Universal avalanches and pressure-dependent scaling law in granular shearing

A comprehensive understanding of granular shearing behaviour is important to investigate the mechanism of geological disasters. We show the avalanche characteristics of the granular shear process and the effects of upper load and shearing velocity on the shearing system by acoustic emission (AE) spectroscopy. The AE absolute energies follow damped power-law distributions with critical exponents ε ranging from 1.25 to 1.45. The exponent ε tends to decrease with the increased upper loads. And the influence of shearing velocity on the energy exponent is negligible. The waiting time distribution shows a mixing form with a power-law distribution and a gamma distribution at small and large time intervals, respectively, which is similar to the unified scaling law of the interoccurrence time in seismology. The aftershock distributions follow the Omori law and the foreshock distributions follow the inverse Omori law with the exponent p/p′ ≈1. The relative magnitudes of main shock energy and the corresponding largest aftershock energy agree well with the Båth’s law in a restricted time interval. Moreover, our results of amplitude and duration distributions, as well as energy-amplitude and amplitude-duration relations, show mean field behaviour. The exponents show approximate consistency with the force integrated mean field model.