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Guidelines for Review and Evaluation of Backcalculation Results
PUBLICATION NO. FHWA-HRT-05-152 FEBRUARY 2006

Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296

FOREWORD This report documents a new approach, called forwardcalculation, used for determining layered elastic moduli from in situ load-deflection data.Guidelines are provided for carrying out forwardcalculation procedures as well as screening backcalculation results using forwardcalculated moduli. This report will be of interest to highway agency engineers involved in pavement analysis, design, construction, and deflection data collection, as well as researchers who will use the Long-Term Pavement Performance (LTPP) load-deflection data to improvedesign procedures and standards for constructing and rehabilitating pavements.

Gary L. Henderson 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 thisdocument. This report does not constitute a standard, specification, or regulation. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document. Quality Assurance Statement The Federal Highway Administration (FHWA) provides high-quality information to serve Government,industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page
1. Report No. 2. Government AccessionNo. 3. Recipient's Catalog No.

FHWA-RD-05-152
4. Title and Subtitle 5. Report Date

Guidelines for Review and Evaluation of Backcalculation Results
7. Author(s)

February 2006
6. Performing Organization Code 8. Performing Organization Report No.

R.N. Stubstad, Y.J. Jiang, and E.O. Lukanen
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

Applied ResearchAssociates, Inc. 7184 Troy Hill Drive, Suite N Elkridge, Maryland 21075-7056
12. Sponsoring Agency Name and Address

11. Contract or Grant No.

DTFH61-02-D-00138
13. Type of Report and Period Covered

Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, Virginia 22101-2296
15. Supplementary Notes

Guidelines—Final Report
14.Sponsoring Agency Code

Contracting Officer’s Technical Representative (COTR): Larry Wiser, HRDI LTPP Data Analysis Contract.
16. Abstract

This document presets a new approach to determining layered elastic moduli from in situ loaddeflection data, which was developed under the Federal Highway Administration’s project for reviewing Long-Term Pavement Performance (LTPP) backcalculation data. Thisapproach is called forwardcalculation, and it differs from backcalculation in that modulus estimates are calculated directly from the load and deflection data using closed-form formulae rather than through iteration. The closedform forwardcalculation equations are used for the subgrade and the bound surface course, respectively, for both flexible and rigid pavement falling weight deflectometer (FWD)data. Intermediate layer moduli are estimated through commonly used modular ratios between adjacent layers. The audience for this document includes highway agency engineers, researchers, and consultants who are involved in pavement analysis, design, construction, and deflection data analysis.
17. Key Words 18. Distribution Statement

Pavements, LTPP, FWD, deflection data, elastic modulus,...