Abstract Manager

The TAC ME Design Subcommittee has been evaluating the AASHTOWare Pavement ME Design (PMED) software since 2007-2008. Between May 2022 and August 2022, two sets of design trials were completed by the Subcommittee with different climatic inputs from nine weather stations across Canada to assess the effect on the PMED software predicted distresses due to changes in physical and mechanical properties of different subgrade soil/fill and subbase and base materials. These design trials included: i) five different untreated native subgrade soils/fill (resilient moduli varied from 25-90 MPa), ii) a 300 mm thick soil cement layer with stabilization of these five different subgrade types, iii) a 300 mm thick layer of crushed rock subgrade combined with these five different type of subgrade soils/fill, iv) six different base (cement treated and granular) materials with varying thickness, and v) two different granular subbase materials.

The results have shown that climate has a significant effect on the predicted IRI and faulting. No design meets the IRI criteria for clay and silt subgrade soils in cold climates. When a crushed rock layer is used as a subgrade, all designs meet the IRI criteria and the effect of underlying native subgrade soils becomes minimal. With native subgrade/fill alone, the predicted IRI decreases as the material stiffness increases, which is a logical trend. Inconsistent and unexplainable trends of the predicted faulting at concrete joints were observed for changes in subgrade type. There was no or negligible effect on the predicted transverse cracking due to changes in subgrade material type and variation in climate. The PMED software is unable to properly model the stabilized soils as subgrade (placed below the granular subbase or base layer). 

In general, stronger and thicker base layers provide lower IRI and faulting with some inconsistencies. As in the case of subgrade materials, the variations of the predicted transverse cracking for changes in base material type and thickness were inconsistent. Weaker subbase materials cause a small increase while thicker subbase layers cause an inconsistent variation of the predicted distresses. Significant differences in predicted distresses, with many inconsistencies in the trends, noted between software v2.6 and 3.0.

The objective of this paper is to present the above stated trial results, analysis and findings. The presented information may help different agencies and other interested individuals in assessing the suitability of the current version of the PMED software when designing concrete pavement structures and varying subgrade, base and subbase materials characteristics.