Pressures at the base of dry flows of angular rock fragments as a function of grain size and flow volume: Experimental results

Abstract

Geophysical granular flows such as pyroclastic flows and rock avalanches kill people and damage properties worldwide. The pressures exerted at their base affect the retarding forces that act on them and, for this reason, affect also their mobility that is important to foresee when assessing natural hazards in mountain regions. Here we present the results of experiments obtained by measuring with a load cell the basal pressures exerted by dry and cohesionless granular flows that descend a curved chute in the laboratory. The interaction between these flows and the chute surface on which they travel is dominated by collisions of particles (and or clusters of particles). A dimensional analysis suggests that the energy dissipation of these flows increases as grain size increases and as flow volume decreases (all the other features equal). Therefore the smaller the grain size and the larger the volume, the larger is expected to be flow mobility. Although, the longer travel distances of the centre of mass of finer grain size flows are easily discernible in our experiments, the effect of volume is probably hidden by additional phenomena such as the deposition first of the frontal part of longer flows on the less-steep more-distal part of the slope that prevents the rear part and the centre of mass of the flows to travel further downhill.