Compaction
• In-situ soils used as:
– Bases for the construction of highway
pavements
– embankments or leveling material for
construction projects
• Compacted to improve their density: M/V
– improves the soil’s strength
– lowers it’s permeability
– reduces future settlement
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Compaction
• Evaluation of density as a result of
compactive efforts with rollers and other
equipment
– common quality control measurement on soils
at construction sites
– density of a compacted soil is measured and
compared to a density goal previously
determined in laboratory tests
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Compaction
Maximum Dry Density
• Maximum dry density must be established
for each soil type
– clay soil after compactive effort 2000 Kg/m3
– granular soil with no compactive effort may be
well above this
• Dry density of a soil fn (water content)
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Compaction
Maximum Dry Density
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Compaction
Maximum Dry Density
Compaction Control
Determine the maximum dry density for a
particular soil under a certain compactive
effort and the water content at which this
density is reached.
MD/V
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Compaction
Maximum Dry Density
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Compaction
Maximum Dry Density
• Compaction Test
– Moisture density test
– Proctor test
• soil is compacted into 10 cm diameter mold
for material passes 4.75 mm sieve (15 cm
mold for coarser material)
• soil is placed in 3 layers
• each layer compacted 25 blows with a 2.5
Kg hammer dropping
30 cm ( 56 blows) 7
ENCI 579
Compaction
Maximum Dry Density
• 25 blow/56 blow compactive efforts are the
same and represent the compactive efforts
of 1930 construction rollers
• Compaction Test
– sample of soil is mixed with water
• mass of compacted sample is measured
• water content determined
– sample of soil is mixed with more water
– repeated until density decreases
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Compaction
Maximum Dry Density
• Modified Compaction Test
– Modified Moisture Density Test
– Modified Proctor Test
• Increased loading on our pavements
• Increased compactive effort of equipment
• Revised test of higher compactive effort is
now often used
– 4.5 Kg hammer, 45 cm drop, 5 layers
– higher maximum dry
w/c
ENCIdensity/lower
579
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Compaction
Maximum Dry Density
Density Sample
Mass of soil plus mold
Mass of mold
Water content sample
Mass of sample plus container
Mass of dry sample plus container
Mass of container
Calculations: Water content sample
Mass of water
Mass of dry soil
Water content (w)
From density sample
Mass of soil in mold
Density (1872 g/943,9cm3)*
Mass
Dry density (1983 kg/m3/1.109)**
ENCI 579
= 5321 g
= 3449 g
*Volume of
standard mold
is 943.9 cm3
= 252.60g
= 238.04 g **Dry density
=
= 104.73 g density/(1+w)
= 14.56 g
= 133.31 g
= 14.56 g/133.31 g = 10.9%
= 1872 g (4.127lb)
= 1.983 g/cm3
= 1788 kg/m3
10
Compaction
Maximum Dry Density
Zero Air Voids (ZAV) Curve
• “the maximum theoretical density of a soil
at various water contents” with no air left in
the soil water mixture
ZAV rD =
rW
1/RD + W
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Compaction
Maximum Dry Density
• Maximum Dry Density of a soil is used in
quality control
• Specification requires a certain % of
maximum dry density at optimum water
content found by the compaction test for
that particular soil
– Ensures density
– Reduces the compactive effort
ENCI 579
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Compaction
Maximum Dry Density
Table 3-1
MAXIMU DRY DENSITY AND OPTIMUM MOISTURE
CONTENT (TYPICAL)
AASHTO
Maximum Dry
Optimum Moisture
Classification
Density (kg/m3)
Content (%)
A – 1 Granular
1850-220
7-15
A – 2 Sands
1750-2150
9-18
A–3
1750-1850
10-18
A – 4 Silts
1500-2100
10-20
A–5
1400-1650
15-30
A – 6 Clays
1500-1900
10-25
A–7
1400-1850
15-30
1400-
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Compaction
Maximum Dry Density
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Compaction
Maximum Dry Density
Note:
• If the soil was below optimum water
content it may be necessary to add water by
spraying
• The most important factor required for
successful compaction is having the correct
water content
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Compaction
Field Density Tests
• Sampling Methods
– sample of compacted material taken
– dry mass of the soil taken is determined
– volume originally occupied by the sample is
measured
– field dry density = dry mass/volume of sample
• Two sampling methods
– balloon densometer
– sand cone apparatus
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Compaction
Field Density Tests
• Balloon densometer
– Dry mass of the soil is determined
– Volume of the sample hole is found by forcing
a liquid filled balloon into the test hole
– A rubber membrane allows the fluid to fill all
the cavities of the hole
– The volume of fluid required is measured
– density calculated
– water content determined
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Compaction
Field Density Tests
• Sand Cone Apparatus
– Dry mass of the soil is determined
– Volume of the test hole is obtained from the
mass of loose sand required to fill the hole
– Sand is a uniform medium sand with a constant
loose density
– Volume=mass of sand / loose density of sand
– density is calculated
– water content determined
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Compaction
Maximum Dry Density
Example 3-4 Sand-Cone Apparatus: A sand cone
holds 851.0 g. The loose density of the sand is
1.430 g/cm3
Field Test Results:
Total weight of the soil
639.5 g
