Abstract
Rock avalanches are catastrophic events involving important granular rock masses (>106 m3) and traveling long distances. In exceptional cases, the runout can reach up to tens of kilometers. Even if they are highly destructive and uncontrollable events, they give important insights to understand interactions between the displaced masses and landscape conditions. However, those events are not frequent. Therefore, the analogue and numerical modelling gives fundamental inputs to better understand their behavior. The objective of the research is to understand the propagation and spreading of granular mass released at the top of a simple geometry. The flow is unconfined, spreading freely along a 45° slope and deposit on a horizontal surface. The evolution of this analogue rock avalanche was measured from the initiation to its deposition with high speed camera. To simulate the analogue granular flow, a numerical model based on the continuum mechanics approach and the solving of the shallow water equations was used. In this model, the avalanche is described from a eulerian point of view within a continuum framework as single phase of incompressible granular material. The interaction of the flowing layer with the substratum follows a Mohr-Coulomb friction law. Within same initial conditions (slope, volume, basal friction, height of fall and initial velocity), results obtained with the numerical model are similar to those observed in the analogue. In both cases, the runout of the mass is comparable and the size of both deposits matches well. Moreover, both analogue and numerical modeling gave same magnitude of velocities. In this study, we highlighted the importance of the friction on a flowing mass and the influence of the numerical resolution on the propagation. The combination of the fluid dynamic equation with the frictional law enables the self-channelization and the stop of the granular mass.
Highlights
Rock avalanches are rare but catastrophic events in which large volume of granular material (>106 m3) flows downslope at high velocities [1]
The first trial was made without any friction law
A mass without friction law does not stop and continue to spread laterally. This is observable in the numerical test without friction
Summary
Rock avalanches are rare but catastrophic events in which large volume of granular material (>106 m3) flows downslope at high velocities (up to 100 m/s) [1] They can cover areas over 0.1 km and reach great and unusual distances of runout. Other theories proposed to reduce the basal friction, as proposed by Kent [12], where entrapped and compressed air fluidizes the landslide or a layer of a trapped air at the base As these events are rare, laboratory experiments can give crucial information about their propagation and the influence of parameters on the mobility under idealized conditions These laboratory experiments are widely used to calibrate numerical models
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