Microsoft PowerPoint - UEMX 2413 Soil Mechanics Chapter 5 UEMX 2413: Soil Mechanics Chong Siaw Yah B Eng (Hons) in Civil Engineering, UTM Ph.D in Geotechnical Engineering, UTM Universiti Tunku Abdul...

Microsoft PowerPoint - UEMX 2413 Soil Mechanics Chapter 5
UEMX 2413: Soil Mechanics
Chong Siaw Yah
B Eng (Hons) in Civil Engineering, UTM
Ph.D in Geotechnical Engineering, UTM
Universiti Tunku Abdul Rahman
Lee Kong Chian Faculty of Engineering & Science
Department of Civil Engineering
Chapter 5: Shear Strength of Soil
Lecture Outline
5.1 Shear Failure
5.2 Shear Strength of Soil
5.3 Laboratory Shear Strength Test
5.4 Stress Path
5.5 Pore Pressure Parameters
5.6 Field Shear Strength Test
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Lecture Outline
5.1 Shear Failure
- Definition of shear failure
- Importance of shear failure in geotechnical design
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5.1 Shear Failure
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5.1 Shear Failure (Cont’)
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5.1 Shear Failure (Cont’)
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Lecture Outline
5.2 Shear Strength of Soil
- Mohr circle
- Failure envelope
- Mohr-Coulomb failure criterion
- Shear Strength parameters
- Effective stress & total stress failure criterion
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5.2 Shear Strength of Soil
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Shear Strength:
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Mohr-Coulomb failure criterion:
5.2 Shear Strength of Soil (Cont’)
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Mohr-Coulomb failure criterion:
5.2 Shear Strength of Soil (Cont’)
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Mohr-Coulomb failure criterion:
5.2 Shear Strength of Soil (Cont’)
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Mohr circles & failure envelope:
5.2 Shear Strength of Soil (Cont’)
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Mohr circles & failure envelope:
5.2 Shear Strength of Soil (Cont’)
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Orientation of failure plane:
5.2 Shear Strength of Soil (Cont’)
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Mohr circles in terms of effective & total stresses:
5.2 Shear Strength of Soil (Cont’)
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Envelopes in terms of effective & total stresses:
5.2 Shear Strength of Soil (Cont’)
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Effective stress failure criterion:
5.2 Shear Strength of Soil (Cont’)
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Total stress failure criterion:
5.2 Shear Strength of Soil (Cont’)
Example:
Given:
Total normal stress,σn =295kPa
Pore water pressure, u=120kPa
c’= 12kPa
φ’=30°
Find the shear strength.
τ= c’ + σ’n tanφ’
Solution:
1. Find σ’n
2. Find τ
σ’n = σn - u
5.2 Shear Strength of Soil (Cont’)
Lecture Outline
5.3 Laboratory Shear Strength Test
- Direct shear test
- Triaxial test:
- UU test
- CU test
- CD test
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5.3 Laboratory Shear Strength Test
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• The shear strength of soil can be tested in laboratory using
‘undistu
ed sample’
• In general, 2 types of tests are widely used in practice: direct shear
test & triaxial test, depending on the shear failure criterion & type of
soil being tested.
• The ultimate purpose of performing these tests is to obtain shear
strength parameters, i.e. c and f.
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Direct shear test:
5.3 Laboratory Shear Strength Test (Cont’)
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Direct shear test:
5.3 Laboratory Shear Strength Test (Cont’)
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Direct shear test:
5.3 Laboratory Shear Strength Test (Cont’)
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Direct shear test:
5.3 Laboratory Shear Strength Test (Cont’)
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Direct shear test:
5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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Triaxial test:
5.3 Laboratory Shear Strength Test (Cont’)
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Triaxial test apparatus:
5.3 Laboratory Shear Strength Test (Cont’)
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Types of triaxial tests:
5.3 Laboratory Shear Strength Test (Cont’)
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Types of triaxial tests:
5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
Example:
A series of drained triaxial tests were ca
ied out on specimens
of a sand prepared at same porosity. The following results were
obtained at failure. Determine the value of the angle of
shearing resistance, φ‘.
Cell Pressure (kN/m XXXXXXXXXX
Principal stress difference (kN/m XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Cell Pressure,
σ'3 (kN/m2)
XXXXXXXXXX
Principal stress difference,
Δσ(kN/m XXXXXXXXXX
Major Principal stress,
σ'1 (kN/m2)
XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Φ’=44°, c’= 0
Effective stress paramete
5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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Loose sand/ NC Clay
Dense sand/ OC Clay
Dense sand/ OC Clay
5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
Example:
A series of undrained triaxial tests were ca
ied out on soil specimens.
The following results were obtained at failure.
• Determine the value of the total stress parameters (c and φ).
• Determine the value of the effective stress parameters (c’ and φ‘).
Cell Pressure, σ3 (kN/m XXXXXXXXXX
Principal stress difference, Δσ
(kN/m XXXXXXXXXX
Pore water pressure, u (kN/m XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Cell Pressure,
σ3 (kN/m2)
XXXXXXXXXX
Principal stress difference,
Δσ (kN/m XXXXXXXXXX
Major Principal stress,
σ1 (kN/m2)
XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Total stress paramete
5.3 Laboratory Shear Strength Test (Cont’)
Cell Pressure,
σ3 (kN/m2)
XXXXXXXXXX
Effective cell pressure,
σ'3 (kN/m2)
XXXXXXXXXX
Principal stress difference,
Δσ (kN/m XXXXXXXXXX
Pore water pressure,
u (kN/m XXXXXXXXXX
Major Principal stress,
σ1 (kN/m2)
XXXXXXXXXX
Effective Major Principal
stress,σ'1 (kN/m2)
XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Effective stress paramete
5.3 Laboratory Shear Strength Test (Cont’)
U=150-70=80kN/m2
5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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5.3 Laboratory Shear Strength Test (Cont’)
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s1’ & s3’ at failure:
5.3 Laboratory Shear Strength Test (Cont’)
Example:
A series of undrained triaxial tests were ca
ied out
on saturated clay specimens. The following results
were obtained at failure.
Determine the value of the undrained of shearing
strength of the clay (c u).
Cell Pressure (kN/m XXXXXXXXXX
Principal stress difference
(kN/m XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
Cell Pressure, σ3 (kN/m XXXXXXXXXX
Principal stress difference, Δσ
(kN/m XXXXXXXXXX
Major Principal stress, σ1
(kN/m XXXXXXXXXX
5.3 Laboratory Shear Strength Test (Cont’)
5.3 Laboratory Shear Strength Test (Cont’)
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For saturated clay,
Φ=0
5.3 Laboratory Shear Strength Test (Cont’)
For saturated clay sample,
Cu = radius of the mohr circle
= 0.5 Principal stress difference
5.3 Laboratory Shear Strength Test (Cont’)

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