Effects of Heavier Truck Loadings amd Super-Single Tires on Subgrades

Abstract

Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractDue to their efficiency and economy, super-single tires have gradually been replacing conventional dual tires in the trucking industry. According to recent studies, super-single tires generate much higher vertical contact stresses than do conventional dual tires, resulting in larger deformations and more severe damage to the subgrade. In order to better assess the higher stresses generated by super-single tires and their effect on the subgrade, analyses are done taking into account soil plasticity rather than simple elastic analysis. In this study, the effects of super-single tires on subgrades for typical road cross-sections are investigated using plane-strain (2D) and 3D static and dynamic finite element analyses. The analyses focus on the sand and clay subgrades rather than on asphalt and base layers. The subgrades are modeled as saturated in order to investigate the effects of porewater pressures under the most severe conditions. The analyses suggest that current flexible pavement design methods are unconservative for the increased loads imposed by super-single tires on the pavement system. Load Equivalent Factors (LEF) and damage factors for super-single tires are suggested for use of those values in design practice. The effects of overlay and subgrade improvement are investigated in order to mitigate the higher strains generated by super-single tire loadings in the subgrade. Subgrade improvement allows decreasing the adverse effects of super-single tires on the subgrades. FE analyses are also done in order to assess the performance of the Indiana typical pavements for the super-heavy loads (occurred in Texas during 1990s). This investigation is to evaluate how much plastic strain by super-heavy loads occurs in the subgrade and asphalt layers as compared with the super-single tire loadings. Key Wordssuper-single tires, subgrades, flexible pavement, finite element analysis, soil plasticity, porewater pressure, contact stress, overlay, subgrade improvement TECHNICAL SummaryTechnology Transfer and Project Implementation Information TRB Subject Code:62-7 Soil Foundation Subgrades November 2002 Publication No.: FHWA/IN/JTRP-2002/20, SPR-2402 Final Report Effects of Heavier Truck Loadings and Super-Single Tires on Subgrades IntroductionIn the last two decades, use of supersingle tires has slightly increased, with the aim of improving efficiency and economy. Since the contact stresses generated by super-single tires are higher than those of conventional dual tires, this change has caused concern about possible damage to pavements designed based on the current design methods. The higher the contact stresses on the pavement surface, the larger the subgrade deformation, and the more severe the damage to the subgrade.In order to investigate the effects of super-single tire loadings on subgrades for typical Indiana road cross-sections, static and dynamic finite element analyses were performed taking into...