the effects of common errors in a backcalculation model on
TRANSCRIPT
![Page 1: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/1.jpg)
The Effects of Common Errors in a Backcalculation Model on
Mechanistic Pavement Design
David P. OrrCornell University
Local Roads Program
![Page 2: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/2.jpg)
CollectFWD Data
Pavement Design
BackCalc
PerformRepair
BuildModel
Accept
Review
CollectSite Data
Pavement Design Process
![Page 3: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/3.jpg)
What are We Looking For?
• Take FWD data Pavement Design
![Page 4: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/4.jpg)
Pavement Model
Weather Affected Subgrade
Subgrade
Granular Subbase
Asphalt Surface
FrozenThawing
Rapid drainageSlow recovery
Refreezing
Asphalt Surface and BaseAsphalt Base
![Page 5: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/5.jpg)
Collection of Data
![Page 6: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/6.jpg)
Backcalculation Model
• FWD data• Load• Deflections• Sensor location
• Pavement• Layers
• Number• Thickness• Thin Layers
• Hard bottom• Seed moduli• Poisson’s ratio• Material model
![Page 7: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/7.jpg)
Effect of Errors in Model
• Errors in the backcalculation model • Errors in backcalculation results
• Errors in pavement design
![Page 8: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/8.jpg)
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
![Page 9: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/9.jpg)
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
![Page 10: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/10.jpg)
Let’s Try This Out
![Page 11: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/11.jpg)
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
![Page 12: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/12.jpg)
Actual Pavement
• Remaining Life 1.5 years• Overlay (10 year life) 1.5 inches
![Page 13: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/13.jpg)
Effect of Error in Asphalt Thickness
![Page 14: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/14.jpg)
Compensating Layer Effect
0123456
6 8 10
Ove
rlay
-in
ches
10-yr overlay
![Page 15: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/15.jpg)
Steps in Analysis
• Apply random errors• Apply bias errors
• Backcalculate moduli• Determine 10-year overlay
thickness
![Page 16: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/16.jpg)
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
![Page 17: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/17.jpg)
Errors to Review
• Errors in FWD data • Errors in the layer thicknesses
![Page 18: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/18.jpg)
Errors in FWD Data
Poor data• ± 2 percent
Better data• ± 0.3 percent
![Page 19: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/19.jpg)
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
![Page 20: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/20.jpg)
Effect of Combined Errors Backcalculated Moduli (psi)
Large Errorll
![Page 21: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/21.jpg)
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
![Page 22: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/22.jpg)
Calibrate & Maintain FWD
![Page 23: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/23.jpg)
Obtain Ground Truth Data
![Page 24: The Effects of Common Errors in a Backcalculation Model on](https://reader031.vdocuments.us/reader031/viewer/2022022417/589af4141a28ab7d468bd74f/html5/thumbnails/24.jpg)
Thank You