Soil Compaction. Compaction Compaction is the method of mechanically increasing the density of soil...
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Transcript of Soil Compaction. Compaction Compaction is the method of mechanically increasing the density of soil...
CompactionCompaction
• Compaction is the method of mechanically increasing the density of soil by removal of air.
• Dry density (d) is the measure of the degree of compaction.
Why Compaction?Why Compaction?
• Increase bearing capacity
• Increase stability of slopes of embankments
• Reduce compressibility
• Reduce permeability
• Reduce volume changes
• Prevent frost damage
Laboratory Compaction TestsLaboratory Compaction Tests
Why Test?
Provide moisture density curve identifying optimum moisture.
Compare the degree of compaction vs. specs (Relative Compaction, R.C.).
Compaction Laboratory Tests Compaction Laboratory Tests
• Standard Proctor Test
• Modified Proctor Test
Standard Vs. Modified Proctor CompactionStandard Vs. Modified Proctor Compaction
Standard ProctorModified Proctor
Zero Air Voids Line
S = 100%
Dry side of optimum
wopt
Wet side of optimum
Moisture-Density CurveMoisture-Density Curve
Test 1 2 3 4
w
t
d
ZAV
wt
d
1
V
Wt
s
ws
r
s
wswsZAV wG
G
S
wGG
e
G
111
Factors affecting CompactionFactors affecting Compaction
• Compactive Effort
• Moisture Content
• Soil Type
Compactive EffortCompactive Effort
Zero air void
Water content w (%)
Dry
den
sity
d (
Mg/
m3 )
Dry
den
sity
d (
lb/f
t3 )
Line of optimums
Modified Proctor
Standard Proctor
Holtz and Kovacs, 1981
d max
wopt
Soil TypeSoil Type
• Grain size distribution.
• Shape of soil grains.
• Specific gravity of soil solids.
• Amount and type of clay minerals.
Soil Type (cont’d)Soil Type (cont’d)
Zero air voids line
Sand, some fines
Clay
Dry Density
Moisture content
d max
OMCConstant compaction energyConstant compaction energy
Check Point MethodCheck Point Method
Check Point Method
Water content w %
wopt
Dry
den
sity
, d
d max
100% saturationLine of optimums
A
B
M
C
X
Y (No)
•1 point Proctor test
•Known compaction curves A, B, C
•Field check point X (it should be on the dry side of optimum)
Holtz and Kovacs, 1981
X
M
Relative CompactionRelative Compaction
Lab
Field
dmax
dmax
γ
γ100R.C.
rDCR .20.080..
Correlation between relative compaction (R.C.) and the relative density Dr
Typical required R.C. = 90% ~ 100%
mind,maxd,d
mind,dmaxd,
minmax
maxr ee
eeD
Elephant and CompactionElephant and Compaction
Heavy Weight
Question?
The compaction result is not good. Why?
He He! I’m smart.
Types of Compaction Types of Compaction
• Vibration
• Impact
• Kneading
• Pressure
Static or Vibratory
Compaction Equipments and Techniques Compaction Equipments and Techniques
• Smooth Wheel rollers
• Sheepsfoot Rollers
• Pad Rollers
• Pneumatic (Rubber-Tired) Rollers
• Grid Rollers
• Vibratory Rollers
Smooth-wheel roller (drum)Smooth-wheel roller (drum)
• 100% coverage under the wheel
• All soil types except for rocky soils.
• Contact pressure up to 380 kPa
• Compactive effort: static weight
• Most common use is for proof-rolling subgrades and compacting asphalt pavement.
Holtz and Kovacs, 1981
Sheepsfoot RollersSheepsfoot Rollers
• 8% ~ 12 % coverage
• Best for clayey soils.
• Contact pressure from 1400 to 7000 kPa
• Compactive effort: static weight and kneading.
Pad Roller
• About 40% coverage
• Best for compacting fine-grained soils (silt and clay).
• Contact pressure is from 1400 to 8400 kPa
• Compactive effort: static weight and kneading.
Pneumatic Rollers Pneumatic Rollers
•80% coverage under the wheel.
•Bet for Granular and fine-grained soils.
•Contact pressure up to 700 kPa.
•Compactive effort: static weight and kneading.
Grid RollersGrid Rollers
• About 40% coverage
• Contact pressure is from 1400 to 8400 kPa
• Best for compacting fine-grained soils (silt and clay).
• Compactive effort: static weight and kneading.
Vibratory CompactorsVibratory Compactors
•Compactive effort: static weight and vibration.
•Suitable for granular soils
Compaction Type Vs. Soil TypeCompaction Type Vs. Soil Type
Materials
Vibrating SheepsfootRollers
Static SheepsfootGrid RollerScraper
Vibrating Plate CompactorVibrating RollerVibrating Sheepsfoot
ScraperRubber-tired RollerLoaderGrid Roller
Lift Thickn
essImpact
Pressure(with
kneading)Vibration
Kneading(with pressure)
Gravel 12+ Poor No Good Very Good
Sand 10+/- Poor No Excellent Good
Silt 6+/- Good Good Poor Excellent
Clay 6+/- Excellent Very Good No Good
Compaction Difficulty Vs. Soil TypeCompaction Difficulty Vs. Soil Type
Fill Materials
PermeabilityFoundation
SupportPavement
SubgradeExpansive
CompactionDifficulty
Gravel Very High Excellent Excellent No Very Easy
Sand Medium Good Good No Easy
Silt Medium Low Poor Poor Some Some
Clay None+ Moderate Poor Difficult Very Difficult
Organic Low Very Poor Not Acceptable Some Very Difficult
Field DensityField Density
• Destructive Testing: Sand Cone Core Cutter Rubber Balloon
• Nondestructive Testing: Nuclear Density
Sand Cone TestSand Cone Test
W1= mass of sand cone before testW2 = mass of sand cone after test W3 = mass of sand filling cone and hole (W3 = W1-W2)W4 = mass of sand filling the cone = sand*Vcone W5 = mass of sand filling the hole = W3-W4
Vhole = W5 / sand
W6 = mass of soil extracted from the whole w = moisture content of soil
W1
W2
Standard Sand with known Gs
W4
W5
wt
d
1
holeV
Wt
6
s
w
W
Ww
Sand Cone Test ProcedureSand Cone Test Procedure
• A small hole (6" x 6" deep) is dug in the compacted material to be tested.
• The soil is removed and weighed, then dried and weighed again to determine its moisture content.
• The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device.
• The dry weight of the soil removed is divided by the volume of sand needed to fill the hole.
• This gives the density of the compacted soil.
Nuclear DensityNuclear Density
• Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content.
• The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission).
• The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit.
• Dense soil absorbs more radiation than loose soil and the readings reflect overall density.
• Water content can also be read, all within a few minutes.