Macro-porosity and skeleton of a cement-gravel-treated granite residual soil for subgrade from CT scanning

Abstract

Granite residual soil can be utilized as subgrade or embankment fillings after proper treatment. In this study, X-ray CT scanning was employed to investigate the effects of cement and cement-gravel treatment on the macro-porosity and skeleton of a granite residual soil. Firstly, the material phases are preliminarily segmented based on the distribution of the grayscale intensity and its physical significance. Then, a brief method for determining the macro-porosity from CT scanning is proposed. For the cement-treated granite residual soil, the macro-porosity determined from CT scanning fits well with that from MIP analysis and it reached the lowest value at a volumetric cement content of about 2%. In addition, a criterion for judging the presence of local and global soil skeleton is proposed based on contact analysis of the coarse-grains. For the cement-gravel-treated granite residual soil, a global gravel skeleton formed when the volumetric gravel content is beyond 30%. These threshold cement and gravel contents from CT analysis would be helpful for the proper treatment of granite residual soil and utilization of the treated soil as filling materials.