The falling weight deflectometer (FWD) test is one of the most commonly used tools for nondestructive evaluation of flexible pavements. Although the test is intrinsically dynamic, the state-of-practice backcalculation techniques used to interpret the FWD records are primarily elastostatic based, partly because of the high computational cost of dynamic multilayered solutions. It has long been known that the foregoing discrepancy may lead to systematic errors in the estimation of pavement moduli in situations of pronounced inertial and resonance phenomena due to the presence of bedrock or seasonal stiff layer. In this investigation, a simple, yet effective algorithm is proposed that allows the static backcalculation analyses to perform well even when dynamic effects are significant. The technique is based on the use of the discrete Fourier transform as a preprocessing tool to filter the dynamic effects and extract the static pavement response from transient FWD records. With the filtered (i.e., zero-frequency) force and deflection values in lieu of their peak counterparts, the static backcalculation can be further performed in a conventional manner, but free of inconsistencies associated with the neglect of dynamic effects. Results based on synthetic deflection records demonstrate a marked improvement in the elastostatic prediction of pavement moduli when the proposed modification is used. The filtering algorithm can be implemented on a personal computer as a preprocessor for the conventional FWD data interpretation, requiring only a minimal increase in the computational effort to backcalculate the pavement moduli.
Samenvatting