conventional flexible pavement structural design design course...1 conventional flexible pavement...

Download Conventional Flexible Pavement Structural Design Design Course...1 Conventional Flexible Pavement Structural Design Methods By: Curtis F. Berthelot Ph.D., P.Eng. Department of Civil

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  • 1

    Conventional Flexible Pavement Structural

    Design Methods

    By:yCurtis F. Berthelot Ph.D., P.Eng.Department of Civil Engineering

    Pavement Structural Design

    Objective of road structural design is to optimize the structural composition of the road structure.

    M b li d t May be applied to: New construction. Rehabilitation construction.

    Conventional Flexible Pavement Structural Design2

  • 2

    Pavement Structural Design

    Structural design needs to consider: Insitu subgrade material Loadings: Repeat axles over life Critical state loadings

    Road structure material constitutive properties/climatic durability.

    Material layer interface compatibility.

    Conventional Flexible Pavement Structural Design3

    Geometrics (grade width and height). Constructability. Future expansion requirements.

    Pavement Structural Design

    Conventional Flexible Pavement Structural Design4

  • 3

    Pavement Structural Design

    Primed Surface

    150 mm Granular Subbase150 mm Granular Drainage Sand

    85 mm Hot Mix Asphalt Concrete

    170 mm Granular Base

    in situ Subgrade(Trimmed and Proof Rolled for Soft Spots)

    350 mm Cement-Emulsion Strengthened in situ GranularPrimed Surface85 mm Hot Mix Asphalt Concrete

    in situ Subgrade(Trimmed and Proof Rolled for Soft Spots)

    Primed Surface85 mm Hot Mix Asphalt Concrete

    Conventional Flexible Pavement Structural Design5

    150 mm Asphalt Stabilized Base Coarse150 mm Granular Base350 mm Full Depth Cement Strengthened Subgrade

    Primed Surface

    in situ Subgrade(Trimmed and Proof Rolled for Soft Spots)

    Pavement Structural Design

    Two primary classes of road users: Private (cars and light trucks) Commercial (heavy trucks)

    Pavement structural design ensures adequate structural integrity to accommodate commercial vehicle loading.

    Primary factors influencing road structural performance over the life of the road asset are: Commercial truck loadings

    Cli i ff

    Conventional Flexible Pavement Structural Design6

    Climatic effects Combined effects of both

  • 4

    n In

    dice

    s

    InitialNew Road

    Changing Field State Conditions (Saskatchewan)

    icea

    bilit

    y or

    Con

    ditio

    n Road Strengthening

    Treatment

    Poorly FundedStop-Gap

    Ongoing Strategic Preservation

    Conventional Flexible Pavement Structural Design7

    Minimum Acceptable Serviceability

    time

    Serv

    i

    Structural Deterioration Under Stop Gap Preservation

    .....n-Year

    Design Life

    Identify Structural Distresses (Materials Structural Failure)

    Conventional Flexible Pavement Structural Design8

  • 5

    Identify Structural Distresses (Materials Structural Failure)

    Conventional Flexible Pavement Structural Design9

    Changing Economy

    Conventional Flexible Pavement Structural Design10

  • 6

    Changing Economy

    Conventional Flexible Pavement Structural Design11

    Provincial Highway System

    Conventional Flexible Pavement Structural Design12

  • 7

    Standard Axles

    2-Tire Steering Axle(5,500 kg)

    4-Tire Single Axle (9,100 kg)

    12-Tire Tridem Axle Group(23,000 kg)

    8-Tire Tandem Axle Group(17,000 kg)

    2 m

    to

    .5 m

    2.3m

    m to

    7

    m

    0.20 m 0.45 m

    Conventional Flexible Pavement Structural Design13

    1.2 1

    2.4 m to 2.6 m2.

    4 m

    3.7

    Non-Standard Axles

    Conventional Flexible Pavement Structural Design14

  • 8

    Based on the phenomenological rutting and fatigue cracking observations of asphalt pavements at the AASHO R d T h l f i bili

    Traffic Load Equivalencies ESAL

    AASHO Road Test, the loss of pavement serviceability resulting from the passage of any axle at a specified weight is equated to the loss in serviceability due to and Equivalent Single Axle Load (ESAL) of 80 kN.

    The fourth power law is used to empirically equate axles at various loadings to the 80 KN single axle.

    Conventional Flexible Pavement Structural Design15

    The total number of Design ESALs for a given vehicle is the ratio of the number of 18-kip single axle l d li i i d li h d

    Traffic Load Equivalencies ESAL

    load applications required to replicate the damage inflicted to the pavement by the vehicle.

    spacings) axle and loads axle (vehiclepavement fail to passes of #axle) kip-(18pavement fail to passes of #ESAL

    Conventional Flexible Pavement Structural Design16

  • 9

    4PKPSI

    Traffic Load Equivalencies ESAL

    80KNPKPSI

    Where:PSI = Change in the Present Serviceability

    Index due to one axle loadP = Applied axle load (KN)P S d d i l l l d (80 KN)

