Stability Control of the Unbound Aggregate Base in Multi-Layer Pavement Structures

Traditionally in the pavement design guides, the cumulative permanent deformation of multi-layered aggregate structures, such as highway pavements and airfield runways, is computed as a function of the number of load repetitions. This implies that the structural integrity of pavement foundations when subjected to one passage of extreme traffic loadings is overlooked. The passage of slow moving heavy traffic loads can potentially constitute a taxing scenario where the structural layers of the pavement undergo high levels of stress close to their failure limit. On the other hand, the anisotropic nature of granular materials imposes more complexity on this issue as the mechanism and probability of failure of such material can be substantially different from that of isotropic material. This paper addresses this problem by providing a mechanistic framework for the stability analysis of anisotropic unbound granular layers subjected to critical loading conditions. Based on the results of elastic analysis, the granular base will most probably remain stable if the material is assumed to be isotropic. However, the analysis of highly anisotropic systems with similar loading conditions resulted in unstable systems. This underscores the significance of departure from isotropic to anisotropic analysis for realistic simulation of the complex nature of the stress paths induced by traffic loadings.