as void or solid, from which simple characteristics of soil-voids were obtained. The characterization of voids indicated that the optical method was proficient in identifying continuous and linear void features, whereas CT readily identified a greater number of voids with higher circularity. The data also suggested that the CT method identified a greater degree of void space in thin section than was evident to the optical classification. The results of binary comparison imply that CT identified a category of void often overlooked by optical imagery classification and therefore would make an excellent complementary technique to the soil micromorphology tool set.