The extraction of engineering properties of pavement layers by dynamic analysis of falling weight deflectometer (fwd) data is demonstrated. Fwd data from two in-service highway sections were analyzed.The fwd data consist of time records of surface loading and surfacedeflections at a range of distances. A texas transportation institute pavement dynamics computer program, scalpot, was used to generatepredicted responses. Physical properties of the pavement were generated by a trial-and-error backcalculation and a systems identification computer program. The pavement surface vertical deflections were characterized by using frequency response functions in the form of magnitude and phase angle plots as a function of frequency. The magnitude plots represent vertical pavement surface deformations resulting from a steady-state sinusoidal surface loading. The phase angle data represent the lag angle between the loading and the surface deflections. The asphaltic concrete surface layer was represented as a three-parameter viscoelastic medium. The base course, subgrade layers, and bedrock layers, if any, were treated as damped elastic solids. These physical properties were backcalculated by matching approximately the frequency-analyzed field data with computed values by varying the scalpot input data set. Good agreement between experimental and computer-predicted responses was obtained using the backcalculatedpavement layer properties. One site with near-surface bedrock was analyzed and good agreement was obtained. This paper appears in transportation research record no. 1293, Backcalculation of pavement moduli 1991 .
Abstract