MechanisticMechanistic--Empirical Empirical P D iP D iPavement DesignPavement Design

David P. Orr, PEDavid P. Orr, PECornell Local Roads ProgramCornell Local Roads ProgramCo oc o ds ogCo oc o ds og

NYSNYS 180180 LaFargevilleLaFargevilleNYSNYS 180 180 -- LaFargevilleLaFargeville

NYSNYS 180180 LaFargevilleLaFargevilleNYSNYS 180 180 -- LaFargevilleLaFargeville800 AADT800 AADT

Q: How thick are the asphalt and Q: How thick are the asphalt and gravel layers?gravel layers?

NYS 180NYS 180 L F illL F ill800 AADT

NYS 180 NYS 180 -- LaFargevilleLaFargeville800 AADT

17 ½ in.17 ½ in.

ME Pavement DesignME Pavement DesignME Pavement DesignME Pavement Design

Why roads failWhy roads failWhy roads failWhy roads failPavement design methodsPavement design methods

M h i iM h i i E i i l d iE i i l d iMechanisticMechanistic--Empirical pavement designEmpirical pavement designThe need for seasonsThe need for seasons

MEME--PDGPDG

Why Roads FailWhy Roads Fail

What is a road?What is a road?What is a road?What is a road?

Road StructureRoad StructureRoad StructureRoad Structure

SurfaceSurfaceSurfaceSurfaceBaseBase

S bbS bbSubbaseSubbaseSubgradeSubgrade

Vehicle LoadsVehicle LoadsVehicle LoadsVehicle Loads

Load

Pavement

Subgrade

Pavement DeflectionPavement DeflectionPavement DeflectionPavement Deflection

Load

Pavement

Subgrade

Pavement DeflectionPavement DeflectionPavement DeflectionPavement Deflection

Load

PavementT

CT

C

C

T

SubgradeT

Pavement FatiguePavement FatiguePavement FatiguePavement Fatigue

Pavement FatiguePavement FatiguePavement FatiguePavement Fatigue

45° 90° 180°

Pavement Failure?Pavement Failure?Pavement Failure?Pavement Failure?

PotholesPotholesPotholesPotholesAlligator cracking Alligator cracking CorrugationsCorrugationsCorrugationsCorrugationsEdge ravelingEdge ravelingRuttingRuttingRuttingRutting

DrainageDrainageDrainageDrainage

Pavement Design MethodsPavement Design MethodsPavement Design MethodsPavement Design Methods

Pavement Design MethodsPavement Design MethodsPavement Design MethodsPavement Design Methods

ExperienceExperienceExperience Experience CatalogCatalog

E i i lE i i lEmpiricalEmpiricalMechanisticMechanistic--EmpiricalEmpirical

ExperienceExperienceExperienceExperience

NYSDOTNYSDOT Comprehensive Comprehensive Pavement Design ManualPavement Design Manual

Black or whiteBlack or white –– Asphalt orAsphalt or PCCPCCBlack or white Black or white Asphalt or Asphalt or PCCPCCMMrr –– Subgrade resilient modulusSubgrade resilient modulusESALESAL 50 d i lif50 d i lifESALsESALs –– 50 year design life50 year design life

AASHTO 1993AASHTO 1993AASHTO 1993AASHTO 1993

( ) 07.8log*32.25.12.4log

20.01log*36.9*log 10

10

101810 −+⎥⎦⎤

⎢⎣⎡

−Δ

+−++= RR M

PSI

SNSZW ( )

( )

07.8log32.2

1109440.0

20.01log36.9log 10

19.5

101810 +

++

+++ RoR M

SN

SNSZW

MechanisticMechanistic--Empirical (MEmpirical (M--E)E)MechanisticMechanistic Empirical (MEmpirical (M E)E)

Strain Base Fatigue Failure CriteriaStrain Base Fatigue Failure CriteriaStrain Base Fatigue Failure CriteriaStrain Base Fatigue Failure Criteria

T

T

V

Q: Which pavement design Q: Which pavement design method do you use?method do you use?

