Experiments and simulations of direct shear tests:: porosity, contact friction and bulk friction

The direct shear testers, in particular the Jenike cell, are widely used to measure the bulk material properties for the design of bulk handling equipment. This paper describes a study of the Jenike shear tester using both experiments and discrete element simulations. A total of 90 tests on spherical glass beads and paired glass beads were performed to study the influence of the particle shape, stress level and packing density on the bulk friction at limiting shear. The data are thus useful for validating particle scale simulations of densely packed granular systems. In an attempt to verify the predictive capability of discrete element method, closely matching 3-dimensional discrete element simulations of the shear tests were performed and compared with the experimental observations. The comparison for single spheres shows good quantitative agreement for the limiting bulk friction when there is a good match in the sample porosity. Further research is needed to produce a comprehensive validation of the discrete element method. Several salient observations from this study provide further insight into the roles of particle shape and contact friction on the resulting packing porosity and bulk friction.