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Perpetual Pavement Design Southeast Pavement Management and Design Conference June 21, 2005 Savannah, Georgia

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  • Perpetual Pavement Design

    Southeast Pavement Managementand Design Conference

    June 21, 2005Savannah, Georgia

  • Goal of Perpetual Pavement Design

    • Design the structure such that there are no deep structural distresses– Bottom up fatigue cracking– Structural rutting

    • All distresses can be quickly remedied from surface

    • Result in a structure with ‘Perpetual’ or ‘Long Life’

  • Surface Distresses Only

    Top Down Cracking

    Non-Structural Rutting

  • How do you compute pavement response?• Flexible pavements consist of multiple layers• Using physical principles, we can calculate

    stresses beneath loads

    Pa

    zr

    t

    H1, E1, µ1

    H2, E2, µ2

    En, µn

  • Linear Elastic System Assumptions

    • Many constitutive models available• Linear Elastic Most Common• Assumptions

    – Homogeneity– Finite thickness– Infinite in horizontal direction– Isotropic– Full friction between layers– No surface shear forces

  • Two-Layer Systems• Analytical solution derived by Burmister (1940’s)• Importance of stiffness ratio (E1/E2)

    Vertical Stress, σz/p

    1.0

    E 1/E 2=

    1.0

    E1/E2=100

    0.70.10.0

    Layer 1

    Layer 2

    Dep

    th, z

    /a

  • Two Layer System – Shear Stress

    Horizontal Shear Stress, τrz/p1.00.0

    E 1/E

    2=1.

    0E1/E2=

    50 Layer 1

    Layer 2

    Dep

    th, z

    /a

  • Two-Layer System – Tensile Stresses

    σx

    Dep

    th, z

    Tension Compression

    Layer 1

    Layer 2

  • Three Layer Systems• Much more complicated system!• Initially solved for a limited set of parameters due to

    computational limitations– µ = 0.5

    • Limited number of locations

    Pa

    H1, E1, µ1 σz1σr1

    H2, E2, µ2 σz2σr2

    σr3

    En, µn

  • Materials

  • 1 2

    BeforeLoading

    3

    AfterLoading -

    Same Sizeas BeforeLoading

    DuringLoading

    Figure 1. How an Elastic Material Behaves.

  • D

    ∆D/2σ∆l

    l

    εl = ∆l/l E = σ/ε

    εt = ∆D/D µ = εl/εt

    Figure 1. Definitions of E and µ.

  • Dynamic Modulus Test

  • Witczak Equation for E*log . . . ( ) . .

    .. . . . ( ) .

    ( . ` . log( ) . log( ))

    E V

    VV V e

    a

    beff

    beff af

    = − + − − −

    −+

    ⎝⎜

    ⎠⎟ +

    − + − ++ − − −

    1249937 0 29232 0 001767 0 002841 0 058097

    08022083871977 0 0021 0 003958 0 000017 0 005470

    1

    200 2002

    4

    4 38 382

    340 6033 3 0 313351 0 393532

    ρ ρ ρ

    ρ ρ ρ ρη

    • bitumen viscosity (dynamic shear rheometer)

    • loading frequency• air voids• effective bitumen content

    • cum. % retained on 19-mm sieve

    • cum. % retained on 9.5-mm sieve

    • cum. % retained on 4.76-mm sieve

    • % passing the 0.075-mm sieve

  • HMA Modulus Versus

    Temperature

    10

    100

    1000

    10000

    0 20 40 60 80 100 120

    Temperature, F

    Mod

    ulus

    , 100

    0 ps

    i

  • Soil Modulus Testing

  • Dynamic Cone Penetration

    Rod

    Reference

    Mass

  • Effect of Moisture Content

    1

    10

    100

    0 5 10 15 20

    Moisture Content, %

    Mod

    ulus

    , ksi

  • FWD Testing

  • Backcalculation

    PavementStructure

    Def

    lect

    ion

    Deflection SensorsLoad

    E = f(Load, Pressure, Deflection, Distance)

  • Traffic

  • AASHO Road Test

    Trucks

  • Single Tire Dual Tire

    Tandem Tridem

  • Layer 1HMA

    E1

    Layer 2Granular Base

    E2

    Layer 2Layer 2Granular BaseGranular Base

    EE22

    Layer 3Subgrade Soil

    E3

    Tire has a total load P, spread over a circulararea with a radius of a, resulting in a contactpressure of p.

