Emergence of Shear Bands in Confined Granular Systems: Singularity of the -Statistics.

The statistics of grain displacements probability distribution function () during the shear of a granular medium displays an unusual dependence with the shear increment upscaling as recently evinced (see "experimental validation of a nonextensive scaling law in confined granular media"). Basically, the of grain displacements has clear nonextensive (-Gaussian) features at small scales, but approaches to Gaussian characteristics at large shear window scales-the ranulence effect. Here, we extend this analysis studying a larger system (more grains considered in the experimental setup), which exhibits a severe shear band fault during the macroscopic straining. We calculate the of grain displacements and the dependency of the -statistics with the shear increment. This analysis has shown a singular behavior of at large scales, displaying a non-monotonic dependence with the shear increment. By means of an independent image analysis, we demonstrate that this singular non-monotonicity could be associated with the emergence of a shear band within the confined system. We show that the exact point where the -value inverts its tendency coincides with the emergence of a giant percolation cluster along the system, caused by the shear band. We believe that this original approach using Statistical Mechanics tools to identify shear bands can be a very useful piece to solve the complex puzzle of the rheology of dense granular systems.