Evaluation of HWD Backcalculation Tools and Methodologies Using FAA National Airport Pavement Test Facility's Data

Accurate estimation of the elastic modulus of pavement layers is essential when examining the condition and load bearing capacity of an airfield pavement. Pavement surface deflections obtained from heavy weight deflectometer (HWD) has been widely used as a non-destructive testing method to obtain the elastic modulus of the pavement layers. The method involves a backcalculation procedure. The accuracy of the backcalculated modulus depends upon the accuracy of the forward calculation method as well as the iteration technique. This paper presents findings from implementing a number of tools and methodologies developed for HWD test analysis using data from the National Airport Pavement Test Facility's HWD Round-up study. Selected tools for backcalculation of the test data represent a variety of methodologies from the typical multilayer elastic theory to the method of equivalent thickness and the artificial neural network. The findings presented in this study formed the basis of the recommendation for improving and upgrading BAKFAA to be used more effectively as a comprehensive and state-of-the-practice airfield pavement backcalculation.