transport and main roads deflection response o benkelman ... · o deflectograph o falling weight...
TRANSCRIPT
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Transport and Main Roads
Deflection Response
o Benkelman Beam
o Deflectograph
o Falling Weight Deflectometer
Transport and Main Roads
Transport and Main Roads
Deflectograph (PAVDEF)Transport and Main Roads
Transport and Main Roads
Heavy weight deflectometerTransport and Main Roads
HWD/FWD Loading system
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Transport and Main Roads
HWD/FWD BowlTransport and Main Roads
Deflection Measurement Devices
• Benkelman Beam - Standard Axle Load
- 550 kPa Contact Stress
• Deflectograph - Standard Axle Load
- 750 kPa Contact Stress
• FWD/HWD - Variable Load
- Variable Contact Stresses
- Fixed Contact Area
Transport and Main Roads
Overlay Design Methodology
• Deflection Reduction Method using Subgrade CBR (D900) Estimate
• Deflection Reduction Method using equivalent CBR from Subgrade Modulus obtained by Back Analysis
• Mechanistic Design Method using calculated insitu Pavement and Subgrade Moduli from Back Analysis
Transport and Main Roads
Typical Deflection Bowl Shapes under a Standard Axle (40 kN) Load for the various Deflection Devices used by Main Roads –
see next slide
Transport and Main RoadsTypical Deflection Bowls Granular base – 40kN Load
LOAD
Transport and Main Roads
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Transport and Main RoadsTypical Deflection Bowls CTB – 40kN Load
Transport and Main Roads
Transport and Main RoadsTypical Deflection Bowls CTB – 40, 60 + 80 kN Loads
Transport and Main Roads
• The absolute value of 40 kN deflection measurements on Bound Heavy Duty Pavements are too low for effective/confident back analysis.
• Need higher loads for testing Bound Heavy Duty Pavements
Transport and Main Roads
Deflection Surveys
The spacing of successive deflection tests is as follows:
Urban Areas
• Both inner and outer wheel paths for all lanes
• 25 m: heavy commercial vehicle lane (usually the outer lane)
• 50 m: fast lane
• 10 m: areas of high distress
Transport and Main Roads
Deflection Surveys
Rural Areas
• Both inner and outer wheel paths for all lanes
• 50 m: all lanes (this would be staggered between adjacent lanes)
The recording for deflection surveys consists of:
• Direction/lane description
• Wheelpath description
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Transport and Main Roads
Typical results from deflection testing
Transport and Main Roads
Deflection vs. Distance
Transport and Main Roads Transport and Main Roads
Deflection Bowl
Transport and Main Roads
Deflection Bowl
Transport and Main Roads
Typical Deflection Bowl
200
250 mm
LOAD
0D200
D250
Rebound Deflection, D0 = Max. Deflect - Residual DeflectD
Residual
MaximumD 900
Deflection Ratio, DR = D250/ DCurvature Function, CF = D - D
0 200
900 mm
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Transport and Main Roads
Benkelman Beam Test
Transport and Main Roads
Residual Deflections
• Residual deflections represent the ‘permanent’ deformation of a pavement
• Residual deflections can be +ve or -ve
Transport and Main Roads
Deflection Ratio
Deflection ratio is used to indicate the stiffness of the pavement structure and is ‘fairly’ independent of surfacing type (AC/spray seal) or sub-grade CBR
Deflection Ratio = D250 / D0
Deflection ratio of:
• > 0.8 indicates CTB or CTSB bound pavement
• 0.6 – 0.8 indicates good quality unbound pavement
• < 0.6 indicates a possible weakness in the pavement materials
Transport and Main Roads
Modulus vs. Deflection Ratio
Transport and Main Roads
Curvature Function
• Curvature function is used to predict the fatigue life of an applied asphalt surfacing overlay or an existing asphalt surfacing
Curvature Function = D0 – D200
o Representative curvature is determined as the mean of the curvature functions
o Representative of C.F. should have a C.V. of < 30%
Transport and Main Roads
D900 Value vs. CBR Value
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Transport and Main Roads
Bowl Survey Data
• Deflection Strength
• Defln. Ratio Stiffness
• Residual Defln. Ratio Upper Pvt. or Surface
• Curvature Asphalt Fatigue
• Deflection 900 Subgrade
Transport and Main Roads
Historic Tolerable Deflection Criterion – Unbound Pavements
Transport and Main Roads
Historic Tolerable Deflection Criterion – Unbound Pavements
Transport and Main Roads
Historic Tolerable Deflection Criterion – Unbound Pavements
Transport and Main Roads
Deflection Reduction Overlay Design Philosophy
Transport and Main Roads
Tolerable DeflectionNormal Design Standard
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Transport and Main Roads
Tolerable DeflectionNormal Design Standard
Transport and Main Roads
Granular Overlay Process
Transport and Main Roads
Design Exercise 1
The results of a Benkelmen beam deflection survey for a section of Toowoomba – Karara Road is attached.
