Objectives

As specific objectives, by the end of the course students should be able to:

• Analyse stress and strain in three dimensional conditions and define pore pressure parameters
• Understand the applications of elasto-plastic models with isotropic volumetric hardening to the behaviour of soils
• Use the Cam Clay model to predict changes of stress and volume in simple shear and triaxial tests
• Predict the onset of yield, failure and ultimate critical states of soil elements subject to any stress path
• Recognise the origins of the undrained strength of clay, and estimate excess pore pressures induced by shearing
• Recognise the origins of the super-critical strength of dense sand and overconsolidated clay in terms of interlocking and dilatancy
• Assess the influence of effective stress history on lateral earth pressure
• Assess the stability of slopes
• Recognise the potential sources of brittle failure in dilatant sands and overconsolidated clay
• Diagnose the delayed failure of overconsolidated clay slopes, and suggest counter-measures
• Diagnose quick clay flowslides, and suggest counter-measures
• Understand the main available tools for geotechnical site investigation, with a focus on field testing
• Apply the theory of cavity expansion in an elastic perfectly plastic medium to the interpretation of pressuremeter test
• Apply the thoery of cavity contraction in an elastic perfectly plastic medium to the prediction of tunnel stability and convergence

Content

Whereas module 3D1 was concerned chiefly with the limiting equilibrium of plastic soil bodies and soil consolidation, 3D2 aims to address modelling of the mechanical behaviour of soils and geotechnical structures. Soils are an order of magnitude more compliant than steel or concrete, so designers have to limit the mobilisation of soil strength to keep ground strains small enough to guarantee the serviceability of adjacent structures. Furthermore, some soils are inherently brittle, and their strength can deteriorate if they are permitted to strain excessively; this can lead to unexpected catastrophic failures. In geotechnical engineering, therefore, strains are often more important than stresses.

The Cam Clay model of soil behaviour is introduced to link concepts of consolidation and shearing, to envision drained and undrained soil behaviour within a single conceptual framework, to distinguish between yielding and failure, and to contrast stress paths that lead to brittle softening with those that lead to stable hardening. These comparisons and contrasts are central to the correct characterisation of soils for geotechnical decision-making. They are the subject of the first example paper.

The module continues with the assessment of the stability of natural slopes and cuts, the characterisation of in-situ stress states as a function of the previous stress history of the site, and considers the stress paths which they will follow as a result of construction. Particular materials, stress paths, and changes in environmental conditions can lead to catastrophic failures. The key to avoiding such failures is either to improve the ductility and continuity of materials and structures, or to take the utmost care in controlling soil strains in service. This material is the subject of the second example paper.

The final part of the course addresses the fundamentals of geotechnical investigation with a focuse on field testing. The objectives, extent, frequency and layout of investigations for the geotechnical characterisation of a site are discussed and the main available geotechnical field tests, including dynamic and static penetration tests, vane shear test, and pressuremeter tests are illustrated. Radial solutions for cavity expansion and contraction in an elastic perfectly plastic medium are applied to the interpretation of pressuremeter tests in clay and bored tunnelling, respectively. This material will form the subject of the third example paper.

Topic 1: Basics - Soil Stress-strain, 3D Stresses & strains and their invariants, pore pressure parameters

Modelling in geortechnical engineering (Lecture 1) 

Modelling forms an implicit part of all engineering design but many engineers are not aware either of the fact that they are making assumptions as part of the modelling or of the nature and consequences of those assumptions. The lecture is an introduction to the course iproviding an overview of the evolution of modelling and the shift of modelling paradigms in science and engineering and in soil mechanics.

Stress/strain invariants (Lecture 2)

3D stresses and strains, Lode's coordinates, strain and strain invariants, work conjugates, pore pressure parameters, stress paths.

Topic 2: Strain hardening elastoplasticity

1D elasto-plasticity (Lecture 3)

Additive decomposition of strain, elasticity, admissible stress, yield criterion, elastic range, flow rule. Kuhn Tucker condition, consistency condition, plastic multiplier. Isotropic and kinematic hardening. Elasto-plastic stiffness.

Linear elasticity and Mohr Coulomb strength criterion (Lecture 4)

Isotropic linear elasticity. Mohr Coulomb Yield criterion with associative flow rule. predicted behaviour for drained and undrained triaxial compression and triaxial extension. Limitations and possible ways to overcome them.

