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Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT 
This report is an archived publication and may contain dated technical, contact, and link information 
Publication Number: FHWAHRT16009 Date: March 2017 
Publication Number: FHWAHRT16009 Date: March 2017 
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This report documents a study conducted to investigate the use of the falling weight deflectometer (FWD) as part of mechanisticempirical pavement design and rehabilitation procedures incorporated within the MechanisticEmpirical Pavement Design Guide (MEPDG) developed by the National Cooperative Highway Research Program and subsequently adopted by the American Association of State Highway and Transportation Officials. The first volume of this threevolume report documents general pavement deflectiontesting procedures and commonly used deflection analysis approaches and a review of backcalculation programs for flexible, rigid, and composite pavement structures. The relevance of the different procedures and approaches to the MEPDG were explored through examination of six case studies evaluated using FWD testing results in the MEPDG, and the findings are presented in the second volume. Based on the case study findings and information from the literature, best practice guidelines for effective testing of existing pavement structures and interpretation of those results as part of a mechanisticempirical pavement evaluation and rehabilitation process were developed and are presented in the third volume. This report is intended for use by pavement engineers as well as researchers involved in rehabilitation design and management of agencies’ pavements.
Cheryl Allen Richter, P.E., Ph.D.
Director, Office of Infrastructure
Research and Development
Notice
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
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Technical Report Documentation Page
1. Report No.
FHWAHRT16009 
2. Government Accession No.  3 Recipient's Catalog No.  
4. Title and Subtitle
Using Falling Weight Deflectometer Data with MechanisticEmpirical Design and Analysis, Volume I: Final Report 
5. Report Date March 2017 

6. Performing Organization Code  
7. Author(s)
Kurt D. Smith, James E. Bruinsma, Monty J. Wade, Karim Chatti, Julie M. Vandenbossche, and H. Thomas Yu 
8. Performing Organization Report No.


9. Performing Organization Name and Address Applied Pavement Technology Inc. 
10. Work Unit No. (TRAIS) 

11. Contract or Grant No. DTFH6106C00046 

12. Sponsoring Agency Name and Address
Federal Highway Administration 
13. Type of Report and Period Covered
Final Report; 10/2006–12/2010 

14. Sponsoring Agency Code


15. Supplementary Notes The FHWA Contracting Officerâ€™s Technical Representative was Nadarajah Sivaneswaran 

16. Abstract
The need to accurately characterize the structural condition of existing pavements has increased with the recent development, release, and ongoing implementation of the MechanisticEmpirical Pavement Design Guide (MEPDG). A number of different material inputs are required in the procedure, and it is important to adequately characterize and define them. The analysis of deflection data collected by the falling weight deflectometer (FWD) provides a quick and reliable way to characterize the properties of the paving layers as well as to assess the loadcarrying capacity of existing pavement structures. With the release of the new MEPDG, there is a pressing need to identify and evaluate the way that FWD testing is integrated into the new design procedure. Moreover, as highway agencies continue to implement the MEPDG, best practices guidance is needed on how to effectively test existing pavement structures and interpret the results as part of a mechanisticempirical pavement evaluation and rehabilitation process.
This document is part of a threevolume report investigating the use of the FWD as part of mechanisticempirical pavement design and rehabilitation procedures. In this volume, general pavement deflectiontesting procedures and commonly used deflection analysis approaches and backcalculation programs are reviewed for flexible, rigid, and composite pavement structures. The relevance of the different procedures and approaches to the current MEPDG are explored through examination of six case studies evaluated using FWD testing results in the MEPDG. These six case studies used pavement sections from the LongTerm Pavement Performance database containing adequate design, construction, and testing data results as a means of assessing the way that FWD deflection data are used in the rehabilitation portion of the MEPDG. Based on the case study findings, and on information from the literature, recommendations for continued improvements and developments in the analysis and interpretation of pavement deflection data were developed.
This is volume I of a threevolume report. The other volumes in the series are FHWAHRT16010, Volume II: Case Study Reports, and FHWAHRT16011, Volume III: Guidelines for Deflection Testing, Interpretation, and Analysis. 

17. Key Words
Falling weight deflectometer, Backcalculation, Deflection data, Structural evaluation, Resilient modulus, Elastic modulus, Subgrade support, Mechanisticempirical pavement design, Rehabilitation design, Overlay design 
18. Distribution Statement
No restrictions. This document is available through the National Technical Information Service, 

