Sensitivity analysis of pore morphology method and X-ray CT imaging in SWCC predictions for Ottawa sand

Abstract

The hydromechanical response of partially saturated soils at macroscale is a manifestation of fundamental physics associated with pore scale. The Soil Water Characteristic Curve (SWCC) is an important state variable which affects mechanical as well as transport properties in a multiphase porous media. In present work, X-ray CT imaging and Pore Morphology Method (PMM) are leveraged to demonstrate robustness of a predictive approach in enhancing understanding of multiphase flow in sands from a pore scale perspective. The 3D microstructure of the Ottawa sand assembly is obtained from attenuation contrast-based X-ray Computed Tomography (CT) which serves as an input to PMM-based predictions. PMM relies on Young Laplace equation and mathematical morphology to simulate drainage and imbibition processes on an actual pore space. This approach is computationally efficient in comparison to computational fluid dynamics approach where highly nonlinear Navier Stokes equation is solved on a computational grid. In addition, the effect of X-ray CT resolution on SWCC predictions for drainage and imbibition is investigated. The effect of the surface roughness on wettability is demonstrated in numerical predictions by varying contact angle of the three-phase system. The spatial distribution of air and water corresponding to different capillary pressures is presented which can be helpful in developing improved multiscale modeling approaches in partially saturated sands.