Stress-strain behaviour at small strains of unbound granular materials and its laboratory tests

Some new aspects of pre-failure deformation and strength characteristics of Unbound granular materials, particularly stress-strain properties at small strains, are described, focusing on recently obtained laboratory stress-strain test data. Recent developments in the static and dynamic testing methods, particularly details of the former, are reviewed. It is shown that strain rate effects are not an important factor for the stiffness at small strains of unbound granular materials. Effects of inherent and stress-induced anisotropy in the deformation and strength characteristics are illustrated, focusing on those with the small strain stiffness. The importance of proper considerations on the stress state-dependency of quasi-elastic deformation properties in modelling the non-linear pre-failure stress-strain relations is emphasized. The effects of stress history and strain acceleration (rate of strain rate) on irreversible strains are demonstrated.