United States Department of Transportation
i
Backcalculation of Layer Parameters for LTPP Test Sections, Volume I: Slab on Elastic Solid and Slab on Dense-Liquid Foundation Analysis of Rigid Pavements
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2001-01-01
[PDF-773.38 KB]
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Edition:Final report; Aug. 1997-July 1998.
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Abstract:This report documents the results of backcalculation of layer material properties for rigid pavements included in the Long Term Pavement Performance (LTPP) program in the United States and Canada using deflection testing data. This study backcalculated the layer material properties for rigid pavements using the slab on elastic solid foundation and the slab on dense-liquid foundation procedures. The "best fit" algorithm was used after consideration of alternative methods of backcalculation. Pre-processing and post-processing utility software were developed to facilitate data handling. The backcalculation analysis was conducted for all General Pavement Studies (GPS), Special Pavement Studies (SPS), and Seasonal Monitoring Program (SMP) test sections. Data tables that include backcalculation parameters were developed for inclusion in the LTPP Information Management Systems (IMS). Key findings include the following: 1. The "best fit" method was selected as the primary backcalculation method for both dense-liquid (DL) and elastic solid (ES) subgrade models. 2. Reasonable backcalculation results were obtained for the large majority of GPS, SPS, and SMP sections. Typical modulus values and ranges are provided for the PCC slab, many types of bases, and the subgrade. 3. Strong correlations were found between backcalculated parameters using DL and ES subgrade models. 4. Temperature curling during the day had a profound effect on the results of backcalculation [making it important to conduct falling weight deflectometer (FWD) basin testing early in the morning to reduce variability in backcalculated values]. 5. Poor correlation was found between backcalculated and laboratory elastic moduli of the concrete slab. 6. A bonded interface between the slab and base produced the best layer moduli for a large majority of the sections (center slab backcalculation).
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