19. Security Classification Unclassified 
20. Security Classification Unclassified 
21. No. of Pages 182 
22. Price N/A 
Form DOT F 1700.7 (872)  Reproduction of completed page authorized 
SI* (Modern Metric) Conversion Factors
Figure 1. Diagram. Typical pavement deflection basin.
Figure 2. Diagram. Comparison of LTE.
Figure 3. Diagram. Schematic of Benkelman Beam device.
Figure 4. Graph. Typical output of vibrating steadystate force generator
Figure 5. Diagram. Schematic of Dynaflect device.
Figure 6. Diagram. FWD testing schematic.
Figure 7. Photo. Dynatest® heavyweight FWD.
Figure 9. Diagram. Schematic of an RDD.
Figure 10. Diagram. RDD loading and deflection measurement systems.
Figure 12. Equation. Conversion of FWD deflection to Benkelman Beam deflection—method1.
Figure 13. Equation. Conversion of FWD deflection to Benkelman Beam deflection—method2.
Figure 14. Equation. Conversion of Dynaflect deflection to Benkelman Beam deflection—method1
Figure 15. Equation. Conversion of Dynaflect deflection to Benkelman Beam deflection—method2
Figure 16. Equation. Conversion of Road Rater™ deflection to Benkelman Beam deflection—method 1
Figure 17. Equation. Conversion of Road Rater™ deflection to FWD deflection.
Figure 18. Diagram. Comparison of typical flexible and rigid pavement deflection responses.
Figure 19. Graph. Nonlinear pavement deflection response.
Figure 20. Graph. HMA elastic modulus as a function of middepth pavement temperature.
Figure 21. Graph. Variation in backcalculated kvalue due to variation in temperature gradient
Figure 22. Graph. Daily variation in the calculated LTEs (leave side of joint)
Figure 25. Graph. Seasonal effects on pavement deflection.
Figure 27. Graph. Seasonal variation in backcalculated subgrade modulus.
Figure 28. Graph. Seasonal variation in LTE and PCC surface temperature.
Figure 29. Diagram. Simply supported beam with a concentrated midspan.
Figure 30. Equation. Maximum deflection of a beam under a fixed load.
Figure 31. Equation. Moment of inertia of rectangular beam.
Figure 32. Diagram. Stress zone under the FWD load.
Figure 33. Equation. Backcalculation of subgrade modulus.
Figure 34. Equation. Computation of the effective modulus of the pavement structure.
Figure 35. Equation. Methodology for computing equivalent thickness.
Figure 36. Equation. Vertical deflection under a uniformly distributed load.
Figure 37. Equation. Vertical deflection under a point load.
Figure 38. Chart. Typical iterative backcalculation flow.
Figure 41. Diagram. ANN architecture.
Figure 42. Equation. Excitation level of a processing element
Figure 43. Equation. Response of a processing element to the net excitation.
Figure 44. Diagram. ANN for backcalculating pavement moduli
Figure 45. Equation. Parameter AREA.
Figure 46. Diagram. Comparison of standard and SHRP sensor configurations for AREA computations
Figure 47. Equation. AREA via trapezoidal rule for standard sensor configuration.
Figure 48. Equation. AREA via trapezoidal rule for SHRP sensor configuration.
Figure 49. Graph. Variation in AREA with ℓ.
Figure 50. Equation. Radius of relative stiffness for dense liquid foundation.
Figure 51. Equation. Radius of relative stiffness for elastic solid foundation.
Figure 52. Equation. Estimation of subgrade support for dense liquid and elastic solid foundations.
Figure 53. Equation. Flexural stiffness of the slab.
Figure 54. Equation. Computation of the PCC elastic modulus for the dense liquid foundation.
Figure 55. Equation. Minimization of the error function.
Figure 56. Equation. Determination of radius of relative stiffness.
Figure 57. Equation. Computation of the PCC elastic modulus for the elastic solid foundation.
Figure 58. Graph. Computing the kvalue.
Figure 59. Equation. OuterAREA method for backcalculation of composite pavements.
Figure 60. Equation. Effective elastic modulus of the composite pavement
Figure 61. Equation. Minimization of the error function.
Figure 62. Equation. LTE calculation.
Figure 63. Diagram. Comparison of examples of poor and good load transfer
Figure 64. Diagram. Comparison of slab curling due to temperature differentials in the slab.
Figure 65. Graph. Example void detection plot using FWD deflection data.
Figure 67. Equation. ISM ratio.
Figure 68. Equation. Odemark transformation.
Figure 69. Equation. Deflection for uniformly distributed load.
Figure 70. Equation. Deflection for point load.
Figure 71. Graph. Surface modulus for a threelayer pavement and a halfspace.
Figure 72. Diagram. Matching measured and calculated deflection basins.
Figure 74. Equation. Deflection basins matched iteratively with the convergence criteria.
Figure 75. Equation. Stressdependent elastic modulus.
Figure 76. Graph. Plot of the inverse of deflection offset versus measured deflection.
Figure 77. Equation. Saturated subgrade with bedrock.
Figure 78. Equation. Nonsaturated subgrade with bedrock or groundwater table.
