Experimental study of shear in granular media

The major factor that governs the behavior of granular materials is the dilatancy phenomenon. Like all media, granular media break. Breaking is generally defined from observations of load-deformation curves in tests where deformations are controlled. The shear consists of a recomposition of voids and consequently in a modification of local forces, which gives a new resistance to the media and causes a variation of the volume. An increase of volume is called ‘dilatancy’. It depends on the initial density. The random distribution of the grains and the difficulties in the determination of the boundary conditions entail a statistical study. Such a study shows that the fluctuations of the coefficient of volume variation are not very sensitive to the normal stress, which only has a delaying effect. Therefore, we show that the behavior of granular media depends on the local friction (grain-grain friction).