Basal Stresses and Seismic Signals Generated by Laboratory Granular Flows: The Role of Basal Particle Agitation in Flow Mobility

The basal stresses generated by rock avalanches, along with the resulting seismic signals, act as important indicators that provide insights into rock avalanche dynamics. Here, an experimental study on the propagation behavior and dynamics of granular flows moving on a 3D-printed bumpy substrate was conducted and the basal stress and seismic signature responses were analyzed. The results indicate that an agitating basal layer emerges in the nearly steady propagation state of the granular flows with increasing particle size, characterized by the base-normal velocity and internal shear behavior. Accompanying the strengthening of basal particle agitation, significant increases in basal stress fluctuations and seismic spikes are observed, and power law functions of the particle size are derived. Correspondingly, an increase in flow mobility is observed along with a transition of the flow regime toward the more collisional regime. Power laws linking the basal stress and seismic signatures with the frictional coefficients of the flows are derived to quantify the effect of basal particle agitation on flow mobility. Our results provide an experimental basis for the hypothesis that basal particle agitation could explain the long runout of rock avalanches.