Sensitivity Analysis of Field-to-Laboratory Subgrade Conversion Factors with AASHTOWare Pavement ME Design

The new AASHTOWare Pavement ME design software incorporates conversion factors into its procedure to correlate the field subgrade soil resilient modulus, measured with the falling-weight deflectometer, with the laboratory equivalent modulus for use in performance prediction. The national conversion factors recommended for use with Pavement ME were determined on the basis of data obtained from the Long-Term Pavement Performance database and were not necessarily accurate for all regions and soil types. Sensitivity analysis results are presented for the effect of field-to-laboratory subgrade modulus conversion factors on the performance of three types of pavement structures in Ontario, Canada: conventional flexible, deep-strength flexible, and composite. This work included simulation of real-world case studies extracted from the Ontario provincial pavement management system (Ontario PMS2) database. Three projects were selected for this study–-Highway 6, Highway 401, and Queen Elizabeth Way–-all located in southwestern Ontario. Required inputs including traffic, material characteristics, and layer thickness information were extracted from PMS2 and used to set up the projects in AASHTOWare Pavement ME. The AASHTOWare Pavement ME was executed with ranges of field-to-laboratory conversion factors for different pavement types. Statistical analyses were carried out to evaluate the effect of changing conversion factors on predicted performance. Study results suggest that the predicted performance of conventional flexible pavement is significantly affected by the subgrade modulus conversion factor. However, the impact of subgrade modulus conversion factors on predicted performance is insignificant for composite and deep-strength flexible pavement sections.