pavement overlay or new design.ppt

7/27/2019 pavement overlay or new design.ppt

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Design of New Flexible Pavement / Overlay


2/20

Design Problem

1. Lane width 3.5m

2. Design life 10 years

3. Year of opening for Traffic 2012

4. Number of lanes 4

Assuming above values design suitable pavement sections

Using AASHTO Guide.


3/20

AASHTOConcept Adoption of Structural Number Concept.

(Calculation of SN for a new pavement on existing road bed soil

for anticipated traf f ic using AASTHO formula.)

This method makes Provision on probability basis.

takes into account -

traffic variation Performance prediction It is also required to identify initial and terminal levels

of Serviceability.

Structural Number (SN) = Structural Coff: x Layer Thickness

SN = ai x Di ( for the i th layer)


4/20

Design of New Flexible Pavement Structure

Using AASHTO Formula

20.01log36.9log 1001810 calcR SNSZW

07.8log32.2

)1(

109440.0

)5.12.4

1(log

10

19.5

10

R

calc

M

SN

PS

a b c

de f

S 0-combined standard error of Traffic prediction and performanceprediction

PSI -Difference between the initial design serviceability index &design terminal serviceability indexMR-Resilience Modulus of Sub Grade in psi

Z RStandard Normal Deviate

W18Predicted Nos. of 18 kip equivalent single axle load application


5/20

Design Inputs in the AASHTO Formula

Calculation

W18(Estimated Future Traffic)

R(Reliability)

S0(Overall standard deviation)

PSI

MR(Resilient modulus of the roadbed soil)
http://localhost/var/www/apps/conversion/tmp/scratch_10/Traffic%20data%208th%20KmNew%20Microsoft%20Excel%20Worksheet%20(2).xlshttp://localhost/var/www/apps/conversion/tmp/scratch_10/Traffic%20data%208th%20KmNew%20Microsoft%20Excel%20Worksheet%20(2).xls


6/20

Design Variations

Traffic

The design procedures are based on cumulative expected 18-kip

equivalent single axle loads (ESAL) during the analysis period. ( 18)

W 18 = D D x D L x 18Where,

D D = A directional distribution factor ( 0.3 ~ 0.7)

DL = Lane distribution factor (where two or more lanes){.81.0 18= the cumulative two-directional 18-kip ESALunits predicted during the analysis period

DD & DL combined together in the RDA manual.


7/20

Traffic

AADT ESA

Growth Factor

Equivalent Standard Axle Load

Factor

CNSA

(7 mil lion)

LaneDistrib

utionFactor
http://localhost/var/www/apps/conversion/tmp/scratch_10/Traffic%20data%208th%20KmNew%20Microsoft%20Excel%20Worksheet%20(2).xls


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Reliability

For variation in both traffic prediction & performance prediction.

Reliability , Pavement Thickness

Reliability for various functional classifications.

Functional

classification

Recommended level of Reliability(%)

Urban Rural

Interstate & other

freeways

85-99.9 80-99.9

Principal Arterials 80-99 75-95

Collectors 80-95 75-95

Local 50-80 50-80

Stage Construction (Overall reliability of the design strategy.)

R = 95%, ZR

= -1.645


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S0

For variation in traffic prediction & pavement performanceprediction for the design traffic.

S0= 0.45 ( for f lexible pavement)


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Serviceability

Ability to serve the traffic which use the facility.

PSI range from 0(impossible road) ~ 5(perfect road)

PSI = P0 - P t

Initial serviceability index

P0=4.2(flexible pavement)

Terminal serviceability index

(lowest index before performed

rehabilitation/resurfacing/reconstruction)

PSI = 2.1

Design serviceability loss


11/20

P1

P2

1.5Np

N1.5 Nf

Existing Pavement

Overlaid Pavement

N Load Applications

Serviceability

Terminal Serviceability Index

Initial Serviceability Index


12/20

MR( Resilience Modulus of Sub Grade in psi)

Sub Grade CBR = 6.0

MR = 145 x 17.6 x CBR0.64 for CBR > 5

= 145 x 17.6 x (6)0.64

= 8033
http://localhost/var/www/apps/conversion/tmp/scratch_10/CBR%20Values%20New%20Microsoft%20Excel%20Worksheet.xlshttp://localhost/var/www/apps/conversion/tmp/scratch_10/CBR%20Values%20New%20Microsoft%20Excel%20Worksheet.xls


13/20

Nomograph

R=95%, S0=0.45,

W18=7million,

Mr=30000,

PSI=2.1

SN(nomograph)=3.0

SN(calc.) = 2.92


14/20

Traffic, ESALs AC (inch) AggregateBase(inch)

Less than 50,000 1.0(or surface

treatment)

4

50,001150,000 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

Minimum Thickness ( inches)


15/20

Results: Proposed Pavement Structures

Layer Thickness (inch)

AC 8 2 4 4

ABC 7 14 8 9

SSB 4 17 17 16

AC(4)

ABC(8)

SSB(17)

SG CBR =6


16/20

Design of OverlayUsing AASHTO Formula

Existing Pavement

Composition

Structural Number of

Existing Pavement

Structural Number to be provided

Structural Number Required{From Flexible pavement

design (= 4.59)}
http://localhost/var/www/apps/conversion/tmp/scratch_10/Pavement%20Composition%20(Ekala-Kotadenia%20road%20(B%20111).dochttp://localhost/var/www/apps/conversion/tmp/scratch_10/Pavement%20Composition%20(Ekala-Kotadenia%20road%20(B%20111).dochttp://localhost/var/www/apps/conversion/tmp/scratch_10/Pavement%20Composition%20(Ekala-Kotadenia%20road%20(B%20111).dochttp://localhost/var/www/apps/conversion/tmp/scratch_10/Pavement%20Composition%20(Ekala-Kotadenia%20road%20(B%20111).doc


17/20

SNExisting

=x

1 ii

da

ai = Strength coefficient of ith Layer

di= Thickness of i th Layer

SN1 Existing = (40x0.4+90x0.14+200x0.09)/25 = 1.9 ( 0+000~5+000)

SN2 Existing = (50x0.4+50x0.14+400x0.09)/25 = 2.5 (5+000~12+000)


18/20

Location SN req. SN existing SNprovided

0+000 ~5+000 4.59 1.90 2.69

5+000 ~12+000 4.59 2.50 2.09

From 0+000 to 5+000

AC(4)

ABC(8)

Existing Pavement

From 5+000 to 12+000

AC(4)ABC(4) but provide

min. tk(i.e. 6)

Existing Pavement


19/20

Existing Pavement

ExtensionExtension

ABC (8/6)

AC (4)

SSB(17)


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THANK YOU

pavement overlay or new design.ppt

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