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LOW VOLUME ROAD DESIGN EMPIRICAL APPROACH. WHAT ARE THE DIFFERENCES ??. Roman Road. 30060. TYPES OF FAILURE. FUNCTIONAL FAILURE STRUCTURAL FAILURE Do they occur at the same time? How do they differ for low volume roads ? Do all users agree ? How do we combine the different views ?.

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LOW VOLUME ROAD DESIGN

EMPIRICAL APPROACH


What are the differences

WHAT ARE THE DIFFERENCES ??


Roman Road

30060


Types of failure
TYPES OF FAILURE

  • FUNCTIONAL FAILURE

  • STRUCTURAL FAILURE

    Do they occur at the same time?

    How do they differ for low volume roads ?

    Do all users agree ?

    How do we combine the different views ?


Total or whole life costs
Total or Whole Life Costs

  • Minimise total costs

    Need to…..

  • predict road deterioration

  • predict the effects of maintenance

  • calculate road agency costs

  • predict road user costs

  • PLUS

  • calculate social ‘benefits’

Models such as HDM 4 ??


What structural design factors does road performance and therefore design depend
What structural design factors does road performance, and therefore design, depend ?

  • strength of subgrade

  • traffic loading

    • wheel loads

    • number of repetitions of wheels

  • strength of pavement layers

  • thickness of pavement layers

  • ?

    • but also time dependant

    • but how?


    try to therefore design, depend ?

    For high traffic roads we control as much as we can to reduce risks of failure to a very low value

    But for low volume roads we

    cannot afford to do so


    Pass fail criteria no risk
    Pass/fail criteria - no risk therefore design, depend ?

    Number of

    samples

    Specification for trunk road

    Strength of material


    BASIC AASHTO METHOD therefore design, depend ?

    1 Estimate traffic loading in equivalent standard axles2 Multiply traffic by regional factor3 Estimate subgrade strength (now as an elastic modulus)

    4 Select serviceability loss (maximum level of acceptable

    deterioration)

    METHOD THEN RECOMMENDS A STRUCTURAL NUMBER, SN


    STRUCTURAL NUMBER (SN) therefore design, depend ?

    SN = a1 h1 + a2 h2 + a3 h3 + ....

    Where a1 , a2 , a3 etc. are strength coefficients for layers 1, 2, 3, etc. and

    h1 , h2 , h3 , etc. are the thicknesses of layers 1, 2, 3

    The strength coefficients are related to normal strength measures such as CBR, unconfined compressive strength, Marshall stability, etc.


    Strength therefore design, depend ? coefficient(a2)

    a2 = {29.14 (CBR) - 0.1977 (CBR)2+ 0.00045 (CBR)3} x 10-4

    0.15

    0.14

    0.10

    0.08

    0.05

    0

    40

    50

    100

    110

    150

    CBR value

    STRENGTH COEFFICIENT, a2 FOR GRANULAR BASE MATERIALS


    Strength therefore design, depend ? coefficient(a3)

    0.150

    0.125

    0.100

    0.075

    0.050

    a3 = 0.01 + 0.065 (log10CBR)

    0.025

    1

    5

    10

    50

    100

    200

    CBR of sub-base

    STRENGTH COEFFICIENT, a3 FOR SUB-BASE MATERIALS


    10 therefore design, depend ? 3

    104

    105

    106

    107

    108

    EQUIVALENT THICKNESS De, INCHES

    45

    x

    40

    x

    x

    x

    x

    x

    x

    x

    35

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    30

    x

    x

    x

    x

    x

    x

    x

    25

    x

    x

    x

    x

    x

    x

    x

    x

    x

    x

    20

    x

    15

    x

    10

    x

    x

    5

    0

    WEIGHTED EQUIVALENT ESA APPLICATIONS

    AASHO "DESIGN" EQUATION COMPARED WITH DATA


    Aashto equation
    AASHTO EQUATION therefore design, depend ?

    Traffic

    Subgrade

    CBR

    Structural

    number

    Allowable

    deterioration

    Reliability


    Effect of reliability
    Effect of ‘Reliability’ therefore design, depend ?

    For

    250,000 esa and

    subgrade CBR = 7%

    95% Reliability SN = 2.54

    85% Reliability SN = 2.29

    a difference of 62 mm of sub-base


    ROAD DETERIORATION therefore design, depend ?

    STATE OF ROADPSI

    FROZEN

    FROZEN

    SPRING

    THAW

    SPRING

    THAW

    TIME or TRAFFIC


    Effect of climate the regional factor
    Effect of climate therefore design, depend ? The ‘regional’ factor

    Illinois in summer

    SN = 2.54

    Dry

    SN = 2.14 (-100mm of sub base)

    Wet

    SN = 2.97 (+110mm of sub base)

    But no guidance available from the Road Test


    ROAD NOTE 31 therefore design, depend ? A PAVEMENT DESIGN GUIDE

    FOR PAVED ROADS

    IN TROPICAL CLIMATES


    Takes account of
    TAKES ACCOUNT OF….. therefore design, depend ?

    • Variability in material properties

    • Uncertainty in traffic estimates

    • Variability in road performance


    Key factors
    KEY FACTORS therefore design, depend ?

    • Influence of tropical climates on the moisture conditions in the subgrade

    • Influence of tropical climates on the nature of soils and rocks

    • High axle loads and tyre pressures

    • Severe conditions imposed on the bituminous surface by tropical climates

    • Inter relationship between design and maintenance


    Estimating equilibrium moisture content
    ESTIMATING EQUILIBRIUM MOISTURE CONTENT therefore design, depend ?

    CATEGORY 3

    No permanent water table

    Arid climate

    Rainfall < 250mm pa


    Estimating equilibrium moisture content1
    ESTIMATING EQUILIBRIUM MOISTURE CONTENT therefore design, depend ?