Plane strain stress paths (Lecture 5)

Stress paths in the ground arising from a variety of construction processes, and relating to a range of representative locations. Use of vertical and horizontal equilibrium equations to estimate total stress paths due to simplified cases of vertical loading or horizontal unloading. Correlation with effective stress paths dictated either by undrained or drained soil conditions. Predicting the approach of soil states to limiting strength envelopes.

Topic 3: Cam-Clay

Shearing of soils: work and dissipation, yield surface and normality (Lecture 6)

Taylor’s work equation. Yield surface in effective stress space. Normality principle guarantees maximum dissipation, providing a plastic flow rule. Derivation of the Cam Clay yield surface. Compressibility and volumetric hardening.

Critical states, normal compression, and yield  (Lecture 7)

Stress dilatancy and critical state. Radial compression lines, critical state line. 3D state surface of shear stress, effective normal stress and specific volume. Drained and undrained shearing of soil at a given density, from points of normal consolidation and overconsolidation

Undrained shear strength,  predicting behaviour of geotechnical structures using using Cam-clay model (Lecture 8)

Undrained shear strength. Predicting behaviour of smooth retaining wall and embankment  on soflt clay. Staged loading. Development of stress-strain relationship of Cam clay model. Application of numerical programs for modern geotechnical analysis.

Topic 4: Slope stability - avoiding catstrophic failure

Slope stability analysis (Lectures 9 and 10)

Occurrence of slope failure in the UK and worldwide. Examples. Modes of movement: falls, topples, slides, and flows. Analysis methods to assess the stability of slopes in sands and clays. Infinite slope, effect of groundwater flow. Finite slope undrained. General Limit equilibrium methods. 

Avoiding catastrophic failure on the dry side (Lecture 11)

Selection of mechanical parameters for the design of engineered slopes. Factors promoting failure on the dry side: brittle failure for dilatant sand and overconsolidated clay. Need to design for critical state friction and worst pore water pressures. 

Delayed failure in clay slopes and catastrophic failure on the wet side (Lecture 12)

Delayed failure in clay slopes due to progressive softening on cycles of wetting/drying.  Factors promoting brittle failure on the dry side: quick clay flowslides, volumetric collapse on saturation for partly saturated slopes. 

Topic 5: Geotechnical Site Investigation

Geotechnical Site Investigation (Lecture 13)

Requirements of geotechnical site investigation. Objectives, extent, frequency and layout of investigations for the geotechnical characterisation of a site. 

In-situ testing (Lecture 14)

Procedures and interpretation of Standard Penetration Test (SPT), Cone Penetration Test (CPT), Field Vane, and pressuremeter tests

Topic 6: Elasto-plastic radial solutions

Cavity Expansion (Lecture 15)

Cavity expansion in elastic perfectly plastic medium. Application to the interpretation of pressuremeter test. Estimation of soil properties from pressuremeter tests in clay: in-situ total horizontal stress, shear modulus, undrained shear strength.

Cavity Contraction (Lecture 16)

Cavity contraction in elastic perfectly plastic medium. Applications to bored tunnelling. Estimation of support pressure required for tunnel stability. Tunnel convergence and settlements above tunnels.

This syllabus contributes to the following areas of the UK-SPEC standard:

Toggle display of UK-SPEC areas.

 
Last modified: 06/01/2022 14:39

Objectives

As specific objectives, by the end of the course students should be able to:

• Analyse stress and strain in three dimensional conditions and define pore pressure parameters
• Understand the applications of elasto-plastic models with isotropic volumetric hardening to the behaviour of soils
• Use the Cam Clay model to predict changes of stress and volume in simple shear and triaxial tests
• Predict the onset of yield, failure and ultimate critical states of soil elements subject to any stress path
• Recognise the origins of the undrained strength of clay, and estimate excess pore pressures induced by shearing
• Recognise the origins of the super-critical strength of dense sand and overconsolidated clay in terms of interlocking and dilatancy
• Assess the influence of effective stress history on lateral earth pressure
• Assess the stability of slopes
• Recognise the potential sources of brittle failure in dilatant sands and overconsolidated clay
• Diagnose the delayed failure of overconsolidated clay slopes, and suggest counter-measures
• Diagnose quick clay flowslides, and suggest counter-measures
• Compute active and passive earth pressure with different theories
• Understand the effects of water on the stability of earth retaining structures
• Recognise the main types of retaining structures and construction methods
• Design basic retining structures

