The modulus backcalculation from Falling Weight Deflectometers is one of the primary means for evaluating in-situ resilient properties of pavement materials. When evaluating material moduli from the same location by usingdeflection data from different sources, it is highly probable that different methodologies will lead to differing results. This study presents a comparative analysis of backcalculated moduli results performed to quantify the differences between the historic Arizona Department of Transportation - Pavement Management System (ADOT-PMS) and the Strategic Highway ResearchProgram Long Term Pavement Performance (SHRP-LTPP) databases. Pavement sections were selected from numerous SHRP sites in Arizona, having both forms of deflection data available at the same location and in the same general time frame. The results of this study indicated that there was a poor correspondence between backcalculated layer moduli from both databases. As a general rule, the degree of layer correspondence improved as layer depths gradually increased (subgrade was the most accurate comparison). On the other hand, fairly good correspondence was obtained for all moduli between two differing backcalculation schemes (MODCOMP v4.2 and MODULUS v6.0). Finally, it was found that the use of the simple, closed form solution to estimate subgrade moduli from the outer geophones, gave comparable answersto the more complex backcalculated solutions based upon total deflection basin results. This gives rise to the possibility that significant reductions in cost and labor can be achieved in maintaining PMS systems and by utilizing the outer geophone equation as an implementation approach for the Mechanistic-Empirical Pavement Design Guide (ME-PDG).
Abstract