ExperienceExperienceExperience Experience CatalogCatalog

E i i lE i i lEmpiricalEmpiricalMechanisticMechanistic--EmpiricalEmpirical

MM--E Pavement DesignE Pavement Design

Critical Fatigue ConceptsCritical Fatigue ConceptsCritical Fatigue ConceptsCritical Fatigue Concepts

Determine failure modeDetermine failure mode mechanisticmechanisticDetermine failure mode Determine failure mode mechanisticmechanisticSelect a failure criteria Select a failure criteria empiricalempirical

D l f il d l?D l f il d l?Develop a failure model? Develop a failure model?

Fatigue Failure CriteriaFatigue Failure CriteriaFatigue Failure CriteriaFatigue Failure Criteria

32 11 kk⎞⎛⎟

⎞⎜⎛ 11

1cr

f EkN ⎟

⎠⎞

⎜⎝⎛

⎟⎟⎠

⎞⎜⎜⎝

⎛=

ε

n(ε)

cr ⎠⎝⎠⎝

ln

ln(Nf)

Locations of Critical StrainsLocations of Critical StrainsLocations of Critical StrainsLocations of Critical Strains

Load

TT T

CT

C

C

T T

CT

C

C

T

T

V

Two Most Common Two Most Common Fatigue Failure CriteriaFatigue Failure Criteria

Tensile strain in the surface (Tensile strain in the surface (εεt)t) crackingcrackingTensile strain in the surface (Tensile strain in the surface (εεt) t) crackingcrackingVertical strain on the subgrade (Vertical strain on the subgrade (εεvv) ) ruttingrutting

9492.3281.16 1

'00432.0)10( ⎟

⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛=

tsurfacef E

ECNε

Asphalt Horizontal Tensile Strain Criteria

10 000

⎠⎝

10,000

stra

in)

1,000

train

(mic

ros

Average CoefficientsK = 220.3 a = 4.260b = -0.85 (Asph. Inst.)E' = 435 100 psi

Hor

izon

tal S

t E = 435,100 psi

100100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000

N b f R titi

H

Number of Repetitions

Asphalt Inst. TRL - 1 Average NAASRA Shell Denmark DTU

902.36 15.619)10( ⎟⎟

⎠

⎞⎜⎜⎝

⎛=

VsubgradefN

ε

Subgrade Vertical Compressive Strain Criteria

⎠⎝ V

10,000

ain)

1,000in (m

icro

stra

Verti

cal S

trai

Average Coefficients

100100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000

V gK = 619.5a = 3.902

, , , , , , , , ,

Number of Repetitions

Denmark DTU Shell Average Nottingham Dorman & Metcalf TRL Asphalt Inst.

902.3⎞⎛

902.36 15.619)10( ⎟⎟

⎠

⎞⎜⎜⎝

⎛=subgradefN

ε ⎠⎝ Vε

4~⎞⎛6 1)10( ⎟⎟⎠

⎞⎜⎜⎝

⎛∝subgradefN

ε ⎠⎝ Vε

4~)( ⎞⎛N)(

()(

)(⎟⎟⎠

⎞⎜⎜⎝

⎛∝

cartruck

truckNcarN Vsubgradef

εε

)()( ⎠⎝ cartruckN Vsubgradef ε

Q: How many passes by a standard Q: How many passes by a standard automobile are needed to equal the automobile are needed to equal the damage of one fully loaded 10damage of one fully loaded 10--wheelwheeldamage of one fully loaded 10damage of one fully loaded 10--wheel wheel

dump truck?dump truck?

