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Numerical simulation tests were carried out using the distinct element method (DEM) with paying much attention to the micro-deformation mechanism leading to the development of shear bands. To do this, the conventional DEM was modified slightly such that the effect of rolling resistance at contact points could be taken into account (called MDEM). It is found that MDEM can be a powerful tool for simulating not only the generation of large voids inside a shear band but also the high gradient of particle rotation along the shear band boundaries, in a quite similar manner to those observed in natural granular soils. It is concluded, based on the numerical simulation tests, thatthe basic micro-deformation mechanism ending up with the formation of shear bands is in the generation of column-like structure during the hardening process and its collapse in the softening process.

SUMMARYWe study the influence of inherent anisotropy, i.e. bedding angle on stress-strain behavior and shear band formation in quasi-static granular media. Plane strain biaxial tests are carried out using two-dimensional distinct element method (DEM). Oval/elliptical-shaped particles are generated by overlapping the discrete circular elements. Particle assemblies with four different bedding angles are tested. Evolution of the microstructure inside and outside the shear band and effect of bedding angle on the microstructure are investigated. Influence of bedding angle on fabric and force anisotropy is studied. It is found that by using non-circular particles, generation of large voids and excess particle rotations inside the shear band are reproduced in a quite similar manner to those of the natural granular soils, which are difficult to produce with standard DEM simulations using circular particles.