Deflection data collected from the falling weight deflectometer (fwd) have mostly been analyzed by using the static layered elastic analysis method. Analysis might be improved by including dynamic effects, such as inertia, damping, and resonance. Results from a finiteelement backcalculation program developed to account for these factors are discussed. The program can perform both static and dynamic backcalculation analyses. Dashpots or dampers are installed at the boundary nodes (bottom and lateral) to simulate half-space conditions, thus avoiding the need to specify a rigid base (say at 20 ft) at the bottom of the subgrade. Such dashpots absorb propagating waves in the dynamic analysis, thus preventing wave reflection off the rigid boundary. Backcalculation results computed from two existing methodsand the proposed method using fwd data obtained at four sites in nevada are compared. The results indicate that the moduli of the asphalt layers are not affected by the type of analysis (static or dynamic) for any of the sites. Lower base and higher subgrade moduli were consistently computed in the dynamic analysis compared with the static analysis. This paper appears in transportation research record no. 1293, Backcalculation of pavement moduli 1991 .
Abstract