Evaluating Flexible Pavement Rut Damage

8/10/2019 Evaluating Flexible Pavement Rut Damage

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Evaluating Flexible Pavement Rut Damage

Caused by Multiple Axle and TruckConfigurations

Hassan Salama, Ph.DResearch associate

Karim Chatti, Ph.D

Associate professor

Michigan State University


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Background

Newly proposed Mechanistic-EmpiricalPavement Design Guide (M-E PDG) in

the U.S. does away with the ESAL

concept and uses instead axle loadspectra to calculate pavement damage

Therefore, it is important to evaluate

pavement damage caused by multiple

axles.


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Background ME-PDG Procedure

Sum the strain values ?

Ignore the strain rate ?


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Background

Two approaches for rutting prediction

Rutting at surface of subgrade layer only

Asphalt Institute (AI) model (Shook et al., 1982)

Shell Petroleum model (Claussen et al., 1977)

Rutting contribution from all pavement layers

New M-E PDG (AC and unbound materials)

VESYS rutting model

( ) * *n np e

=


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VESYS Rutting Model

( ) ( ) ( ) ( )

( ) ( )

AC base

SG

1 1AC basep AC ,AC base ,base

1 1AC base

1SGSG ei,SG

1SG

1- 1-

1-

K K

i ei i eii i

K

ii

h n h n

h n

= =

=

= +

+

p

= Constant indicating the rate of rutting decrease as the number= Constant indicating the rate of rutting decrease as the number of loadof load

applications increases.applications increases.

= Constant of proportionality between plastic and elastic strain= Constant of proportionality between plastic and elastic strain, and, and

= Compressive vertical elastic strain at the middle of the layers,e

= Number of load applications,n

= Layer thickness for AC, combined base and subgrade layers, respectively (mm),

= Number of axle groups,K

= Subscript indicating axle group,i

= Total cumulative rut depth (mm),

h

PDPsPDPs


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VESYS Rutting Model Calibration

The most likely solution for PDPs ( & )

obtained for 109 pavement sections withinthe SPS-1 experiment based on the analysisof transverse surface profile

(Salama et al, 2006 TRB publication)

Material properties, structural and climaticdata were introduced into the multiple linearregression models

(Salama et al, 2006 TRB presentation)


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Multiple Linear Regression Models for PDPs

( )0.555 1.013 0.58 0.732

105105.124* * *( ) *( )HMA Strain P VFA MAA T =

4.102 0.2136.746 * *HMA AC FI

=

0.0985 0.102 0.066 1.9822002.724*10 *modulus *Thickness * *base P GI =

3 0.808 0.8096.2567.1977 *10 * *Thickness *strainbase base =

5 0.043 1.89 0.116 0.036 0.3260.14321.385 10 * * * * * * wet daysSG

strain GI PI D FI =

304.1*594.22*764.0*41.2mod*6310*575.2 PIGIstrainulusSG

=

AC

Base

SG


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AnalysisAxle and Truck configurations used in the analysis

Pavement cross-sections and moduli


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Strain Pulses under Multiple AxlesKENLAYER (Huang, 1993)

Single axle 13 kips & tire pressure 100 psi

Multiple axle Multiple of 13 kips & spacing 42


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Strain Pulses for Thick Pavement

0.0E+00

5.0E-05

1.0E-04

1.5E-04

0 200 400 600 800

Distance, in

Strain

0.0E+00

5.0E-05

1.0E-04

1.5E-04

0 200 400 600 800

Distance, in

Strain

0.0E+00

5.0E-05

1.0E-04

1.5E-04

0 200 400 600 800

Distance, in

Strain

8-axle groupAC layer

Base layer

SG1 layer


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Strain Pulses for Thin Pavement8-axle group

AC layer

Base layer

SG1 layer

-5.0E-050.0E+005.0E-051.0E-041.5E-042.0E-042.5E-04

0 200 400 600 800

Distance, in

Strain

-5.0E-050.0E+005.0E-05

1.0E-041.5E-042.0E-042.5E-04

0 200 400 600 800

Distance, in

Strain

-5.0E-050.0E+005.0E-051.0E-041.5E-042.0E-04

2.5E-04

0 200 400 600 800

Distance, in

Strain


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Calculated PDPs

The PDPs for the two cross-sections were calculated

from the regression equations based on pavement layer

thicknesses and moduli

Other variables were assumed at the mean values of

the range used to develop the regression equations


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Rut Damage

0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

0 100 200 300 400 500 600 700 800

Distance, in

Strain

Strain underneath the axles

Strain outside the axlesStrain outside the axles

Procedure 1- strain values underneath each axle within an

axle group

Procedure 2- strain values underneath the axles andoutside the axle group until the strain becomes negligible