1. Determine homogenous lots for both inner and outer wheelpaths.
2. Compare the representative values of the following for the homogenous sections for both inner and outer wheel paths:
- rebound deflections
- residual deflections
- deflection ratio
- curvature function
Transport and Main Roads
Design Exercise 1 (cont.)
3. For these sections, based on the deflection results, comment on the following:
- stiffness of the pavement material
- condition of the subgrade
Transport and Main Roads
Selection of Homogenous Lots
• Study bowl plots and delete bad bowls
• If AC surfacing – temperature correction
• Plot rebound deflections and residual deflections (check high/low)
• Visually subdivide rebound deflection plots into uniform subsections
Transport and Main Roads
Selection of Homogenous Lots (cont.)
• Determine statistical valueso Mean ( )
o Standard Deviation (s.d.)
o Coefficient of variation (s.d./ )
For both IWP and OWP for rebound deflection
• If CV < 30% lot is homogenous
• If CV > 30% lot requires further subdivision until CV is < 30%
x
x
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Transport and Main Roads Transport and Main Roads
Transport and Main Roads
Moisture Correction Factors
Depend on:
• Subgrade type
• Rainfall
• Location of water table
• Pavement type
Transport and Main Roads
Moisture Correction (cont.)
• Moisture correction factors are applied to the IWP Deflections in order to simulate the worst expected conditions in the outer wheel path
Transport and Main Roads
Seasonal Correction Factors
Transport and Main Roads
Moisture Correction
• Moisture movement occurs in pavements generally in the outer wheel paths only (assuming reasonable pavement drainage)
• CBR of the subgrade also varies with moisture
• Example:
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Transport and Main Roads
Asphalt Fatigue
• Tensile Strain in asphalt depends on:o Traffic (E.S.A.’s)o Temperatureo Thickness
Transport and Main Roads
Curvature Function
• Curvature function is used to predict the fatigue life of an applied asphalt surfacing overlay or an existing asphalt surfacing
Curvature Function = D0 – D200
Transport and Main Roads
Curvature Function
Curvature Function = D0 – D200
oRepresentative curvature is determined as the mean of the curvature functions
Transport and Main Roads
Asphalt Overlay Process
Transport and Main Roads
Asphalt correction factor for deflection
Asphalt Temperature Correction for Deflection
y = 0.0028e5.8857x
y = 0.2209e1.5235x
y = 0.1709e1.7818x
y = 0.1344e2.0138x
y = 0.0975e2.3295x
y = 0.0341e3.3809x
y = 0.0147e4.2176x
y = 0.0624e2.7687x
0.5
1
1.5
2
2.5
3
3.5
4
0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1
Deflection Adjustment Factor
WM
AP
T /
T m
easu
red
50Existing Asphalt Thickness (mm)200 250 30015010075 125
Transport and Main Roads
Asphalt Stiffness Relationships
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Transport and Main Roads
Worked example of QDMR procedures for asphalt overlay design
Transport and Main Roads
Asphalt Overlay Process
1. For Subgrade Life NS & D900 value, determine Dtol
Transport and Main Roads
Asphalt Overlay Process (cont)
2. Check Dtol > or < DREP deflection
3. Determine thickness (TAC) for curvature before overlay and design traffic (ESA’s)
Transport and Main Roads
