scholarly journals Strength Theory Model of Unsaturated Soils with Suction Stress Concept

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Pan Chen ◽  
Changfu Wei ◽  
Jie Liu ◽  
Tiantian Ma
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Theory Model ◽  
Strength Analysis ◽  
New Model ◽  
Suction Stress ◽  
Strength Change ◽  
Stability Of Slopes ◽  
Moisture State ◽  
The Stability

A theoretical model is developed for describing the strength property of unsaturated soils. The model is able to predict conveniently the strength changes of unsaturated soils undergoing repeated changes of water content. Suction stress is adopted in the new model in order to get the sound form of effective stress for unsaturated soils. The shear strength of unsaturated soils is dependent on its soil-moisture state based on the results of shear experiments. Hence, the parameters of this model are related tightly to hydraulic properties of unsaturated soils and the strength parameters of saturated soils. The predictive curves by the new model are coincident with experimental data that underwent single drying and drying/wetting cycle paths. Hence, hysteretic effect in the strength analysis is necessary to be considered to predict the change of shear strength of unsaturated soils that underwent drying/wetting cycles. Once the new model is used to predict the change of shear strength, lots of time could be saved due to avoiding heavy and complicated strength tests of unsaturated soils. Especially, the model can be suitable to evaluate the shear strength change of unsaturated soils and the stability of slopes experienced the drying/wetting cycles.

scholarly journals Safety Factor of Unsaturated Soil Slopes considering the Intermediate Principal Stress Effect and Different Profiles of Matric Suction

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhaoxin Li ◽  
Changguang Zhang ◽  
Jingyuan Zhao ◽  
Qing Yan
Keyword(s):  
Shear Strength ◽  
Principal Stress ◽  
Safety Factor ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Matric Suction ◽  
Intermediate Principal Stress ◽  
Stress Effect ◽  
Soil Slopes ◽  
The Stability

Profiles of matric suction are critical for assessing the stability of unsaturated soil slopes, and the strength of unsaturated soils is affected by the intermediate principal stress. This study presents a theoretical formulation of safety factor for infinite unsaturated soil slopes under four different profiles of matric suction using the limit equilibrium method. The unified shear strength equation under plane strain conditions is adopted to capture the effect of intermediate principal stress on the strength of unsaturated soils. The proposed formulation of safety factor is found to have good comparability and broad applicability. The validity of the proposed formulation is demonstrated by comparing its predictions with the results of the extended shear strength method and the finite element method available in the literature. Parametric studies show that the effect of intermediate principal stress on the stability of unsaturated soil slopes is significant; the difference of safety factor among four suction profiles is pronounced, and the safety factor is highest for a linear suction profile. In addition, the safety factor changes with the infiltration depth in two stages, decreases with the slope angle, and increases with effective strength parameters. The results of this study are capable of providing beneficial guidance for optimization designs and disaster preventions of unsaturated soil slopes.

scholarly journals Parametric evaluation of shear strength parameters on the stability of cut slope: a case study from Mahabaleshwar road section, India

2016 ◽  
Vol 51 ◽  
pp. 73-76
Author(s):  
Suman Panthee
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Shear Strength ◽  
Internal Friction ◽  
Factor Of Safety ◽  
Slope Failure ◽  
Cut Slope ◽  
Stability Of Slopes ◽  
Proportional Relation ◽  
The Stability

Stability of rock cut slopes depends upon the type of material, discontinuity attributes and geometry present in any location. Although, gravity remains the constant important factor in dictating the slope failure but other parameters like shear strength and available shear stress along the slope also decides the stability of the slopes to great extent. The strength of the material comes from the internal bonding between the mineral grains, contact between the particles and the ability of the material to respond to the stress conditions. Variation of these material attributes fluctuate the cohesion and angle of internal friction that constitutes the most important properties in defining the strength of any material. Rock resists shear stress by these two internal mechanisms. Numerical simulation by Finite Element Method technique is attempted for assessing the stability cut slope. An attempt has been made in this study to document the behavior of strength of the material in terms of stability of slopes by parametric study of cohesion and internal friction. This study carried to understand how the factor of safety changes with reference to change in cut slope height, cohesion and internal friction of the discontinuities that attributes the shear strength of discontinuities. The study is based on Finite Element Modeling (FEM). From the study it is found that factor of safety has strongly proportional relation with cohesion and internal friction but shown inversely proportional relation with height of cut slope.

Strength of tree roots and landslides on Prince of Wales Island, Alaska

1979 ◽  
Vol 16 (1) ◽  
pp. 19-33 ◽  
Author(s):  
Tien H. Wu ◽  
William P. McKinnell III ◽  
Douglas N. Swanston
Keyword(s):  
Shear Strength ◽  
Root System ◽  
Forest Cover ◽  
Safety Factors ◽  
In Situ Tests ◽  
Tree Roots ◽  
Stability Of Slopes ◽  
Before And After ◽  
The Stability

The stability of slopes before and after removal of forest cover was investigated. Porewater pressures and shear strengths were measured and the soil properties were determined by laboratory and in situ tests. A model of the soil–root system was developed to evaluate the contribution of tree roots to shear strength. The computed safety factors are in general agreement with observed behaviors of the slopes. Decay of tree roots subsequent to logging was found to cause a reduction in the shear strength of the soil–root system.

