Weakening, compaction and creep from vibration in sheared granular materials

The strength and stability of granular materials like sands and powders corresponds to the strength and stability of soils, asphalt, building and industrial materials, gouge filled earthquake faults, hillslopes, and more. Passing vibrations and transient perturbations have been thought to play a role in determining dynamic friction during sliding in such systems as well as trigger failure in static grain packs. With laboratory experiments and discrete element method simulations, we show that low amplitude high frequency vibrations are capable of significantly reducing frictional resistance over a range of velocities in actively shearing systems. Near yield, coefficient of friction decreases with increasing acoustic energy raised to a power of -0.2. Susceptibility to creep, compaction and weakening depends on grain shape, vibration amplitude, frequency, system resonances and system pressure. Exposure to (and generation of) vibration during shear of granular materials is common in many industrial and transport processes, and granular materials’ susceptibility to vibrational weakening may play a pivotal role in these processes.