Comparison between the Simplified AUSTROADS Sublayering Approach and the Exact Nonlinear Solutions for the Unbound Flexible Pavements

In the mechanistic pavement design, it is common practice that the coarse and fine grained materials are modelled as linear elastic materials. The main reason for this is to use a simple set of parameters to represent each layer which in this case are the elastic modulus and Poisson ratio. However, it is well known that the unbound coarse granular materials and the fine grained subgrade materials behave nonlinearly under the traffic loading. The Australian mechanistic empirical design method (AUSTROADS) uses a simplified approach to account for the nonlinear behaviour of the unbound coarse and fine grained materials. In this paper the Austroads quasi-linear analysis is compared with the exact nonlinear analysis to examine the validity of this approach. The Austroads quasi-linear analysis provided better solutions than the linear elastic analysis without sublayering, however, it needs some adjustment to provide better match with the exact nonlinear analysis solution