Content

Whereas module 3D1 was concerned chiefly with the limiting equilibrium of plastic soil bodies and soil consolidation, 3D2 aims to address modelling of the mechanical behaviour of soils and geotechnical structures. Soils are an order of magnitude more compliant than steel or concrete, so designers have to limit the mobilisation of soil strength to keep ground strains small enough to guarantee the serviceability of adjacent structures. Furthermore, some soils are inherently brittle, and their strength can deteriorate if they are permitted to strain excessively; this can lead to unexpected catastrophic failures. In geotechnical engineering, therefore, strains are often more important than stresses.

The Cam Clay model of soil behaviour is introduced to link concepts of consolidation and shearing, to envision drained and undrained soil behaviour within a single conceptual framework, to distinguish between yielding and failure, and to contrast stress paths that lead to brittle softening with those that lead to stable hardening. These comparisons and contrasts are central to the correct characterisation of soils for geotechnical decision-making. They are the subject of the first example paper.

The module continues with the assessment of the stability of natural slopes and cuts, the characterisation of in-situ stress states as a function of the previous stress history of the site, and considers the stress paths which they will follow as a result of construction. Particular materials, stress paths, and changes in environmental conditions can lead to catastrophic failures. The key to avoiding such failures is either to improve the ductility and continuity of materials and structures, or to take the utmost care in controlling soil strains in service. This material is the subject of the second example paper.

The final part of the course addresses the fundamentals of earth pressures and earth retaining structures. This will start from a review of the main tools available for the calculation of earth pressure, including upper bound, lower bound and limit equilibrium methods, followed by consideration of the main retaining structures types and construction methods (gravity, embedded, composite walls and other support systems).  Finally the course will address the basic design of simple retaining structures.

Topic 1: Basics - Soil Stress-strain, 3D Stresses & strains and their invariants, pore pressure parameters

Modelling in geortechnical engineering (Lecture 1) 

Modelling forms an implicit part of all engineering design but many engineers are not aware either of the fact that they are making assumptions as part of the modelling or of the nature and consequences of those assumptions. The lecture is an introduction to the course iproviding an overview of the evolution of modelling and the shift of modelling paradigms in science and engineering and in soil mechanics.

Stress/strain invariants (Lecture 2)

3D stresses and strains, Lode's coordinates, strain and strain invariants, work conjugates, pore pressure parameters, stress paths.

Topic 2: Strain hardening elastoplasticity

1D elasto-plasticity (Lecture 3)

Additive decomposition of strain, elasticity, admissible stress, yield criterion, elastic range, flow rule. Kuhn Tucker condition, consistency condition, plastic multiplier. Isotropic and kinematic hardening. Elasto-plastic stiffness.

Linear elasticity and Mohr Coulomb strength criterion (Lecture 4)

Isotropic linear elasticity. Mohr Coulomb Yield criterion with associative flow rule. predicted behaviour for drained and undrained triaxial compression and triaxial extension. Limitations and possible ways to overcome them.

Plane strain stress paths (Lecture 5)

Stress paths in the ground arising from a variety of construction processes, and relating to a range of representative locations. Use of vertical and horizontal equilibrium equations to estimate total stress paths due to simplified cases of vertical loading or horizontal unloading. Correlation with effective stress paths dictated either by undrained or drained soil conditions. Predicting the approach of soil states to limiting strength envelopes.

Topic 3: Cam-Clay

Shearing of soils: work and dissipation, yield surface and normality (Lecture 6)

Taylor’s work equation. Yield surface in effective stress space. Normality principle guarantees maximum dissipation, providing a plastic flow rule. Derivation of the Cam Clay yield surface. Compressibility and volumetric hardening.

Critical states, normal compression, and yield  (Lecture 7)

Stress dilatancy and critical state. Radial compression lines, critical state line. 3D state surface of shear stress, effective normal stress and specific volume. Drained and undrained shearing of soil at a given density, from points of normal consolidation and overconsolidation

Undrained shear strength,  predicting behaviour of geotechnical structures using using Cam-clay model (Lecture 8)

Undrained shear strength. Predicting behaviour of smooth retaining wall and embankment  on soflt clay. Staged loading. Development of stress-strain relationship of Cam clay model. Application of numerical programs for modern geotechnical analysis.

