Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show. Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.

1. 1
Geotechnical Engineering–I [CE-221]
BSc Civil Engineering – 4th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/2016session-geotech-i
Lecture # 13
6-Mar-2018

2. 2
Soil is essential construction material of most
construction projects:
 Retaining walls, Embankments,
 Highways,
 Airports,
 Dams, Dikes, etc.
Advantages of using soil:
 Easy availability
 Durable, and long-lasting
 Low cost
“SOIL” as Construction Material

3. 3
Typical soils at in-situ state
 weak, highly compressible, or have high permeability
 Not ideal for construction projects
Improvement of engineering properties (soil stabilization) is
required;
 Chemical stabilization
 Mechanical stabilization
In most civil engineering projects, whenever soils are
imported or excavated and re-applied, they are compacted.
“SOIL” as Construction Material
Compaction

4. 4
Ground improvement technique in which soil is densified
through external compactive effort.
Measurement of Compaction
→ in terms of dry unit weight, d
+ water =
Compactive
effort
COMPACTION

5. 5
Loose soil
Solids
Air
Water
Solids
Air
Water
Compacted soil
Soil densification by applying mechanical energy to
reduce air voids
 reduces air content, but not the water content
 can’t compact saturated soil (almost always true)
COMPACTION

6. 6
 Soil strength → Increase
– Bearing capacity
– Slope stability, etc
 Volume changes → Decrease
– Settlement
– Swell potential, etc
 Hydraulic conductivity → Decrease
BENEFITS OF COMPACTION

7. 7
 Soil type
− gradation, composition, minerals, etc.
 Compaction effort
 Moisture content
FACTORS AFFECTING
DEGREE OF COMPACTION

8. 8
EFFECT OF MOISTURE CONTENT
Moisture content, w (%)
DryDensity,γd
Dry side of Optimum
Water acts as a lubricant →
becomes easy for particles to
rearrange and orient.
Wet side of Optimum
Too much water → replaces
soil particles
Optimum Moisture →
density is maximum
OptimumMoisture
Content(OMC)
Max. dry
density (γd(max))
Dry side of optimum Wet side of optimum
Optimum moisture content (OMC): Moisture content of soil at which maximum density
can be achieved for a given compactive effort.
Compaction curve

9. 9
EFFECT OF MOISTURE CONTENT
Property Side of Optimum
Dry Wet
Soil Structure
More random
(Flocculent)
More oriented
(parallel)
Shear Strength More Less
Stress ~ strain
behavior
Brittle Ductile
Swelling
More → high water
deficiency
Less
Permeability More Less
Compressibility More Less

10. 10
USE OF COMPACTION CURVE
USE Compaction
Moisture Content
Reason
Core of
earthen dam
Wet of OMC - To reduce coefficient of
permeability and;
- To prevent cracking of core
Subgrade of
pavements
Dry of optimum,
or at OMC
- To have better shear strength of soil
- To limit volume changes in sub-
grade
Fills Dry of optimum or
at OMC
- To facilitate easy construction; and
- For better strength

11. 11
EFFECT OF SOIL TYPE
OMC of fine-grained
soils is higher than
coarse-grained soils.

12. 12
With increase in compaction
effort;
 OMC decreases
 γd increases
EFFECT OF COMPACTION ENERGY
Moisture content, w (%)
DryDensity,γd
OMC
OMC

13. 13
With increase in compaction
effort;
 OMC decreases
 γd increases
EFFECT OF COMPACTION ENERGY

14. 14
Ultimate goal → to obtain compaction curve of soil
Test Procedure → Standard Proctor Test
(ASTM ASTM D-698 or AASHTO T-99)
SOIL COMPACTION –
LABORATORY EVALUATION

15. 15
Ultimate goal →
STANDARD PROCTOR TEST
(ASTM D-698 or AASHTO T-99)
Moisture content, w (%)
DryDensity,γd
Drop height = 12 in
25 blows/layer
5.5 lb
w1
γb(1) = W/V
25 blows/layer
w2 (w2 > w1)
γb(2)
Repeat the test
by adding
more water
Repeat the same
procedure by
adding more and
more water every
time.
)1( w
b
d




to obtain compaction curve of soil.
→ OMC & γd(max)

16. 16
Developed by R.R. Proctor (1933)
Equipment
 Volume of mold = 1/30 ft3 (943.3 cm3)
 Diameter of mold = 4 in (101.6 mm)
 Weight of hammer = 5.5 lb (2.45 kg)
 Drop height = 12 in (305 mm)
 Soil compacted in 3 layers
 25 blows per layer
STANDARD PROCTOR TEST
33
2
10944.0
)3()/25()3048.0()/81.9(495.2
m
layerslayerblowsmsmkg
E 



Volume of mold
Number of
blows per layer
Number of
layers
Weight of
hammer
Height of
drop of
hammer
  
E =
Compaction
Energy, E
)/375,12(/7.592 33
ftlbftmkJE 

(ASTM D-698 or AASHTO T-99)

17. 17
 Corresponds to 100%
saturation.
 Compaction curve always
lie on the left of ZAVC.
 because S > 100% is not
possible
S <100%
ZERO AIR VOID (ZAV) CURVE
s
Gw
e
e
G sws
d 

 ;
1


s
Gw
G
s
ws
d


1



18. 18
15
16
17
18
19
20
5 10 15 20 25
Dryunitweightd(kN/m3)
Moisture content, w (%)
S= 100%
90%
80%
70%
60%
Gs = 2.69
ZERO AIR VOID (ZAV) CURVE
 Also known as full
saturation curve.
 Similar curves can
be drawn for
various degrees of
saturation.
s
Gw
G
s
ws
d


1



19. 19
CONCLUDED
REFERENCE MATERIAL
An Introduction to Geotechnical Engineering (2nd Edition)
By R. D. Holtz, W. D. Kovacs and T. C. Sheahan
Chapter #5
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #6