Exploring the macro- and micro-scale response of an idealised granular material in the direct shear apparatus

The development of the distinct element method (DEM) has presented researchers with a tool to obtain detailed information about the particle-scale interactions during the standard element tests routinely used by both practising engineers and researchers. The current study considers the response of a granular material in the direct shear apparatus by coupling physical tests with equivalent DEM simulations. An idealised granular material, comprising uniform steel spheres, was considered in this study so that the specimen geometry and surface friction characteristics could be accurately replicated in the DEM simulations. The macro-scale response of the physical test specimens is compared with the macro-scale response observed in the DEM simulations for the purposes of validation of the numerical model. Using the DEM model the sensitivity of the macro-scale response to factors including the surface friction ( both interparticle friction and particle-boundary friction) and the specimen generation approach is explored. The study also considers the stress inhomogeneities that develop within the specimen during testing. Considering a representative numerical specimen, an in-depth analysis of the micro-scale responses of the specimen is presented, including the distribution of the contact forces, the particle displacements and the particle rotations. The variation in volumetric and shear strains within the specimen is also considered. The response of this ideal granular material is shown to be sensitive to small variations in fabric.