A modification to the van Genuchten model for improved prediction of relative hydraulic conductivity of unsaturated soils

2020 ◽  
Author(s):  
Xingxing Kuang ◽  
Jiu Jimmy Jiao ◽  
Jipeng Shan ◽  
Zhenlei Yang
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Van Genuchten Model ◽  
Relative Hydraulic Conductivity

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

2018 ◽  
Vol 20 (3) ◽  
pp. 699-707 ◽  
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.

scholarly journals A Fractal Approach for Predicting Unsaturated Hydraulic Conductivity of Deformable Clay

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Gaoliang Tao ◽  
Xueliang Zhu ◽  
Jianchao Cai ◽  
Henglin Xiao ◽  
Qingsheng Chen ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Quantitative Description ◽  
Fractal Model ◽  
Reference State ◽  
Deformation Condition ◽  
Simple Method ◽  
Unsaturated Hydraulic Conductivity ◽  
Deformed State ◽  
Relative Hydraulic Conductivity

The relative hydraulic conductivity is one of the key parameters for unsaturated soils in numerous fields of geotechnical engineering. The quantitative description of its variation law is of significant theoretical and technical values. Parameters in a classical hydraulic conductivity model are generally complex; it is difficult to apply these parameters to predict and estimate the relative hydraulic conductivity under deformation condition. Based on the fractal theory, a simple method is presented in this study for predicting the relative hydraulic conductivity under deformation condition. From the experimental soil-water characteristic curve at a reference state, the fractal dimension and air-entry value are determined at a reference state. By using the prediction model of air-entry value, the air-entry values at the deformed state are then determined. With the two parameters determined, the relative hydraulic conductivity at the deformed state is predicted using the fractal model of relative hydraulic conductivity. The unsaturated hydraulic conductivity of deformable Hunan clay is measured by the instantaneous profile method. Values of relative hydraulic conductivity predicted by the fractal model are compared with those obtained from experimental measurements, which proves the rationality of the proposed prediction method.

On the Improvement of Hydraulic Conductivity Function in Van Genuchten-Mualem Model

2014 ◽  
Vol 513-517 ◽  
pp. 4417-4420 ◽  
Author(s):  
Yeong Mog Park ◽  
Seboong Oh ◽  
Inchul Jin ◽  
Kyun Kwon Oh
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Rapid Change ◽  
Model Fit ◽  
Soil Water Retention ◽  
Rapid Reduction ◽  
Integration Interval ◽  
Van Genuchten Model ◽  
Conductivity Function

Hydraulic conductivity (HC) is deduced indirectly from soil water retention curves (SWRC) by Mualem model, but the mathematical calculation in the Mualem model is sensitive to integration interval near saturation. After the van Genuchten model fit actual SWRC, the van Genuchten-Mualem (VGM) HC is integrated simply by an analytical function for unsaturated soils. However the analytical solution on VGM HC results in the rapid change of HC near saturation. For unsaturated soils sampled in Korea, SWRCs and unsaturated HCs were obtained by experiments. The HC experiments were compared with the HC models from the SWRCs. As a result, VGM models of HC function underestimate the unsaturated HC and show rapid reduction near saturation. It is found that a modification in VGM model should be required to predict accurate HC functions.

scholarly journals A Statistical Model for the Relative Hydraulic Conductivity of Water Phase in Unsaturated Soils

2011 ◽  
Vol 02 (04) ◽  
pp. 484-492 ◽  
Author(s):  
Nadarajah Ravichandran ◽  
Shada Krishnapillai
Keyword(s):  
Hydraulic Conductivity ◽  
Statistical Model ◽  
Unsaturated Soils ◽  
Water Phase ◽  
Relative Hydraulic Conductivity

On the hydraulic conductivity of unsaturated soils

1975 ◽  
Vol 12 (7) ◽  
pp. 93
Author(s):  
A. Feodoroff ◽  
E. Galula
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils

Simulating transient infiltration in unsaturated soils

1998 ◽  
Vol 35 (6) ◽  
pp. 1093-1100 ◽  
Author(s):  
J R McDougall ◽  
I C Pyrah
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Flow Model ◽  
Unsaturated Flow ◽  
Surface Region ◽  
Infiltration Rate ◽  
Soil Suction ◽  
Wetting Front ◽  
Near Surface ◽  
Unsaturated Hydraulic Conductivity

Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.

