A new approach for investigating the permanent deformation behaviour of unbound granular material using the repeated loading triaxial apparatus

Abstract

Rutting caused by the permanent deformation of unbound materials (unbound granular material ( UGM ) and pavement subgrade), is one of the principal damage modes for low traffic flexible pavements. In spite of this, the French pavement design method does not permit accurate predictions of this rutting [1]: the design is based on linear elastic calculations, and the elastic modulus values of the unbound granular materials are based on an empirical classification; the design criterion with regard to rutting consists solely of limiting vertical elastic strain e z at the top of the unbound layers, and furthermore depends only on traffic conditions. This paper will propose a new approach for studying permanent deformation in unbound granular materials under cyclic loading, and developing permanent deformation models that can be used to predict pavement rutting. Our approach is based on results of laboratory tests performed with the repeated load triaxial apparatus.