pavement evaluation: principles and...
TRANSCRIPT
![Page 1: Pavement Evaluation: Principles and Practicenottingham.ac.uk/~evzncpe/docs/nottinghamdesignmethod.pdf · METHOD Dr Andrew Collop Reader in Civil Engineering University of Nottingham](https://reader034.vdocuments.us/reader034/viewer/2022042104/5e8241a27256384e797b31cd/html5/thumbnails/1.jpg)
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NOTTINGHAM DESIGN METHOD
Dr Andrew CollopReader in Civil EngineeringUniversity of Nottingham
CONTENTS• Introduction• Traffic • Design temperatures• Material properties• Allowable strains• Asphalt thickness design• Corrections• Example
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INTRODUCTION• Chart based approach (based on
computer analysis)• Simplified structure:
– 3 layers– Standard dual wheel load (40kN)– Fixed Poisson’s ratio’s– Standard granular layer (200mm,
100MPa)
SIMPLIFIED STRUCTURE
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DESIGN VARIABLES• 3 design variables
– Asphalt thickness – Asphalt stiffness modulus– Elastic stiffness of subgrade
• Correction for separate wearing course
• Correction for non-standard (thickness) granular layer
FLOW CHART
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TRAFFIC• Average vehicle speed required
– From knowledge of road situation– Err on the slow side (more conservative)
• Cumulative number of standard axles also required
STANDARD AXLESMethod 1: Estimated from procedure
developed at TRL1. Estimate initial daily number of CVs
in one direction (C0) and expected percentage growth rate (r)
2. Calculate mid-life flow (Cm) using (x = design life in years)
Cm = C0 (1 + 0.01 r)0.5x
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STANDARD AXLES3. Calculate proportion of CVs using
slow lane at mid-life (P) (P = 1 for single carriageways)
P = 0.97 – 4 x 10-5 Cm
4. Calculate cumulative number of CVs using slow lane during design life
Cc = 365 P C0 [(1 + 0.01r)x – 1]0.01r
STANDARD AXLES5. Convert to the number of million
standard axles (msa)
N = D Cc x 10-6
6. D is the damage factor determined from (y = year of opening + 0.5x –1945)
D = 0.35 - 0.26 0.93y + 0.082 (0.92y + 0.082) (3.9Cm/1550)
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METHOD 2: CHART
STANDARD AXLESMethod 3: Use Equivalence Factor (EF)
approach (needs detailed data)1. EF determined using (W is in kN,
80kN = standard axle)
EFw = (W / 80)4
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STANDARD AXLES2. Consider initial traffic loading
spectrum for 1 day and calculate equivalent number of std axles (Aw = number of axles of load ! In 1 day)
N0 = Σ (Aw EFw)
STANDARD AXLES
N = 0.0365 P N0 [(1 + 0.01r)x – 1]r
2. Cumulative number calculated from
P = 0.97 – 4 x 10-5 Nm
Nm = N0(1 + 0.01r)0.5x
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FLOW CHART
SUBGRADE STIFFNESS• Resilient modulus required (elastic
modulus)• Approximate procedure adopted• Based on CBR• Value in MPa
E3 = 10 x CBR• Alternative for cohesive soils (Ip =
plasticity Index Percentage)
E3 = 70 - Ip
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FLOW CHART
DESIGN TEMPERATURES• Based on Annual Average Air
Temperature (AAAT)• Rutting temperature takes into
account diurnal variations in both temperature and traffic loading
Trut = 1.47 x AAAT
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DESIGN TEMPERATURES• Fatigue temperature also takes into
account cumulative damage effects
Tfat = 1.92 x AAAT
FLOW CHART
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BITUMEN STIFFNESS• Loading time• Temperature• Binder properties
– Softening Point (SP)– Penetration– Penentration Index (PI) – calculated
from SP and Pen
LOADING TIME• Estimated from average commercial
vehicle speed and asphalt layer thickness
• Approximate relationship also used
T (secs) ≈ 1 / V (km/hr)
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LOADING TIME
BITUMEN STIFFNESS
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ASPHALT STIFFNESS• Calculated from bitumen stiffness
and volumetrics (VMA)• Valid for traffic loading only (elastic
region)
ASPHALT STIFFNESS
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FLOW CHART
ASPHALT STRAIN• Allowable tensile asphalt base strain
calculated (either to critical conditions of failure)
• Depends on binder grade (SP), volume of binder & traffic loading
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ASPHALTSTRAIN
SUBGRADE STRAIN• Allowable compressive subgrade strain
calculated (either to critical conditions of failure)
• Depends on type of asphaltic material and traffic loading
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SUBGRADE STRAIN
SUBGRADE STRAIN• Rut factor used for materials other
than Hot Rolled Asphalt (HRA)– Hot Rolled Asphalt (HRA) = 1– Dense Bitumen Macadam (DBM) = 1.56– Modified HRA = 1.37– Modified DBM = 1.52
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FLOW CHART
ASPHALT THICKNESS • Determine asphalt layer thickness
required• Depends on
– Mixture stiffness– Subgrade stiffness– Asphalt strain– Subgrade strain
• 2 thickness calculated (deformation and fatigue)
• Minimum is design thickness
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ASPHALTTHICKNESS
FLOW CHART
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GRANULAR CORRECTION• Reduce design thickness if granular
sub-base thickness > 200mm
∆h1 = ∆h2 [53 – 2.8 E1 + 0.5 E3]300
∆h1 = ∆h2 [26.5 – 0.5 E1 - 0.23 E3]300
Deformation
Fatigue
SURFACING CORRECTION• Reduce design thickness if type and
thickness of surfacing known (rutting design temperature only)
Hb = hw EwE1
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SURFACING CORRECTION
WORKED EXAMPLE
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WORKED EXAMPLETraffic Data• Initial volume = 1,500 CVs/day, single
carriageway• Growth rate = 3%/annum• Life = 20 years• Average speed of CVs = 60km/hr• AAAT = 9oC• Year road opened to traffic = 1984
WORKED EXAMPLE• Soil plasticity index = 38%• Carry out detailed design calculations
to failure using 4 typical bases (Table 1) for a pavement with a 200mm granular sub-base.
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SOLUTION• For deformation, design temperature
= 1.47 x 9 = 13.2oC• For fatigue, design temperature
= 1.92 x 9 = 17.3oC• Cumulative number of CVs = 14.7msa• Damage Factor = 2.72• Design Traffic = 2.72 x 14.7 = 40msa• Elastic subgrade stiffness = 70 – 38
= 32 MPa (say 30MPa)
SOLUTION• Asphalt stiffness
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SOLUTION• Maximum allowable asphalt strain (µε)
– HRA 130– DBM 54– Modified HRA 120– Modified DBM 108
• Maximum allowable subgrade strain (µε)– HRA 161– DBM 182– Modified HRA 175– Modified DBM 181
SOLUTION• Minimum layer thicknesses