U.S. Department of Transportation
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Federal Highway Administration Research and Technology
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Review of the Long-Term Pavement Performance (LTPP) Backcalculation Results
Primary Topic: Surface and Other Considerations
Description: This report is a comprehensive review and evaluation of the Long-Term Pavement Performance (LTPP) backcalculation data. In this study forward calculation 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.
FHWA Publication Number: FHWA-HRT-05-150
Publication Year: 2006
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