3D finite elements modelling of rut depth evolution of flexible pavements with the shakedown theory

Rutting, due to permanent deformations of unbound materials, is one of the principal damage modes of low traffic pavements. Flexible pavement design methods remain empirical. These mechanistic methods do not take into account the inelastic behaviour of these materials (only linear elasticity is used as mechanical model) and do not predict the rutting under cyclic loading. The objective of this paper is to use a simplified method, based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings, to estimate the permanent deformations of unbound granular materials (UGM) subjected to traffic loading. Based on repeated load triaxial tests, a general procedure has been developed for the determination of the material parameters of the constitutive model. Finally, the results of a finite elements modelling of the long-term behaviour of a flexible pavement with the simplified method are presented and compared to the results of a full scale pavement experiment performed at LCPC. The initial stress state, water content and anisotropy of the granular layers are taken into account in this framework. Finally the calculation of the rut depth evolution with time is carried out.