Compaction is a ground improvement technique where soil is densified through external effort such as vibratory rollers, impact rollers, or pneumatic rubber tired rollers. The compaction curve shows the relationship between dry density and water content, with maximum dry density achieved at the optimum water content. Higher compactive effort results in a lower optimum water content and higher maximum dry density. Field compaction is tested through density measurements, which are compared to specifications defined by laboratory compaction tests. Dynamic compaction techniques like vibroflotation and stone columns can also be used to densify soils through pounding or vibration.

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Compaction
N. Sivakugan
Duration = 10 minutes

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What is compaction?
A simple ground improvement technique, where the soil
is densified through external compactive effort.
+ water =
Compactive
effort

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Compaction Curve
Water content
Dry
density
(
d
)
optimum
water content
d, max
Soil grains densely packed
- good strength and stiffness
- low permeability

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Compaction Curve
What happens to the relative quantities of the three phases
with addition of water?
Water content
Dry
density
(
d
)
soil
water
air
difficult to expel all air
lowest void ratio and
highest dry density at
optimum w

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Zero Air Void Curve
All compaction points should lie
to the left of ZAV curve
- corresponds to 100% saturation
Water content
Dry
density
(
d
)
Zero air void curve (S=100%)
s
w
s
d
wG
G


1
:
Eq


S<100%
S>100% (impossible)

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Effect of Compactive Effort
Increasing compactive
effort results in:
E1
E2 (>E1)
 Lower optimum water
content
 Higher maximum dry
density
Water content
Dry
density
(
d
)

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Compaction and Clay Fabric
Higher water content or higher
compactive effort gives more
dispersed fabric.
more dispersed fabric
more
dispersed
fabric
Water content
Dry
density
(
d
)

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Line of Optimum
Water content
Dry
density
(
d
)
Compaction curves
for different efforts
Line of optimum

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Filed Compaction
Pneumatic rubber tired roller
Different types of rollers (clockwise
from right):
 Vibratory roller
 Smooth-wheel roller
 Sheepsfoot roller

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Field Compaction
Compacts effectively only to 200-300 mm; therefore,
place the soil in shallow layers (lifts)
Smooth Wheeled Roller

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Field Compaction
 for compacting very small areas
Vibrating Plates
 effective for granular soils

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Field Compaction
 Provides kneading action; “walks out” after compaction
Sheepsfoot Roller
 Very effective on clays

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Field Compaction
 Provides deeper (2-3m) compaction. e.g., air field
Impact Roller

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Compaction Control
-a systematic exercise where you check
at regular intervals whether the
compaction was done to specifications.
e.g., 1 test per
1000 m3 of
compacted soil
• Minimum dry density
• Range of water content
Field measurements (of d) obtained using
• sand cone
• nuclear density meter

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Laboratory Compaction Test
- to obtain the compaction curve and define the
optimum water content and maximum dry density for a
specific compactive effort.
hammer
Standard Proctor: Modified Proctor:
• 3 layers
• 25 blows per layer
• 5 layers
• 25 blows per layer
• 2.7 kg hammer
• 300 mm drop
• 4.9 kg hammer
• 450 mm drop
1000 ml compaction mould

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Compaction Control Test
compacted ground
d,field = ?
wfield = ?
Compaction
specifications
Compare!
w
d

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Dynamic Compaction
- pounding the ground by a heavy weight
Suitable for granular soils, land fills
and karst terrain with sink holes.
Crater created by the impact
Pounder (Tamper)
solution cavities in
limestone
(to be backfilled)

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Dynamic Compaction
Pounder (Tamper)
Mass = 5-30 tonne
Drop = 10-30 m

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Dynamic Compaction

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Vibroflotation
Vibroflot (vibrating unit)
Length = 2 – 3 m
Diameter = 0.3 – 0.5 m
Mass = 2 tonnes
Practiced in several forms:
 vibro–compaction
 stone columns
 vibro-replacement
Suitable for granular soils
(lowered into the ground
and vibrated)

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Vibroflotation

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Vibroflotation

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Vibroflotation

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Vibroflotation

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Vibroflotation

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Vibroflotation

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Stone Columns
vibrator makes a
hole in the weak
ground
hole backfilled ..and compacted Densely compacted
stone column

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Blasting
Aftermath of blasting
Fireworks?
For densifying granular soils

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Earthmoving Equipment
Large Excavator (see minivan on left for scale)
David and Goliath?

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Earthmoving Equipment
Grader for spreading soil

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Earthmoving Equipment
Bulldozer for spreading soil evenly

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Earthmoving Equipment
Loader

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Earthmoving Equipment
Backhoe

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Earthmoving Equipment
Crawler mounted Hydraulic Excavator

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Earthmoving Equipment
Rock Breaker