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Simulation of hysteresis in soil-water retention with a correlation between the invading pressure to the governing effective flow area

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2020-03-23
Sattari, Amir Shoarian
Siebelist, Marlena
Toker, Nabi Kartal
Wuttke, Frank
In order to determine the soil-water retention (SWR) behavior of a particulate medium, the invading phase pressure in the inter-particle level is correlated to the governing effective pore area in the wetting and drying paths. In a three-phase medium that consists of air, wetting fluid and solids, the invading phase on the drying path is air, whereas on the wetting path the wetting fluid advances into the cavities. On a drying path where the area of a cavity is minimum, the air-entry pressure (AEP) of a pore throat is determined by numerically solving the Young-Laplace curvature equation. This can be done using the finite difference method and Newton-Raphson (Jacobian) approximation technique. Next, a relation between the pore area and the value of AEP is developed by varying the distance between solids around the pore throat. Similarly, the water-entry pressure (WEP) is correlated to a maximum pore area of cavity. After packing the particulate domain with the given particle size distribution (PSD) and void ratio values, the primary/main drying and wetting paths of the wetting fluid are simulated and the effect of hysteresis in SWR is shown. It is considered that the total suction equals to matric suction value and the water bridges between two adjacent particles are formed in the form of pendular rings. In this study, the considered material is non-plastic and the shrinkage and swelling during the drying and wetting phases or any change in pore structure are neglected. The simulation results are compared to experimentally determined as well as estimated data from the literature and a great agreement between the results is found, which offers a reliable way around conducting tedious and expensive SWR tests.