Unsaturated flow in coarse porous media

2005 ◽  
Vol 42 (1) ◽  
pp. 252-262 ◽  
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 soil–water 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.

A relationship describing the shear strength of unsaturated soils

1999 ◽  
Vol 36 (2) ◽  
pp. 363-368 ◽  
Author(s):  
Daud W Rassam ◽  
David J Williams
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Nonlinear Regression ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Three Dimensional ◽  
Matric Suction ◽  
Linear Increase ◽  
Soil Water Characteristic Curve ◽  
Stress Dependent

A relationship describing the shear-strength profile of a desiccating soil deposit is essential for the purpose of analysis, especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation-dependent shear-strength value. The matric-suction profile of a desiccating soil deposit is nonlinear. Up to the air-entry value, an increase in matric suction is associated with a linear increase in shear strength. Beyond air entry, as the soil starts to desaturate, a nonlinear increase in shear strength occurs. The soil-water characteristic curve is stress dependent, as is the shear-strength gain as matric suction increases. In this paper, a three-dimensional, nonlinear regression analysis showed that a power-additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction. The proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength.Key words: air-entry value, matric suction, nonlinear regression, soil-water characteristic curve, tailings, unsaturated shear strength.

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.

Soil-water characteristic curve and consolidation behavior for a compacted silt

2007 ◽  
Vol 44 (3) ◽  
pp. 266-275 ◽  
Author(s):  
Trinh Minh Thu ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong
Keyword(s):  
Soil Water ◽  
Volume Change ◽  
Unsaturated Soils ◽  
Water Pressure ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Confining Stress ◽  
Soil Water Characteristic Curve ◽  
Triaxial Cell ◽  
Isotropic Consolidation

Measurement of the soil-water characteristic curve (SWCC) in the laboratory is commonly conducted under zero confining pressure. However, in the field, the soil is under a confining stress. Therefore, it is important to study the effects of the confining stress on SWCC. In addition, the consolidation curve is normally generated under saturated conditions. However, the soil above the water table is usually unsaturated. Hence, it is also necessary to investigate the effects of matric suction on the characteristics of the consolidation curves. This paper presents the SWCCs under different net confining stresses and the isotropic consolidation curves under different matric suctions that describe the volume change characteristics of unsaturated soils with respect to stress state variables, net normal stress, and matric suction. A series of SWCCs was determined for statically compacted silt specimens in a triaxial cell apparatus under different net confining stresses. Isotropic consolidation tests under different matric suctions were also carried out. The results of the SWCC tests show that the air-entry value increased with increasing net confining stress. The yield points (i.e., yield suction, s0) obtained from the SWCC tests also increased with increasing net confining stress. The results of isotropic consolidation tests indicate the strong influence of matric suction on compressibility and stiffness of the compacted silt specimens.Key words: soil-water characteristic curve, isotropic consolidation, pore-water pressure, volume change, NTU mini suction probe, matric suction.

Model for the prediction of shear strength with respect to soil suction

1996 ◽  
Vol 33 (3) ◽  
pp. 379-392 ◽  
Author(s):  
S K Vanapalli ◽  
D G Fredlund ◽  
D E Pufahl ◽  
A W Clifton
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Experimental Studies ◽  
Matric Suction ◽  
Glacial Till ◽  
Soil Suction ◽  
Soil Water Characteristic Curve

Experimental studies on unsaturated soils are generally costly, time-consuming, and difficult to conduct. Shear strength data from the research literature suggests that there is a nonlinear increase in strength as the soil desaturates as a result of an increase in matric suction. Since the shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to matric suction, it is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. This paper describes the relationship between the soil-water characteristic curve and the shear strength of an unsaturated soil with respect to matric suction. Am empirical, analytical model is developed to predict the shear strength in terms of soil suction. The formulation makes use of the soil-water characteristic curve and the saturated shear strength parameters. The results of the model developed for predicting the shear strength are compared with experimental results for a glacial till. The shear strength of statically compacted glacial till specimens was measured using a modified direct shear apparatus. Specimens were prepared at three different water contents and densities (i.e., corresponding to dry of optimum, and wet of optimum conditions). Various net normal stresses and matric suctions were applied to the specimens. There is a good correlation between the predicted and measured values of shear strength for the unsaturated soil. Key words: soil-water characteristic curve, shear strength, unsaturated soil, soil suction, matric suction.

scholarly journals Effect of hysteresis of soil-water characteristic curves on infiltration under different climatic conditions

2016 ◽  
Vol 53 (2) ◽  
pp. 273-284 ◽  
Author(s):  
Rashid Bashir ◽  
Jitendra Sharma ◽  
Halina Stefaniak
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Unsaturated Flow ◽  
Expansive Soils ◽  
Characteristic Curve ◽  
Ground Surface ◽  
Temporal Distribution ◽  
Climatic Conditions ◽  
Wide Range ◽  
And Storage

This paper presents results of a numerical modelling exercise that investigates the effects of hysteresis of the soil-water characteristic curve (SWCC) on the infiltration characteristics of soils subjected to four different climatic conditions — from very dry to wet — within the Canadian province of Alberta. Multi-year climate datasets from four different natural regions and subregions of Alberta are compiled, classified, and applied as the soil–atmosphere boundary condition in one-dimensional finite element unsaturated flow models using Hydrus-1D software. Multi-year simulations are carried out with and without consideration of the SWCC hysteresis. Simulation results are analyzed in terms of water balance at the ground surface and temporal distribution and storage of water within the soil domain. It is demonstrated that hysteresis of the SWCC can significantly affect the prediction of flow, redistribution, and storage of water in the unsaturated zone. It is found that for soils that exhibit hysteretic SWCC, consideration of hysteresis in unsaturated flow modelling results in the prediction of lower infiltration and less movement of water through the soil. It is also found that the use of wetting parameters results in the prediction of increased infiltration and movement of water compared with the predictions using drying or hysteretic parameters. It is concluded that, for soils that exhibit a greater degree of SWCC hysteresis, it is important to measure both the drying and wetting branches of the SWCC accurately and that accurate simulation of hysteretic behaviour requires climate datasets at appropriate resolution. The results presented in this paper highlight the importance of considering SWCC hysteresis for a wide range of geotechnical problems, such as soil cover design, prediction of groundwater recharge, contaminant transport through unsaturated soils, soil erosion, slope stability, and swelling–shrinkage of expansive soils.

