Effect of Subgrade, Subbase and Base Materials on the PMED Software Predicted Distresses in Jointed Plain Concrete Pavement

Abstract
Between  May  2022  and  August  2022,  the  Transportation  Association  of  Canada  (TAC)  Mechanistic  Empirical (ME) Pavement Design Subcommittee has completed a number of design trials to assess the effect on the AASHTOWare Pavement ME Design (PMED) software predicted distresses in jointed plain concrete pavement (JPCP) due to varying subgrade and subbase and base materials. These trials were run with climatic inputs from nine different climate stations across Canada, five different untreated native subgrade soils/fill, five different soil cement layers, a crushed rock subgrade, six different base (cement treated and granular) materials with varying thickness and 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 physical properties improves. The physical properties of subgrade soils have more influence on the predicted IRI than their stiffness. 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  climatic  exposure.  Currently,  PMED  software  is  unable to model the stabilized soils as subgrade.

In general, good quality and thicker base layers provide lower IRI and faulting with some inconsistencies. The variations of the predicted transverse cracking for changes in base material type and thickness were inconsistent. Poor quality 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, were noted between the PMED software v2.6 and v3.0.