    Conventional Flexible Pavement Structural Design17

    P80KN = Standard single axle load (80 KN)K = Regression constant

    Typical ESALs

    15400 k

    Gross Weight36200 kgs356 KN

    80.000 LbsTruck Factor

    USA

    15400 kgs151 kN

    34.000 Lbs1.11

    15400 kgs151 kN

    34.000 Lbs1.11

    5440 kgs54 kN

    12000 Lbs0.23

    +2.45

    5500 kgs54 kN

    12125 Lbs0.24

    17000 kgs167 kN

    37500 Lbs1.67

    17000kgs167 kN

    37500 Lbs1.67

    Gross Weight39500 kgs

    428 kN87100 Lbs

    Truck Factor3.58+

    Canada

    Gross Weight

    Conventional Flexible Pavement Structural Design18

    5500 kgs54 kN

    12125 Lbs0.24

    17000 kgs167 kN

    37500 Lbs1.67

    17000 kgs167 kN

    37500 Lbs1.67

    23000 kgs226 kN

    50700 Lbs1.32

    Gross Weight62500 kgs

    614 kN137800 Lbs

    Truck Factor4.90+ +

    Note: Pt = 2.5; SN = 3

    Canada Canada

  • 10

    Empirically calibrated from the AASHO Road Test:

    Determined a universal load equivalency pavement

    Traffic Load Equivalencies ESALs

    damage relationship.

    Found that pavement deterioration in terms of damage occurring from an 80-KN axle load appeared to have a fourth power relationship to the actual axle load applied to the pavement.

    4

    Conventional Flexible Pavement Structural Design19

    4

    80(KN)LoadAxleDamage Pavement Relative

    KN

    Given that an 80 KN axle load is assumed to have a pavement damage equivalency of 1.0, by the fourth

    Traffic Load Equivalencies ESAL

    power pavement relationship, a 160 KN single axle load (twice that of an 80 KN axle load) inflicts 16 times the damage of that of an 80 KN axle load.

    Likewise, a 40 KN axle load inflicts only 0.0625 times the damage of an 80 KN axle load.

    The fourth pavement damage relationship does not

    Conventional Flexible Pavement Structural Design20

    p g papply to all pavement or field state conditions.

  • 11

    Structural Design Methods

    Across Canada, transportation agencies have developed standard pavement thickness equivalencies based on years of experienceyears of experience.

    There are four primary methods to perform structural pavement design: Empirical based layer equivalents Nomograghs Shell curves (SDHT) Asphalt Institute curves

    Conventional Flexible Pavement Structural Design21

    Asphalt Institute curves Surface deflection methods Multilayer mechanistic theory methods

    Empirical Structure Layer Thickness Equivalencies

    B.C. 1 mm Asphalt Conc.- 2 mm gravel base (mm)- 25 mm sandy gravel subbase

    Alberta 1 mm Asphalt Conc.- 2.25 mm crushed gravelp g- 1.75 mm soil cement- 1.25 mm asphalt treated gravel

    Saskatchewan Considered as a variable and therefore not used

    Manitoba 1 mm Asphalt Conc.- 2 mm gravel base- 1.5 mm sand asphalt or soil cement- 2 mm lime treated clay

    Ontario 1 mm Asphalt Conc.- 1 mm treated base( h l )

    Conventional Flexible Pavement Structural Design22

    (asphalt or cement)- 2 mm granular A base- 3 mm granular (B. C. D) subbase

    1 mm Full Depth AC- 2.7 mm granular A base (tentative)

  • 12

    Quebec 1 mm Asphalt Conc.- 2 mm crushed rock base- 2.5 mm gravel base or subbase- 5 mm sand subbase

    Empirical Structure Layer Thickness Equivalencies

    - 1.25 mm soil cement(150 mm thick or less)- 2 mm soil cement (more than 150 mm)- 33 mm lime stabilized clay- 18 mm asphalt stabilized base

    Newfoundland 1 mm Asphalt Conc.- 25 mm graded crushed rock- 2.5 mm graded crushed gravel- 2 mm soil cement stabilized- 3 mm gravel subbase

    4 mm sandy gravel

    Conventional Flexible Pavement Structural Design23

    - 4 mm sandy gravelNew Brunswick 1 mm Asphalt Conc.- 2 mm crushed rock

    - 2 mm soil cement (150 mm thickness and over)- 2 mm (or less) asphalt stabilized base- 3 mm gravel subbase

    AASHTO Flexible Pavement Design

    Function of any road is to safely and smoothly carry vehicular traffic from one point to anotherp

    Serviceability: Ability of a pavement to serve the traffic for which it is designed

    Performance: Ability of the pavement to satisfactorily serve traffic over a period of time

    Conventional Flexible Pavement Structural Design24

  • 13

    AASHTO Flexible Pavement Design

    Conventional Flexible Pavement Structural Design25

    Five basic steps to SMHI pavement structure thickness design of new roads: D t i i d d i i t i f ti

    SMHI Pavement Structural Design

    Determine required design input information: traffic projections. in situ subgrade performance properties.

    Determine pavement layer thicknesses; Prepare construction plan (may be staged); Perform economic evaluation (materials quantities

    d h l di ) d

    Conventional Flexible Pavement Structural Design26

    and haul distances), and; Iterate to final structural

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