5,0005,000--10,00010,0005,0005,000 10,00010,000

Elastic Layer TheoryElastic Layer TheoryForward CalculationForward Calculation

P, aP, a

EE11,,ηη11,t,t11ΘΘ TrafficTrafficPP = Load= Load

EE22,,ηη22,t,t22RR

P P Load Loada a = Area= Area

Pavement layersPavement layers

EE33,,ηη33,t,t33Stress Stress σσX,Y,ZX,Y,ZStrainStrain εεX Y ZX Y Z

Pavement layersPavement layersEEii = Modulus= Modulusηηii == Poisson’s ratioPoisson’s ratioStrain Strain εεX,Y,ZX,Y,Z

Disp. Disp. δδX,Y,ZX,Y,Z

ηηii Poisson s ratioPoisson s ratiottii = Thickness= Thickness

EE44,,ηη44,,∞∞

Miner’s Hypothesisyp

n ffnD =

D = amount of damage (%)

fNdamage (%)

f

Simple PavementSimple PavementSimple PavementSimple Pavement

AsphaltAsphalt 8 inches8 inches 158,000 psi158,000 psi

Subbase 12 inches 36 400 psiSubbase 12 inches 36,400 psi

Upper Subgrade 30 inches 14,700 psi

Lower Subgrade ∞ 13,300 psi

9492.3281.16 1

'00432.0)10( ⎟

⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛=

tsurfacef E

ECNε

ESALESAL LoadLoad9 0009 000 lbslbs

Asphalt Horizontal Tensile Strain Criteria

10 000

⎠⎝ ⎠⎝ t 9,000 9,000 lbslbs

10,000

stra

in)

1,000

train

(mic

ros

Average CoefficientsK = 220.3 a = 4.260b = -0.85 (Asph. Inst.)E' = 435 100 psi

Hor

izon

tal S

t E = 435,100 psi

100100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000

N b f R titi

H

Number of Repetitions

Asphalt Inst. TRL - 1 Average NAASRA Shell Denmark DTU

ESALESAL LoadsLoadsESALESAL LoadsLoads

ESALESAL LoadLoad NNffn9,000 9,000 lbslbs 9,420,0009,420,000fn

D =fN

5,000 5,000 AADTAADT nnff ==4,710,0004,710,000

f

ff

Single LoadSingle LoadSingle LoadSingle Load

%504,710,000=== fn

D %50000,420,9fN

D

Miner’s Hypothesis

ε 121 ≤+nnD

yp

ε(log

scale)

12

2

1

1 ≤+=NN

D)

ε2 Load level 2

ε1 Load level 1

N NNf (log scale)

Nf2 Nf1

Miner’s Hypothesisyp

n ,...,seasonTfn

D = ∑,,

jiDfN ∑

== ,..1,1,...,

jiji

f ,, j

1≤D 1≤D

ME DesignME DesignME DesignME Design

TrafficTraffic SeasonsSeasonsTrafficTrafficP P = Load= Loadaa = Area= Area

SeasonsSeasonsAnnualAnnualDailyDailya a Area Area

Pavement layersPavement layersEEii = Modulus= Modulus

DailyDailyLongLong--termterm

Asphalt agingAsphalt agingEEii Modulus Modulusηηii = = Poisson’s ratioPoisson’s ratiottii = Thickness= Thickness

Asphalt agingAsphalt agingCrackingCracking……ttii Thickness Thickness ……

BackcalculationBackcalculationBackcalculationBackcalculationThe process of The process of

iiconverting converting measured measured pavement pavement deflections into deflections into l d lil d lilayer modulilayer moduli

How Backcalculation How Backcalculation 1. Select

Works…Works…2 U S d

Pavement layer / FWD Sensor

100

mils

2. Use Seed Value Initial deflection

10

ctio

n, m

deflection3. Select 2nd

modulus 1

Def

lec

2nd deflection4. Use FWD

0.11,000 10,000 100,000

M d l i

deflection to estimate modulusModulus, psi modulus

The Need for SeasonsThe Need for Seasons

Seasonal ChangesSeasonal ChangesSeasonal ChangesSeasonal Changes

Frozen Rapid drainage RefreezingFrozenThawing

Rapid drainageSlow recovery

Refreezing

Granular Subbase

Asphalt Surface and Base

Weather Affected Subgrade

Granular Subbase

Weather Affected Subgrade

Jan. Dec.

