scholarly journals Verification of the Fredlund (2019) Unsaturated Shear Strength Function

Geosciences ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 151
Author(s):  
Thi Phuong An Tran ◽  
Delwyn G. Fredlund
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Function ◽  
Past Research ◽  
Research Literature ◽  
Reference Points ◽  
Degree Of Saturation ◽  
Anchor Points

There has been a proliferation of equations proposed to describe the unsaturated shear strength envelope going back to the 1970s. However, there have been limited studies to verify the suitability of one unsaturated shear strength equation over another. Most proposed shear strength equations have attempted to relate the shear strength of an unsaturated soil to some aspect(s) of the soil–water characteristic curve (SWCC). Estimation procedures have generally focused on using that of air-entry value (AEV) as defined by the drying (or desorption) branch of the degree of saturation SWCC (S-SWCC). This paper studies the suitability of using two “anchor points” (or reference points) along the drying S-SWCC to estimate the unsaturated soil shear strength function. The anchor points referred to are the air-entry value (AEV) of the soil and the “residual suction point” of the soil defined in terms of the S-SWCC. Shear strength conditions associated with both so-called anchor points are used as “boundary conditions” that should be satisfied when estimating the shear strength function for unsaturated soils. Past research laboratory measurements published in the research literature are used as part of the verification process for this study.

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.

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.

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.

The shear strength of unsaturated soils

1978 ◽  
Vol 15 (3) ◽  
pp. 313-321 ◽  
Author(s):  
D. G. Fredlund ◽  
N. R. Morgenstern ◽  
R. A. Widger
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Research Literature ◽  
Test Results ◽  
State Variables ◽  
Limited Data ◽  
Laboratory Test Results

The shear strength of an unsaturated soil is written in terms of two independent stress state variables. One form of the shear strength equation is[Formula: see text]The transition from a saturated soil to an unsaturated soil is readily visible. A second form of the shear strength equation is[Formula: see text]Here the independent roles of changes in total stress σ and changes in pore-water pressure uw are easily visualized.Published research literature provides limited data. However, the data substantiate that the shear strength can be described by a planar surface of the forms proposed. A procedure is also outlined to evaluate the pertinent shear strength parameters from laboratory test results.

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.

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.

Controlling parameter for unsaturated soil property functions: validated on the unsaturated shear strength

2015 ◽  
Vol 52 (3) ◽  
pp. 374-381 ◽  
Author(s):  
Reto Schnellmann ◽  
Harianto Rahardjo ◽  
Hans R. Schneider
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Property ◽  
Degree Of Saturation ◽  
Prediction Equations ◽  
Controlling Parameter ◽  
Predicted Values ◽  
Soil Behaviour ◽  
Selection Of

Prediction equations for unsaturated soil property functions have become more attractive because laboratory tests of unsaturated soils are time consuming and expensive. To ensure that predicted soil property functions represent soil behaviour reasonably well, appropriate selection of the parameter that controls the performance of these prediction equations becomes imperative. Deduced from the typical desaturation characteristics of a soil, the effective degree of saturation has emerged to be the controlling parameter for unsaturated soil property functions. In this paper, soil suction is considered to become ineffective in affecting unsaturated soil property functions at and beyond the residual state. Comparisons between experimental shear strength data and predicted values obtained using the concept proposed in this study show a good agreement.

Soil Strength Reduction Method Induced by Variation of Water Content

2012 ◽  
Vol 170-173 ◽  
pp. 847-852
Author(s):  
Peng Ming Jiang ◽  
Zhong Lei Yan ◽  
Peng Li
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Reduction ◽  
Actual State ◽  
Soil Slope ◽  
Simple Method ◽  
The Common ◽  
The Stability

As the complexity of unsaturated soil theory, and it must have a long test period when we study the unsaturated soils, so the conventional design analysis software does not provide such analysis, so we can imagine that such a slope stability analysis does not accurately reflect the actual state of the slope. Based on the known soil moisture content，this paper use the soil water characteristic curve and strength theory of unsaturated soil to calculate the strength reduction parameters of soil which can calculate the stability of the soil slope when using the common calculation method. It is noticeable that this method can be extended and applied if we establish regional databases for this simple method, and these databases can improve the accuracy of the calculation of slope stability.

Capillary-based effective stress formulation for predicting shear strength of unsaturated soils

2015 ◽  
Vol 52 (12) ◽  
pp. 2067-2076 ◽  
Author(s):  
Jean-Marie Konrad ◽  
Marc Lebeau
Keyword(s):  
Shear Strength ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Adsorbed Water ◽  
Soil Strength ◽  
Liquid Films ◽  
Degree Of Saturation ◽  
Stress Parameter ◽  
Effective Stress Parameter

A number of investigations have shown that the shear strength of unsaturated soils can be defined in terms of effective stress. The difficulty in this approach lies in quantifying the effective stress parameter, or Bishop’s parameter. Although often set equal to the degree of saturation, it has recently been suggested that the effective stress parameter should be related to an effective degree of saturation, which defines the fraction of water that contributes to soil strength. A problematic element in this approach resides in differentiating the water that contributes to soil strength from that which does not contribute to soil strength. To address this difficulty, the paper uses theoretical considerations and experimental observations to partition the water retention function into capillary and adsorptive components. Given that the thin liquid films of adsorbed water should not contribute to effective stress, the effective stress parameter is solely related to the capillary component of water retention. In sample calculations, this alternative effective stress parameter provided very good agreement with experimental data of shear strength for a variety of soil types.

Sign in / Sign up

Export Citation Format

Share Document