3.Flexible Pavement

7/29/2019 3.Flexible Pavement

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AASHTOflexiblepavementdesign


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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Relatedto

Roughness Rutdepth


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Cracking Patching


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0 5

PresentServiceabilityIndex

Poor Excellent


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Initial(pi) brandnew

Termina pt e oreresur acingreconstruction

ecommen e va ue

Initial 4.2or4.5

Terminal 2.5

or

3.0


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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.


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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D

r

r


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ForfinegrainsoilswithCBRof10orless

2

r


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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Thicknessofeachlayercanbereducedifmateria strengt isa ovet eminimumva ue


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Thicknessof

surface

(1),

base

(2),

and

subbase (3)

SN DaDaDa

Strengt

coe c ento

sur ace

1 ,

ase

2 ,

an

subbase (3)


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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affectedby

empera ure a n a


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erma

s ress

Creepproperties

Freezing/thawing

Watergets

layers


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Resilientmodulusof

roadbedvarieswith

time

season


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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Incorporatingafactor

for

the

base

and

su ase coe c en

Modification

to

SN

332211SN DaDaDa

33322211

SN mDamDaDa


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Quality of Drainage Water removed within*

Excellent 2 hours

Fair 1 week

oor mon

Very Poor (water will not drain)

*Timerequiredtodrainthebaselayerto50%

sa ura on.


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Quality of

Percent of Time Pavement Structure is Exposed to MoistureLevels Approaching Saturation

Drainage

Less than 1% 1 5% 5 25%

Greater than

25%

. . . . . . .

Good 1.35 1.25 1.25 1.15 1.15 1.00 1.00

Fair 1.25 1.15 1.15 1.05 1.00 0.80 0.80

Poor 1.15 1.05 1.05 0.80 0.80 0.60 0.60

Very Poor 1.05 0.95 0.95 0.75 0.75 0.40 0.40


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability

Designmethod

Example


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performedsatisfactorily

during

the

design

.

99%reliability=99%chanceforsuccessful


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FunctionalClassification

ecommen e eve o e a y

Interstate and 85 99.9 80 99.9

Principal 80 - 99 75 95

Collectors 80 - 95 75 95

Local 50 - 80 50 - 80


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ZR =standard

normal

variate

0

( )


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Reliability(R%) ZR

50 0.000

60 0.253

70 0.524

800.841

.

95 1.645

.

97 1.881

.

99 2.327

. .

99.993.750


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99%oftheareaundercurve

ZR =2.327


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Trafficforecast

Flexiblepavement 0.40 0.50

Rigidpavement 0.30 0.40


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability Designmethod

Example


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numberand

the

thickness

of

each

layer

,


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MR =5000psiPSI=1.9

X103

95%reliability

=

5

x

106

ESAL SN

=

5.0


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ra c, sp a oncre e ggrega e ase

Less than 50,000 1.0 (or surface 4

50,001 150,000 2.0 4

150,001 500,000 2.5 4

500 001 2 000 000 3.0 6

2,000,001 7,000,000 3.5 6

Greater than 7,000,000 4.0 6


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Pavementperformance

Traffic

Subgrade material

Materialof

construction

Environment

Drainage

Reliability Designmethod

Example


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Determineasuitableflexiblepavementstructureforan

2x106.

It

is

estimated

that

it

takes

about

aweek

for

water

tobedrainedfromwithinthe avementandthe avement

structurewillbeexposedtomoisturelevelsapproaching

saturationfor

30%

of

the

time.

The

following

additional

informationisavailable.

2 ,

CBRvalue

of

base

course

material

=100,

Mr =31,000lb/in

2

CBRvalueofsubbase coursematerial=22,Mr =13,500lb/in2

CBRvalueofsubgrade coursematerial=6


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=

Standarddeviation

(S0)

=0.45

(0.4

0.5

for

Initialserviceabilityindex(p

i)=4.5

Terminalserviceabilityindex(pt)=2.5


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=

Standarddeviation

(S0)

=0.45

(0.4

0.5

for

Trafficload=2x106 ESALs

MR ofsubgrade =1500x6=9000psi(forfinegrainsoilswithCBRof10orless)

PSI=pt pi =

4.5

2.5

=2.0


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MR =9000psiPSI=2.0

X103

99%reliability

=

2

x

106

ESALSN=4.1

SN mDamDaDa


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33322211SN mDamDaDa

Itis

estimated

that

it

takes

about

aweek

for

water

to

be

drainedfromwithinthepavementandthepavement

saturationfor

30%

of

the

time.

