(199a) Scaling Effect in Dem Simulations of Direct Shear Test

For quasi-static applications such as land subsidence or the initial stage of embankment failure, the rate effect is small. In these cases the bulk friction of the granular material is most conveniently obtained by a direct shear test. However, commercially available direct shear apparatus are small in relation to particle size for a wide range of applications. In parallel with this situation, granular materials handling systems face more troubles than their fluid counterparts. Numerical simulations of granular systems offer a way to make improvements. Constrained by the simulation time requirement, much smaller number of particles than reality can be incorporated in these simulations. As a result, either the size of the equipment has to be reduced, or the size of the particles has to be enlarged in these simulations. To investigate the possibility of using direct shear apparatus for a wider range of particles, and to shed some light on scaling laws for such an apparatus, a direct shear test is performed in this study using Discrete Element Models to study the scaling effect. It is found that by scaling properly, it is possible to use direct shear box for bulk friction measurement when the size of the box is roughly 10 times the particles size. It is also shown that overburden plays an important role in the bulk friction. Lastly, it is surprising to observe that contact friction affects the scaling law in such a way that the lower the contact friction, the more dependent the bulk friction is to the shear box size.

KEYWORDS: Granular Materials, Scaling, DEM Simulation, Shear Box.