Topic 4: Slope stability - avoiding catstrophic failure

Slope stability analysis (Lectures 9 and 10)

Occurrence of slope failure in the UK and worldwide. Examples. Modes of movement: falls, topples, slides, and flows. Analysis methods to assess the stability of slopes in sands and clays. Infinite slope, effect of groundwater flow. Finite slope undrained. General Limit equilibrium methods. 

Avoiding catastrophic failure on the dry side (Lecture 11)

Selection of mechanical parameters for the design of engineered slopes. Factors promoting failure on the dry side: brittle failure for dilatant sand and overconsolidated clay. Need to design for critical state friction and worst pore water pressures. 

Delayed failure in clay slopes and catastrophic failure on the wet side (Lecture 12)

Delayed failure in clay slopes due to progressive softening on cycles of wetting/drying.  Factors promoting brittle failure on the dry side: quick clay flowslides, volumetric collapse on saturation for partly saturated slopes. 

Topic 5. Geotechnical Investigation

Geotechnical Site Investigation (Lecture 13)

Requirements of geotechnical site investigation. Objectives, extent, frequency and layout of investigations for the geotechnical characterisation of a site. 

In-situ testing (Lecture 14)

Procedures and interpretation of Standard Penetration Test (SPT), Cone Penetration Test (CPT), Field Vane, and pressuremeter tests

Topic 6: Elasto-plastic radial solutions

Cavity Expansion (Lecture 15)

Cavity expansion in elastic perfectly plastic medium. Application to the interpretation of pressuremeter test. Estimation of soil properties from pressuremeter tests in clay: in-situ total horizontal stress, shear modulus, undrained shear strength.

Cavity Contraction (Lecture 16)

Cavity contraction in elastic perfectly plastic medium. Applications to bored tunnelling. Estimation of support pressure required for tunnel stability. Tunnel convergence and settlements above tunnels.

This syllabus contributes to the following areas of the UK-SPEC standard:

Toggle display of UK-SPEC areas.

 
Last modified: 01/11/2023 08:59

Objectives

As specific objectives, by the end of the course students should be able to:

• Use plastic deformation mechanisms, compatibility factors, and equilibrium factors to predict structural distortions by scaling up shear stress-strain curves
• Use the Cam Clay model to predict changes of stress and volume in simple shear and triaxial tests.
• Predict the onset of yield, failure and ultimate critical states of soil elements subject to any stress path.
• Recognise the origins of the undrained strength (“apparent cohesion”) of clay, and estimate excess pore pressures induced by shearing
• Recognise the origins of the super-critical strength (“true cohesion”) of overconsolidated soils in terms of interlocking and dilatancy
• Assess the influence of effective stress history on the current state of lateral earth pressure.
• Derive and plot stress distributions around expanding or contracting cavities.
• Analyse the pressuremeter test using elasticity and plasticity, and be able to deduce strength and stiffness parameters from a test curve.
• Analyse the stability of, and settlement due to, tunnel construction.
• Generate appropriate values of shear stiffness, or mobilised shear strength, for soils with power law stress-strain curves beyond their linear-elastic limit.
• Recognise the potential sources of brittleness in soils, and suggest appropriate stress path triaxial tests to better define the problem
• Diagnose the delayed failure of overconsolidated clay slopes, and suggest counter-measures.
• Diagnose quick clay flowslides, and suggest counter-measures.
• Assess the stability of slopes.

Content

Whereas module 3D1 was concerned chiefly with the limiting equilibrium of plastic soil bodies and soil consolidation, 3D2 aims to address ground deformations and to avoid brittle failures. Soils are an order of magnitude more compliant than steel or concrete, so designers have to limit the mobilisation of soil strength to keep ground strains small enough to guarantee the serviceability of adjacent structures. Furthermore, some soils are inherently brittle, and their strength can deteriorate if they are permitted to strain excessively; this can lead to unexpected catastrophic failures. In geotechnical engineering, therefore, strains are often more important than stresses.

The Cam Clay model of soil behaviour is introduced to link concepts of consolidation and shearing, to envision drained and undrained soil behaviour within a single conceptual framework, to distinguish between yielding and failure, and to contrast stress paths that lead to brittle softening with those that lead to stable hardening. These comparisons and contrasts are central to the correct characterisation of soils for geotechnical decision-making. They are the subject of the first examples paper.

