New Patterns in High-Speed Granular Flows, or How Supported Regimes Could Explain Frictional Velocity-Weakening in Landslides

Abstract:

We conduct extensive numerical simulations of granular flows down inclines with frictional side walls using a discrete element model (DEM). We obtain a steady state (SDF flow) for all the flow configurations we have investigated, varying extensively the inclination angle and the mass hold-up.

Our simulations reveal the existence of unexpected SFD regimes which were never reported in the literature. These new regimes emerge from the destabilization of SFD unidirectional flows upon increase of the mass holdup and the slope. They are characterized by complex internal structures including secondary flows, heterogeneous particle volume fraction, symmetry breaking and dynamically maintained order.

Interestingly, despite their overall diversity, these regimes are shown to obey universal scaling laws. We identify a simple dependency of the limit velocity on the mass hold-up and inclination angle. In steady state, the mass flow rate simply scales as the 5/4 power of the mass holdup, or equivalently, the velocity scales as the 1/4 power of the mass holdup.

These results open new perspectives for interpreting the features of geophysical granular flows. The scaling aforementioned could for instance explain, in a very simple and elegant way, the frictional velocity weakening in landslides on Earth and other planetary bodies observed in a recent publication [1].

Reference:

[1] Frictional velocity-weakening in landslides on Earth and on other planetary bodies, Antoine Lucas, Anne Mangeney, Jean Paul Ampuero, Nature Communications 5, 3417 (2014).