A numerical examination of the hollow cylindrical torsional shear test using DEM

This paper presents results of three-dimensional simulations of the hollow cylindrical torsional shear test using the discrete element method. Three typical stress states that can be applied in the hollow cylindrical apparatus (HCA), i.e. triaxial, torsional compression and pure torsional, are examined in terms of the distributions of stresses and strains in the HCA sample. The initiation and propagation of the shear bands in the sample were characterized by porosity and shear strain rate distributions in the sample. The results show that the shear strain rate contour is a better indicator for shear band development than the porosity contours. It is demonstrated that the stresses and strains measured in the shear zone are significantly different from the boundary measurements and the average values used in HCA testing. Initially, the peak strength measured from the boundary forces was found to be slightly lower than that measured in the shear band. Subsequently, due to the formation of shear band, the stress ratio from boundary forces decreased significantly especially when the major principal stress is oriented 30° and 45° from the vertical. The evolutions of porosity, coordination number and particle rotation at different locations in the sample were also monitored. Finally, the appropriateness of the HCA is evaluated in comparison with previously published data.