Nineteenth Canadian Geotechnical Colloquium: The soil-water characteristic curve: a historical perspective

1998 ◽  
Vol 35 (5) ◽  
pp. 873-894 ◽  
Author(s):  
S Lee Barbour
Keyword(s):  
Shear Strength ◽  
Conceptual Model ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Constitutive Relationship ◽  
Water Phase ◽  
Degree Of Saturation ◽  
Capillary Model ◽  
Soil Water Characteristic Curve

The constitutive relationship between water content or degree of saturation and suction is called the soil-water characteristic curve. The soil-water characteristic curve provides a conceptual framework in which the behavior of unsaturated soils can be understood. A historical review illustrates how the work of early researchers in soil science and geotechnical engineering laid the foundation for our current understanding of this relationship. Key elements of these early studies were a conceptual understanding of the soil-water characteristic curve as a relationship between the mass or volume of water stored within the soil and the energy in the water phase. It was on the basis of this conceptual model that current methods of measuring the soil-water characteristic curve were developed. Interpretative models for the distribution and geometry of the water phase in an unsaturated soil based on the capillary model have provided a useful conceptual model for understanding the effects of soil texture, gradation, void ratio, and compaction on the soil-water characteristic curve. The capillary model has also provided the foundation for recently developed techniques to predict the functional relationship between degree of saturation and shear strength, coefficient of permeability, coefficient of diffusion, and adsorption for unsaturated soils.Key words: unsaturated soils, soil-water characteristic curve, suction, shear strength, permeability, contaminant transport.

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.

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.

Predicting the permeability function for unsaturated soils using the soil-water characteristic curve

1994 ◽  
Vol 31 (4) ◽  
pp. 533-546 ◽  
Author(s):  
D.G. Fredlund ◽  
Anqing Xing ◽  
Shangyan Huang
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Residual Water ◽  
Soil Water Characteristic Curve ◽  
Coefficient Of Permeability ◽  
Permeability Function

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 106 kPa), was proposed by the first two authors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an evaluation of the residual water content is no longer required in the prediction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content relationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the data and the theory was excellent. It was found that the integration can be done from zero water content to the saturated water content. Therefore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function. Key words : coefficient of permeability, soil-water characteristic curve, unsaturated soil, water content, soil suction.

Effect of stress state on the unsaturated shear strength of a weathered granite

2005 ◽  
Vol 42 (2) ◽  
pp. 624-631 ◽  
Author(s):  
In-Mo Lee ◽  
Sang-Gyu Sung ◽  
Gye-Chun Cho
Keyword(s):  
Shear Strength ◽  
Stress State ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Triaxial Tests ◽  
Residual Soil ◽  
Normal Stresses ◽  
Soil Water Characteristic Curve ◽  
Model Soil

The effect of stress state on the unsaturated shear strength of a Korean residual soil was studied using modified triaxial tests. Experimental results show that the soil-water characteristic curve and shear strength of this soil are significantly affected by the change of net normal stresses. This effect should be taken into consideration in the model to precisely describe the shear strength envelope of unsaturated soils. Thus, a new model for estimation of unsaturated shear strength is proposed using the soil-water characteristic curve and the saturated shear strength parameters.Key words: prediction model, soil-water characteristic curve, matric suction, triaxial test, unsaturated shear strength.

The relationship of the unsaturated soil shear strength to the soil-water characteristic curve

1996 ◽  
Vol 33 (3) ◽  
pp. 440-448 ◽  
Author(s):  
D G Fredlund ◽  
Anqing Xing ◽  
M D Fredlund ◽  
S L Barbour
Keyword(s):  
Shear Strength ◽  
Prediction Model ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Function ◽  
Soil Parameters ◽  
Angle Of Internal Friction ◽  
Soil Water Characteristic Curve

The measurement of soil parameters, such as the permeability and shear strength functions, used to describe unsaturate soil behaviour can be expensive, difficult, and often impractical to obtain. This paper proposes a model for predicting the shear strength (versus matric suction) function of unsaturated soils. The prediction model uses the soil-water characteristic curve and the shear strength parameters of the saturated soil (i.e., effective cohesion and effective angle of internal friction). Once a reasonable estimate of the soil-water characteristic curve is obtained, satisfactory predictions of the shear strength function can be made for the unsaturated soil. Closed-form solutions for the shear strength function of unsaturated soils are obtained for cases where a simple soil-water characteristic equation is used in the prediction model. Key words: soil suction, soil-water characteristic curve, shear strength function, unsaturated soil.

