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Publication Number: FHWA-HRT-05-150
Date: February 2006
Review of The Long-Term Pavement Performance (LTPP) Backcalculation Results
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This report is a comprehensive review and evaluation of the Long-Term Pavement Performance (LTPP) backcalculation data. In this study, a new approach, called forwardcalculation was developed to determine layered elastic moduli from in situ load-deflection data with procedures and results documented. the entire set of LTPP-computed parameters of backcalculation results was screened using forwardcalculated moduli.
Although users cannot reject any backcalculated modulus value merely because it is outside a reasonable or acceptable range, the forwardcalculated values were, in most cases, more stable on a section-by-section basis than the backcalculated values in the LTPP database. The exception was the portion of the backcalculated database based on slab-on-dense-liquid and slab-on-elastic-solid theory, where the correspondence between the two rigid pavement analysis techniques was excellent and both the backcalculated and forwardcalculated moduli and k-values were very stable.
It is recommended that the backcalculated database be retained as is, with the addition of the complementary forwardcalculated dataset and screening flags, so the database user can decide which method is more suitable to the application.
This report will interest highway agency engineers involved in pavement analysis, design, construction, and deflection data collection, as well as researchers who use LTPP load-deflection data to improve design procedures and standards for constructing and rehabilitating pavements.
Gary L. Henderson
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.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.
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TECHNICAL REPORT DOCUMENTATION PAGE
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS
4. INITIAL LTPP BACKCALCULATION
DATA SCREENING RESULTS
6. LTPP BACKCALCULATION DATABASE
LIST OF FIGURES
Figure 1. Equation. Composited
Subgrade Modulus at an Offset.
LIST OF TABLES
Table 1. Hogg Model