Shear band development in modified DEM: importance of couple stress

Numerical simulation tests were carried out using the distinct element method (DEM) with great interest in how large couple stress is actually generated in a shear band. To do this, the conventional DEM was modified slightly, so that the effect of rolling resistance at contact points can be taken into account (called MDEM). It has been found that MDEM provides a powerful tool in 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 of natural granular soils; and that couple stress, although it is very small, is certainly developed in a consistent manner with the particle relation gradient developed in a shear band.