Capillary pressure–saturation curves of thin hydrophilic fibrous layers: effects of overburden pressure, number of layers, and multiple imbibition–drainage cycles

Unsaturated fluid flow in thin porous media depends on hydraulic properties, such as the capillary pressure, P c, as a function of saturation, S. We measured this relationship for two different types of compressible thin hydrophilic fibrous layers under varying conditions. Among other factors, we changed the number of layers and the overburden pressure (i.e. the confined solid pressure applied on top of the sample) imposed on one layer or a stack of layers. Applying an overburden pressure drastically affected the [Formula: see text] curves. However, increasing the number of fibrous layers had little impact on the capillary pressure–saturation curves. We also investigated the effect of multiple imbibition–drainage cycles on the [Formula: see text] data. Measured data points were used to find general expressions for the [Formula: see text] relationships of compressible thin porous media. Existing quasi-empirical correlations used in vadose zone hydrology, notably expressions by van Genuchten (Van Genuchten MTh. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci Soc Am J 1980; 44: 892-898) and Durner (Durner W. Hydraulic conductivity estimation for soils with heterogeneous pore structure. Water Resour Res 1994; 32: 211–223) for single- and dual-porosity media, respectively, were employed to fit the measured data points.

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Historical development of soil-water physics and solute transport in porous media

Water Science & Technology Water Supply ◽

10.2166/ws.2007.007 ◽

2007 ◽

Vol 7 (1) ◽

pp. 59-66 ◽

Cited By ~ 4

Author(s):

D.E. Rolston

Keyword(s):

Porous Media ◽

Hydraulic Conductivity ◽

Solute Transport ◽

Soil Water ◽

20Th Century ◽

Water Flow ◽

Unsaturated Soils ◽

Transport Processes ◽

Transport In Porous Media ◽

Unsaturated Hydraulic Conductivity

The science of soil-water physics and contaminant transport in porous media began a little more than a century ago. The first equation to quantify the flow of water is attributed to Darcy. The next major development for unsaturated media was made by Buckingham in 1907. Buckingham quantified the energy state of soil water based on the thermodynamic potential energy. Buckingham then introduced the concept of unsaturated hydraulic conductivity, a function of water content. The water flux as the product of the unsaturated hydraulic conductivity and the total potential gradient has become the accepted Buckingham-Darcy law. Two decades later, Richards applied the continuity equation to Buckingham's equation and obtained a general partial differential equation describing water flow in unsaturated soils. For combined water and solute transport, it had been recognized since the latter half of the 19th century that salts and water do not move uniformly. It wasn't until the middle of the 20th century that scientists began to understand the complex processes of diffusion, dispersion, and convection and to develop mathematical formulations for solute transport. Knowledge on water flow and solute transport processes has expanded greatly since the early part of the 20th century to the present.

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Capillary pressure-dependent anisotropy of layered unsaturated soils

Canadian Journal of Soil Science ◽

10.4141/cjss09047 ◽

2010 ◽

Vol 90 (2) ◽

pp. 319-329 ◽

Cited By ~ 3

Author(s):

J. Zhu ◽

D. Sun

Keyword(s):

Hydraulic Conductivity ◽

Transfer Function ◽

Bulk Density ◽

Capillary Pressure ◽

Soil Texture ◽

Unsaturated Soils ◽

Particle Diameter ◽

Hydraulic Parameters ◽

Conductivity Anisotropy ◽

Shape Factors

This paper presents an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore capillary-pressure-dependent anisotropy in relation to soil texture and soil bulk density. The effects of capillary pressure (or saturation degree) on the hydraulic conductivity anisotropy of unsaturated soils are still poorly understood. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the particle diameter. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The results illustrate that the inter-relationships of soil texture, bulk density, and hydraulic properties may produce vastly different characteristics of anisotropic unsaturated soils.Key words: Anisotropy, unsaturated soils, capillary pressure-dependent

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Evaluation of hydrodynamic characteristics of porous media from one-step outflow experiments using RETC code

Journal of Hydroinformatics ◽

10.2166/hydro.2018.148 ◽

2018 ◽

Vol 20 (3) ◽

pp. 699-707 ◽

Cited By ~ 4

Author(s):

P. Londra ◽

G. Kargas

Keyword(s):

Porous Media ◽

Hydraulic Conductivity ◽

Unsaturated Soils ◽

Simulation Models ◽

Parametric Models ◽

Water Retention Curve ◽

Hydrodynamic Characteristics ◽

Van Genuchten Model ◽

One Step ◽

Fitting Parameters

Abstract The ability of simulation models to accurately predict water flow and solute transport in unsaturated soils usually depends on the accuracy of the parametric models used to describe the water retention curve θ(h) and unsaturated hydraulic conductivity Κ(θ). Experiments were conducted to determine θ(h) and Κ(θ) relationships of six different porous media. θ(h) relationships were determined using Haines-type assembly or Richards' pressure cell chambers, depending on the soil type. K(θ) relationships were determined using the one-step outflow method. RETC code was used to analyze hydraulic properties. Experimental data were compared with those predicted by the Mualem-van Genuchten model using RETC for two prediction scenarios with three fitting parameters a, n, θr. The first scenario uses as input data the experimental θ(h) and saturated hydraulic conductivity (Ks) measurements and the second, the experimental θ(h), K(θ) and Ks measurements for two types of conductivity regression analysis. Concerning the second scenario, the Mualem model parameter p as an additional fitting parameter was also examined. Analysis of the results showed that the best method for predicting both the θ(h) and K(θ) relationships is to use simultaneously the experimental θ(h), K(θ) and Ks data with four fitting parameters a, n, θr, p.

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Unsaturated flow in coarse porous media

Canadian Geotechnical Journal ◽

10.1139/t04-070 ◽

2005 ◽

Vol 42 (1) ◽

pp. 252-262 ◽

Cited By ~ 16

Author(s):

Jeff R Reinson ◽

Delwyn G Fredlund ◽

G Ward Wilson

Keyword(s):

Porous Media ◽

Hydraulic Conductivity ◽

Soil Water ◽

Unsaturated Soils ◽

Unsaturated Flow ◽

Characteristic Curve ◽

Matric Suction ◽

Coarse Grained ◽

Capillary Barrier ◽

Coarse Porous Media

Design of effective capillary barrier systems requires a thorough understanding of the soilwater interactions that take place in both coarse- and fine-grained unsaturated soils. Experimental observations of water flow through coarse porous media are presented to gain greater understanding of the processes and mechanisms that contribute to the movement and retention of water in coarse-grained unsaturated soils. The use of pendular ring theory to describe how water is held within a porous material with relatively low volumetric water contents is explored. Experimental measurements of seepage velocity and volumetric water content were obtained for columns of 12 mm glass beads using digital videography to capture the movement of a dye tracer front at several infiltration rates. An estimated curve for hydraulic conductivity versus matric suction is shown and compared to a theoretical curve. The method is shown to provide a reasonable predictive tool.Key words: soil-water characteristic curve, hydraulic conductivity curve, water permeability function, capillary barrier, matric suction.

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