Determination of the relationship among capillary pressure, saturation and interfacial area: a pore unit assembly approach

Three state variables namely, degree of saturation (Sw), capillary pressure (Pc) and specific air-water interfacial area (aaw) are indispensable for modelling coupled processes relevant to unsaturated soils mechanics, agriculture, and contaminant hydrology. They play a key role in simulating various phenomena and the determination of various parameters and physical characteristics such as the unsaturated soil shear strength, field capacity, wilting point, air and water diffusivity and the rate of dissolution of contaminants. The determination of soil water retention curve (Sw-Pc) as well as the specific interfacial area (aaw) using available experimental techniques is a challenging and time consuming task. Therefore, a numerical technique that employs basic soil properties to obtain these variables is of much value and high practical and theoretical importance. In the current study, the porous network extracted from a discrete element model (the so-called pore unit-assembly) has been used to directly model the drying and wetting processes inside a granular soil packing and to obtain the values of Pc, Sw and aaw. The results of the simulations are in good agreement with the experimental data, which points to the efficacy and adequacy of the introduced algorithms and involved assumptions for this purpose.