Quantitative characterization of drying-induced cracks and permeability of granite residual soil using micron-sized X-ray computed tomography.

Drying-induced cracks negatively impacts the performance of soils in the context of global warming. Traditional testing approaches used for the cracking characterization of soils are mainly based on surface observation and qualitative inspections. In this study, a temporal investigation of micron-sized X-ray computed tomography (Micro-CT) tests was performed on the granite residual soil (GRS) during desiccation for the first time. Through three-dimensional (3D) reconstructions and seepage simulations, the dynamic evolution of drying-induced cracks and permeability that evolved (0 to 120 h) was visually characterized and intensively quantified. Experimental results show that the averaged area-porosity ratio varies as an increasing trend, appearing fast at first and slowly thereafter during desiccation.. Observed by 3D reconstruction models, connected cracks rapidly propagated through the samples while isolated cracks occupied small volumes and remained almost unchanged. The pore-diameter distribution of GRS reveals that the propagation of connected cracks is essential in influencing soil cracking. The simulated permeability is generally comparable with measuring ones with an acceptable error margin, demonstrating the accuracy of seepage models. The increasing permeability from both experiments and numerical simulations indicates the desiccation process severely impacts the hydraulic properties of soils. This study provides an adamant evidence that the Micro-CT is an effective and feasible tool for the elucidation of drying-induced crack evolutions and in building numerical models for permeability validation.