Quality of DrainageWater removed

*

Excellent 2 hours

Good 1 day

Fair 1 weekoor mon

Very Poor (water will not drain)

Quality ofDraina e

Percent of Time Pavement Structure is Exposed to MoistureLevels Approaching Saturation

m=0.80

Less than 1% 1 5% 5 25%

25%

Excellent 1.40 1.35 1.35 1.30 1.30 1.20 1.20

Good 1.35 1.25 1.25 1.15 1.15 1.00 1.00

Fair 1.25 1.15 1.15 1.05 1.00 0.80 0.80

Poor 1.15 1.05 1.05 0.80 0.80 0.60 0.60

Very Poor 1.05 0.95 0.95 0.75 0.75 0.40 0.40


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33322211SN mDamDaDa

Finda1,a2,anda3fromcharts


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.

Resilientmodulus

of

asphalt

concrete

at

68

F=450,000

lb/in

2


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CBRvalueofbasecoursematerial=100 M =31 000lb in2


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CBRvalueofsubbase coursematerial=22,Mr =13,500lb/in2


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..

. . . . .. . .. .

. ..

D2

1

SN2

SN1 . . . . . . . . .. . . .

SN3

Subbase Course D3

RoadbedCourse

111SN Da

222112SN mDaDa

333222113 = .

UsecharttofindSN2 ChangeMR totheoneofsubbase


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2

MR =13,500psiPSI=2.0

X103

99%reliability

=

2

x

10

6

ESALSN

2=3.6

UsecharttofindSN1 ChangeMR totheoneofbase


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1

MR =31,000psiPSI=2.0

X103

99%reliability

=

2

x

10

6

ESALSN

1=2.7

SN D

Values

SN1 2 7


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SN1 =a1D1SN1 2.7

2.7=0.44xD1SN3 4.1

a1 0.44

D1 =6.13

in

a2 0.14

a3 0.10

Roundedupto6.5in

(usually

rounded

up

to

the

nearest

0.5

in)SN1*=0.44x6.5=2.86

* .

Values

SN1 2 7


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SN1 2.7

SN2 =SN1*+a2D2m2SN3 4.1

a1 0.44

3.6=2.86

+(0.14

xD2 x

0.80)

a2 0.14

a3 0.10

D2 =6.61in

Roundedupto7.0in

SN2*=2.86

+(0.14

x7.0

x0.80)

=3.644

Values

SN1 2 7


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SN1 2.7

SN3 =SN2*+a3D3m3SN3 4.1

a1 0.44

4.1=3.644

+(0.10

xD3 x

0.80)

a2 0.14

a3 0.10

D3 =5.7in

Roundedupto6.0in

SN3*=3.644

+(0.10

x6.0

x0.80)

=4.124

ShouldbeclosedtotheSNthatyougotatthebeginning


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Therefore,thepavementconsistsof

.

7in

of

granular

base

Th ffi h d i l f d f l l i


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Thetrafficonthedesignlaneofaproposedfourlaneruralinterstate

g waycons sts

o

truc s.

c ass cat on

stu es

ave

s own

thatthetruckfactorcanbetakenas0.45,designasuitableflexible

pavementiftheAADTonthedesignlaneduringthefirstyearof

operationis1,000andpi =4.2.

Designlife=20years

Reliability

level

=

95%Standarddeviation=0.45

pt =2.5

Thepavement

structure

will

be

exposed

to

moisture

levels

approachingsaturation20%ofthetimeanditwilltakeabout1week

. , , ,

22,and70,respectively. MR fortheasphaltconcreteis450,000psi.

Documents

3.Flexible Pavement