Evaluation of Laboratory and Backcalculated Resilient Moduli from the Wes Track Experiment

Abstract

Resilient modulus is a critical material property required for the characterization of pavement layers used in modern mechanistic-based pavement design. Because of its fundamental nature, resilient modulus provides a meaningful basis for simulating the effect that an individual layer has on pavement response and performance. Resilient modulus can be determined by laboratory testing or by an analytical procedure known as backcalculation involving the interpretation of nondestructive testing. Unfortunately, resilient modulus results determined from laboratory testing and those determined from backcalculation generally do not agree. The issue of characterizing in situ moduli is addressed by presenting the results of an analysis and comparison of resilient modulus values determined from laboratory testing and those established through backcalculation of falling weight deflectometer (FWD) data from the WesTrack experiment in northern Nevada. These two basic methodologies for resilient modulus determination are reviewed, and many of their known weaknesses and limitations are identified. The backcalculated modulus values were determined using Washington State Department of Transportation’s EVERCALC computer program and FWD data obtained from WesTrack pavement sections at the onset of truck loading. The laboratory-based resilient modulus values were determined using a combination of test results on remolded and recompacted WesTrack materials and the KENLAYER computer program to estimate the modulus under the state of stress created by the FWD during testing. The results of this investigation continue to support the suspicion that significant differences do exist between resilient moduli determined from backcalculation and those determined through laboratory testing. Accordingly, some general observations are made concerning possible improvements in each methodology and concerning which of the two methodologies is better suited for a thorough pavement evaluation and design process. Overall, a better understanding of the problems associated with accurately characterizing pavement support under in-situ conditions is presented.