Dry weight of the soil
547.9 g
Initial weight of the sand-cone apparatus 4527.8g
final weight of the sand-cone apparatus 3223.9g
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Compaction
Maximum Dry Density
Calculations:
Mass of the sand used
Mass in test hole
Volume of test hole
Field dry density
Field water content
4527.8g-3223.9g = 1303.9g
1303.9g-851.0g = 452.9 g
452.9 g
= 316.7 cm3
1.430 g/cm3
547.9g/316.7 cm3 = 1.730 g/ cm3
639.5-547.9 = 16.7%
547.9
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Compaction
Field Density Tests
• Nuclear Moisture-Density Gauge
– Results are available within minutes
• Increases equipment efficiency
• Know that your construction methods are correct
– Gamma rays are emitted into the soil
• absorbed by the soil according to it’s density
• rays that pass through the soil are measured by a
detector
• density is then calculated
ENCI 579
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Compaction
Field Density Tests
• Nuclear Moisture-Density Gauge
– Neutron radiation emitted into the soil
• neutrons loose energy when they collide with
hydrogen atoms in the soil water
• detector measures the amount of moderated neutrons
• water content can be calculated
– Direct transmission mode
– Backscatter mode
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Compaction
Field Density Tests
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Compaction
Maximum Dry Density
• Corrected Maximum Dry Density
– compaction test is usually done on materials
finer than 4.75 mm
– sample contains coarse grained sized particles
• gravel in a soil composed mainly of fine grains can
be compacted to 90% of their theoretical maximum
density
• assuming gravel RD=2.65
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Compaction
Maximum Dry Density
Example Laboratory maximum density of a soil is
1900 kg/m3. Specifications require 95%
compaction. In the filed, dry density of the soil is
found to be 1810kg/m3. A visual check of the soil
in the field indicates that it contains about 20%
gravel sizes. (Scales can be used for a more
accurate determination of the percentage of
gravel.) Check for compaction.
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Compaction
Maximum Dry Density
Corrected maximum dry density is:
0.80 x 1900kg/m3 + 0.20 x (90% x 2.65 x 1000kg/m3
= 1520 kg/m3 + 477kg/m3 = 1997kg/m3
Percent compaction is 1810/1997 = 90.6% and is
not acceptable
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Compaction
Operation and Quality Control
• Highway components that require
compaction:
– Subgrade (15-30cm) in depth, provides the
foundation for the pavement structure
– Fill material used to bring the soil surface up to
the subgrade level (15-30 cm compacted lifts)
– Backfill material
– Layers in granular material used in pavement
– Asphalt layers at the surface
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Compaction
Compaction Equipment
• Compaction Equipment
– Consists of various types of rollers and tamping
equipment
– self propelled
– compacting wheels equipped to vibrate
• 1500-2500 cycles/minute for most soils and granular
materials
– smooth steel drums
– drums with pads or “feet”
ENCI 579
– rubber tires
29
Compaction
Compaction Equipment
• Vibratory Smooth Drum Rollers
–
–
–
–
–
–
–
one steel drum and rubber tired drive wheels
two steel drums one of which is the driver
effective for gravel, sand, silt soils
granular base courses and asphalt mixtures
mass of the drum is between 2-15 tonnes
utilized in layers from 0.5-1.0 meters in depth
usually require 3-5 passes to produce specified
density
ENCI 579
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Compaction
Compaction Equipment
• Vibratory Smooth
Drum Rollers
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Compaction
Compaction Equipment
• Padded Wheel or “Sheep’s Foot” Rollers
– pads on the rotating drum and may vibrate
– effective in clay and silty clay soils
– punching action breaks the clay’s bonds which
resist rearrangement of the grain structure
– pressure exerted by the pad 1000-5000 kpa
depending on the size of the roller
– utilized in layers of 15-30 cm in depth
– usually require 3-5 passes to achieve density
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Compaction
Compaction Equipment
• Padded Wheel or
“Sheep’s Foot” Rollers
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Compaction
Compaction Equipment
• Pneumatic Tire Rollers
– 2-12 rubber tires on each axle
– individual tires wobble or weave or move lower
than adjacent tires to improve the kneading
action
– effective in clay and granular soils and asphalt
mixtures can be kneaded and compacted
– effective depths for soils or base courses is up
to 15 cm (larger units of 40-50 tonnes 30 cm)
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Compaction
Compaction Equipment
• Pneumatic Tire Rollers
ENCI 579
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Compaction
Compaction Equipment
• Smooth Drum Non-vibratory Rollers
– used for finishing or sealing passes on soils and
granular layers
– final leveling passes on asphalt layers
• Vibrating Plates or Tampers
– used for trench backfills
– around structures where larger equipment can’t
operate
– larger tamping equipment is usually attached to
excavators or otherENCI
equipment
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Compaction
Quality Control
• Determine which materials are to be sampled and
tested
• Frequency of the testing and type of tests to be
performed on the material
• Transportation authorities usually have
specifications outlining these criteria
– Moisture Density 1/ soil type (or 5000 m subgrade)
– Field Compaction 4/500 m of each layer
• Method Specification vs EPS Specifications
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