Friction versus texture at the approach of a granular avalanche.

We perform an analysis of the granular texture of a granular bed close to stability limit. Our analysis is based on a unique criterion of friction mobilization in a simulated two-dimensional packing. In this way, we recover the bimodal character of granular texture and the coexistence of weak and strong phases in the sense of distinct contacts populations. Moreover, we show the existence of a well-defined subset of contacts within the weak contact network. These contacts are characterized by their important friction and form a highly coherent population in terms of fabric. They play an antagonistic role with respect to force chains. Thus, we are able to discriminate between incoherent contacts and coherent contacts in the weak phase and to specify the role that the latter plays in the destabilization process.