Effect of the Variability of Seasonal Moduli Adjustment Factors on the Mechanistic-Empirical Overlay Design

Abstract

The Seasonal Adjustment Factor (SAF) is a key input in the mechanistic-empirical overlay design system for flexible pavements. The SAF accounts for the environmental changes on the pavement layer properties. It adjusts the elastic modulus of an unbound layer from one season (e.g. reference normal season) to another. A sensitivity analysis was conducted to study the effect of variation of the SAF values on the flexible overlay design thickness. The study was performed using the WINFLEX 2000 overlay design software. The analysis of the results indicates that the overlay thickness is more sensitive to changes in the moduli values during the spring thaw. The overlay thickness may increase by about 21% if 80% reduction in the moduli values were obtained in the subgrade and base layers, which could be the worst-case scenario during the spring thaw. Winter freeze was found to have little or no effect on the overlay thickness.