Base Course Resilient Modulus for the Mechanistic-Empirical Pavement Design Guide

The mechanistic-empirical pavement design guidelines (MEPDG) recommend use of material modulus in lieu of structural number for pavement base layer thickness design. In this study a methodology was developed to determine a single effective modulus for a base layer using laboratory nonlinear modulus characterization data and a nonlinear finite element response model. With this model, a single representative modulus can be determined by a back calculation procedure in which pavement surface deflections from a nonlinear analysis are matched via an equivalent linear analysis. An equivalent linear analysis using effective moduli for both an unbound base and the subgrade can predict the structural response of an asphalt surface layer in a flexible pavement. It should be possible to utilize these structural response predictions in the assessment of cracking performance of the surface layer. However, caution is warranted in predicting the structural response of the unbound base and subgrade layers using an equivalent linear analysis. Use of an effective modulus for a nonlinear base layer appears reasonable for very thick pavement structures, but appears to under predict vertical strain at the top of subgrade.