ABSTRACT
Backcalculation of in-situ moduli is essential for pavement analysis and design. However, unconventional pavements (subgrade stiffer than granular base) present a challenge to backcalculation due to reasons such as compensating layer effects. This study describes a methodology to determine an optimum backcalculation cross-section for nine unconventional pavement test sections constructed at the National Center for Asphalt Technology Test Track in Alabama, USA. The unbound materials also exhibited different stress-sensitivity behaviour. Historically, the effect of the unconventional stiffness profile and the different stress-sensitivity is that as-built cross-sections have yielded unacceptably low backcalculated aggregate base moduli. Falling weight deflectometer testing provided 2916 deflection basins for this study, which were backcalculated using EVERCALC 5.0. Nine cross-sections were evaluated based on deflection basin fit and reasonableness of the backcalculation results. The study converged on pavement structure consisting of the as-built asphalt layer thickness over a pseudo-base (as-built aggregate base thickness plus 400 mm of subgrade soil) over the subgrade as the optimum backcalculation cross-section that minimized the effects of the unconventional stiffness profile and the different stress-dependency characteristics.
