Self-channelisation in Dry Granular Flows
IPGP - Îlot Cuvier
Séminaires Dynamique des fluides géologiques
Dense granular flows can spontaneously self-channelise by forming a pair of parallel-sided static levees on both sides of a central flowing channel. This process prevents lateral spreading and maintains the flow height, and hence mobility, for longer, enabling the grains to run out considerably further than spreading flows. Since levees commonly form in hazardous geophysical mass flows, such as snow avalanches, debris flows, and pyroclastic flows, this has important implications for risk management in mountainous and volcanic regions. In this talk, we will discuss the process of self-channelisation and levee formation in three different scenarios, starting with the fundamental ingredients responsible for self-channelisation in monodisperse avalanches down an inclined plane. Using a depth-averaged model we show that not only a non-monotonic friction law is required to incorporate frictional hysteresis, but higher-order viscous-like terms are crucial in selecting the fully-developed self-channelised state observed in small-scale lab experiments. This fully-developed state is then used to shed light on the three-dimensional particle segregation, which occurs within bidisperse self-channelised flows. We conclude by discussing a monodisperse avalanche down a cone. In striking contrast to the case of a flow down an inclined plane, the granular front becomes unstable and breaks down into a series of self-channelised channels, generating a beautiful and a priori unexpected fingering pattern.