Asphalt Overlay exercise
Fill in the top white cells of spreadsheet
• temp.zone number – see Queensland map sheet 34
• temperature of existing asphalt – see FWD printout - sheet 12
• Depth of existing asphalt – see trench profile –sheet 3
• Asphalt correction factor for deflection – see sheet 36
Transport and Main Roads
Overlay Design (cont)
• Temperature Corrections
o Deflections affected by temperature
o Zones for Queensland
o Corrections to both deflection and curvature functions
Transport and Main Roads
ZONE 1WMAPT > 35°
Gympie
South
Pacific
Ocean
Gulf of
Carpentaria
New South Wales
South
Australia
Nor
ther
n
Ter
rito
ry
Clermont
Barcaldine
CLONCURRY
Normanton
Camooweal
Winton
Tambo
Taroom
Coolangatta
ROCKHAMPTON
Gold Coast
Thursday Island
Bundaberg
Weipa
Hebel
LONGREACH
CAIRNS
BRISBANE
ST GEORGE
MilesMorven
Mt GarnetKarumba
MT ISA
GOONDIWINDI
Roma
Hughenden
TOWNSVILLE
Mackay
Charters Towers
Rolleston
Westwood
Dululu
Gayndah
Toowoomba
WARWICK
Blackall
Emerald
CHARLEVILLE
Augathella
CUNNAMULLA
Maryborough
ZONE 2WMAPT > 32°35° >
ZONE 3WMAPT > 29°32° >
ZONE 4WMAPT29° >
Temperature zones for design of pavements with asphalt layers
Sheet 34
WMAPT - Weighted Mean Annual Pavement Temperatures
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Transport and Main Roads
Asphalt Fatigue Criteria
Transport and Main Roads
Influence of Temperature Variations
1. Rebound Deflection (D0)
2. Curvature Function (D0 – D200)
Transport and Main Roads
Asphalt correction factor for deflection
Asphalt Temperature Correction for Deflection
y = 0.0028e5.8857x
y = 0.2209e1.5235x
y = 0.1709e1.7818x
y = 0.1344e2.0138x
y = 0.0975e2.3295x
y = 0.0341e3.3809x
y = 0.0147e4.2176x
y = 0.0624e2.7687x
0.5
1
1.5
2
2.5
3
3.5
4
0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1
Deflection Adjustment Factor
WM
AP
T /
T m
easu
red
50Existing Asphalt Thickness (mm)200 250 30015010075 125
Transport and Main Roads
Asphalt correction factor for curvature function – see sheet 37
Transport and Main Roads
• Speed Correctionso Modulus increases with rate of loading
o Speed of beam testing must lower than operating traffic speed
o Corrections
o Applicable for asphalt overlay on asphalt
Transport and Main Roads
Chart 14 – Zone 3 – 80kph
Asphalt Overlay Design (2600MPa): Zone 4 - 50kph, Zone 3 - 80kph
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600
Deflection Before Overlay
Def
lect
ion
Aft
er O
verl
ay
50mm
75mm
100mm125mm
150mm
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Transport and Main Roads
Before and After Deflections Asphalt overlay chart
CHART 14-Asphalt Overlay Design (2600MPa): Zone 3 - 80kph
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600
Deflection Before Overlay
Def
lect
ion
Aft
er O
verl
ay
50mm
75mm
100mm125mm
150mm
0.56
0.64
0.745 0.874
less than 50 mm thick
110 mm
Aft
er
Before
Transport and Main RoadsChart 30
Asphalt Overlay Design: Zone 3 - 80kph
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Design Traffic (ESA)
Cu
rvat
ure
Bef
ore
Ove
rlay
1E5 1E6 1E7
75mm 100mm 125mm 150mm
Chart 30 -
3E6
0.242
0.198
Design Traffic (ESA)
Transport and Main Roads
Chart 30 Zone 3 -80Kph
Asphalt Overlay Design: Zone 3 - 80kph
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Design Traffic (ESA)
Curv
ature
Bef
ore
Ove
rlay
1E5 1E6 1E7
75mm 100mm 125mm 150mm