FRACTAL-BASED MODELS STUDY OF THE RELATIVE HYDRAULIC CONDUCTIVITY AND SWCC OF BENTONITE BY SYNCHROTRON RADIATION SAXS AND X-RAY COMPUTED TOMOGRAPHY

Fractal-based approaches have become popular for describing the hydraulic functions. The SWCC and relative hydraulic conductivity were calculated and compared based on fractal models by the fractal dimension (D) determined by small angle X-ray scattering (SAXS) and X-ray computed tomography (CT). Pore structure parameters including pore size, D, tortuosity and tortuosity fractal dimension, porosity, characteristic length were investigated. The SWCC and relative hydraulic conductivity were predicted, compared and verified. The results indicated that the D of GMZ01, calculated by SAXS and CT were 2.60 and 2.72, respectively, and the difference was small. The D of GMZ01 calculated by CT was 2.62. D calculated by SAXS and CT has a large difference. Nitrogen adsorption revealed the effectiveness of SAXS in predicting porosity in the nanoscale self-similar interval. A SWCC fractal model considering the tortuosity fractal dimension was improved. The tortuosity of GMZ01, CaGMZ, GMZ07 and SY are calculated as 1.53, 1.47, 1.60 and 1.29, respectively. When the tortuosity was considered, the hydraulic conductivity became lower. For GMZ01, the SWCC predicted by the fractal dimension measured by SAXS was closer to the experimental data than the SWCC predicted by the fractal dimension measured by CT. The fractal model was difficult to describe SWCC under low matric suction, while the predicted SWCC had a good correlation with the experimental value in high matric suction. The relative hydraulic conductivity calculated by Xu and Yu model was larger than that calculated by Xu model.