Mechanistic-empirical evaluation of the Mn/ROAD low-volume road test sections.

摘要

The objective of this study was to utilize Illinois Department of Transportation (IDOT) mechanistic-empirical procedures and Mn/ROAD low-volume road (LVR) data and information to verify/refine/modify analysis and design concepts and procedures for LVR flexible pavements. Laboratory test results, field distress measurements, and FWD test data were used to study the effect of granular material quality on pavement performance and deflection response. The results from the rapid shear tests and permanent deformation tests show that the rutting potential of a granular material can be characterized from rapid shear test at 15-psi confining pressure. The rapid shear test results at 15-psi confining pressure reflect the rutting trends observed in the field. There is no significant effect of granular material quality on the conventional flexible pavement deflection response. The field measured pavement responses were compared to the ILLI-PAVE (finite element program) predicted pavement responses. Estimate of pavement responses is fairly accurate in the case of test sections with thick (higher than 5-inch) asphalt concrete (AC) surface. The analyses of field FWD data showed that Area Under Pavement Profile (geometric shape factor of deflection basin) can be used to predict the strains at the bottom of AC layer. The 'Design Time' concept was utilized to consider temperature effects on AC fatigue computations. The analyses showed that the 'Design Time' is primarily effected by AC thickness. The granular layer thickness and subgrade type (sand or cohesive) do not have any effect on 'Design Time'. Effect of subgrade type on pavement response and performance was studied. In the IDOT mechanistic-empirical design procedure, the design criteria for conventional flexible pavements are AC fatigue and subgrade stress ratio (deviator stress/unconfined compressive strength). In the Mn/ROAD LVR test sections, no AC fatigue was observed, and the subgrade stress ratios (0.2-0.4) were in the acceptable range (0.5-0.7). However, some of the conventional flexible test sections experienced severe rutting which was attributed to the granular layer. The pavement granular base layer must possess sufficient shear strength/rutting resistance (for a given asphalt concrete thickness) to minimize rutting within the granular layer.