Micro-mechanical investigation of non-coaxial plastic flow of granular materials

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Whilst experimental data has clearly demonstrated that soil behaviour is generally non-coaxial (i.e. non-coincidence of stress tensor and plastic rate of deformation tensor), most soil models currently in use in geotechnical practice are still based on the plastic potential theory which often predicts coaxiality. Recent work suggests that ignoring non-coaxial soil behaviour would lead to unsafe design in practice and is therefore dangerous. In order to develop accurate micromechanical-based, non-coaxial plasticity models, we need to further our understanding of the micromechanics of non-coaxial flow of granular materials. Current research suggests that soil fabric and its evolution are the main reason for its non-coaxial behaviour. Soil intrinsic properties, such as particle geometries and interactions, are also important factors to the observed degree of non-coaxiality. At present, however, we have no detailed knowledge about their relationships and mechanisms. The purpose of this present project is therefore two-fold: (a) to seek fundamental understanding of the physics of non-coaxial soil behaviour; and (b) to facilitate the development of micromechanical plasticity models. We plan to achieve this purpose by using discrete element modelling (DEM) of granular materials under various stress conditions involving principal stress rotation. Experimental data on stress rotation tests of granular materials will be used to check the validity of the numerical DEM simulations.