ACTIVITY

Lecture (3 hours)

WEEK 6

At the end of this lecture/week, the students

will be able to :

LEARNING OUTCOMES

Learning Outcomes :

1. Discuss the purpose and objectives of engineering properties tests in the context of designing geotechnical structures

2. Determine important engineering properties of soils based on the analysis of laboratory test data

Week 6 : (3HL) Coverage : Laboratory tests to

determine engineering properties of soils : Strength,

Compressibility and Permeability

1.0 Overview

2.0 Scope of laboratory test

3.0 Mechanical properties tests

and their application

OUTLINE of PRESENTATION

LABORATORY TESTING

Based on the soil exploration works carried

out two types of samples are normally

retrieved from the site. These are disturbed

and undisturbed samples.

1.0 Overview.

The engineer/designer must specify the

tests that need to be carried out in the

laboratory so that relevant and appropriate

parameters are obtained to be used in the

design of the geotechnical structures.

LABORATORY TESTING

BS Standards BS1377:1990, BS5930:1999

American Standards ASTM

Malaysian Standards MS

Standards for testing

LABORATORY TESTING

BS Standards BS1377:1990, BS5930:1999

Shear Box Test

Triaxial test (UCT, UU, CIU, CID)

Vane Shear test

Compressibility test

Permeability Tests

Find the correct references for each test in the

BS and the equivalent ASTM

Standards for testing

LABORATORY TESTING

3.1 Strength test

3.1.1 Shear Box

3.1.2 Triaxial Test

3.1.3 Vane Shear test

3.2 Compressibility Test

3.3 Permeability Test

3.0 Mechanical Properties of Soils

LABORATORY TESTING

SHEAR STRENGTH OF SOILS

Shear Box Apparatus & Accessories

3.1.1 Shear box

apparatus and

its accessories

SHEAR STRENGTH OF SOILS

Shear box apparatus

Schematic diagram of a shear box apparatus

SHEAR STRENGTH OF SOILS

Data analysis of shear box test

SHEAR STRENGTH OF SOILS

Triaxial sample

SET-UP OF THE

SAMPLES

TESTS AVAILABLE

Unconfined compression

test (UCT)

Unconsolidated undrained

test (UU)

Consolidated isotropically

undrained test (CIU)

Consolidated isotropically

drained test (CID)

3.1.2 Triaxial Test

SHEAR STRENGTH OF SOILS

Interpretation of test results

UNCONFINED COMPRESSION TEST

Is a special case of triaxial

compression, carried out at

zero cell pressure (σ3 = 0).

SHEAR STRENGTH OF SOILS

Interpretation of test results

UNCONFINED COMPRESSION TEST

Is a special case of triaxial

compression, carried out at

zero cell pressure (σ3 = 0).

Mohr-Coulomb plot for the unconfined

compression test

SHEAR STRENGTH OF SOILS

Triaxial apparatus and accessories

SHEAR STRENGTH OF SOILS

Diagram of Triaxial cell

THE TRIAXIAL CELL

AND POSITION OF

THE SAMPLE

SHEAR STRENGTH OF SOILS

Interpretation of test results

INTERPRETATION OF TRIAXIAL TEST RESULTS

Strains and stresses in the triaxial test (a) Principal strains

(b) Cell pressure only (c) Stresses at shear failure

SHEAR STRENGTH OF SOILS

Failure modes

(a) Brittle shear

failure (b) Intermediate

shear failure Plastic yielding

failure

MODE OF SHEAR FAILURE IN THE TRIAXIAL TEST

SHEAR STRENGTH OF SOILS

Interpretation of test results

OBTAINING MOHR-COULOMB PARAMETERS

Three specimens of the same soil usually tested at

different cell pressures and a Mohr circle drawn for each

peak or ultimate failure stress. Common tangent drawn as

the strength envelope.

SHEAR STRENGTH OF SOILS

Graphical representation of strength

Comparison of Mohr circles for drained and undrained tests

SHEAR STRENGTH OF SOILS

Graphical representation of strength

Undrained test envelopes for a normally consolidated clay

SHEAR STRENGTH OF SOILS

Graphical representation of strength

Typical example of Mohr circles construction

SHEAR STRENGTH OF SOILS

Graphical representation of strength

ANALYSIS OF SHEAR STRENGTH

DATA TO OBTAIN SHEAR STRENGTH

PARAMETERS USING STRESS PATH

CONCEPT

(a) HALF DIFFERENCE HALF SUM PLOT

(b) SPACE PLOT

SHEAR STRENGTH OF SOILS

Graphical representation of strength

BEFORE WE PROCEED, PLEASE

DEFINE THE FOLLOWING TERMS:

Mohr Circles

Stress Paths

Normally consolidated clay

Overconsolidated clay

SHEAR STRENGTH OF SOILS

Graphical representation of strength

STRESS POINT AND MOHR COULOMB FAILURE ENVELOPES

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(a) STRESS PATHS FOR TRIAXIAL TEST (Half Difference Vs Half Sum

(a) Drained Test

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(b) Consolidated Undrained Test (Normally consolidated clay)

(a) STRESS PATHS FOR TRIAXIAL TEST (Half Difference Vs Half Sum

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(c) Consolidated Undrained Test (Overconsolidated clay)

(a) STRESS PATHS FOR TRIAXIAL TEST (Half Difference Vs Half Sum

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(a) STRESS PATHS FOR TRIAXIAL TEST (Half Difference Vs Half Sum)

Correlation between the parameters from Shear strength

envelope and the stress point failure envelope

)'

tan

1- (tan

1-sin

' ' sin

' cos

a'

'c

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(a) PRINCIPAL STRESS ELEMENT

(b) PRINCIPAL STRESS SPACE

(B) SPACE PLOT

SHEAR STRENGTH OF SOILS

Graphical representation of strength

STRESS PATH IN PRINCIPAL STRESS

SPACE

(a) Drained test (back pressure = uo)

SHEAR STRENGTH OF SOILS

Graphical representation of strength

STRESS PATH IN PRINCIPAL STRESS

SPACE

(b) Consolidated undrained test

SHEAR STRENGTH OF SOILS

Graphical representation of strength

(b) STRESS PATHS FOR TRIAXIAL TEST (Space Plot)

Correlation between the parameters from Shear

strength envelope and the stress point failure envelope

1 ' 2

1 - ' 2sin '

1 '

1 - '

2

2 ' sin

1-

tan

tan

tan

tan

)' sin -(1 b' 2

1 'c

Shear vane

Apparatus

3

x 4

2 2

x 2

dddhdcT

u

FIELD RESULTS & ANALYSIS I

3.1.3 Vane Shear Tests