Incorporating elasto-plasticity in granular layer pavement design

Full-scale heavy vehicle simulator (HVS) testing of pavements incorporating granular layers indicated that granular materials behave elasto-plastically when subjected to repeated traffic loading. Elasto-plastic behaviour implies that permanent deformation takes place with every load repetition, although traffic loading normally induces stresses well below the failure stress of the material as defined bythe Mohr–Coulomb failure envelope. In the development of design a method for granular layers, cognizance should therefore be taken of the permanent deformation that occurs with each load repetition. In this Paper, the development ofa design method for limiting rutting granular layers developed from data obtained through full-scale HVS testing and using the principle of S–N curves, is described. HVS data indicated that the model generally used to describe the relation between permanent strain development and number of load repetitions does not give reliable estimates of the permanent deformation at large numbers of load repetitions. The design method described here recognizes the elasto-plastic behaviour of granular materials and uses an improved model to describe the relation between permanent deformation development and number of load repetitions. This design method was found to give reasonable predictions of the loading capacity of in-service low volume roads comprising mainly granular layers