The concept of a ‘Reynolds–Taylor state’ and the mechanics of sands

A novel conceptual model of the mechanics of sands is developed within a thermomechanical framework. Central to this model is the realisation that volume changes in granular materials are induced by two mechanisms. One is purely kinematic, and is a result of individual grains having to move over each other in a shear deformation: the ‘Reynolds effect’. This is the defining characteristic of the mechanics of granular materials. The second cause of volume changes is as a direct response to changes in stress, as in any standard continuum. These conceptual ideas are used to systematically develop a family of elastic/plastic models, involving non-associated flow rules, isotropic and kinematic hardening, and induced anisotropy. The recognition of the two distinct mechanisms of volume change shows that the classical concept of a critical state must be replaced with the more general concept of a ‘Reynolds–Taylor state’ to better explain the observed experimental behaviour in sands. In this state, which is attaine...