S 3-3 Pavement Design in UK & Future Developments A_Collop

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    Pavement design in the UKand future developments

    Andy CollopProfessor of Civil EngineeringDirector of NTEC

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    Outline

    Standard UK pavement design

    Foundation Upper pavement

    Long Term Pavement Performance Model(LTPPM)

    Summary

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    UK pavement design

    HA method for Trunk Roads & Motorways

    Includes long-life designs (> 80 msa)

    40 year design life (can be 20 years) Semi-empirical (analytical alternatives

    allowed) Divided into foundation design and upper

    pavement design

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    Foundation design

    Where does the foundation start?

    Upperpavement

    Pavement

    foundation

    SurfacingUpper Base

    Lower Base

    Subbase

    Capping

    Subgrade

    HD26

    HD25

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    Philosophy

    Based around the concept of a Surface

    Modulus (half-space)

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    Foundation classes

    Class 1 50MPa Capping Only (< 20 msa)

    Class 2 100MPa Granular Subbase (< 80 msa)

    Class 3 200MPa Weak Cemented Subbase

    (including hydraulically bound)

    Class 4 400MPa Strong Cemented Subbase

    (including hydraulically bound)

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    HD25

    Standard DesignsStandard Designs for Classes 2 and 3 (+

    Class 1 for non HA roads); restrictedchoice of materials; CONSERVATIVE

    Performance DesignsPerformance Designs for Classes 1 to 4;very wide choice of materials; much more

    testing specified; MORE REALISTIC

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    0

    100

    200

    300

    400

    500

    600

    700

    0 50 100 150

    Subgrade Stiffness Modulus (MPa)

    Th

    ickness(m

    m)

    Capping, MCHW1 Series 600

    Total Foundat ion thickness, Subbase Types 1,

    2, 3 and R

    Total Foundat ion thickness, Subbase Types

    CBGMA or CBGMB, C3/4 or C5/6

    CBR (%)

    2 3 5 8 10 12 15 20 25

    Class 2

    Standard Class 2

    (100MPa)

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    Performance designs

    Basis of Designs:

    Three criteria

    Surface deflection(relates to Surface

    Modulus)

    Subgrade Strain(relates to rutting)

    Practical minimumthicknesses

    40kN

    Subbase

    Capping

    Subgrade

    Surface

    deflection

    Subgrade

    strain

    10000MPa layer assumed 1.5m below

    surface of subgrade

    Circularcontact area,

    radius 151mm

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    Performance Class 2

    (100MPa)

    0

    100

    200

    300

    400

    500

    0 50 100 150Subgrade Stiffness Modulus (MPa)

    SubbaseThickness(mm)

    E(subbase) = 150MPa

    E(subbase) = 200MPa

    E(subbase) = 250MPa

    Class 2

    CBR (%)

    2 3 5 8 10 12 15 20 25

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    Performance Class 3

    (200MPa)

    0

    100

    200

    300

    400

    500

    0 50 100 150Subgrade Stiffness Modulus (MPa)

    SubbaseThickness(mm)

    E(subbase) = 500MPa

    E(subbase) = 750MPa

    E(subbase) = 1000MPa

    E(subbase) = 2000MPa

    Class 3

    CBR (%)

    2 3 5 8 10 12 15 20 25

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    Stiffness measurement

    Table 3.1 Equilibrium Subgrade CBR Estimation

    High Water Table Low Water Table

    Poor

    ConstructionConditions

    Average

    ConstructionConditions

    Good

    ConstructionConditions

    Poor

    ConstructionConditions

    Average

    ConstructionConditions

    Good

    ConstructionConditions

    Soil PI

    (%)

    Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick

    Heavy Clay

    Silty Clay

    Sandy Clay

    70

    60

    50

    40

    30

    20

    10

    1.5

    1.5

    1.5

    2

    2.52.5

    1.5

    2

    2

    2

    2.5

    3.54

    3.5

    2

    2

    2

    2.5

    34

    3

    2

    2

    2.5

    3

    45

    6

    2

    2

    2

    2.5

    3.54.5

    3.5

    2

    2.5

    2.5

    3

    57

    7

    1.5

    1.5

    2

    2.5

    33

    2.5

    2

    2

    2

    2.5

    3.54

    4

    2

    2

    2

    3

    45

    4.5

    2

    2

    2.5

    3

    46

    7

    2

    2

    2

    3

    4

    6

    6

    2.5

    2.5

    2.5

    3.5

    6

    8

    >8

    Silt* - 1 1 1 1 2 2 1 1 2 2 2 2

    Sand (poorly

    graded)

    Sand (well

    graded)

    Sandy Gravel

    (well graded)

    -

    -

    -

    ------------------------------------------------------------20------------------------------------------------------------

    ------------------------------------------------------------40------------------------------------------------------------

    ------------------------------------------------------------60------------------------------------------------------------

