X-ray CT-based 3D characterization of desiccation cracking in compacted expansive soil under varying vertical stress states

Compacted expansive soils are used as hydraulic barriers in landfill liners, deep nuclear waste disposal facilities, the core of earthen dams, seal layers of CO2 storage, etc. In the absence of high-quality fill material, they also serve as embankments for highways/railways, foundation soil for buildings, and man-made slopes. The compacted soil in these applications may experience wetting-drying (W-D) under different vertical stress levels within their service life. The present knowledge available regarding the desiccation cracking behavior of compacted soils ignores the influence of applied vertical stress. This study characterizes the 3D desiccation cracking behavior of a compacted expansive soil subjected to alternate W-D cycles under different vertical stress levels using the X-ray computed tomography (XCT) technique. Modified temperature-controlled oedometers were developed to apply W-D cycles on specimens subjected to different vertical stress levels. Quantification of various geometrical and morphological parameters of 3D crack networks was done using digital image analysis techniques. The results from this study highlight the beneficial effects of high vertical stress in controlling the growth of crack networks during alternate W-D cycles. Moreover, the digital models of 3D soil-crack systems were developed, and their characteristics, like porosity, aperture size distribution, fractal dimension, fracture surface, fracture density, connectivity, etc., were determined, which can be helpful in permeability and seepage modeling in cracked soil media using various stochastic methods and numerical tools.