Subgrade and Pavements

7/27/2019 Subgrade and Pavements

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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

Subgrade and Pavements

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