Dr. Muhammad Irfan Civil Engg. Dept. – UET Lahore Email: mirfan1@msn.com Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session Lecture # 3 13-Sep-2017

1. 1
Geotechnical Engineering–II [CE-321]
BSc Civil Engineering – 5th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session
Lecture # 3
13-Sep-2017

2. 2
DETERMINATIONOFSOILSHEARSTRENGTH
(c, φ or c’, φ’)
Laboratory tests
on representative samples
Field tests
Direct shear test
Unconfined compression test
Triaxial shear test
Simple shear test
Torsional ring shear test
Plane strain triaxial test
Laboratory vane shear test
Laboratory fall cone test
Vane shear test
Torvane
Pocket penetrometer
Fall cone
Pressuremeter
Static cone penetrometer
Standard penetration test
Assignment: Brief intro of each

3. 3
z
σv
σv
σhσh
Before construction
Representative soil
sample
z
σv + Δσ
σhσh
During and after
construction
σv + Δσ
FIELD STRESS CONDITIONS

4. 4
Step 1
Application of initial
stress condition
σv
σv
σh
σh
Representative soil
sample from site
0
00
0
Step 2
Application of
disturbing/structural load
σv + Δσ
σhσh
σv + Δσ
t
σv
σv
τ
τ
LAB SIMULATION OF
FIELD CONDITIONS

5. 5
DIRECT SHEAR TEST
- Schematic Illustration -
t tan cf
P

6. 6
Components of Shear Box Preparation of Sand specimen
Porous
Plates
DIRECT SHEAR TEST
- Specimen Preparation -

7. 7
Leveling the top surface of
specimen
Specimen preparation
completed
Pressure plate
DIRECT SHEAR TEST
- Specimen Preparation -

8. 8
Step 1: Apply a vertical load to the specimen and wait for
consolidation
Porous
Plates
Pressure Plate
Steel BallP
Proving ring
to measure
shear force
F
Soil Specimen
DIRECT SHEAR TEST
- Test Procedure -

9. 9
P
Pressure plate
Steel Ball
Proving ring
to measure
shear force
F
Porous
Plates
DIRECT SHEAR TEST
- Test Procedure -
Step 2: Lower box is subjected to a horizontal displacement at a
constant rate

10. 10
Shear Box
Loading frame to
apply vertical load
Dial gauge to
measure vertical
displacement
Dial gauge to
measure horizontal
displacement
Proving ring
to measure
shear force
DIRECT SHEAR TEST

11. 11
sampleofAreasectional-Cross
(P)forceNormal
stressNormal 
sampleofAreasectional-Cross
(F)surfaceslidingat thedevelopedresistanceShear
stressShear t
Cross-sectional area of the sample changes
with the horizontal displacement
DIRECT SHEAR TEST
- Calculations -
t tan cf
hBAA oC  .
Ac = Corrected Area
Ao = Original Area
B = Width
h = Sample Deformation

12. 12
DIRECT SHEAR TEST
- Calculations -
DDG constant = 0.01mm/div
Proving Ring constant = 0.8lb/div
Weight of Hanger = 8 lb 15 ounce
= 8.94lb
Normal Load = 20lb
Total Normal Load = 28.94lb
Sample#
Normal
Load,
N
Horizontal
D/R
Horizontal
Displacement,
∆H
Col#3×L.C
Corrected
Area,
Ac =A0-b∆H
Load Dial
Reading
Horizontal
Shear Force,
F
Col#6×PRC
Normal
Stress,
σn=N/AC
Shear
Stress,
τ=F/AC
(lb) (mm) (cm2
) (lb) (kN/m2
) (kN/m2
)
1 2 3 4 5 6 7 8 9
2
28.94 0 0.0 36.00 0.0 0.0 35.77 0.00
28.94 20 0.2 35.88 17.0 13.6 35.89 16.87
28.94 40 0.4 35.76 21.0 16.8 36.01 20.91
28.94 60 0.6 35.64 23.0 18.4 36.13 22.97
Sample Calculations

13. 13
tf1
Normal stress = 1
How to determine shear
strength parameters c
and  ?
Shearstress,t
Shear displacement
tf2
Normal stress = 2
tf3
Normal stress = 3
Shearstressatfailure,tf
Normal stress, 

Mohr – Coulomb
failure envelope
DIRECT SHEAR TEST
- Analysis of Results -
t tan cf

14. 14
DIRECT SHEAR TEST
- Stress ~ Strain Relationships -
Shearstress,t
Shear displacement
Dense sand/ OC clay
tf
Loose sand/ NC clay
tf
Dense sand/OC Clay
Loose sand/NC Clay
Changeinheight
ofthesample
ExpansionCompression
Shear displacement

15. 15
DIRECT SHEAR TEST ON CLAYS
Failure envelopes of clay from drained direct shear tests
Shearstressatfailure,tf
Normal stress, 
’
Normally consolidated clay (c’ = 0)
• Horizontal displacement applied at a very slow rate to allow
dissipation of pore water pressure
• One test would take several days to finish
Over-consolidated clay (c’ ≠ 0)

16. 16
INTERFACE TESTS ON DIRECT
SHEAR TEST APPARATUS
• Friction angle between soil and structural material (concrete, steel, wood, etc.)
• Used in many foundation design and retaining wall problems
t tan af c
Where,
ca = adhesion,
 = angle of internal friction
Foundation material
Soil
P
S
Foundation material
Soil
P
S

17. 17
DIRECT SHEAR TEST
-- Advantages & Disadvantages --
Advantages
 Relatively simple and quick test.
 Interface strength parameters can be determined.
Disadvantages
 Failure occurs along predetermined failure plane.
 Area of the sliding surface changes as the test progresses.
 Non-uniform distribution of shear stress along failure
surface.
 Reliable ‘mostly’ for granular soils only.

18. 18
ANGLE OF REPOSE
The steepest angle to
which a loose granular
material can be piled
without slumping.
Angle of repose ≈ Friction angle

19. 19
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #12
Geotechnical Engineering – Principles and Practices – (2nd Edition)
Coduto, Yueng, and Kitch
Chapter #12
Essentials of Soil Mechanics and Foundations – Basic Geotechnics – (7th Edition)
David F. McCarthy
Chapter #11