Figure 79. Graph. Natural period, T_{d}, from sensor deflection time histories.
Figure 80. Illustration. Etok conversion process incorporated in the MEPDG.
Figure 81. Equation. Computation of radius of relative stiffness.
Figure 82. Equation. AREA parameter for foursensor configuration.
Figure 83. Equation. AREA parameter for sevensensor configuration.
Figure 84. Equation. AREA parameter for eight to ninesensor configuration.
Figure 85. Equation. Relationship between AREA and ℓ.
Figure 86. Equation. Nondimensional deflection coefficient
Figure 87. Equation. Calculation of kvalue.
Figure 88. Equation. Computation of PCC elastic modulus.
Figure 89. Equation. Minimization of the error function.
Figure 90. Equation. Calculated deflection at specified location.
Figure 91. Equation. Solutions for C constants.
Figure 92. Equation. Error function.
Figure 93. Equation. Minimization of error function.
Figure 94. Equation. kvalue determination.
Figure 95. Equation. Radius of relative stiffness determination.
Figure 96. Equation. Concept of effective stiffness.
Figure 97. Equation. Effective stiffness determination.
Figure 98. Equation. Equivalency of Poisson’s ratio for all plates.
Figure 99. Equation. Equivalency of plate stiffnesses.
Figure 100. Equation. Moduli ratio.
Figure 101. Equation. Computation of upper plate elastic modulus.
Figure 102. Equation. Computation of lower plate elastic modulus.
Figure 103. Equation. Bonded case effective stiffness.
Figure 104. Equation. Elastic modulus of the upper plate.
Figure 105. Equation. Relative error between the measured and calculated deflections.
Figure 106. Equation. Mean absolute relative error for deflection basin.
Figure 107. Equation. Adjustment factor for radius of relative stiffness.
Figure 108. Equation. Adjustment factor for the deflection directly under the load plate.
Figure 109. Equation. Conversion to equivalent square slab.
Figure 111. Equation. Calculation of kvalue.
Figure 112. Equation. Estimate of flexural strength based on elastic modulus.
Figure 113. Diagram. Layout of joint LTE testing on HMA/PCC.
Figure 114. Equation. OuterAREA for sevensensor configuration.
Figure 116. Equation. kvalue determination.
Figure 117. Equation. Nondimensional deflection coefficient for deflection.
Figure 118. Equation. Radius of relative stiffness.
Figure 119. Equation. Determination of elastic modulus.
Figure 120. Equation. Relationship between the equivalent plate and the pavement layers.
Figure 121. Equation. Determination of moduli of the HMA and PCC layers.
Figure 123. Equation. Minimization of the error function, F.
Figure 124. Equation. Empirical correlation between HMA modulus and temperature.
Table 1. Summary of available backcalculation programs.
Table 2. Flexible pavement analysis programs.
Table 3. Commonly available backcalculation computer programs for flexible pavements.
Table 4. Dynamic backcalculation programs for flexible pavements.
Table 5. Regression coefficients for AREA versus radius of stiffness relationship.
Table 6. Regression coefficients for nondimensional deflection coefficient
Table 8. Recommended condition factor values used to adjust moduli of intact slabs.
Table 9. Damage estimates for JPCP based on percent slabs cracked.
Table 10. Damage estimates for CRCP based on punchouts per mile.
Table 11. Pavement condition rating based on damage estimates for JPCP and CRCP.
Table 12. Coefficients for nondimensional deflection coefficients.
Table 13. Summary of selected case study pavement sections.
3D  threedimensional  
AASHTO  American Association of State Highway and Transportation Officials  
AI  Asphalt Institute  
ANN  artificial neural network  
CRCP  continuous reinforced concrete pavement  
EBITD  effective builtin temperature difference  
EICM  Enhanced Integrated Climatic Model  
ESAL  equivalent single axle load  
FAA  Federal Aviation Administration  
FEA  finite element analysis  
FFT  fast Fourier transform  
FHWA  Federal Highway Administration  
FWD  falling weight deflectometer  
GPR  groundpenetrating radar  
HMA  hotmix asphalt  
HMA/PCC  Hotmix asphalt overlaid portland cement concrete  
ISM  impulse stiffness modulus  
JPCP  jointed portland cement concrete pavements  
JRCP  jointed reinforced concrete pavement  
LTE  load transfer efficiency  
LTPP  longterm pavement performance  
MEPDG  MechanisticEmpirical Pavement Design Guide  
MET  method of equivalent thickness  
NCAT  National Center for Asphalt Technology  
NCHRP  National Cooperative Highway Research Program  
NDT  nondestructive testing  
PCC  portland cement concrete  
QA/QC  quality assurance/quality control  
RDD  rolling dynamic deflectometer  
RWD  rolling wheel deflectometer  
SHRP  Strategic Highway Research Program  
SID  system identification  
SPS  Specific Pavement Studies  
SVD  singular value decomposition  
TELTD  total effective linear temperature difference  
USACEWES  U.S. Army Corps of Engineers—Waterways Experiment Station  