Entrapment, stability, and persistence of air bubbles in soil water

Soil Research ◽  
1969 ◽  
Vol 7 (2) ◽  
pp. 79 ◽  
Author(s):  
AJ Peck
Keyword(s):  
Hydraulic Conductivity ◽  
Moisture Content ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Equilibration Time ◽  
Air Bubbles ◽  
Air Entrapment ◽  
Water Characteristics ◽  
Spherical Bubbles ◽  
Entrapped Air

Air bubbles in soil water affect both hydraulic conductivity and moisture content at a given capillary potential. Consequently changes in the volume of entrapped air, which are not included in the specification of relationships between hydraulic conductivity, moisture content, and capillary potential, will affect all soil-water interactions. Current understanding of the process of air bubble entrapment during infiltration suggests that, in nature, significant air entrapment will often occur. It is shown that infiltrating water can dissolve only a very small volume of air, much less than the amount usually entrapped. Air bubbles in saturated soils are unstable since their pressure must exceed atmospheric, resulting in a diffusive flux of dissolved air from bubbles to menisci contacting the external atmosphere. However, stable bubbles are possible in unsaturated soils. Bubbles which are constrained by pore architecture to non-spherical shapes are usually stable, and spherical bubbles can be stable when the magnitude of the capillary potential exceeds about 3 bars. An approximate analysis of the characteristic time of bubble equilibration indicates that, in an example, it is of order 104 sec, but it may be greater or less by at least a factor 10. Since the equilibration time will be often at least as large as the period of significant soil temperature changes, it cannot be assumed that the entrapped air in a field soil is in an equilibrium state. In such circumstances unstable bubbles may be quasi-permanent. It is suggested that the slow growth of entrapped bubbles may account for the anomalously slow release of water observed in some outflow experiments. Changes of entrapped air volume may also account for the reported dependence of soil-water characteristics on the magnitude of the steps of capillary potential.

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

2007 ◽  
Vol 7 (1) ◽  
pp. 59-66 ◽  
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.

Method for Quick Prediction of Hydraulic Conductivity and Soil-Water Retention of Unsaturated Soils

2018 ◽  
Vol 2672 (52) ◽  
pp. 108-117 ◽  
Author(s):  
Shaoyang Dong ◽  
Yuan Guo ◽  
Xiong (Bill) Yu
Keyword(s):  
Finite Element ◽  
Hydraulic Conductivity ◽  
Soil Properties ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Characteristic Curve ◽  
Soil Water Retention

Hydraulic conductivity and soil-water retention are two critical soil properties describing the fluid flow in unsaturated soils. Existing experimental procedures tend to be time consuming and labor intensive. This paper describes a heuristic approach that combines a limited number of experimental measurements with a computational model with random finite element to significantly accelerate the process. A microstructure-based model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The model is converted into a finite element model, in which the intrinsic hydraulic properties of each phase (soil particle, water, and air) are applied based on the microscopic structures. The bulk hydraulic properties are then determined based on discharge rate using Darcy’s law. The intrinsic permeability of each phase of soil is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturation. The results match the experimental data closely. Mualem’s equation is applied to fit the pore size parameter based on the hydraulic conductivity. From these, the soil-water characteristic curve is predicted from van Genuchten’s equation. The simulation results are compared with the experimental results from documented studies, and excellent agreements were observed. Overall, this study provides a new modeling-based approach to predict the hydraulic conductivity function and soil-water characteristic curve of unsaturated soils based on measurement at complete dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will be of benefit in introducing unsaturated soil mechanics into engineering practice.

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