Subgrade

Seasonal ModelsSeasonal ModelsSeasonal ModelsSeasonal Modelss

Mod

ulus

J A J OJ A J ODate

Subbase Seasonal Subgrade SubgradeSubbase Seasonal Subgrade Subgrade

Effect of Changing Effect of Changing Season LengthsSeason Lengths

Initial inputsInitial inputsInitial inputsInitial inputs7 days of Spring thaw7 days of Spring thaw

NN 660 000660 000 ESALESALNNff = 660,000 = 660,000 ESALsESALs

Increase SpringIncrease Spring--thaw from 7 to 28 daysthaw from 7 to 28 daysNNff = 490 000= 490 000 ESALsESALsNNff 490,000 490,000 ESALsESALs

26.2% decrease in lifespan26.2% decrease in lifespan

Number of Days of ThawNumber of Days of ThawNumber of Days of ThawNumber of Days of Thaw

Seasonal Response TechniquesSeasonal Response TechniquesSeasonal Response TechniquesSeasonal Response Techniques

Calculate average annual responseCalculate average annual responseCalculate average annual responseCalculate average annual responseDetailed hourly calculations Detailed hourly calculations

R iR iRepresentative yearRepresentative year

AASHTOAASHTO Pavement Design GuidePavement Design GuideAASHTO AASHTO Pavement Design GuidePavement Design Guide

32.2810181 −= xMxu 32.2810181 −= xMxu

uu Relative damageRelative damage

1018.1= Rf xMxu 1018.1= Rf xMxu

uuff -- Relative damage,Relative damage,MMRR -- Roadbed soil Roadbed soil resilient modulus (psi)resilient modulus (psi)resilient modulus (psi)resilient modulus (psi)

Q: Which layers in the pavement Q: Which layers in the pavement change seasonally?change seasonally?

All of themAll of themAll of themAll of them

dulu

s M

od

J A J ODate

Subbase Seasonal Subgrade Subgrade

Expanded Seasonal Pavement Expanded Seasonal Pavement Moduli ModelsModuli Models

FWDFWD Testing SitesTesting SitesFWDFWD Testing SitesTesting Sites

Ph IPhase I

Phase IIPhase II

Frost Depth > 1,100 mmFrost Depth < 600 mmFrost Depth < 600 mmPlasticity Index > 12

MEME--PDGPDG

Critical VariablesCritical VariablesCritical VariablesCritical Variables

TrafficTrafficNeed to account for overloadsNeed to account for overloads

WeatherWeatherDaily changesDaily changesSeasonalitySeasonality

Pavement structure & materialsPavement structure & materialsThicknessThicknessQuality of constructionQuality of construction

LongLong--term changesterm changesAll variablesAll variables

MM--E Design GuideE Design GuideMM E Design GuideE Design Guide

QuestionsQuestionsQuestionsQuestions

Q: What are the primary 2 failure Q: What are the primary 2 failure modes for asphalt pavement?modes for asphalt pavement?

Tensile strain in the surfaceTensile strain in the surfaceTensile strain in the surfaceTensile strain in the surfaceFatigue crackingFatigue cracking

C i i h b dC i i h b dCompressive strain on the subgradeCompressive strain on the subgradeSubgrade ruttingSubgrade rutting

Q: When is a pavement the strongest?Q: When is a pavement the strongest?Q: When is a pavement the strongest?Q: When is a pavement the strongest?

WinterWinterWinterWinter

Q: When is a pavement the weakest?Q: When is a pavement the weakest?Q: When is a pavement the weakest? Q: When is a pavement the weakest?

Spring thawSpring thawSpring thawSpring thaw

Q: Backcalculation should be Q: Backcalculation should be used on all pavements?used on all pavements?

NoNoNoNo

Thank YouThank YouDavid OrrDavid Orr

Senior EngineerSenior EngineerC ll L l R d PC ll L l R d PCornell Local Roads ProgramCornell Local Roads Program

416 Riley416 Riley--Robb HallRobb HallIthaca NY 14853Ithaca NY 14853Ithaca, NY 14853Ithaca, NY 14853

607607--255255--80338033dpo3@cornell.edudpo3@cornell.edup @p @

www.clrp.cornell.eduwww.clrp.cornell.edu