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Instabilities in sands

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    Instabilities in sands
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    The purpose of this dissertation is to contribute to the detection of the onset of geomechanical instabilities in sands under dry/drained and saturated/undrained conditions. ln order to accomplish this objective, a framework for detecting instabilities based on either a mathematical concept (i.e., loss of uniqueness - bifurcation) or physical one (i.e., Hill 's instability) is generated to derived criteria applicable to the most common instabilities: localized drained instability in dense sands (shear bands), diffuse undrained instability in loose sands (Iiquefaction) and diffuse drained instability in loose and dense sands (debris flow). Each one of these three instabilities is studied independently. The criteria are compared against experimental results available in the literature, and reasonable agreement is achieved. From a practical perspective, the contributions of this work expand the repertoire of potential instabilities that have been reported in case studies of puzzling slope instability failures under drained and undrained conditions.

    Atributos LU

    TítuloInstabilities in sands
    AutorAlfonso Mariano Ramos Cañón
    Tabla de ContenidoIntroduction

    1.1. The problem
    1.2. Aim
    1.3. Outline

    2. Theoretical Framework of Instabilities in Sands
    2.1. Second-Order Work
    2.1.1. First and Second Law of Thermodynamics
    2.1.2. Total Energy and Helmholtz Free Energy
    2.1.3. Instability Criterion for Symmetric Stiffness Matrix
    2.1.4. Instability Criterion for Nonsymmetric Stiffness
    2.1.5. Second-Order Work in an Undrained Triaxial Test

    2.2. Loss of Uniqueness - Bifurcation

    2.3. Shear Bands - Bifurcation
    2.3.1. Compatibility and equilibrium conditions

    3. Constitutive Models 35

    3.1. Von Wolffersdorff Hypoplastic Constitutive Model
    3.2. Manzari - Dafalias Elastoplastic Constitutive Model
    3.2.1. Critical State Line
    3.2.2. Elasticity
    3.2.3. Yield Function
    3.2.4. Plastic Potential
    3.2.5. Evolution Laws

    4. Strain Localization Based on the Bifurcation Theory: An Application for use with the Hypoplastic Constitutive Model

    4.1. Aspects Affecting Shear Bands in Finite Element
    4.1.1. Plane Strain Biaxial Test
    4.1.2. Biaxial Simulations using FEM
    4.1.3. Aspects of the Shear Band studied
    4.1.4. Discussion
    4.1.5. Concluding Remarks

    4.2. Bifurcation Analysis under Plane Strain Conditions

    4.3. Bifurcation Analysis for a General Stress Path
    4.3.1. Numerical Results in Element Test
    4.3.2. Concluding Remarks

    5. Diffuse Instability in Sand under Undrained Loading Conditions - Liquefaction

    5.1. Definitions of Liquefaction
    5.1.1. Cyclic Mobility
    5.1.2. Flow Liquefaction

    5.2. Flow Liquefaction Criterion

    5.3. Applicability of Criterion for Detecting the Onset of Flow Liquefaction
    5.3.1. Monotonic Loading Conditions
    5.3.2. Cyclic Loading Conditions

    5.4. Predictions of Flow Liquefaction
    5.4.1. Experiments by Verdugo and Ishihara (1996)
    5.4.2. Experiments by Yamamuro and Covert (2001)
    5.4.3. Experiments by Qadimi and Coop (2007)
    5.4.4. Experiments by Pradahn (1989)
    5.4.5. Concluding Remarks

    5.5. Numerical Analysis of the Influence of Picnotropy, Barotropy and Anisotropy of Initial Stresses on the Onset of Flow Liquefaction under Static Loading Conditions
    5.5.1. Introduction
    5.5.2. Validation of the Criterion for Detecting Static Liquefaction under Anisotropic Initial
    Conditions of Stress
    5.5.3. Numerical Simulations
    5.5.4. Concluding Remarks

    6. Diffuse Instability in Sand Under Drained Loading Conditions

    6.1. Introduction
    6.2. Drained Instability Criterion

    6.3. Numerical Predictions
    6.3.1. Instability Predictions in Dilative Sand
    6.3.2. Instability Predictions of Contractive Sand

    6.4. Discussion
    6.5. Concluding Remarks

    7. Conclusions

    7.1. Summary
    7.2. Recommendations for Further Study

    Appendix A. Loss of Uniqueness under Mixed Controlled Test
    A.1. Loss of Uniqueness on Stress Controlled Test
    A.2. Loss of Uniqueness in Strain Controlled Test
    A.3. Test under Mixed Stress and Strain Control
    A.4. Shear Band Analysis Based on Nov Concept

    Appendix B. Integration of Hypoplastic Constitutive Model 181

    Appendix C. Integration of the Manzari Dafalias Constitutive
    C.1. Midpoint Rule Algorithm
    C.2. Back Euler Algorithm. Implicit Integration
    C.3. Analytical Derivatives for the Implicit Algorithm

    Año de Edición2010
    Núm. Páginas225
    Peso (Físico)400
    Tamaño (Físico)17 x 24 cm

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