Experimental Research on Soil-Water Characteristic Curve of Unsaturated Soils

2013 ◽  
Vol 353-356 ◽  
pp. 554-557
Author(s):  
Xu Xu ◽  
Fu You Zhang ◽  
Ming Gu
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Storage Capacity ◽  
Characteristic Curve ◽  
Water Storage ◽  
Matric Suction ◽  
Water Storage Capacity ◽  
Soil Water Characteristic Curve ◽  
Change Trend ◽  
Main Factors

The soil-water characteristic curve (SWCC) reflects water storage capacity, Measuring it accurately is important in engineering. This paper concluded main factors of SWCC, measured soil-water characteristic of loess under conditions of different dry densities, the curve of volume water content, saturation and matric suction were presented, the curves showed similar change trend, saturation mainly determined the matric suction when matric suction was small.

scholarly journals A Numerical Model to Predict Matric Suction Inside Unsaturated Soils

10.14311/588 ◽  
2004 ◽  
Vol 44 (4) ◽  
Author(s):  
A. Farouk ◽  
L. Lamboj ◽  
J. Kos
Keyword(s):  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Coarse Grained ◽  
Soil Parameters ◽  
Measuring Devices ◽  
Proposed Model ◽  
Testing Techniques ◽  
The Relationship ◽  
Water Contents

The objective of this research is to introduce a numerical simulation model to predict approximate values of the matric suction inside unsaturated soils that have low water contents. The proposed model can be used to predict the relationship between the water content and the matric suction of a studied soil to construct the soil-water characteristic curve. In addition, the model can be utilized to combine the predicted matric suction with the soil parameters obtained experimentally, which enables us to explain how matric suction can affect the behaviour of unsaturated soils, without the need to utilize advanced measuring devices or special testing techniques. The model has given good results, especially when studying coarse-grained soils.

How to predict hydraulic conductivity of unsaturated soils from an incomplete soil water characteristic curve?

2020 ◽  
Author(s):  
Xingwei Ren ◽  
Qidong Fang ◽  
Xiaojun Chen
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Ground Surface ◽  
Experimental Conditions ◽  
Flow Process ◽  
Soil Water Characteristic Curve ◽  
Wide Range ◽  
Extensive Experimental Data

<p>Unsaturated soils are those in which pore is filled partially with water and partially with air. They are the most relevant porous medium to human activities, and cover almost all the soils near the ground surface. Hydraulic conductivity (HC) is one of the most important and useful properties of unsaturated soils in numerous studies, including governing flow process, settlement of soil foundations, migration of groundwater and gas hydrate. Unfortunately, direct measurement of HC for unsaturated soils is very difficult with high uncertainty due to its nature of complexity and limited experimental conditions. Thus, indirect estimation of HC from soil water characteristic curve (SWCC) becomes an alternative way and being widely used all over the world.</p><p>Because of the difficulty to reach high suction at the residual state of unsaturated soils, however, the SWCC obtained by laboratory experiments is often incomplete, which will lead to an unreliable estimation of hydraulic conductivity. However, no study has been published on how to estimate hydraulic conductivity of unsaturated soils with incomplete SWCC. In response to this situation, an innovative method was proposed based on the classical van Genuchten model and Mualem model. The proposed method was evaluated by extensive experimental data from existing literature and proved to have an excellent performance in predicting a complete SWCC for a wide range of soils. Also, it exhibits certain superiority in predicting hydraulic conductivity. The limitations of the proposed method were comprehensively discussed, and its corresponding improvement strategies were also addressed. This paper presents a practical way to obtain a more reliable hydraulic conductivity from incomplete SWCC.</p>

scholarly journals A Methdology for Estimation of Soil Water Charactreristic Curve for Unsaturated Cohesive Soils

2017 ◽  
pp. 1046-1054
Author(s):  
H. Ghasemzadeh ◽  
M. R. Abdi ◽  
N. Ganjian ◽  
K. Shakiba Nia
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Unsaturated Flow ◽  
Characteristic Curve ◽  
Experimental Methods ◽  
Cohesive Soils ◽  
Fine Content ◽  
Initial Void Ratio ◽  
Soil Media ◽  
The Relationship

Many environmental issues involve transport of contaminants in unsaturated porous soil media. Unsaturated flow plays a significant role in wastewater infiltration and treatment. Transport of contaminants in unsaturated porous subsurface media is of significant importance due to the risks which contaminants pose to the environment. Mechanics of unsaturated soils is perhaps the most important issue in prediction of unsaturated flow including contaminant transport in the environment. The SWCC, “soil water characteristic curve”, can be used to determine various characteristics of the unsaturated soil media. In fact, it illustrates the relationship between soil suction and moisture content. Experimental methods for assessment of the SWCC are often time consuming and expensive. The SWCC can be estimated using specific characteristics of soils to avoid the costs of experimental methods. This paper aims at demonstrating that the SWCC for cohesive soils can be estimated using the PI, fine content, initial void ratio and the Van Genuchten equation.

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