SUB: GEOTECHNICAL ENGINEERING MODULE-47A
MODULE- 47A
Compaction
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Compaction means pressing the soil particles close to each other by mechanical
methods. During compaction air is expelled from voids and density increases. Due to
compaction shear strength of soil increases hence the stability and bearing capability of soil
increases. Due to compaction permeability and compressibility decreases, hence seepage will
decrease.
Standard proctor test:
Mould Size (dia) : 100 mm
Height: 127.3 mm
Capacity: 1000 ml
Rammer mass: 2.6 kg
Free drop: 310 mm
No. of layers: 3
No. of blows: 25
If % soil retained on 4.75 mm sieve is more than 20%, larger mould is to be used.
d= 150 mm
Height =127.3 mm
Capacity = 2250 ml.
The No. of blows
Modified Proctor Test:
Rammer mass: 4.89 kg
Free drop: 450 mm
No. of layers: 5
No. of blows: 25
It is about 4.56 times of standard proctor test.
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SUB: GEOTECHNICAL ENGINEERING MODULE-47A
OMC: The water content corresponding to the max dry density is known as the optimum
moisture content.
Zero % air void line or 100% saturation line.
Zero air void line and 100% saturation line are identical.
But 10 % air void line and 90 % saturation line are not- identical.
Compaction curves of standard proctor test and modified proctor test.
(1) Standard proctor test
(2) Modified proctor test
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SUB: GEOTECHNICAL ENGINEERING MODULE-47A
Factor effecting compaction:
1. Water Content: At low water content lubrication is less and it is very difficult to re-
arrange the soil particles. As water content increases lubrication increase and air voids
decreases. At OMC air voids becomes constant. After OMC air will not go out and
the added water increases the total voids so that density decreases.
2. Amount of Compaction: As water content less than OMC, by increase of
compaction, dry density increases, initially at high rate and later the rate decreases
and becomes zero.
3. Type of soils: Coarse grained soils can be compacted to higher dry density than fine
grained soil. If we add fines to the coarse grained soil, dry density further increases.
This trend will continuous up to fill the voids, after that dry density decreases.
4. Method of compaction: For the same amount of compactive effort, the dry density
depends upon whether the method of compaction utilizes kneading action, dynamic
action or static action.
Effect of Compaction on properties of soil:
1. Soil Structure: Soils compacted dry of optimum have a flocculated structure and wet
of optimum have a dispersed structure. In dry of optimum, attractive forces are
predominant and in wet of optimum repulsion forces are predominant.
2. Permeability: Permeability decreases with increase in water content on dry side of
OMC. There is an improved orientation of particles and corresponding reduction in
size of voids which cause decrease in permeability. The minimum permeability occurs
at slightly above OMC.
3. Swelling: A soil compacted dry of the OMC has high water deficiency and more
random orientation of particles and has more swelling.
4. Pore Water Pressure: Sample compacted dry of OMC has less pore water pressure.
5. Shrinkage: Wet of optimum can pack more efficient and therefore more shrinkage.
6. Compressibility: Due to flocculated structure on dry of OMC the soil has less
compressibility.
7. Stress-Strain relationship: The soils compacted dry of OMC have a steeper stress
curve than those on wet side.
8. Shear Strength: The soils compacted dry of OMC have higher shear strength.
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SUB: GEOTECHNICAL ENGINEERING MODULE-47A
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Types of rollers:
(1)Smooth-wheel rollers: Useful for finishing operations, and for compacting granular base
course of highways.
(2)Pneumatic- typed rollers: These rollers are effective for compacting cohesive as well as
cohesion less soils.
(3)Sheep-foot rollers: Useful for cohesive soils.
(4)Vibratory rollers: Suitable for granular soils.
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