Modified state-surface approach to the study of unsaturated soil behavior. Part I: Basic concept

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.

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Modified state-surface approach to the study of unsaturated soil behavior. Part II: General formulation

Canadian Geotechnical Journal ◽

10.1139/t08-137 ◽

2009 ◽

Vol 46 (5) ◽

pp. 553-570 ◽

Cited By ~ 34

Author(s):

Xiong Zhang ◽

Robert L. Lytton

Keyword(s):

Unsaturated Soil ◽

Material Properties ◽

Stress Path ◽

Companion Paper ◽

Soil Behavior ◽

Unified Framework ◽

Collapsible Soil ◽

Surface Approach ◽

As Stress ◽

A Minor

In the previous companion paper, a modified state-surface approach was proposed to algebraically represent unsaturated soil behavior under isotropic stress conditions. The present paper proposes a general theoretic formulation for the modified state-surface approach based on the theory proposed by Fredlund and co-workers. The signs and physical meanings of the material properties, the shapes of the loading–collapse (LC) and suction increase (SI) yield curves, and the mechanisms used in the Barcelona basic model (BBM) to model unsaturated soil behavior are discussed. Some other problems, such as stress-path independency and its implication on material properties, as well as coupling effects between the LC and SI curves, are also discussed. Based on analysis, it was found that with a minor modification, the modified state-surface approach can be used to study both unsaturated expansive and collapsible soil behavior in a unified framework.

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Research on the small strain stiffness behavior of soft clay under complex stress path

10.1109/ichceswidr54323.2021.9656469 ◽

2021 ◽

Author(s):

Kaiping Xu

Keyword(s):

Soft Clay ◽

Stress Path ◽

Small Strain ◽

Complex Stress ◽

Small Strain Stiffness ◽

Complex Stress Path

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The Studies of Rock Damage Softening Statistical Constitutive Model under True Triaxial Stress State

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.580-583.312 ◽

2014 ◽

Vol 580-583 ◽

pp. 312-315

Author(s):

Hui Mei Zhang ◽

Xiang Miao Xie ◽

Geng She Yang

Keyword(s):

Constitutive Model ◽

Strain Curve ◽

Stress Path ◽

Complex Stress ◽

Model Parameters ◽

Stress Strain ◽

Deformation And Failure ◽

True Triaxial ◽

Complex Stress Path ◽

The Impact

From the feature of rock micro-unit failure obeys Poisson random distribution, the damage softening statistical constitutive of was established under true triaxial confinement based on D-P criterion, so the impact of the intermediate principal stress on rock deformation and failure was considered in theory, and the actual engineering rock complex stress path evolution was reflected more realistically. Furthermore, according to the geometrical conditions of stress-strain relationship, the theoretical relationship between constitutive model parameters and the stress-strain curve characteristic parameters during the process of rock softening and deforming, which enhance the adaptability of the model. Finally, the rationality of the model verified by the measured data.

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Unsaturated soils in the context of tropical soils

Soils and Rocks ◽

10.28927/sr.2021.068121 ◽

2021 ◽

Vol 44 (3) ◽

pp. 1-25

Author(s):

José Camapum de Carvalho ◽

Gilson Gitirana

Keyword(s):

Unsaturated Soil ◽

Unsaturated Soils ◽

Structural Characteristics ◽

Soil Formation ◽

Soil Classification ◽

Tropical Soils ◽

Engineering Practice ◽

Soil Behavior ◽

Specific Behavior ◽

Engineering Problems

The practice of geotechnical engineering in tropical climate regions must consider the use of unsaturated soil concepts. However, these concepts must also take into account the specific behavior traits of tropical soils, particularly those related to soil aggregation, pore structure, and mineralogy. This paper will initially present considerations on the typical properties of unsaturated tropical soils as well as fundamental concepts. Throughout the article, several engineering problems will be presented alongside reflections on the complex interaction between the numerous variables involved in the modeling and engineering practice of tropical unsaturated soil behavior. The paper addresses issues related to soil formation, chemical and mineral composition, physical properties, tropical soil classification, and structural characteristics of soils. Issues related to compaction and the influence of weathering, geomorphology and bioengineering are also addressed.

