The Effects of Common Errors in a Backcalculation Model on ...
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The Effects of Common Errors in a Backcalculation Model on Mechanistic Pavement Design David P. Orr Cornell University Local Roads Program
Transcript of The Effects of Common Errors in a Backcalculation Model on ...
The Effects of Common Errors in a Backcalculation Model on
Mechanistic Pavement Design
David P. OrrCornell University
Local Roads Program
CollectFWD Data
Pavement Design
BackCalc
PerformRepair
BuildModel
Accept
Review
CollectSite Data
Pavement Design Process
What are We Looking For?
• Take FWD data Pavement Design
Pavement Model
Weather Affected Subgrade
Subgrade
Granular Subbase
Asphalt Surface
FrozenThawing
Rapid drainageSlow recovery
Refreezing
Asphalt Surface and BaseAsphalt Base
Collection of Data
Backcalculation Model
• FWD data• Load• Deflections• Sensor location
• Pavement• Layers
• Number• Thickness• Thin Layers
• Hard bottom• Seed moduli• Poisson’s ratio• Material model
Effect of Errors in Model
• Errors in the backcalculation model • Errors in backcalculation results
• Errors in pavement design
Space and Time
Subb
ase
Mod
ulus
(M
Pa)
1 Jan 051 Oct 041 Jul 041 Apr 041 Jan 041 Oct 03
100000
10000
1000
100
10
Max - SubbaseUpper Q. - SubbaseAvg. SubbaseLower Q. - SubbaseMin - Subbase
Moduli
Site_Nam = Arcadia
Random Error
±0.08 mil (±2 µ)
Systematic Error
True Deflection
16 mils(400 μ)
Measured Deflection
2%0.3%
Random Error
±0.04 mil (±1 µ)
Random & Bias Errors
Let’s Try This Out
Pavement Model
Asphalt 8.0 inches 158,000 psi
Subbase 12.5 inches 36,400 psi
Upper Subgrade 30.0 inches 14,700 psi
Lower Subgrade ∞ 13 300 psi
Actual Pavement
• Remaining Life 1.5 years• Overlay (10 year life) 1.5 inches
Effect of Error in Asphalt Thickness
Compensating Layer Effect
0123456
6 8 10
Ove
rlay
-in
ches
10-yr overlay
Steps in Analysis
• Apply random errors• Apply bias errors
• Backcalculate moduli• Determine 10-year overlay
thickness
Values in Thousands
0
0
0
0
0
0
0
0
Mean=14623
14.1 14.375 14.65 14.925 15.14.1 14.375 14.65 14.925 15.
Mean=14623
Simulation
• @Risk software• 500 simulations
Errors to Review
• Errors in FWD data • Errors in the layer thicknesses
Errors in FWD Data
Poor data• ± 2 percent
Better data• ± 0.3 percent
Errors in Layer Thicknesses
Poor data• ± 1 inch surface• ± 3 inch subbase• ± 6 inch upper
subgrade
Better data• ± 0.5 inch surface• ± 1.5 inch subbase• ± 3 inch upper
subgrade
Effect of Combined Errors Backcalculated Moduli (psi)
Large Errorll
Effect of Combined ErrorsOverlay Thickness (inches)
Average 5th % 95th %rge Errors 2.2” 0” 4.75”
mall Errors 1.4” 1” 1.75”
Distribution for Overlay/W15
Mean=2.228
0 1 2 3 4 5 6 70 1 2 3 4 5 6 7
Mean=2.228
Distribution for Overlay/W15
0
1
2
3
4
5
6 Mean=1.424
0 1 2 3 4 5 6 70 1 2 3 4 5 6 7
Mean=1.424
Calibrate & Maintain FWD
Obtain Ground Truth Data
Thank You