Strain influence curve under an 8-axle group


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Results

axlesingleatoduedepthRut

groupaxlegivenatoduedepthRut=AF

axlesingleatoduedepthRut

kgiven trucatoduedepthRut=TF

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Stan.-Axle Single Tandem Tridem Quad 8-axles

Axle configurations

Rutde

pth,in

AC Base SG TotalAs an exampleAs an example

Total and per layer rutdepth for axles due to

one million repetitions


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Procedure 2

Axle factors - section 1

Truck factor - section 1

Axle factors - section 2

Truck factor- section 2

0.0

1.02.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

Single Tandem Tridem Quad 8-axles

Axle configurations

Axlefactor

.

AC Base SG Total

0.0

1.02.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

Single Tandem Tridem Quad 8-axles

Axle configurations

Axlefactor

.

AC Base SG Total

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

S5 S1T2 S1T2Tr2 S3T2Q1 S1T1E1

Ttruck configurations

Truckfactor

.

AC Base SG Total

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

S5 S1T2 S1T2Tr2 S3T2Q1 S1T1E1

Truck configurations

Truckfactor

.

AC Base SG Total


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Laboratory Results

Sample preparation Unconfined cyclic

compression load test set up


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Loading and unloading time

tS 9 tS tS 9 tS tS 9 tS time

Stress

9 tT tT 9 tT tT 9 tTtT

Sustain stress

Stress

time

1

2

Interaction= 1/2

time9 tQtQ9 tQtQ9 tQtQ

Stress

timetS1T1E1 9 tS1T1E1 tS1T1E1

Stress

Single axle

Tandem axle

Quad axle

Truck S1T1E1


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Laboratory Axle Factor

R2= 0.98

0

1

2

3

45

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10

Axle configuration

Axle

factor

Identity line

axle group single axle

axle group

single axle

1

Damage of the axle group=

1Damage of the single axle

f f

f

f

N NAF

N

N

= =

Near proportionality of rut damage for multiple axlesNear proportionality of rut damage for multiple axles


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Laboratory Axle factors

R2= 0.97

0

1

2

34

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10

Axle configuration

Axlefactor

Identity line

R2= 0.98

0

1

2

34

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10

Axle configuration

Axlefactor

Identity line

Fatigue Rutting


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Comparison with M-E PDG Prediction Tandem Axle

0.0

0.5

1.0

1.5

2.0

2.5

Lab

M-EP

DG

procedure

M-EP

DG

Softw

are

Lab

M-EP

DG

procedure

M-EP

DG

Softw

are

Method of calculating Axle Factor

A

xleFactor

RuttingFatigue


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Laboratory Truck Factortruck single axle

truck

single axle

1

Damage of the truck=

1Damage of the single axle

f f

f

f

N NTF

N

N

= =

02468

10121416

S5

S5

S1T2

S1T2

S1T2Tr2

S1T2Tr2

S3T2Q1

S3T2Q1

S1T1E1

S1T1E1

Truck configurations

Truc

kfactor

. 5-axles 11-axles

variable rest periods between axle groups affect the cumulativevariable rest periods between axle groups affect the cumulative rutrutdamage differentlydamage differently


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ConclusionsThere is little to no interaction between

axles for vertical strains within the AC layer

The interaction between axles in the base

layer increases with increasing AC layerthickness

There is always high interaction betweenaxles in the subgrade layer vertical strainresponse


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ConclusionsMechanistically, Rutting damage is

proportional to the number of axles within

an axle group or truck

Laboratory results confirmed the near

proportionality of rut damage for multipleaxles

For trucks, the variable rest periodsbetween axle groups appear to affect thecumulative rut damage differently


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Thank you!

Any questions?

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Evaluating Flexible Pavement Rut Damage