Evaluation of unbound/subgrade material rutting and resilient behaviour based on initial density and saturation degree

Unbound pavements with thin surface seals constitute the majority of the lightly and moderately trafficked road networks in Australia. In such pavements, it is considered that seals do not offer much structural support, whereas most of the load coming from the traffic is supported by unbound granular materials and subgrade soil. Hence, accurate estimation of the mechanical properties of such materials is crucial for the satisfactory performance of pavements. In the present study, a constant radial stiffness triaxial (CRST) test was performed on a silty sand, which is typical of the material used in subbase and subgrade layers. The major advantage of the CRST test over the conventional repeated load triaxial test is that the confining pressure is dynamically applied due to a constant radial stiffness boundary condition. It is argued that the CRST test better replicates the stress path typically encountered by geo-materials under the action of traffic loading on pavements. A laboratory investigation was undertaken with different initial dry densities and degree of saturations to develop empirical models of plastic strain (rutting), resilient modulus and Rvalue. Based on the models developed, isograms of these aforesaid parameters are drawn on the compaction plane for the first time and a method is conceptualized for compaction control during field construction providing pathways to performance-based compaction specification.