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  • INTRODUCTION OF SOIL MECHANICS
    • GEOTECHNICAL LESSONS FROM FAILURES
    • BASIC GEOLOGY
    • INTRODUCTION OF SOILS INVESTIGATION
    • PHASE RELATIONSHIPS
    • Importance of soil compaction
    • HEAD AND PRESSURE VARIATION IN A FLUID AT REST
    • GEOLOGICAL CHARACTERISTICS AND PARTICLE SIZES OF SOILS
    • Composition of the Earth’s Crust
    • PHASES OF A SOILS INVESTIGATION
    • PHYSICAL STATES AND INDEX PROPERTIES OF FINE-GRAINED SOILS
    • INTERPRETATION OF PROCTOR TEST RESULTS
    • DARCY’S LAW
    • COMPOSITION OF SOILS
    • SOILS EXPLORATION PROGRAM
    • DETERMINATION OF THE LIQUID, PLASTIC, AND SHRINKAGE LIMITS
    • SOIL CLASSIFICATION SCHEMES
    • FIELD COMPACTION
    • FLOW PARALLEL TO SOIL LAYERS
    • Surface Forces and Adsorbed Water
    • Soil Identifi cation in the Field
    • DETERMINATION OF THE HYDRAULIC CONDUCTIVITY
    • DETERMINATION OF PARTICLE SIZE OF SOILS
    • Soil Sampling
    • Falling-Head Test
    • Particle Size of Fine-Grained Soils
    • Groundwater Conditions
    • Pumping Test to Determine the Hydraulic Conductivity
    • COMPARISON OF COARSE-GRAINED AND FINE-GRAINED SOILS
    • Types of In Situ or Field Tests
    • GROUNDWATER LOWERING BY WELLPOINTS

  • SOIL WATER AND WATER FLOW
    • STRESSES AND STRAINS
    • STRESS AND STRAIN INVARIANTS
    • IDEALIZED STRESS–STRAIN RESPONSE AND YIELDING
    • Hooke’s Law Using Stress and Strain Invariants
    • PLANE STRAIN AND AXIAL SYMMETRIC CONDITIONS
    • STRESS PATHS
    • Axisymmetric Condition
    • Plotting Stress Paths Using Two-Dimensional Stress Parameters
    • ANISOTROPIC, ELASTIC STATES
    • Mohr’s Circle for Stress States
    • Mohr’s Circle for Strain States
    • The Principle of Effective Stress
    • Effective Stresses Due to Geostatic Stress Fields
    • Effects of Capillarity
    • Effects of Seepage
    • LATERAL EARTH PRESSURE AT REST
    • STRESSES IN SOIL FROM SURFACE LOADS
    • Strip Load
    • Uniformly Loaded Rectangular Area
    • Vertical Stress Below Arbitrarily Shaped Areas

  • STRESS DISTRIBUTIONCOMPRESSIBILITY AND SETTLEMENT
    • BASIC CONCEPTS
    • TYPICAL RESPONSE OF SOILS TO SHEARING FORCES
    • BASIC CONCEPTS
    • Consolidation Under a Constant Load—Primary Consolidation
    • Effects of Increasing the Normal Effective Stress
    • Soil Yielding
    • Void Ratio and Settlement Changes Under a Constant Load
    • Effects of Soil Tension
    • Primary Consolidation Parameters
    • Coulomb’s Failure Criterion
    • CALCULATION OF PRIMARY CONSOLIDATION SETTLEMENT
    • Taylor’s Failure Criterion
    • Procedure to Calculate Primary Consolidation Settlement
    • Mohr–Coulomb Failure Criterion
    • ONE-DIMENSIONAL CONSOLIDATION THEORY
    • PRACTICAL IMPLICATIONS OF THE FAILURE CRITERIA
    • Solution of Governing Consolidation Equation Using Fourier Series
    • INTERPRETATION OF THE SHEAR STRENGTH OF SOILS
    • Finite Difference Solution of the Governing Consolidation Equation
    • LABORATORY TESTS TO DETERMINE SHEAR STRENGTH PARAMETERS
    • SECONDARY COMPRESSION SETTLEMENT
    • Conventional Triaxial Apparatus
    • Oedometer Test
    • Unconfi ned Compression (UC) Test
    • Determination of the Coeffi cient of Consolidation
    • Consolidated Undrained (CU) Compression Test
    • Determination of the Past Maximum Vertical Effective Stress
    • POREWATER PRESSURE UNDER AXISYMMETRIC UNDRAINED LOADING
    • PRECONSOLIDATION OF SOILS USING WICK DRAINS
    • OTHER LABORATORY DEVICES TO MEASURE SHEAR STRENGTH
    • Hollow-Cylinder Apparatus
    • FIELD TESTS

