Dynamical stress in force chains of granular media traveling on a bumpy terrain and the fragmentation of rock avalanches

Abstract

The dynamics of grain fragmentation is usually ignored in the study of rapid granular flows. This is realistic for experiments on small-scale chutes or in many industrial processes where the specific granular energy is too small for particles to break but is unrealistic for natural rock avalanches, where the extremely comminuted state is perhaps the most evident aspect of the deposit. Based on observations of natural landslide deposits, it has been suggested that the stress may increase along a sequence of force chains formed by the granular material. However, simple calculations show that rock avalanche deposits exhibit a much more advanced degree of fragmentation than explainable with the static chain model. It is thus deduced that fragmentation along force chains must be combined with the effect of a bumpy topography. A simple model of a force chain moving on a rugged incline is then introduced, which exhibits increased fragmentation rate in the presence of a bumpy topography. It is shown that both the wave number and amplitude of the topographic undulations are significant in the efficiency of fragmentation.

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide‐Avalanches: Insights From Discrete Element Analyses

“…The thickness of these lines is proportional to the force magnitude. According to De Blasio (), the evolution of force chains during a dynamic impact process can lead to the increase of impacting stresses and consequently increase the intensity of rock fragmentation. In Figure , it can be observed that at impact, the large contact forces and the corresponding internal damages arise immediately from the bottom frontal corner of the block (see Figures a and b).…”

Rock avalanche deposits store quantitative evidence on internal shear during runout

“…De Blasio [] and De Blasio and Crosta [, ], however, present a different stress‐driven grain fragmentation model, proposing that the grain‐size reduction (fragmentation) occurs only on steep slopes with angles greater than 70° above flat terrain and is caused by high normal stress induced by collision of the rock mass with the flat ground. Such abrupt slope breaks occur mostly at the foot of the source area, implying that the fragmentation should occur mostly near the beginning of the transport.…”

“…Pervasive fragmentation (breakage) of rock debris during transport is one hypothesis explaining both rock avalanche stratigraphy and high mobility De Blasio andCrosta, 2014, 2015]. Many studies investigate potential mechanisms through which breakage and high mobility may occur [e.g., Davies andMcSaveney, 2002, 2009;Crosta et al, 2007;Taboada and Estrada, 2009;Imre et al, 2010;De Blasio, 2011;Cagnoli and Romano, 2012;Wang et al, 2015;Zhang et al, 2016].…”

Stochastic Equation of Fragmentation and Branching Processes Related to Avalanches

“…[14,15,21], however, in these papers the used fragmentation processes are deterministic. In the articles [20,24,28] a discrete time branching process is associated to an avalanche.…”