    CATEGORY 2

    Deep water table but rainfall sufficient to

    produce seasonal changes under the road

    Rainfall >250mm pa. per year and seasonal


    Estimating equilibrium moisture content2
    ESTIMATING EQUILIBRIUM MOISTURE CONTENT therefore design, depend ?

    CATEGORY 1

    Water table sufficiently close to the surface

    to control the subgrade moisture content

    (This depends on the type of soil)


    An example of coping with risk therefore design, depend ?

    100

    80

    60

    Cumulative percentage

    40

    20

    0

    4

    8

    12

    CBR (DCP) per cent


    CBR at therefore design, depend ?

    equilibrium

    moisture

    content

    Soaked

    CBR

    Required

    pavement

    thickness

    Soil A

    5%

    15%

    300mm

    Common to area

    where designs

    developed

    8%

    300mm ?

    Soil B

    5%

    Rare


    Consideration of the road design environment for lvsr s
    Consideration of the Road Design Environment for LVSR’s therefore design, depend ?

    AVAILABLE MATERIALS

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN


    The road design or risk environment
    THE ROAD DESIGN OR “RISK” ENVIRONMENT therefore design, depend ?

    • AVAILABLE MATERIALS

    • Alternative & thin bituminous

    • surfacings

    • Pavement materials

      • Marginal materials

      • Standards

    • Subgrade & road formation

    • Problem soils

    • Moisture sensitivity

    • Stabilisation options and treatments

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY


    Pass fail criteria
    Pass/fail criteria therefore design, depend ?

    Number of

    samples

    Specification for trunk road

    Strength of material


    Consideration of the road design environment for lvsr s1
    Consideration of the Road Design Environment for LVSR’s therefore design, depend ?

    PREVAILING

    CLIMATE

    DRAINAGE AND HYDROLOGY

    AVAILABLE MATERIALS

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN


    The road design or risk environment1
    THE ROAD DESIGN OR “RISK” ENVIRONMENT therefore design, depend ?

    PREVAILING CLIMATE

    Rainfall (intensity, distribution)

    Temperature (evaporation & diurnal change)

    Future change or unpredictability

    • AVAILABLE MATERIALS

    • Alternative & thin bituminous

    • surfacings

    • Pavement materials

      • Marginal materials

      • Standards

    • Subgrade & road formation

    • Problem soils

    • Moisture sensitivity

    • Stabilisation options and treatments

    DRAINAGE AND HYDROLOGY

    Ground & surface

    water flow

    Hydro-genesis

    Demand of terrain

    Modifying influences

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY


    Consideration of the road design environment for lvsr s2
    Consideration of the Road Design Environment for LVSR’s therefore design, depend ?

    PREVAILING

    CLIMATE

    DRAINAGE AND HYDROLOGY

    AVAILABLE MATERIALS

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN

    CONSTRUCTION


    The road design or risk environment2
    THE ROAD DESIGN OR “RISK” ENVIRONMENT therefore design, depend ?

    • AVAILABLE MATERIALS

    • Alternative & thin bituminous

    • surfacings

    • Pavement materials

      • Marginal materials

      • Standards

    • Subgrade & road formation

    • Problem soils

    • Moisture sensitivity

    • Stabilisation options and treatments

    PREVAILING CLIMATE

    Rainfall (intensity, distribution)

    Temperature (evaporation & diurnal change)

    Future change or unpredictability

    DRAINAGE AND HYDROLOGY

    Ground & surface

    water flow

    Hydro-genesis

    Demand of terrain

    Modifying influences

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY

    CONSTRUCTION

    Quality control

    Capacity, training & experience

    Selection and use of plant

    Influence of construction traffic


    Consideration of the road design environment for lvsr s3
    Consideration of the Road Design Environment for LVSR’s therefore design, depend ?

    PREVAILING

    CLIMATE

    DRAINAGE AND HYDROLOGY

    AVAILABLE MATERIALS

    GEOMETRICS AND CROSS-SECTIONPROFILES

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN

    TRAFFICCHARACTERISTICS

    OTHERS

    MAINTENANCE

    CONSTRUCTION

    CONSTRAINTS OF THE “GREEN” ENVIRONMENT


    The road design or risk environment3
    THE ROAD DESIGN OR “RISK” ENVIRONMENT therefore design, depend ?

    TRAFFICCHARACTERISTICS

    Axle loading

    Tyre pressures

    Seasonality

    Position

    Growth projections

    PREVAILING CLIMATE

    Rainfall (intensity, distribution)

    Temperature (evaporation & diurnal change)

    Future change or unpredictability

    DRAINAGE AND HYDROLOGY

    Ground & surface

    water flow

    Hydro-genesis

    Demand of terrain

    Modifying influences

    MAINTENANCE

    Capacity & skills

    Funding

    Programming

    GEOMETRICS AND

    CROSS-SECTION PROFILES

    Road width

    Crown height

    Demand of terrain

    Sealed shoulders

    CONSTRAINTS OF THE “GREEN” ENVIRONMENT

    Constrained alignments

    Access to materials

    Depletion of resources

    Terrain stability

    OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY

    • OTHER

    • Technology solution

      • labour based

      • Intermediate equip

    • Safety

    • Institutional environment capacity

    • Financing

    • Political pressure

    • Design period

    • Road side activity

    • AVAILABLE MATERIALS

    • Alternative & thin bituminous

    • surfacings

    • Pavement materials

      • Marginal materials

      • Standards

    • Subgrade & road formation

    • Problem soils

    • Moisture sensitivity

    • Stabilisation options and treatments

    CONSTRUCTION

    Quality control

    Capacity, training & experience

    Selection and use of plant

    Influence of construction traffic


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