Comminution-Induced Transient Frictional Behavior in Sheared Granular Halite

Abstract

Grain comminution is commonly observed in numerous geological settings. To elucidate the role of grain comminution in dry granular friction, we sheared breakable halite (NaCl) grains using a ring-shear configuration at a constant slip rate under various normal stresses. We observed transient frictional behaviors: a constant regime exhibiting a high friction coefficient at small slip displacements, and a weakening regime showing a substantial decay in friction at large slip displacements. The characteristic slip lengths for both regimes decreased with normal stress and were characterized by similar exponents. Micro-X-ray tomography revealed the evolution of microstructure from distributed grain comminution to progressive shear localization for these two regimes. We propose that the filling processes of comminuted fine particles, during which fine particles saturate and then overflow the shear zone, define transient frictional behaviors. This study may hold significant implications for natural shear systems, given the ubiquity of comminution and localization phenomena.