The falling weight deflectometer (FWD) test applies an impulsive force on the surface of pavement and measures surface deflections at several locations. Although the test is dynamic, static backcalculation is commonly conducted to estimate pavement layer moduli using peak values of the impulsive force and surface deflections. However, falling weight defiectometers produced by the different manufacturers often differs in loading duration. The difference may affect backcalculation results, because the FWD test is dynamic in nature.

The key issue of this paper is to investigate the effect of the difference on backcalculated layer moduli. First, the difference is numerically studied by conducting static backcalculation on the peak deflection data generated from dynamic analysis with three different loading durations. Secondly, both static and dynamic backcalculations are carried out on the sets of deflections measured by three FWDs with different loading duration. Although the difference between static and dynamic backcalculation results are conspicuous in the case of numerical simulation, but the difference is not significant when actual data are used.