The falling weight deflectometer (FWD) has been used in the evaluation of material properties of pavement systems for many years. The load amplitude and frequency content are intended to provide deformation levels similar to those induced by truck wheel loads. Interpretation of the in situ measured data is normally based on an elastic solution and therefore does not take into account the possible existence of localised nonlinearities. The objective of this work was to develop some understanding of the potential for nonlinear behaviour in the FWD test. Analytical studies were conducted using both a linear iterative solution and a nonlinear solution with the generalised cap model to reproduce the nonlinear soil behaviour. Three pavement sections in Texas were considered using the finite discrete model. By varying the level of loads FWD deflection basins, induced strains, and inelastic material properties were obtained. The results of this study indicate that material nonlinearities are localised and are important for FWD tests on flexible pavements where the subgrade is relatively soft or the pavement is thin. In these cases, nonlinear effects increase peak displacements by at least 50 percent under a 20,000-lb load but are negligible for receivers at 3 ft or more from the source. In general, a FWD test with a load of 2,000 lb or less would not result in any apparent nonlinear effects at any pavement site. For FWD tests on rigid pavements or flexible pavements with a relatively stiff subgrade, nonlinearities are also less pronounced. (Author/publisher)
Samenvatting