Transcript Soil Compaction Compaction • Compaction is the method of mechanically increasing the density of soil by removal of air. • Dry density (gd)

Soil Compaction
Compaction
• Compaction is the method of mechanically
increasing the density of soil by removal of air.
• Dry density (gd) is the measure of the degree of
compaction.
Why Compaction?
• Increase bearing capacity
• Increase stability of slopes of embankments
• Reduce compressibility
• Reduce permeability
• Reduce volume changes
• Prevent frost damage
Laboratory 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
• Standard Proctor Test
• Modified Proctor Test
Standard Proctor Test
V = 1/30 ft3
(944 cc)
Ww
w
Ws
W
gt 
V
gd 
gt
1 w
S r e  w Gs
Standard Vs. Modified Proctor Compaction
Standard Proctor
Modified Proctor
Moisture-Density Curve
Zero Air Voids Line
S = 100%
Dry side of optimum
Wet side of optimum
W
gt 
V
Test
gd 
1
2
3
gt
1 w
wopt
4
w
gt
gd
gZAV
g ZAV
Gs g w
Gs g w
Gs g w



wGs 1  wGs
1 e
1
Sr
Allowable Moisture
Allowable Moisture = (OMC – 3%) to (OMC + 2%)
Factors affecting Compaction
• Compactive Effort
• Moisture Content
• Soil Type
Zero air
void
Line of
optimums
gd max
Modified
Proctor
Standard
Proctor
wopt
Water content w (%)
Holtz and Kovacs, 1981
Dry density d (lb/ft3)
Dry density gd (Mg/m3)
Compactive Effort
Soil Type
• Grain size distribution.
• Shape of soil grains.
• Specific gravity of soil solids.
• Amount and type of clay minerals.
Soil Type (cont’d)
Dry
Density Sand, some fines
Zero air
voids line
gd max
Clay
OMC
Constant compaction energy
Moisture
content
Check Point Method
Check Point Method
Line of
optimums
100% saturation
• Known compaction
curves A, B, C
• Field check point X
(it should be on the
dry side of optimum)
Dry density, gd
• 1 point Proctor test
A
Y (No)
gd max
B
XX
MM
C
wopt
Water content w %
Holtz and Kovacs, 1981
Relative Compaction
 γ dmax Field 

R.C.  100 
 γ dmax 
Lab 

Correlation between relative compaction (R.C.)
and the relative density Dr
R.C.  80  0.20 .Dr
Dr 
g d,max g d g d,min 

e min  g d g d,max g d,min 
e max  e
e max
Typical required R.C. = 90% ~ 100%
Field Compaction
Elephant and Compaction
He He! I’m smart.
Question?
The compaction result is
not good. Why?
Heavy Weight
Types of Compaction
• Vibration
• Impact
• Kneading
• Pressure
Static or Vibratory
Compaction Equipments and Techniques
• Smooth Wheel rollers
• Sheepsfoot Rollers
• Pad Rollers
• Pneumatic (Rubber-Tired) Rollers
• Grid Rollers
• Vibratory Rollers
Smooth-wheel roller (drum)
• 100%
wheel
coverage
under
the
• All soil types except for rocky
soils.
• Contact pressure up to 380
kPa
• Compactive effort: static weight
• Most common use is for proofrolling subgrades and
compacting asphalt pavement.
Holtz and Kovacs, 1981
Sheepsfoot 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 finegrained soils (silt and clay).
• Contact pressure is from 1400
to 8400 kPa
• Compactive effort: static weight
and kneading.
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 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 Compactors
•Compactive effort: static weight and
vibration.
•Suitable for granular soils
Compaction Type Vs. Soil Type
Materials
Vibrating
Static
Sheepsf
Sheepsfoot
oot
Grid Roller
Rollers
Scraper
Lift
Thickn
ess
Gravel
Impact
Pressure
(with
kneading)
Vibrating Plate
Compactor
Vibrating Roller
Vibrating
Sheepsfoot
Vibration
Scraper
Rubber-tired
Roller
Loader
Grid Roller
Kneading
(with pressure)
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 Type
Fill Materials
Gravel
Sand
Silt
Clay
Organic
Permeability
Foundation
Support
Very High
Excellent
Medium
Pavement
Subgrade
Expansive
Compaction
Difficulty
Excellent
No
Very Easy
Good
Good
No
Easy
Medium Low
Poor
Poor
Some
Some
None+
Moderate
Poor
Difficult
Very Difficult
Low
Very Poor
Not Acceptable
Some
Very Difficult
Field Density
• Destructive Testing:
Sand Cone
 Core Cutter
 Rubber Balloon

• Nondestructive Testing:

Nuclear Density
Sand Cone Test
W1
Standard Sand with
known Gs
W2
W4
W5
W1= mass of sand cone before test
W2 = mass of sand cone after test
W3 = mass of sand filling cone and hole
(W3 = W1-W2)
W4 = mass of sand filling the cone = gsand*Vcone
W5 = mass of sand filling the hole = W3-W4
Vhole = W5 / gsand
W6 = mass of soil extracted from the whole
Ww
w = moisture content of soil
w
W6
gt 
Vhole
gd 
gt
1 w
Ws
Sand 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.
Core Cutter
Static Load
Suitable for
cohesive soils only
W
gt 
V
gd 
5 in
gt
1 w
4 in
Rubber Balloon
Nuclear 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.
Nuclear Density