Solid-like and liquid-like granular flows on inclined surfaces under vibration - Implications for earthquake-induced landslides

Earthquake-induced landslides can result in serious property damage and significant casualties. Although extensive research has been conducted to investigate their extraordinarily long runout, the underlying mechanism remains a very challenging open problem. In this paper, we explore the effect of vibration on landslide runout through simulations of simplified granular chute flows using the discrete element method with a focus on surface-normal vibration. We show that the mobility of the flows is enhanced by low-frequency vibration for inclination angles of both 19 degrees and 24 degrees. The flows are, however, strikingly different - solid-like for the former and liquid-like for the latter, as revealed by their microstructure and stress states. The vibration enhances the mobility through reduction in the normal load and in the solid volume fraction for the 19 degrees and the 24 degrees flows respectively. This work reveals complexities in the rheological states and the dynamic responses of inclined-surface granular flows under vibration, serving as an initial step to unravelling the full dynamic mechanisms of the long runout of earthquake-induced landslides.