    PavementReactions

    Deflection (δ)

    Tensile Strain (εt)

    Compressive Strain (Compressive Strain (εεvv))

    Nohorizontalboundary, assumelayersextendinfinitely.

    h1

    h2

    No bottom boundary, assume soil goes on infinitely.

    Figure 2. Layered Elastic Model Representation of a Pavement.

  • 0

    100

    200

    300

    400

    20 30 40 50 60Wheel Load, kN

    Tran

    sver

    seSt

    rain

    , µε

    Test Section 21

    LayeredElasticResults

    Mn/ROADMeasurements

    Figure 4. A Comparison of Measured Strains and Computed Strainsat Mn/ROAD. (After Timm et al., 1998, Development of Mechanistic-Empirical Pavement Design, Transportation Research Record No. 1629, Transportation Research Board, Washington, DC.)

  • Layer 1HMA

    E1h1 Tensile Strain (εt)

    Thickness vs. Tensile StrainH

    MA

    Ten

    sile

    St ra

    in

    HMA Thickness

  • Modulus vs. Tensile Strain

    Layer 1HMA

    E1h1 Tensile Strain (εt)

    HM

    A T

    ens i

    le S

    t rain

    HMA Modulus

  • HMA Thickness

    Sub

    grad

    e C

    omp r

    ess i

    v e S

    tr ain

    E1

    E2EE22

    E3

    h1

    h2

    Compressive Strain (Compressive Strain (εεvv))

    Thickness vs. Compressive Strain

  • Traditional M-E Design

    Log N

    Log ε

  • Perpetual Pavement Design

    No Damage Accumulation

    Log N

    Log ε

    ThresholdStrain

  • Normal Fatigue Testing Results VersusEndurance Limit Testing

    0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    Normal Range forFatigue Testing

    0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    Normal Range forFatigue Testing

  • εt

    εv

    Transfer Functions

  • Miner’s Hypothesis

    • Provides the ability to sum damage for a specific distress type

    •• D = D = ΣΣ nnii/N/Ni i ≤≤ 1.01.0where ni = actual number of loads

    during condition iNi = allowable number of loads

    during condition i

  • 0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    Normal Range forFatigue Testing

    0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    0

    200

    400

    600

    800

    1000

    1200

    1000 100000 10000000 1.1E+08

    Number of Loads to Failure

    Stra

    in, (

    10E

    -06)

    Endurance Limit

    Region of DamageAccumulation

    NoDamageAccumulation

  • Probabilistic Design – Monte Carlo Simulation

    Thickness

    f

    Material Properties

    f

    Axle Weight

    f

    MonteCarlo

    RandomSampling

    MechanisticModel

    Pavement Response

    f % Below Threshold

    % Above Threshold

  • % Below Threshold

    • Design should have high % below threshold

    f

    Pavement Response

    % Below Threshold

    How much ‘damage’ does this

    area correspond to?

  • ‘Damage Computation’• For responses exceeding threshold, compute N

    using transfer function– User defined

    • Calculate damage accumulation rate– Damage / MESAL

    f

    Pavement Response

    % Below Threshold

    DamageMESAL

  • Estimated Long Life

    • Convert damage rate into an estimated life– Use traffic volume and growth– Calculate when damage = 0.1

    • Use for Low Vol. Roads (t ~30 yrs.)

    10 - 20/wk 3 - 5/wk 10 - 20/wk

    Low Volume Traffic

  • PerRoad 2.4• Sponsored by APA• Developed at Auburn University / NCAT• M-E Perpetual Pavement Design and Analysis Tool• Help File is the Users Manual• Press F1 at Any Time for Help File

    Perpetual Pavement DesignGoal of Perpetual Pavement DesignSurface Distresses OnlyHow do you compute pavement response?Two-Layer SystemsTwo Layer System – Shear StressTwo-Layer System – Tensile StressesThree Layer SystemsMaterialsDynamic Modulus TestWitczak Equation for E*HMA Modulus VersusTemperatureSoil Modulus TestingDynamic Cone PenetrationEffect of Moisture ContentFWD TestingBackcalculationTraditional M-E DesignPerpetual Pavement DesignMiner’s HypothesisProbabilistic Design – Monte Carlo Simulation% Below Threshold‘Damage Computation’Estimated Long LifePerRoad 2.4