Dynamic Time Domain Backcalculation of Layer Moduli, Damping, and Thicknesses in Flexible Pavements

Abstract

A dynamic time domain method was developed to backcalculate the layer moduli, damping ratios, and thicknesses of asphalt pavements from dynamic falling weight deflectometer test data. The method uses the SAPSI program as a forward routine and a Newton-Raphson method for the backcalculation. The advantage of the time domain approach is that SAPSI can match selected features of the measured time histories directly, and inaccurate measurements at the ends of histories can be ignored. The peak deflections and the time lag between the peak of the load and the peak of the deflections at different sensors are matched. The Newton algorithm in MICHBACK is adopted to perform the backcalculation. The new algorithm is capable of backcalculating the moduli, damping ratios, and thicknesses of three-layer flexible pavements reasonably well. Backcalculations based on synthetic time histories generated using SAPSI show excellent stability and accuracy. Backcalculation using measured time histories yields less accurate results. Possible sources for the discrepancies when using field data are addressed.