  • SHEAR STRENGTH
    • ALLOWABLE STRESS AND LOAD AND RESISTANCE FACTOR DESIGN
    • COLLAPSE LOAD USING THE LIMIT EQUILIBRIUM METHOD
    • Prediction of the Behavior of Coarse-Grained Soils Using CSM
    • BEARING CAPACITY EQUATIONS
    • ELEMENTS OF THE CRITICAL STATE MODEL
    • MAT FOUNDATIONS
    • FAILURE STRESSES FROM THE CRITICAL STATE MODEL
    • BEARING CAPACITY OF LAYERED SOILS
    • Undrained Triaxial Test
    • SETTLEMENT CALCULATIONS
    • MODIFICATIONS OF CSM AND THEIR PRACTICAL IMPLICATIONS
    • Primary Consolidation Settlement
    • RELATIONSHIPS FROM CSM THAT ARE OF PRACTICAL SIGNIFICANCE
    • DETERMINATION OF BEARING CAPACITY AND SETTLEMENT OF COARSE-GRAINED SOILS
    • Relationships Among the Tension Cutoff, Mean Effective Stress, and Preconsolidation Stress
    • Cone Penetration Test (CPT)
    • Relationships Among Undrained Shear Strength, Critical State Friction Angle, and Preconsolidation Ratio
    • Plate Load Test (PLT)
    • Relationship Between the Normalized Undrained Shear Strength of One-Dimensionally Consolidated or Ko-Consolidated and Isotropically
    • SHALLOW FOUNDATION ANALYSIS USING CSM
    • Relationship Between the Normalized Undrained Shear Strength at Initial Yield and at Critical State for Overconsolidated Fine-Grained Soils Under Triaxial Test Condition
    • Dense, Coarse-Grained Soils
    • Relationship Between Direct Simple Shear Tests and Triaxial Tests
    • Relationship for the Application of Drained and Undrained
    • Relationship Among Excess Porewater Pressure, Preconsolidation Ratio, and Critical State Friction Angle
    • Undrained Shear Strength, Liquidity Index, and Sensitivity
    • SOIL STIFFNESS
    • STRAINS FROM THE CRITICAL STATE MODEL
    • Shear Strains
    • CALCULATED STRESS–STRAIN RESPONSE
    • APPLICATION OF CSM TO CEMENTED SOILS

  • SLOPE STABILITY
    • TYPES OF PILES AND INSTALLATION
    • TWO-DIMENSIONAL FLOW OF WATER THROUGH POROUS MEDIA
    • BASIC CONCEPTS OF LATERAL EARTH PRESSURES
    • SOME CAUSES OF SLOPE FAILURE
    • Pile Installation
    • FLOWNET SKETCHING
    • COULOMB’S EARTH PRESSURE THEORY
    • Construction Activities
    • LOAD CAPACITY OF SINGLE PILES
    • INTERPRETATION OF FLOWNET
    • RANKINE’S LATERAL EARTH PRESSURE FOR A SLOPING BACKFILL AND A SLOPING WALL FACE
    • INFINITE SLOPES
    • PILE LOAD TEST (ASTM D 1143)
    • FLOW THROUGH EARTH DAMS
    • LATERAL EARTH PRESSURES FOR A TOTAL STRESS ANALYSIS
    • ROTATIONAL SLOPE FAILURES
    • METHODS USING STATICS FOR DRIVEN PILES
    • SOIL FILTRATION
    • APPLICATION OF LATERAL EARTH PRESSURES TO RETAINING WALLS
    • METHOD OF SLICES
    • PILE LOAD CAPACITY OF DRIVEN PILES BASED ON SPT AND CPT RESULTS
    • TYPES OF RETAINING WALLS AND MODES OF FAILURE
    • APPLICATION OF THE METHOD OF SLICES
    • LOAD CAPACITY OF DRILLED SHAFTS
    • STABILITY OF RIGID RETAINING WALLS
    • PROCEDURE FOR THE METHOD OF SLICES
    • PILE GROUPS
    • STABILITY OF FLEXIBLE RETAINING WALLS
    • STABILITY OF SLOPES WITH SIMPLE GEOMETRY
    • ELASTIC SETTLEMENT OF PILES
    • Analysis of Sheet Pile Walls in Mixed Soils
    • CONSOLIDATION SETTLEMENT UNDER A PILE GROUP
    • BRACED EXCAVATION
    • SETTLEMENT OF DRILLED SHAFTS
    • MECHANICAL STABILIZED EARTH WALLS
    • PILE-DRIVING FORMULAS AND WAVE EQUATION
    • OTHER TYPES OF RETAINING WALLS
    • LATERALLY LOADED PILES
    • MICROPILES

