subgrade and pavements
TRANSCRIPT
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ANDI OGENG ALAMSYAH
D62108270
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PAVEMENT STRUCTURE
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TYPES OF SUBGRADES
a Material in place; soils in a cut section
b Imported material; borrow material and
regular excvation material
c
Treated material; improves engineeringproperties of the soil, provides platform
to compact subsequent layers
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DEPTH OF SUBGRADES
Type of load applications The pavement type
Flexible 2
Rigid 1,5
Mine haul access Dynamic/very heavy Flexible 1,5
Rail Dynamic/very heavy Flexible/rigid 1,25
Flexibe 1
Rigid 0,75
Industrial building Dynamic/static/heavy Rigid 0,75
Flexible 0,75
Rigid 0,5
Walkways/bike paths Static/light Rigid/flexible 0,25
Major roadDynamic heavy
Minor roadsDynamic/medium
Application Type of load Pavement typeSubgrade
depth (m)
Commercial and
residential buildingStatic/medium Rigid 0,5
AirportDynamic/extra heavy
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CONTACT PRESSURE OF PAVEMENT TYPES
Flexible
foundations, onsands and claysapproximately
similar
Rigid foundations
On sands, maximum
pressure is at middle On clays, maximum
pressure is at edge
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CONTACT PRESSURE OF THICKNESS STRUCTURE
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SUBGRADE STRENGTH
The subgradestrenght defined ofsoaked CBR
CBR or CaliforniaBearing Ratio is asimple strength testthat compares thebearing capacity of
subgrade materialand as meaning ofdesigning the roadpavement required fora particular strength
of subgrade.
The stronger thesubgrade on theCBR, the less thick it
is necessary todesign and constructthe road pavement.
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SUBGRADE STRENGTH CLASSIFICATION
3% - 10% Medium10% - 30% Strong
> 30 % Extremely strong
2% - 3% Weak
1% - 2% Very weak
< 1 % Extremely weak
Geotextile reinforcement and/or separation layerand/or a working platform typically required
Geotextile separation layer and/or a working platform
typically required
Sub-base to base quality material
Good subgrade to sub base quality material
CommentsSoaked CBRStrength
classification
Geotextile reinforcement and separation layer with a
working platform typically required
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VOLUMETRICALLY ACTIVE CLAYS
volumetricallyactive clays
Swelling due
to wetting /shringkage
due to drying
Swellingpressures
wheremovement is
prevented
Loss ofstrength dueto swelling or
shrinkage
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SUBGRADE VOLUME CHANGE
A subgrade strengthcriteria based on CBRnot be adequate for
volume change criteria.
The Weighted PlasticityIndex (WPI) can be
used for asesesment
Materials with a verylow volume change
material potential tendsto be high CBR material
Clayes material may stillhave swell after days.
Any WPI > 3200 shoulduse a 7 day soaked test
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MINIMISING SUBGRADE VOLUME CHANGE
Placing the material as close as possible to its equilibrium moisture contentand density
Giving the pavement thickness may be sufficient for nothing improved
subgrade layer.
Stabilizationing of the subgrade may be required, for the thickness indicated.
Providing a suitable non volumetrically active capping layer
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SUBGRADE MOISTURE CONTENT
500 50% - 90% OMC 70%-100% OMC 50%-80% OMC
500-1000 70%-120% OMC
1000-1500 70%-110% OMC 110%-130% OMC 110%-140% OMC 1500 130% - 160% OMC
WPI < 1200 (Low
Correlation)
(Medium
Correlation)
WPI > 3200 (High
Correlation)
Equilibrium Moisture Content
Median annual
rainfall
Median value forall rainfall
80% OMC 100% OMC 115% OMC
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SUBGRADE STRENGTH CORRECTION FACTOR
CBR value needs to be factored to be used appropriately in itsclimatic environment
Soil with PI < II Soil with PI> II
Rainfall 600mm 1 - 1,5 1,4 - 1,8
600mm < rainfall 1000 mm
0,6 - 1,1 1 - 1,4Rainfall > 1000 mm 0,4 - 0,9 0,6 - 1
Climatic zone Soil Type
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TYPICAL VALUES OD SUBGRADE CBR
eg Sandstones, granite, greywacke, All 20
Well Graded, poorly graded
GM,GC All 15
eg Shales, mudstones All
Sands SM, SC Silty, clayey Good 10
Sands SM, SC Silty, clayey Poor 7
Inorganic Silts ML Low plasticity Good
Inorganic Silts ML Low plasticity Poor 5
Inorganic Clays CL Low plasticity Good
Inorganic Clays CH High plasticity Good
Inorganic Silts MH High plasticity Good 3
Inorganic Clays CL Low plasticity Poor
Inorganic Silts MH High plasticity Poor
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PROPERTIES OF MECHANICALLY STABLE
GRADINGS
Gradation is the key aspect to obtaining a mechanically stable pavement
The first step in development of a suitable specifications
40% -20% 70% - 40% 0%-40%
20% -10% 40% - 20% 40%-60%
15%- 10% 20% - 10% 60%-70%
Light traffic
Heavy traffic wearing course
Heavy traffic base course
> 50 % > 80% 0%
% passing 75 micron
"fine material"
% passing 425 micron
medium sand or less% > 2 mm gravel sizeAppication
Unstable in wet due to high
volume change
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SOIL STABILIZATION WITH ADDITIVES
Bitumen(asphalt)additives
typically 1to10%. Best suited
to ClayeyGravels
Lime additivestypically 1,5% to 8%.Best suited to silts
and clays
Cement additvetypicaly 5 to
10%. Bestsuited to clayey
sands
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TYPICAL PAVEMENT STRENGTH
REQUIREMENTS
Conditions CBR strength
"Standard" requirements 80% soaked
Low Traffic roads 6o% unsoaked
30%
> 30% unsoaked
>15%
Comments
Rural traffic roads/arid to
semi-arid regions
On Major roads at least 100 mm of
pavement layer > 80% CBR
Top 100 mm of base layer
Subbase
Upper subbase
Lower subbase
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CBR VALUES OF PAVEMENT MODULUS
Pavements requirecompaction to
achieve its requiredstrength anddeformationproperties
Existing pavementswoud have reducedvalues for asphalt
and cementedmaterials to reduced
cracking.
Degree ofanisotropy is ratio of
vertical to horizontalmodulus
1 for asphalt andcemented material
2 for granular material
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TYPICAL VALUES OF EXISTING PAVEMENT
MODULUS (AUSTROADS, 2004)
Cracked Modulus (Mpa)
15 105025 880
40 620
Cemented material Post fatigue phase 500
Existing Pavement Layer
Asphalt at temperature (C)
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POISSON RATIO OF ROAD MATERIALS
Poisson ratio is the ratio of the relative transverse (horizontal) strain
normal to the axial (vertical) strain in the direction of the applied load.
Poisson Ratio0,40
0,35
0,30
0,25-0,400,3
0,15
MaterialAsphaltic
Granular
Cement Treated
Subgrade Soils
Unweathered Bedrock Subgrade
Weathered Rock Subgrade