Matching Distress Definitions in Field and in MEPDG for Local Calibration Danny X. Xiao, Kelvin C.P. Wang, Kevin D. Hall
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Matching Distress Definitions in Field and in MEPDG
for Local Calibration
Danny X. Xiao, Kelvin C.P. Wang, Kevin D. Hall
MEPDG
� Mechanistic-Empirical Pavement Design Guide
from FHWA
Goal of Calibration
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Measurement (in.)
Before Calibration
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Measurement (in.)
After Calibration
Initial results of MEPDG calibration in Arkansas
y = 0.2022x
R² = -0.053
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Pre
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Measurement, ft/mi
Comparison of Longitudinal Cracking_LTPP
(National Calibration Method)
N=145
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Measurement, ft/mi
Comparison of Transverse Cracking_LTPP
(National Calibration Method)
y = 0.2022x
R² = -0.053
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Measurement, %
Comparison of Alligator Cracking_LTPP
(National Calibration Method)
N=145
Two reasons
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Measurement (in.)
Comparison of measurement and prediction
Variability of Measured Distress
� It has been recognized for a long time.
� Rada, G. et al. (1997, 1998), Variability of LTPP distress data
� Goodman, S. (2001), Variability of C-LTPP distress data
� Larson C. (2000), QA/QC of pavement distress data in Virginia
� Schwartz C. (2007), Uncertainty of distress measurement and MEPDG
� Flintsch, G. and McGhee, K. (2009), NCHRP Synthesis 401: Quality management of pavement condition data collection
Problem statement
� Do differences in distress definitions between LTPP and MEPDG affect calibration?
� Is longitudinal cracking in wheelpath alligator cracking?
� Should one use a weighting function to combine low, medium and high severities?
1. Do differences in distress definitions between LTPP and MEPDG affect calibration?
LTPP
� “As a pavement distress dictionary, the manual will improve communications within the pavement community by fostering more uniform and consistent definitions of pavement distress.”
Type Severity Amount
(Distress Identification Manual for LTPP, 2003)
MEPDG
� “Mechanistic–empirical procedures use pavement models based on the mechanics of materials to predict pavement responses (deflections, strains, and stresses) and empirically based transfer functions to estimate distress initiation and development based on these responses.”
(NCHRP Synthesis 401, 2009)
Alligator cracking
LTPP
MEPDG
(Image from Distress
Identification Manual for
LTPP, 2003)
(Image from NCHRP 1-37A
final report, 2004)
Longitudinal cracking
LTPP
MEPDG
(Image from Distress
Identification Manual for
LTPP, 2003)
(Image from NCHRP 1-37A
final report, 2004)
Distress Models in MEPDG
Bottom-up(alligator) cracking Top-down(longitudinal) cracking
(Equations from NCHRP 1-37A final report, 2004)
Transverse (LTPP) or thermal (MEPDG)?
(Image from Distress Identification
Manual for LTPP, 2003)
Transverse cracking
� No predicted thermal cracking, but we did see transversecracking in field.
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Measurement, ft/mi
Comparison of Transverse Cracking
(National Calibration Method)
Recommendation
Type Severity Amount Location Mechanism
5thVersion
� 2. Is longitudinal cracking in wheelpath alligator cracking?
Data source
� 18 sections LTPP
� 8 sections PMS
Consider longitudinal_WP as alligator?
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Alligator Cracking, %
Influence of longitudinal cracking on alligator
cracking_LTPP
N=145
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%)
Alligator cracking (%)
Influence of longitudinal cracking on alligator
cracking_PMS
N=280
Longitudinal_WP as alligator?
y = 0.2022x
R² = -0.053
y = 0.2265x
R² = -0.015
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Pre
dic
tion
, %
Measurement, %
Comparison of Alligator Cracking_LTPP
Alligator Cracking
Alligator+Longitudinal_WP
Equality
Linear (Alligator Cracking)
Linear (Alligator+Longitudinal_WP)
N=145
y = 0.0214x
R² = -0.516
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Pre
dic
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Measurement (%)
Comparison of Alligator Cracking_PMS
Alligator
Alligator+Longitudinal_WP
Equality
Linear (Alligator)
N=280
Longitudinal_NWP
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Pre
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(ft
/mi)
Measurement (ft/mi)
Comparison of Longitudinal Cracking _PMS
Longitudinal_WP
Longitudinal_NWP
Equality
N=280
y = 0.2022x
R² = -0.053 y = 0.2205x
R² = -0.004
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/mi
Measurement, ft/mi
Comparison of Longitudinal Cracking_LTPP
Longitudinal_WP
Longitudinal_NWP
Equality
Linear (Longitudinal_WP)
Linear (Longitudinal_NWP)
N=145
An important assumption
Longitudinal cracking in wheelpath is alligator cracking.
As pavement deteriorates, longitudinal cracking will decrease as alligator cracking increases.
As pavement deteriorates, longitudinal cracking will increase as alligator cracking increases.
Development of alligator cracking
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Alligator Cracking, %
Development of alligator cracking_LTPP
Longitudianl_WP
Longitudinal_NWP
Transverse
N=145
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Alligator cracking (%)
Development of alligator cracking_PMS
Longitudinal_WP
Longitudinal_NWP
Transverse
N=280
� 3. Should one use a weighting function to combine low, medium and high severities?
Combine different severities together
� Pavement Condition Index (PCI), deduct value
� Low: medium : high = 3: 6: 10 (Chou C.,1997)
� MEPDG national calibration
for transverse cracking:
for alligator and longitudinal cracking:
Total Measured cracking = Low_severity + Medium severity + High_Severity
Weighting function: use or not use?
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Weighted Alligator Cracking, %
Influence of weighting on alligator cracking_LTPP
Alligator
Equality
N=145
y = 0.2022x
R² = -0.053
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Weighted Longitudinal Cracking, ft/mi
Comparison of Longitudinal Cracking_LTPP
Longitudinal_WP
Longitudinal_NWP
Equality
Linear (Longitudinal_WP)
Weighting or not? (cont.)
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Measurement, %
Comparison of Alligator Cracking_LTPP
Unweighted
Weighted
Equality
N=145
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Pre
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Measurement, ft/mi
Comparison of Longitudinal Cracking_LTPP
Unweighted Longitudinal_WP
Weighted Longitudinal_WP
Equality
N=145
Weighting or not? (cont.)
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Pre
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Measurement (ft/mi)
Comparison of Transverse Cracking_PMS
Weighted
Unweighted
Equality
N=725
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Pre
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Measurement, ft/mi
Comparison of Transverse Cracking_LTPP
Weighted Transverse
Unweighted Transverse
Equality
N=145
Conclusions
� Do differences in distress definitions between LTPP and MEPDG affect calibration?
ANSWER: Yes, so the gap between LTPP and MEPDG should be considered.
� Is longitudinal cracking in wheelpath alligator cracking?
ANSWER: Yes, it is recommended.
� Should one use a weighting function to combine low, medium and high severities?
ANSWER: Based on data shown, cannot support or reject the use of weighting function.
Thank you!
Questions?
Suggestions?
(Fall at the University of Arkansas, by Dr. Nam Tran)
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