Branch : Civil Engineering
Subject : Soil Mechanics
Unit : STRESS DISTRIBUTIONCOMPRESSIBILITY AND SETTLEMENT

LABORATORY TESTS TO DETERMINE SHEAR STRENGTH PARAMETERS


A Simple Test to Determine Friction Angle of Clean Coarse-Grained Soils:


The critical state friction angle, f9cs, for a clean coarse-grained soil can be found by pouring the soil into a loose heap on a horizontal surface and measuring the slope angle of the heap relative to the horizontal. This angle is sometimes called the angle of repose, but it closely approximates f9cs.

 

Shear Box or Direct Shear Test:
A popular apparatus to determine the shear strength parameters is the shear box. This test is useful when a soil mass is likely to fail along a thin zone under plane strain conditions. The shear box (Figure ) consists of a horizontally split, open metal box. Soil is placed in the box, and one-half of the box is moved relative to the other half. Failure is thereby constrained along a thin zone of soil on the horizontal plane (AB). Serrated or grooved metal plates are placed at the top and bottom faces of the soil to generate the shearing force.

 

Vertical forces are applied through a metal platen resting on the top serrated plate. Horizontal forces are applied through a motor for displacement control or by weights through a pulley system for load control. Most shear box tests are conducted using displacement control because we can get both the peak shear force and the critical shear force. In load control tests, you cannot get data beyond the maximum or peak shear force. The horizontal displacement, Dx, the vertical displacement, Dz, the vertical loads, Pz, and the horizontal loads, Px, are measured. Usually, three or more tests are carried out on a soil sample using three different constant vertical forces. Failure is determined when the soil cannot resist any further increment of horizontal force. The stresses and strains in the shear box test are diffi cult to calculate from the forces and displacements measured. The stresses in the thin (dimension unknown) constrained failure zone (Figure ) are not uniformly distributed, and strains cannot be determined.

 

Only the results of one test at a constant value of Pz are shown in Figure . The results of (Px)p and (Px)cs plotted against Pz for all tests are shown in Figure . If the soil is dilatant, it would exhibit a peak shear force (Figure 10.19a, dense sand) and expand (Figure , dense sand), and the failure envelope would be curved (Figure , dense sand). The peak shear stress is the peak shear force divided by the cross-sectional area (A) of the test sample; that is,

The critical shear stress is

In a plot of vertical forces versus horizontal forces (Figure), the points representing the critical horizontal forces should ideally lie along a straight line through the origin. Experimental results usually show small deviations from this straight line, and a “best-fi t” straight line is conventionally drawn. The angle subtended by this straight line and the horizontal axis is fcs. Alternatively,

For dilatant soils, the angle between a line from the origin to each peak horizontal force that does not lie on the “best-fi t” straight line in Figure and the abscissa (normal effective stress axis) represents a value of f9p at the corresponding vertical force. Recall from Section 10.5 that f9p is not constant, but varies with the magnitude of the normal effective stress (Pz/A). Usually, the normal effective stress at which f9p is determined should correspond to the maximum anticipated normal effective stress in the fi eld. The value of f9p is largest at the lowest value of the applied normal effective stress, as illustrated in
Figure . You would determine f9p by drawing a line from the origin to the point representing the peak horizontal force at the desired normal force, and measuring the angle subtended by this line and the horizontal axis. Alternatively,

You can also determine the peak dilation angle directly for each test from a plot of horizontal displacement versus vertical displacement, as illustrated in Figure 10.19b. The peak dilation angle is

We can fi nd ap from

Questions of this topic


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