The module continues with the characterisation of in situ stress states as a function of the previous stress history of the site, and considers the stress paths which they will follow as a result of construction. Pressuremeter testing of soils gives data of their in situ stress-strain behaviour which can also be assessed via triaxial tests on samples trimmed from high-quality cores. Such stress-strain data can be applied within plastic deformation mechanisms to the prediction of ground displacements in the design and construction of tunnels, retaining walls and foundations. These strain-related issues are addressed in the second examples paper.

Particular materials, stress paths, and changes in environmental conditions can lead to catastrophic failures. The key to avoiding such failures is either to improve the ductility and continuity of materials and structures, or to take the utmost care in controlling soil strains in service. This is the subject of the third examples paper.

Topic 1: Basics: Soil Stress-strain, 3D Stresses & strains and their invariants, Prof K Soga

Stress/strain invariants and soil behaviour (Lecture 1)

Typical stress-strain behaviour of sand and clay, Dilation, contraction and critical state, total and effective stress, 3D stresses and strains, strain and strain invariants, stress paths.

Direct shear, simple shear and triaxial test  (Lecture 2)

Different laboratory test methods to evaluate stiffness and strength of soils. Undrained and drained tests.

Topic 2: The Cam Clay model, Prof K Soga

Shearing of soils: work and dissipation, yield surface and normality (Lecture 3)

Taylor’s work equation, recast in terms of shearing resistance comprising friction and dilation angles. Yield surface in effective stress space. Normality principle guarantees maximum dissipation, providing a plastic flow rule. Derivation of the Cam Clay yield surface.

Critical states,normal compression, and yield  (Lecture 4)

A Cam Clay yield surface projected over an elastic swelling-line on a specific volume plot. Derivation of a critical state line parallel to a normal compression line; 3D state surface of shear stress, effective normal stress and specific volume.

Understanding drained and undrained shearing using Cam-clay model (Lecture 5)

Drained shearing of soil at a given density, but from points of normal consolidation and overconsolidation; different peak angles, same ultimate angle. Undrained shearing from same points; different peak undrained strengths, same ultimate strength. Remoulded undrained strength is due to friction, with effective stresses modified by excess pore pressures induced by shearing; is only a function of density.

Stress-strain relationship (Lecture 6)

Development of stress-strain relationship of Cam clay model. Application of numerical programs for modern geotechnical analysis.

Topic 3: In situ stresses, stress paths, and pressuremeter testing , Prof R J Mair

Stress history dictates in situ lateral earth pressure (Lecture 7)

Sedimentation, burial, erosion, and variations of water table. Overconsolidation ratio, definition of earth pressure coefficient and its variation with stress history. Influence of lateral extension due to an adjacent excavation.

Stress paths for retaining walls and foundations (Lecture 8)

Use of vertical and horizontal equilibrium equations to estimate total stress paths due to simplified cases of vertical loading or horizontal unloading. Correlation with effective stress paths dictated either by undrained or drained soil conditions. Predicting the approach of soil states to limiting strength envelopes.

Stress paths and triaxial tests (Lecture 9)

TaylorStress paths in the ground arising from a variety of construction processes, and relating to a range of representative locations. The capability of assessing soil response in appropriate triaxial stress path tests on representative samples recovered from the field.

The pressuremeter test (Lecture 10)

Meynard and Self-Boring Pressuremeters. Kinematics of cylindrical expansion in soil shearing at constant volume; derivation of strains. Radial equilibrium equation. If soil were linear elastic – cavity pressure versus cavity strain, shear modulus. Radial and circumferential stress changes at the cavity boundary, zero excess pore pressures.

Inferring soil stiffness and strength from a pressuremeter test (Lecture 11)

Gibson and Anderson solution for perfectly elastic-plastic soil. Cavity pressure versus logarithm of expansion ratio. Estimating undrained strength both from plastic gradient, and from extrapolated limit pressure. Alternative solution for power-law soil; Bolton and Whittle solution for unload-reload loops.

Application of pressuremeter data to tunnel design and construction (Lecture 12)

Tunnelling technology, face support, ground loss, settlement trough, lining pressure. Equivalent radial contraction of a cylindrical cavity. Estimating ground loss as a function of tunnel support. Stability of a tunnel face.

