The Effect of Asphalt Layer Thickness Variations on Pavement Evaluation Using the Falling Weight Deflectometer

This paper presents a model for statistically correcting asphalt layer stiffness moduli determined from the Falling Weight Deflectometer (FWD) test to account for asphalt layer thickness variations. Both random variations in asphalt layer thickness and a difference between the mean asphalt layer thickness and the constant value of asphalt layer thickness used in the back-analysis procedure (ie mean thickness error) are included and the model has been validated using published data. The model shows that the mean value of back-calculated asphaltic material stiffness modulus is primarily influenced by incorrect assumptions regarding the mean asphalt layer thickness, whereas the standard deviation of the back-calculated asphaltic material stiffness modulus is also sensitive to variations in the thickness of the asphalt layer around the mean level.