Bearing capacity under cyclic loading — offshore, along the coast, and on land. The 21st Bjerrum Lecture presented in Oslo, 23 November 2007This paper represents the written version of the 21st Bjerrum Lecture. While it has been edited for the present publication, it retains the general structure of the original lecture, which was intended for a general geotechnical audience. The Bjerrum Lecture is presented in Oslo in alternate years by the Norwegian Geotechnical Society with the support of the Bjerrum Memorial Fund (Laurits Bjerrums Minnefond).

2009 ◽  
Vol 46 (5) ◽  
pp. 513-535 ◽  
Author(s):  
Knut H. Andersen
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
General Structure ◽  
Stress Path ◽  
Shear Stresses ◽  
Foundation Design ◽  
Cyclic Shear ◽  
Stability Of Slopes ◽  
Practical Design ◽  
The Stability

Cyclic loading can be important for the foundation design of structures, both offshore, along the coast, and on land, and for the stability of slopes. This is illustrated by several examples. The paper discusses how soil behaves under cyclic loading, both for structures and for slopes, and shows that the cyclic shear strength and the failure mode under cyclic loading depend strongly on the stress path and the combination of average and cyclic shear stresses. Diagrams with the cyclic shear strength of clay, sand, and silt that can be used in practical design are presented. Comparisons between calculations and model tests indicate that foundation capacity under cyclic loading can be determined on the basis of cyclic shear strength determined in laboratory tests.

The effect of air flow on the shear strength of soil in compressed-air tunneling

2001 ◽  
Vol 38 (6) ◽  
pp. 1187-1200 ◽  
Author(s):  
A A Javadi ◽  
C PM Snee
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Air Flow ◽  
Three Dimensional ◽  
Element Model ◽  
Air Pressure ◽  
Compressed Air ◽  
Internal Support ◽  
Triaxial Cell ◽  
The Stability

This paper presents a method for studying the variation in shear strength of soil due to the air flow in compressed-air tunneling. The method is based on application of the shear strength theories of unsaturated soils in conjunction with a finite element model, developed by the authors, for analyzing the flow of the air through soils. The formulation of the problem, the numerical model, the design and modification of the triaxial cell and the laboratory testing program, and the results are presented and studied with particular reference to compressed-air tunneling. The results are presented and interpreted using the concepts and theory of shear strength for unsaturated soils. The results of the tests indicate the way in which the air pressure increases the stability of the ground, besides being an internal support, prior to the installation of the temporary or permanent lining. From the results of the tests, a three-dimensional failure envelope was plotted that can be used to predict the change in shear strength of the soil due to a change in the air pressure, in compressed-air tunneling. This information can be used to assess the risk of tunnel collapse and blow out. It also improves the current understanding of the interaction between the compressed-air tunneling method and the ground.Key words: compressed-air tunneling, air flow, unsaturated soils, shear strength.

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.

Application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure

2010 ◽  
Vol 47 (9) ◽  
pp. 955-970 ◽  
Author(s):  
Byeong-Su Kim ◽  
Satoru Shibuya ◽  
Seong-Wan Park ◽  
Shoji Kato
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Confining Pressure ◽  
Direct Shear ◽  
Shear Testing ◽  
Soil Water Retention ◽  
Overburden Pressure ◽  
Suction Stress ◽  
Saturated State ◽  
Direct Shear Testing

The primary objective of this study is to evaluate effects of suction on shear strength of unsaturated soils under low confining pressure and to examine the relationships between suction, shear strength behavior, and volumetric deformation using newly developed direct shear testing equipment for compacted weathered granite soils. The soil-water retention curves (SWRCs) of unsaturated soils were obtained under various overburden pressures. To analyze test results from the direct shear test under unsaturated conditions, a new method, suction stress–SWRC method (SSM), is proposed to determine the suction value for each overburden pressure and the suction stresses. As a result, it has been found that the stress states at the peak shear strength point are on the same failure line for the saturated state when the suction stress is treated as a component of confining pressure. The relationship between stress ratio and dilatancy for the saturated state can be extended to the unsaturated state. It is also noted that the estimated unsaturated shear strengths using the SSM agree well with the measured values from laboratory testing.

scholarly journals The mechanics of landslides in Leda clay

1970 ◽  
Vol 7 (3) ◽  
pp. 285-296 ◽  
Author(s):  
W. J. Eden ◽  
R. J. Mitchell
Keyword(s):  
Shear Strength ◽  
Field Observations ◽  
Normal Stresses ◽  
Stress Range ◽  
Stability Of Slopes ◽  
Shearing Resistance ◽  
Mode Of Failure ◽  
Leda Clay ◽  
The Stability ◽  
Drained Shear Strength

An appraisal of the drained shear strength of Leda clay under low effective normal stresses has resulted in a new appreciation of its behavior in this stress range which can be applied to consideration of the stability of slopes. Closely spaced planes of weakness existing in the apparently intact clay give rise to dilatant behavior and predominantly frictional shearing resistance. This mode of failure is consistent with field observations that have been compiled from numerous landslides; three of these landslides are analyzed in this paper.

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