Topic 4: Avoiding catastrophic soil failures - Prof K Soga

Deterioration of overconsolidated clays – delayed failure of slopes (Lecture 13)

Example: Skempton’s London Clay slopes and LUL embankments. Analysis: cyclic mobilisation of internal friction in excess of critical state angle leading to ultimate failure. Need to design for critical state friction and worst pore water pressures. The error of relying on “true cohesion”.

Quick clay flowslides – origins and avoidance   (Lecture 14)

Example: Rissa landslide. Analysis: structure of quick clays, wetter than liquid limit, but peculiarly quasi-stable. Role of isostatic uplift, sodium ion concentration reducing due to fresh water leaching.

Slope stability analysis (Lecture 15 & 16)

Analysis methods to assess the stability of slopes in sands and clays. Infinite slope, effect of groundwater flow, embankment construction.

This syllabus contributes to the following areas of the UK-SPEC standard:

Toggle display of UK-SPEC areas.

 
Last modified: 19/01/2021 12:22

Objectives

As specific objectives, by the end of the course students should be able to:

• Use plastic deformation mechanisms, compatibility factors, and equilibrium factors to predict structural distortions by scaling up shear stress-strain curves
• Use the Cam Clay model to predict changes of stress and volume in simple shear and triaxial tests.
• Predict the onset of yield, failure and ultimate critical states of soil elements subject to any stress path.
• Recognise the origins of the undrained strength (“apparent cohesion”) of clay, and estimate excess pore pressures induced by shearing
• Recognise the origins of the super-critical strength (“true cohesion”) of overconsolidated soils in terms of interlocking and dilatancy
• Assess the influence of effective stress history on the current state of lateral earth pressure.
• Derive and plot stress distributions around expanding or contracting cavities.
• Analyse the pressuremeter test using elasticity and plasticity, and be able to deduce strength and stiffness parameters from a test curve.
• Analyse the stability of, and settlement due to, tunnel construction.
• Generate appropriate values of shear stiffness, or mobilised shear strength, for soils with power law stress-strain curves beyond their linear-elastic limit.
• Recognise the potential sources of brittleness in soils, and suggest appropriate stress path triaxial tests to better define the problem
• Diagnose the delayed failure of overconsolidated clay slopes, and suggest counter-measures.
• Diagnose quick clay flowslides, and suggest counter-measures.
• Assess the stability of slopes.

Content

Whereas module 3D1 was concerned chiefly with the limiting equilibrium of plastic soil bodies and soil consolidation, 3D2 aims to address ground deformations and to avoid brittle failures. Soils are an order of magnitude more compliant than steel or concrete, so designers have to limit the mobilisation of soil strength to keep ground strains small enough to guarantee the serviceability of adjacent structures. Furthermore, some soils are inherently brittle, and their strength can deteriorate if they are permitted to strain excessively; this can lead to unexpected catastrophic failures. In geotechnical engineering, therefore, strains are often more important than stresses.

The Cam Clay model of soil behaviour is introduced to link concepts of consolidation and shearing, to envision drained and undrained soil behaviour within a single conceptual framework, to distinguish between yielding and failure, and to contrast stress paths that lead to brittle softening with those that lead to stable hardening. These comparisons and contrasts are central to the correct characterisation of soils for geotechnical decision-making. They are the subject of the first examples paper.

The module continues with the characterisation of in situ stress states as a function of the previous stress history of the site, and considers the stress paths which they will follow as a result of construction. Pressuremeter testing of soils gives data of their in situ stress-strain behaviour which can also be assessed via triaxial tests on samples trimmed from high-quality cores. Such stress-strain data can be applied within plastic deformation mechanisms to the prediction of ground displacements in the design and construction of tunnels, retaining walls and foundations. These strain-related issues are addressed in the second examples paper.

Particular materials, stress paths, and changes in environmental conditions can lead to catastrophic failures. The key to avoiding such failures is either to improve the ductility and continuity of materials and structures, or to take the utmost care in controlling soil strains in service. This is the subject of the third examples paper.

Topic 1: Basics: Soil Stress-strain, 3D Stresses & strains and their invariants, Prof K Soga

Stress/strain invariants and soil behaviour (Lecture 1)

Typical stress-strain behaviour of sand and clay, Dilation, contraction and critical state, total and effective stress, 3D stresses and strains, strain and strain invariants, stress paths.