    * estimated assuming some probability of material saturating

    CBR

    DCP

    Springbox

    Chart

    FWD

    Plate Loading

    Triaxial

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    Other layer combinations

    Any combination of layers possible

    The designer has to carry out a Multi-Layer Linear Elastic analysis to ensure

    that the criteria are all satisfied Surface deflection

    Subgrade strain Practical minimum thickness

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    Outline

    Standard UK pavement design

    Foundation Upper pavement

    Long Term Pavement Performance Model(LTPPM)

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    Background

    LTPPM developed with University of

    Cambridge (Cebon)

    Similar concept to MMOPP (Ullidtz)

    Flexible (asphalt) pavements

    Deterministic iterative procedure (profile &damage tracking)

    Aggregate damage type of approach

    V hi l

    V hi l

    V hi l

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    LTPPM

    Dynamicvehicle/axlegroup models

    Primaryresponsecalculation

    Damagecalculation

    Feedbackmechanisms

    Tyre forces

    Time

    Forc

    e

    Vehicle

    simulation

    Theoretical road damage

    Distance along road

    Damage

    Road damage model

    Lo g N

    Log

    Materialproperties

    Time

    Strain

    Road strain at each point

    Road model

    Road response calculation

    Distance

    Strain

    Influence

    function

    Environment

    static

    Surfaceruttingfedbackintovehiclemodel

    Fatigue

    damagefedbackinto

    primaryresponsemo

    del

    Tyre forces

    Time

    Forc

    e

    Vehicle

    simulation

    Theoretical road damage

    Distance along road

    Damage

    Road damage model

    Lo g N

    Log

    Materialproperties

    Time

    Strain

    Road strain at each point

    Road model

    Road response calculation

    Distance

    Strain

    Influence

    function

    Environment

    static

    Surfaceruttingfedbackintovehiclemodel

    Fatigue

    damagefedbackinto

    primaryresponsemo

    del

    Tyre forces

    Time

    Forc

    e

    Vehicle

    simulation

    Theoretical road damage

    Distance along road

    Damage

    Road damage model

    Lo g N

    Log

    Materialproperties

    Time

    Strain

    Road strain at each point

    Road model

    Road response calculation

    Distance

    Strain

    Influence

    function

    Environment

    static

    Surfaceruttingfedbackintovehiclemodel

    Fatigue

    damagefedbackinto

    primaryresponsemo

    del

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    Example

    Effect of road friendly suspensions

    2 classes of pavement simulated

    Major road (350mm asphalt)

    Minor road (125mm asphalt)

    Typical 3 layer flexible pavement structure

    4oC to 18oC variation in MMAT

    S rface profile e ol tion

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    Surface profile evolution

    (Major road)

    -0.03

    -0.02

    -0.01

    0

    0.01

    0.02

    0.03

    0 10 20 30 40 50 60 70 80 90 100

    Distance / m

    SurfacePro

    fileElevation

    /m

    36 million load passes(10 years)

    72 million load passes(20 years)

    Initial profile

    Rutting evolution

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    Rutting evolution(Major road)

    0

    2

    4

    6

    8

    10

    12

    14

    16

    0 10 20 30 40 50 60 70 80

    Load Passes (Million)

    AverageR

    utDepth/mm

    'Critical' rut depth

    Steel fleetRoad friendly fleet

    20 years

    Fatigue evolution

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    Fatigue evolution(Major road)

    0

    0.5

    1

    1.5

    2

    2.5

    3

    3.5x10-3

    0 10 20 30 40 50 60 70 80

    Load Passes (Million)

    95th

    PercentileFatigueDamage

    Steel fleet

    Road friendly fleet

    20 years

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    Fatigue evolution

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    Fatigue evolution(Minor road)

    Steel fleet

    Road friendly fleet

    20 years

    0

    0.2

    0.4

    0.6

    0.8

    1

    0 0.2 0.4 0.6 0.8 1 1.2

    Load Passes (Million)

    9

    5thPercentile

    FatigueDam

    age

    'Critical' fatigue damage

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    Predictions

    % increase in life changing from steel to

    road friendly (air) suspensions

    Major Minor

    EC 24% 42%

    LTPPM (3.5) 3% 39%

    LTPPM (1) 0% 90%

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    Outline

    Standard UK pavement design

    Foundation Upper pavement

    Long Term Pavement Performance Model(LTPPM)

    Summary

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    Summary UK design

    Foundation design + upper pavement

    design

    4 performance levels (surface modulus)

    for foundations

    More flexible designs (wider range of

    materials)

    Performance designs allowed

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    Summary LTPPM (2)

    Different modes of deterioration predicted

    for different classes of pavement

    Changing from steel to air increases life of

    major road by

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    Pavement design in the UKand future developments

    Andy CollopProfessor of Civil EngineeringDirector of NTEC

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