Pavement-falling weight deflectometer interaction using dynamic finite-element analysis

In almost all linear elastostatic programs used in backcalculation procedures, a uniform pressure distribution is assumed for the applied load. As such, the loading system of any falling weight deflectometer (FWD) should be designed so that the load transferred to the pavement is uniform. This is difficult because the pressure distribution under the FWD is also affected by the pavement profile being tested. The other aspect of the FWD testing that is typically ignored is the dynamic nature of the load. The dynamic effects are related to the pulse width as well as the variation in the stiffness of the subgrade. A finite-element study has been carried out to investigate the significance of these parameters on the determination of the remaining lives of pavements. Cases where the imparted load would or would not yield a uniform pressure distribution under the FWD plate are identified. An investigation of the effects of the plate-pavement interaction on the static interpretation of the dynamic deflections is presented. The results indicate that the dynamic nature of the load may more significantly affect the deflections measured away from the load, whereas the plate-pavement interaction may affect the deflection of the first sensor. The errors in the estimation of the layer moduli that would be obtained from the standard backcalculation procedures are also determined. The results of this study confirm that the plate-pavement interaction and the dynamic effects are important for the FWD test on flexible pavements.