Generalized hydraulic conductivity model for capillary and adsorbed film flow
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PAPER
Generalized hydraulic conductivity model for capillary and adsorbed film flow Ke Chen 1 & He Chen 1 Received: 22 October 2019 / Accepted: 26 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Commonly used transport models of unsaturated flow assume that the movement of pore water is dominated mainly by capillary flow and they neglect adsorbed film flow. These models have been proven to be successful at high and intermediate saturations but typically underestimate the hydraulic conductivity in the dry range, where water movement in equilibrium conditions is dominated by adsorbed film flow. Given these considerations, this paper proposes a simplified configuration of pore water that accounts for the transport processes of both capillary and film flow. Based on the mechanisms of soil water retention, a conception of the specific thickness of the adsorbed film is defined to describe the adsorption strength and adsorption capacity of porous media. Furthermore, a statistical physically based model of relative hydraulic conductivity in the full range of suction is derived. Fractal and Monte Carlo methods are used to determine the pore size distribution of porous media and then the corresponding specific model of relative hydraulic conductivity is derived. The results show that the proposed model agrees well with the experimental data in the entire suction range. It is also found that the pore size distribution of porous media controls the transport characteristic of capillary water but not adsorption film flow which is only related to the mineral content, mineral species, and specific surface area. Additionally, the influences of the model parameters on the transport of porous media are also addressed. Keywords Hydraulic properties . Adsorbed film flow . Matric suction . Fractal . Numerical modeling
Introduction Estimating the hydraulic conductivity of unsaturated porous media is fundamental to the accurate modeling of hydrological processes such as seepage, evaporation and solute transport in porous media (Durner and Fluhler 2005; Šimůnek 2005; Collis-George 2010). Measurement of the hydraulic conductivity of an unsaturated porous medium is very time consuming and difficult, especially at a low value of saturation. As an alternative to direct measurement, models have been extensively and intensively studied to estimate the hydraulic conductivity of unsaturated porous media (Burdine 1953; Brooks and Corey 1964; Mualem 1976; van Genuchten 1980; Alexander and Skaggs 1986; Kosugi 1996; Guarracino et al. 2014). * He Chen [email protected] Ke Chen [email protected] 1
Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
Accurately predicting the hydraulic conductivity of porous media over the entire range of matric heads remains a persistent challenge. This may be due to the complexity of the pore structure network and the different water retention mechanisms of soil in the dry and wet ranges. So-called capillarydependent models such as the Mualem model (
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