Estimation of pavement-layer moduli using nonlinear optimization technique

Falling Weight Deflectometer (FWD) testing is used for nondestructive structural evaluation of existing pavements. The deflection data from FWD can be used for estimation of layer moduli by an iterative technique. In the calculation process, commonly known as backcatculation, comparison is done between calculated deflections from a suitable theory and those measured by the FWD. The estimated moduli values correspond to the best fit of the measured deflection basin. In the present study, a nonlinear optimization technique has been used to estimate the layer moduli in the backcalculation process. The backcalculation scheme developed is applicable to 3-layer to 6-layer pavements. The method was verified by simulated deflection data from elastic-layer theory and FWD-deflection measurements on 13 in-service pavements in Arizona. They were found to approximate closely the manual approach of matching deflection basins. The algorithm has been coded in a computer program called the Arizona Deflection Analysis Method (ADAM).