mechanistic empirical pavement design
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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
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NYSNYS 180180 LaFargevilleLaFargevilleNYSNYS 180 180 -- LaFargevilleLaFargeville
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NYSNYS 180180 LaFargevilleLaFargevilleNYSNYS 180 180 -- LaFargevilleLaFargeville800 AADT800 AADT
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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
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17 ½ in.17 ½ in.
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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
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Why Roads FailWhy Roads Fail
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What is a road?What is a road?What is a road?What is a road?
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Road StructureRoad StructureRoad StructureRoad Structure
SurfaceSurfaceSurfaceSurfaceBaseBase
S bbS bbSubbaseSubbaseSubgradeSubgrade
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Vehicle LoadsVehicle LoadsVehicle LoadsVehicle Loads
Load
Pavement
Subgrade
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Pavement DeflectionPavement DeflectionPavement DeflectionPavement Deflection
Load
Pavement
Subgrade
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Pavement DeflectionPavement DeflectionPavement DeflectionPavement Deflection
Load
PavementT
CT
C
C
T
SubgradeT
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Pavement FatiguePavement FatiguePavement FatiguePavement Fatigue
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Pavement FatiguePavement FatiguePavement FatiguePavement Fatigue
45° 90° 180°
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Pavement Failure?Pavement Failure?Pavement Failure?Pavement Failure?
PotholesPotholesPotholesPotholesAlligator cracking Alligator cracking CorrugationsCorrugationsCorrugationsCorrugationsEdge ravelingEdge ravelingRuttingRuttingRuttingRutting
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DrainageDrainageDrainageDrainage
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Pavement Design MethodsPavement Design MethodsPavement Design MethodsPavement Design Methods
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Pavement Design MethodsPavement Design MethodsPavement Design MethodsPavement Design Methods
ExperienceExperienceExperience Experience CatalogCatalog
E i i lE i i lEmpiricalEmpiricalMechanisticMechanistic--EmpiricalEmpirical
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ExperienceExperienceExperienceExperience
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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
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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
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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
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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
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MM--E Pavement DesignE Pavement Design
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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?
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Fatigue Failure CriteriaFatigue Failure CriteriaFatigue Failure CriteriaFatigue Failure Criteria
32 11 kk⎞⎛⎟
⎞⎜⎛ 11
1cr
f EkN ⎟
⎠⎞
⎜⎝⎛
⎟⎟⎠
⎞⎜⎜⎝
⎛=
ε
n(ε)
cr ⎠⎝⎠⎝
ln
ln(Nf)
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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
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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
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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
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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.
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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
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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
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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,,∞∞
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Miner’s Hypothesisyp
n ffnD =
D = amount of damage (%)
fNdamage (%)
f
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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
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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
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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
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Single LoadSingle LoadSingle LoadSingle Load
%504,710,000=== fn
D %50000,420,9fN
D
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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
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Miner’s Hypothesisyp
n ,...,seasonTfn
D = ∑,,
jiDfN ∑
== ,..1,1,...,
jiji
f ,, j
1≤D 1≤D
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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 ……
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BackcalculationBackcalculationBackcalculationBackcalculationThe process of The process of
iiconverting converting measured measured pavement pavement deflections into deflections into l d lil d lilayer modulilayer moduli
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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
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The Need for SeasonsThe Need for Seasons
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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
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Seasonal ModelsSeasonal ModelsSeasonal ModelsSeasonal Modelss
Mod
ulus
J A J OJ A J ODate
Subbase Seasonal Subgrade SubgradeSubbase Seasonal Subgrade Subgrade
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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
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Number of Days of ThawNumber of Days of ThawNumber of Days of ThawNumber of Days of Thaw
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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
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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)
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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
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Expanded Seasonal Pavement Expanded Seasonal Pavement Moduli ModelsModuli Models
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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
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MEME--PDGPDG
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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
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MM--E Design GuideE Design GuideMM E Design GuideE Design Guide
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QuestionsQuestionsQuestionsQuestions
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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
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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
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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
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Q: Backcalculation should be Q: Backcalculation should be used on all pavements?used on all pavements?
NoNoNoNo
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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
[email protected]@cornell.edup @p @
www.clrp.cornell.eduwww.clrp.cornell.edu