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.

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.

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.

The Study of Correction Method for Soil-Water Characteristic Curve of Swelling-Shrinking Soil

2013 ◽  
Vol 712-715 ◽  
pp. 873-876
Author(s):  
Peng Du ◽  
Xiao Ling Liu ◽  
Xiao Ying Li
Keyword(s):  
Soil Water ◽  
Volume Fraction ◽  
Characteristic Curve ◽  
Correction Method ◽  
Matric Suction ◽  
Engineering Properties ◽  
Water Volume ◽  
Volume Deformation ◽  
Water Volume Fraction ◽  
The Relationship

The swelling-shrinking soil embodies the features of expanding when absorbing water and shrinking when drying out; its engineering properties are sensitive to water fluctuation. Mainstream test instruments of SWCC cannot accurately get its relationship between matric suction and water volume fraction. So a correction method based on the results of shrinkage test is carried out. The method is accomplished by using the volume deformation which is obtained in shrinkage test to calculate its real water volume fraction and then combining the results of SWCC test and finally constructing the relationship between matric suction and water volume fraction. Through real application, this method is proved to be feasible and essential.

scholarly journals Microstructure of Compacted Loess and Its Influence on the Soil-Water Characteristic Curve

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Xiao Xie ◽  
Ping Li ◽  
Xiaokun Hou ◽  
Tonglu Li ◽  
Guowei Zhang
Keyword(s):  
Soil Water ◽  
Characteristic Curve ◽  
Great Influence ◽  
Matric Suction ◽  
Constitutive Relationship ◽  
Wetting And Drying ◽  
Soil Water Characteristic Curve ◽  
High Suction ◽  
Water Contents ◽  
Compacted Loess

Soil-water characteristic curve (SWCC) is a key constitutive relationship for studying unsaturated soil, and as is known, microstructure of the soil has great influence on the mechanical behaviour of the soil. In this study, the wetting and drying soil-water characteristic curves (SWCCs) of loess compacted at three different water contents were measured using the filter paper method. And microproperties of compacted loess were obtained by the mercury intrusion method (MIP) and scanning electron microscope (SEM). Results show that the compaction water contents have significant influence on the SWCC and microstructure. The pore size distribution (PSD) curves have great differences in macropore range and are similar in micropore range. Loess compacted at optimum and dry of optimum are generally connected, while there are certain number of nonintruded pores in loess compacted at wet of optimum. The SWCC curves vary significantly in low suction (ua − uw < 1000 kPa) and tend to converge together in high suction (ua − uw ≥ 1000 kPa). Hysteresis in the SWCCs is more obvious for loess compacted at optimum and dry of optimum in the matric suction of 0∼100 kPa; however, there is a pronounced hysteresis for loess compacted at wet of optimum in full matric suction range. The characteristic of the SWCCs including their hysteresis can be well interpreted from the loess microstructure.

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.

Volume–mass unsaturated soil constitutive model for drying–wetting under isotropic loading–unloading conditions

2011 ◽  
Vol 48 (2) ◽  
pp. 280-313 ◽  
Author(s):  
Hung Q. Pham ◽  
Delwyn G. Fredlund
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Research Literature ◽  
Degree Of Saturation ◽  
Soil Conditions ◽  
Constitutive Relationships ◽  
Proposed Model ◽  
Wide Range

A rigorous volume–mass constitutive model is proposed for the representation of drying–wetting under isotropic loading–unloading conditions for unsaturated soils. The proposed model utilizes concepts arising from soil physics and geotechnical engineering research and requires readily obtainable soils data for soil properties. The model can be used to predict void ratio and water content constitutive relationships (and therefore degree of saturation) for a wide range of unsaturated soils. Various stress paths (i.e., loading–unloading and drying–wetting) can be simulated, and hysteresis associated with the soil-water characteristic curve is taken into account. Two closed-form equations for the volume–mass constitutive relationships are presented for soils starting from slurry conditions. A number of test results (i.e., from experimental programs reported in the research literature) were used during the verification of the proposed volume–mass constitutive model. The volume–mass constitutive model captures key unsaturated soil conditions such as air-entry value, water-entry value, and residual conditions. The proposed model appears to satisfactorily predict unsaturated soil behavior for soils ranging from low compressible sands to high compressible clays.

