Unbound Aggregate Rutting Models for Stress Rotations and Effects of Moving Wheel Loads (05-1688)**
In Tai Kim, University of Illinois, Urbana-Champaign
Erol Tutumluer, University of Illinois, Urbana-Champaign

This paper presents the latest research findings on stress rotations due to moving wheel loads and their effects on permanent deformation or rut accumulation in pavement granular layers. Realistic pavement stresses induced by moving wheel loads were examined in the unbound aggregate base and subbase layers and the important effects of rotation of principal stress axes were indicated for a proper characterization of the permanent deformation behavior. To account for the rutting performances of especially thick granular layers, a comprehensive set of repeated load triaxial tests were conducted in the laboratory. Triaxial test data were obtained and analyzed from testing aggregates under various realistic in-situ stress paths due to moving wheel loading. Permanent deformation characterization models were then developed based on the experimental test data to include the static and dynamic stress states and the slope of stress path loading. The models that also considered the stress path slope variations predicted best the stress path dependency of permanent deformation accumulation. In addition, multiple stress path tests conducted to simulate the extension-compression-extension type rotating stress states under a wheel pass gave much higher permanent strains than those of the compression only single path tests. The findings indicated actual traffic loading simulated by the multiple path tests could cause greater permanent deformations or rutting damage especially in the loose base/subbase when compared to deformations measured from a dynamic plate loading or a constant confining pressure type laboratory test.