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Numerical and Experimental Analysis of Horizontal Stress Changes and Soil Collapse During Chemical Dissolution in a Modified Oedometer Cell

Soils and Rocks ◽

10.28927/sr.391019 ◽

2016 ◽

pp. 19-27

Author(s):

Cecilia Lins ◽

Nayra Silva ◽

Leonardo Guimarães ◽

Analice Lima ◽

Igor Gomes

Keyword(s):

Unsaturated Soils ◽

Horizontal Stress ◽

Sample Volume ◽

General Purpose ◽

Dissolution Process ◽

Solid Matrix ◽

Soil Behavior ◽

Mineral Concentration ◽

Basic Model ◽

Stress Changes

The purpose of this paper is to investigate the horizontal stress evolution and soil collapse during the cement dissolution process using a combination of experimental and numerical methods. The experimental procedure was carried out using a modified oedometer cell with horizontal stress measurements and synthetic samples in order to simulate simultaneous cement dissolution, stress changes and sample deformation. The samples were loaded at a constant vertical stress and exposed to a reactive fluid which dissolved the cementation of the artificial soil. During the dissolution process, sample volume decreased and horizontal stress changes were observed. Initially the horizontal stress decreased due to grain mass loss and then increased due to solid matrix rearrangement. Numerical simulation of these coupled chemical and mechanical processes was performed using a general purpose finite element code capable of performing numerical analysis of engineering problems. The constitutive model adopted to reproduce the soil behavior is an extension of the Barcelona Basic Model for unsaturated soils including the cement mineral concentration as state variable. Some new features were incorporated to the original elasto-plastic model in order to represent the results observed in the experiments. In this paper a good agreement between experimental and numerical results was achieved.

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Investigating the Effect of Geocell Changes on Slope Stability in Unsaturated Soil

Tehnički glasnik ◽

10.31803/tg-20190606115822 ◽

2020 ◽

Vol 14 (1) ◽

pp. 66-75

Author(s):

Behnam Mehdipour ◽

Hamid Hashemolhosseini ◽

Bahram Nadi ◽

Masoud Mirmohamadsadeghi

Keyword(s):

Slope Stability ◽

Unsaturated Soil ◽

Unsaturated Soils ◽

Bending Strength ◽

Load Capacity ◽

Three Dimensional ◽

Bending Moment ◽

Soil Conditions ◽

Vertical Side ◽

Basic Model

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell acts like a beam in the soil due to the geocell having a height (three-dimensional). Due to its flexural properties, it has moment of inertia as well as bending strength, which reduces the displacement and increases the safety factor of the slope. Taking into consideration unsaturated conditions of soil contributes a lot to making results close to reality. One of the well-known models among elastoplastic models for modeling unsaturated soils is Barcelona Basic Model, which has been added to the FLAC2D software by codification. Changes in thickness, length and number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell layer, the joint strength, the mobilized tensile strength, and the bending moment are increased. At u/H = 0.2, an increase in the bending momentum of about 20% occurs with increasing geocell thickness. In u/H = 1, the increase in bending momentum is 10.4%. In addition, by increasing the thickness of the geocell, the Value of moment of the inertia increases and, as a result, the amount of geocell reinforcement bending moment increases.

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Modified state-surface approach to the study of unsaturated soil behavior. Part III: Modeling of coupled hydromechanical effect

Canadian Geotechnical Journal ◽

10.1139/t11-089 ◽

2012 ◽

Vol 49 (1) ◽

pp. 98-120 ◽

Cited By ~ 12

Author(s):

Xiong Zhang ◽

Robert L. Lytton

Keyword(s):

Unsaturated Soils ◽

Coupling Effect ◽

Degree Of Saturation ◽

Compression Tests ◽

Soil Behavior ◽

Volume Changes ◽

Surface Approach ◽

Soil Skeleton ◽

Hydromechanical Behavior ◽

Undrained Conditions

A modified state-surface approach (MSSA) was proposed in the authors’ previous study to investigate volume change of the soil skeleton for unsaturated soils. This paper discussed the coupling effect between volume changes of soil skeleton, water phase, and air phase for unsaturated soils based on the proposed MSSA and experimental results presented by other researchers. The MSSA was further extended to study the coupled hydromechanical behavior for unsaturated soils. Besides void ratio constitutive surface, conventional unique water content and degree of saturation constitutive surfaces were also divided into elastic and plastic regions by loading–collapse (LC) yield curves and simultaneously used to describe the coupled hydromechanical behavior for unsaturated soils. A general theoretic formulation was derived for the simultaneous use of the MSSA under isotropic conditions. Based on the derived formulation, existing elastoplastic models were reviewed, and compatibility and consistency in modeling the mechanical and hydraulic behavior of unsaturated soils were discussed. Afterwards, the results of a number of suction-controlled laboratory isotropic compression tests at different suctions were used to demonstrate the ability of the proposed approach to reproduce the observed soil behavior quantitatively and soil behavior under undrained conditions qualitatively.

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Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results

Canadian Geotechnical Journal ◽

10.1139/t98-093 ◽

1999 ◽

Vol 36 (1) ◽

pp. 1-12 ◽

Cited By ~ 39

Author(s):

C Rampino ◽

C Mancuso ◽

F Vinale

Keyword(s):

Unsaturated Soil ◽

Unsaturated Soils ◽

Soil Mechanics ◽

Stress Path ◽

Matric Suction ◽

Silty Sand ◽

Compression Tests ◽

Water Drainage ◽

Triaxial Cell ◽

Unsaturated Soil Mechanics

This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav - ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction.

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