Sensitivity of the Pavement ME Design Software Predicted Distresses in Flexible Pavements to Subgrade Soils and Granular Subbase Materials

Subgrade is the foundation of a pavement structure and ultimately bears the stress from the applied traffic load. Based on the historical design methods and agency experiences, subgrade soils including granular fills and their stiffness have significant impact on the design and construction of pavements. Alternatively, granular subbase and base material constitute significant portions of flexible pavement structures. In empirical design methods, 1 mm of asphalt concrete (AC) equates to 3-5 mm of granular subbase thickness. By substituting a part of AC layer with additional granular subbase, agencies could design and construct economic pavement structures that provide adequate structural capacity with improved drainage and frost protection. There are concerns that the newest pavement design and analysis tool, named the AASHTOWare Pavement ME Design (PMED) software, is not yet able to consider the effect of unbound base, subbase and subgrade materials properly.

Between November 2021 and January 2022, Transportation Association of Canada (TAC) ME Pavement Design Subcommittee completed two sets of design trials to assess the sensitivity of PMED software predicted distresses to the physical and mechanical properties of different subgrade and subbase materials. The design trials included: i) four different untreated native subgrade soils and a select granular fill with varying physical and mechanical properties, and ii) three different subbase material types with varying stiffness, thickness and gradation. The results have shown negligible to high sensitivity of the predicted distresses to the variation of subgrade types and their stiffness as well as the subbase material stiffness, thickness and gradation with some inconsistencies.


Ahammed, M. Alauddin
Podborochynski, Diana
Chan, Susanne
Dhaliwal, Arma

Session title

Innovations in Pavement Management, Engineering and Technologies









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