A simple air pressure gauge for unsaturated soils

2007 ◽  
Vol 44 (8) ◽  
pp. 1013-1018 ◽  
Author(s):  
Julio  Ángel Infante Sedano ◽  
Sai K. Vanapalli ◽  
Vinod K. Garga
Keyword(s):  
Unsaturated Soils ◽  
Low Cost ◽  
Pressure Gauge ◽  
Matric Suction ◽  
Coarse Grained ◽  
Water Characteristics ◽  
Main Components ◽  
Column Pressure ◽  
Boyle’S Law ◽  
Air Column

This paper presents the design details of a simple compressible air column pressure gauge system. The main components of this pressure gauge consist of a Mariotte bottle, plastic tubing, and a graduated scale. This low-cost gauge design is based on applying the principle of Boyle’s law for gases, which makes it particularly well-suited for the measurement of soil–water characteristics of coarse-grained soils, which desaturate at a faster rate, particularly in the low matric suction range of 0–10 kPa. Among its many uses, this precise gauge is best employed in the axis translation technique to measure matric suction in the range of 0–700 kPa.

Determination of the Shear Strength of Unsaturated Loess Based on the Fractal Model Theory of Unsaturated Soils

2012 ◽  
Vol 170-173 ◽  
pp. 25-28
Author(s):  
Jing Yu Chen ◽  
Ying Hai
Keyword(s):  
Shear Strength ◽  
Model Theory ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Fractal Model ◽  
North West ◽  
The North ◽  
Unsaturated Loess ◽  
The Relationship

The shear strength value of unsaturated loess is required in the design in geotechnical engineering in the North and the North West of China. In 2004, a new method, that is the fractal model theory, was proposed for determining the shear strength of unsaturated soil. Based upon the fractal model theory, the surface fractal dimension DS and the air entry value of two unsaturated loess samples are obtained from their soil-water characteristic curve (SWCC), the shear strength contribution due to matric suction of the two loess samples is determined, a new approach for determination of the shear strength of unsaturated loess with its SWCC is presented. By comparing results of this paper with those of the laboratory tests, the relationship between the SWCC and the shear strength of unsaturated loess is discussed and the validity of the fractal model theory for unsaturated loess is explained.

Model for predicting tensile strength of unsaturated cohesionless soils

2018 ◽  
Vol 55 (9) ◽  
pp. 1313-1333 ◽  
Author(s):  
Penghai Yin ◽  
Sai K. Vanapalli
Keyword(s):  
Tensile Strength ◽  
Characteristic Curve ◽  
Experimental Studies ◽  
Friction Angle ◽  
Matric Suction ◽  
Degree Of Saturation ◽  
Engineering Practice ◽  
Cohesionless Soils ◽  
Proposed Model ◽  
Earth Structures

The influence of tensile strength on the behaviour of cohesionless soils is typically ignored in geotechnical engineering practice. However, the tensile cracking and subsequent failure characteristics of earth structures, such as dams, slopes and embankments, are significantly influenced by the tensile strength. For this reason, a semi-empirical model is proposed for predicting the variation of the tensile strength of unsaturated cohesionless soils with the degree of saturation, using the soil-water characteristic curve (SWCC) as a tool. The proposed model is capable of predicting the tensile strength arising from matric suction and surface tension, which are related to saturated pores and to the air–water interface associated with water bridges around interparticle contacts in unsaturated pores, respectively. Information about (i) the matric suction (ua– uw), the capillary degree of saturation (Sc), and the residual degree of saturation (Sr) derived from the SWCC; (ii) the mean particle size (d50) and the coefficient of uniformity (Cu) from the grain-size distribution curve; (iii) the void ratio (e); and (iv) the friction angle ([Formula: see text]) at low normal stress level is required to employ this model. The proposed model is validated by comparing the prediction results with measured tensile strength of 10 different unsaturated cohesionless soils (including five sandy soils and five silty soils). The proposed model is promising for use in engineering practice applications as it only requires conventional soil properties, alleviating the need for cumbersome experimental studies for the determination of tensile strength of unsaturated cohesionless soils.

Sign in / Sign up

Export Citation Format

Share Document