Direct shear, simple shear and triaxial test  (Lecture 2)

Different laboratory test methods to evaluate stiffness and strength of soils. Undrained and drained tests.

Topic 2: The Cam Clay model, Prof K Soga

Shearing of soils: work and dissipation, yield surface and normality (Lecture 3)

Taylor’s work equation, recast in terms of shearing resistance comprising friction and dilation angles. Yield surface in effective stress space. Normality principle guarantees maximum dissipation, providing a plastic flow rule. Derivation of the Cam Clay yield surface.

Critical states,normal compression, and yield  (Lecture 4)

A Cam Clay yield surface projected over an elastic swelling-line on a specific volume plot. Derivation of a critical state line parallel to a normal compression line; 3D state surface of shear stress, effective normal stress and specific volume.

Understanding drained and undrained shearing using Cam-clay model (Lecture 5)

Drained shearing of soil at a given density, but from points of normal consolidation and overconsolidation; different peak angles, same ultimate angle. Undrained shearing from same points; different peak undrained strengths, same ultimate strength. Remoulded undrained strength is due to friction, with effective stresses modified by excess pore pressures induced by shearing; is only a function of density.

Stress-strain relationship (Lecture 6)

Development of stress-strain relationship of Cam clay model. Application of numerical programs for modern geotechnical analysis.

Topic 3: In situ stresses, stress paths, and pressuremeter testing , Prof R J Mair

Stress history dictates in situ lateral earth pressure (Lecture 7)

Sedimentation, burial, erosion, and variations of water table. Overconsolidation ratio, definition of earth pressure coefficient and its variation with stress history. Influence of lateral extension due to an adjacent excavation.

Stress paths for retaining walls and foundations (Lecture 8)

Use of vertical and horizontal equilibrium equations to estimate total stress paths due to simplified cases of vertical loading or horizontal unloading. Correlation with effective stress paths dictated either by undrained or drained soil conditions. Predicting the approach of soil states to limiting strength envelopes.

Stress paths and triaxial tests (Lecture 9)

TaylorStress paths in the ground arising from a variety of construction processes, and relating to a range of representative locations. The capability of assessing soil response in appropriate triaxial stress path tests on representative samples recovered from the field.

The pressuremeter test (Lecture 10)

Meynard and Self-Boring Pressuremeters. Kinematics of cylindrical expansion in soil shearing at constant volume; derivation of strains. Radial equilibrium equation. If soil were linear elastic – cavity pressure versus cavity strain, shear modulus. Radial and circumferential stress changes at the cavity boundary, zero excess pore pressures.

Inferring soil stiffness and strength from a pressuremeter test (Lecture 11)

Gibson and Anderson solution for perfectly elastic-plastic soil. Cavity pressure versus logarithm of expansion ratio. Estimating undrained strength both from plastic gradient, and from extrapolated limit pressure. Alternative solution for power-law soil; Bolton and Whittle solution for unload-reload loops.

Application of pressuremeter data to tunnel design and construction (Lecture 12)

Tunnelling technology, face support, ground loss, settlement trough, lining pressure. Equivalent radial contraction of a cylindrical cavity. Estimating ground loss as a function of tunnel support. Stability of a tunnel face.

Topic 4: Avoiding catastrophic soil failures - Prof K Soga

Deterioration of overconsolidated clays – delayed failure of slopes (Lecture 13)

Example: Skempton’s London Clay slopes and LUL embankments. Analysis: cyclic mobilisation of internal friction in excess of critical state angle leading to ultimate failure. Need to design for critical state friction and worst pore water pressures. The error of relying on “true cohesion”.

Quick clay flowslides – origins and avoidance   (Lecture 14)

Example: Rissa landslide. Analysis: structure of quick clays, wetter than liquid limit, but peculiarly quasi-stable. Role of isostatic uplift, sodium ion concentration reducing due to fresh water leaching.

Slope stability analysis (Lecture 15 & 16)

Analysis methods to assess the stability of slopes in sands and clays. Infinite slope, effect of groundwater flow, embankment construction.

This syllabus contributes to the following areas of the UK-SPEC standard:

Toggle display of UK-SPEC areas.

 
Last modified: 13/09/2018 14:39