Modeling unsaturated hydraulic conductivity of granular soils using a combined discrete element and pore-network approach

Unsaturated hydraulic conductivity is an essential input data for many engineering problems involving water flow through unsaturated soils. The paper aims to present a pore-scale model for predicting unsaturated hydraulic conductivity along the drying path and the wetting path. The present work focuses on using basic properties of granular soils like grain size distribution and porosity to model unsaturated hydraulic conductivity. The approach is based on combining the discrete element method for modeling granular soil packing with pore network modeling. The fluid flow is simulated by incorporating pore-scale phenomena, which include piston-like advance and corner flow (wetting layers) in the drying process and piston-like advance, pore body filling, and snap-off in the wetting process. The predicted unsaturated hydraulic conductivity compares favorably to the experimental data available from the literature for various granular soils. There are also comparisons to previously published physically-based models, and the suggested model outperforms them for the materials investigated. The numerical framework presented effectively predicts the hysteretic unsaturated hydraulic conductivity curves and can account for changes in unsaturated hydraulic conductivity with different initial void ratios.