Evaluation of capillary water retention effects on the development of the suction stress characteristic curve

2020 ◽  
Vol 57 (10) ◽  
pp. 1439-1452 ◽  
Author(s):  
Emad Maleksaeedi ◽  
Mathieu Nuth
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Soil Water Retention ◽  
Retention Model ◽  
Suction Stress ◽  
Effective Degree

The suction stress characteristic framework is a practical approach for relating the suction and the water-filled pore volume to the stress state of unsaturated soils. It predicts the effective stress by developing the suction stress characteristic curve from the soil-water retention curve. In this framework, the effective degree of saturation is usually calculated by the empirical water retention model of van Genuchten (published in 1980). In this paper, the use of a generalized soil-water retention model proposed by Lu in 2016, which differentiates the role of capillary and adsorption mechanisms, in the suction stress characteristic framework is studied. A redefinition of the effective degree of saturation is suggested, by choosing the retention state where capillarity approaches zero instead of the residual retention state. The validity of this assumption is examined using experimental data obtained by unsaturated shear strength and retention tests and datasets collected from the literature. The proposed definition is applicable for a variety of soils where capillarity is the dominant mechanism in producing suction stress within the range of suction 0–1500 kPa. In addition, it is observed that the generalized soil-water retention model presents a more realistic prediction of unsaturated shear strength compared with empirical water retention models.

scholarly journals Collapse behaviour of unsaturated compacted soil with different initial densities

2007 ◽  
Vol 44 (6) ◽  
pp. 673-686 ◽  
Author(s):  
De'an Sun ◽  
Daichao Sheng ◽  
Yongfu Xu
Keyword(s):  
Experimental Data ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Initial Density ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Compacted Soil ◽  
Soil Water Characteristic Curve ◽  
Volume Decrease

Very few experimental data on the mechanical behaviour of unsaturated soils exists, particularly on the collapse behaviour under general stress states, because of the technical difficulties and time-consuming nature of measuring suction and deformation. This paper presents the results of a series of controlled-suction triaxial tests on the collapse behaviour of an unsaturated compacted clay with different initial dry densities and suctions. The collapse behaviour here includes deformation characteristics, such as volume changes, and hydraulic characteristics, such as saturation changes. It is found that the wetting-caused collapse mainly depends on the mean net stress and the initial density, and that the volume decrease reaches a maximum when the specimen is under the initial yielding mean net stress. It is also found that the soil-water characteristic curve in terms of suction and degree of saturation shifts upwards with increasing specimen density. The soil-water characteristic curve of a compacted soil mainly depends upon the current density, not directly upon the stress state. In addition, experimental data show that the collapse occurs mainly in an intermediate range of suction levels, which are neither very high nor very low, and that the wetting-caused volume decrease is accompanied by an increase in the degree of saturation.Key words: unsaturated soil, density, triaxial test, suction, collapse, degree of saturation.

Stiffness and shear strength of unsaturated soils in relation to soil-water characteristic curve

Géotechnique ◽  
2016 ◽  
Vol 66 (8) ◽  
pp. 627-647 ◽  
Author(s):  
Z. Han ◽  
S. K. Vanapalli
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Soil Water Characteristic Curve

Influence of soil type and stress state on predicting shear strength of unsaturated soils using the soil-water characteristic curve

2011 ◽  
Vol 48 (12) ◽  
pp. 1886-1900 ◽  
Author(s):  
Wan Soo Kim ◽  
Roy H. Borden
Keyword(s):  
Shear Strength ◽  
Stress State ◽  
Soil Water ◽  
Soil Type ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Soil Types ◽  
Strength Data ◽  
Soil Water Characteristic Curve ◽  
Predicted Values

Comprehensive studies on the prediction of unsaturated shear strength were performed using three commonly used empirical procedures: Fredlund et al. approach (published in 1996), Vanapalli et al. approach (published in 1996), and Khalili and Khabbaz method (published in 1998). Shear strength data published in the literature for 15 soils were examined using these procedures. Comparisons between measured and predicted values of unsaturated shear strength are presented for different soil types. The effect of stress state on the prediction of shear strength is also discussed.

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