Long-Term Pavement Performance Program Determination of In-Place Elastic Layer Modulus: Backcalculation Methodology and Procedures

2015Jiang, YanDistribution number: HRDI-30/12-15(500)EPDFTech ReportFHWA-HRT-15-036DTFH61-11-C-00051Pavement performanceBackcalculationFalling weight deflectometersDeflection testsUnited StatesUnited States. Federal Highway Administration. Office of Infrastructure Research and DevelopmentVon Quintus, Harold L.Rao, ChetanaIrwin, Lynne H.Applied Research Associates, Inc.United States. Federal Highway Administration. Office of Infrastructure Research and DevelopmentTurner-Fairbank Highway Research CenterJiang, Yan JaneFederal Highway AdministrationDeflection data have been measured at periodic intervals with a falling weight deflectometer on all rigid, flexible, semirigid, and rehabilitated pavement test sections included in the Long-Term Pavement Performance (LTPP) program. A common use of deflection data is to backcalculate in-place layered elastic modulus values. The Federal Highway Administration sponsored earlier studies to backcalculate elastic layer modulus values from deflection basins measured on all LTPP test sections and included those computed values in the LTPP database.(3\u20135) While the earlier studies focus on the use of nonlinear methods and were considered to have minimal success, Some of the methods used have advanced within the past decade. As such, there was a need to revisit the methods used to improve on the results.This report summarizes all activities completed to backcalculate the elastic layered modulus from deflection basins measured on all test sections included in the LTPP program. Specifically, the report documents the tools, data analyses, backcalculation and forward calculation packages, and procedures used to calculate, on a production basis, the in-place elastic layer modulus of the LTPP test sections. Multiple packages (including BAKFAA, EVERCALC\ua9, MICHBACK\ua9, MODULUS, MODCOMP\ua9, and the area and best fit methods) were considered and evaluated for estimating layered elastic modulus values on a production basis. (See references 6\u201310.) The methods used in production for backcalculating elastic layer moduli include a combination of EVERCALC\ua9 and MODCOMP\ua9 for all types of pavements and the best fit method for rigid pavements. The methods and procedures, including the pre- and post-processing tools, have been automated so the results can be recreated by others not directly involved in development of the tools and procedures. The report also summarizes the results from the production runs to calculate the elastic layered modulus of flexible and rigid pavements (new construction and rehabilitation) as well as demonstrate the application and use of the results.74