Using X-ray computed tomography to quantify pore characteristics in a shrink-swell clay

Shrink-swell soils swell when wetting and shrink when drying. This shrinkage creates cracks that may measure >10 cm in width and >1 m in depth when the soil is dry. Current numerical models are not able to accurately represent these dynamic pore characteristics and often soil shrink-swell processes are not taken into consideration at all. In order to incorporate these dynamic characteristics into numerical models, it is necessary to first quantify changes in pore characteristics—pore number, connectivity, size distribution, and tortuosity—that accompany changes in soil water content. X-ray computed tomography (CT) is a technology used to visualize the internal structure of an object and can be used to observe and quantify pore spaces in a soil sample. The goal of this project was to improve our understanding of dynamic porosity in shrink-swell soil by using X-ray CT scanning to quantify pore space characteristics in shrink-swell soils at two soil water contents: after wetting and oven-dried. Three intact soil cores were wetted, scanned using X-ray CT, then dried and scanned again. ImageJ and MATLAB software were used for image processing and analysis of structural changes within the cores. Our results show a statistically significant difference in pore network characteristics between wet and dried cores, with higher porosity, smaller pores, lower connectivity, and higher tortuosity values for the wet cores. These results have important implications for numerical simulations of soil water flow, which often disregard porosity dynamics due to shrinkage.