DEVELOPMENT AND IMPLEMENTATION OF NEW MODULUS BACKCALCULATION PROGRAMS USING THE PEDD METHODOLOGY

This paper presents an overview of the Pavement Evaluation Based on Dynamic Deflections (PEDD) software and its backcalculation methodology for backcalculation of pavement moduli. The backcalculation procedure involves an iterative application of the multilayered elastic theory to calculate the in situ Young's modulus of the pavement layers. The test load is simulated by an equivalent static load. Surface deflections are predicted using assumed values of the Young's modulus and Poisson's ratio of the pavement layers. It has been enhanced to conduct nonlinear analysis of modulus backcalculated from FWD data. The PEDD methodology has been extended to develop a new program, FWDSOIL, for backcalculating modulus of subgrade sections and a simplified program, University of Mississippi version of the PEDD program (UMPED), for backcalculating modulus of asphalt pavement layers. Several example applications are described. The PEDD program generates reasonably accurate moduli compared to the MODULUS5 and several other backcalculation programs investigated in this study. The PEDD backcalculation methodology has remained unchanged since 1984. The PEDD backcalculated methodology has been validated for asphalt pavements by 3-D finite element simulations. 3-D finite element simulation models have also verified results of the FWDSOIL program for subgrade sections.