Precision of back-calculation analysis and independent parameters-based models in estimating the pavement layers modulus-Field and experimental study

The main objectives of this research were to present new method of back-calculation analysis and to compare the obtained results with destructive testing. Several sections in Shush-Andimeshk and Semnan-Damghan highways were evaluated by ground penetrating radar for estimating the layer thickness and falling weight deflectometer (FWD) at different load levels for estimating the elastic moduli of pavement layers. At the same sections, some cores were extracted and tested to measure the elastic modulus using the indirect tensile and dynamic triaxial methods for bound and unbound layers, respectively. The FWD data were analyzed by ELMOD6.0 software as a conventional back-calculation method. Furthermore, a new method was proposed by implementing a code using BASIC programming language and the obtained results were compared with those from ELMOD6.0 and laboratory results. Based on these investigations the proposed method had higher conformity to destructive testing results than conventional back-calculation method. In addition to back-calculation based models, models were developed based on the independent variables such as surface curvature index and base damage index. Using the latter models the layer modulus can be estimated without using the complicated back-calculation analysis methods.