Granular flow experiments on the interaction with stationary runout path materials and comparison to rock avalanche events

Abstract

The central focus of this work is to study the processes acting well below the surface of a moving rock or debris avalanche during travel over stationary substrate material. Small‐scale physical models at a linear scale of 1:104 used coal as avalanche analogue material and different granular material simulating sedimentary substrates varying in frictional resistance, thickness and relative basal boundary roughness, as well as inerodible, non‐deformable runout path conditions. Substrate materials with the least frictional resistance showed the greatest response to granular flow overriding, becoming entirely mobilized beneath and ahead of the moving mass and producing the longest runout observed with a unique deposit profile shape. With a smooth substrate basal contact, failure occurred along this plane and avalanche and substrate became coupled during runout. With a rough base, however, temporary force chains of grain contacts in the substrate prevailed longer, imparted their resistance to motion/shear into the granular flow, and the flow rear section consequently halted earlier than when moving over substrates with a weak base. Reducing substrate thickness diminished the effect of basal contact roughness on granular flow runout and deposit length. Inerodible, non‐deformable substrate conditions caused changes in granular flow behaviour from essentially en masse sliding on low‐friction surfaces to increasing granular agitation over rougher paths. Copyright © 2012 John Wiley & Sons, Ltd.

Fundamental changes of granular flow dynamics, deposition, and erosion processes at high slope angles: Insights from laboratory experiments

“…In experiments on dense granular flows moving over an erodible bed, Rowley et al [] and Dufresne [] also observed waves in the bed that were generated by entrainment of the substrate. In both these studies, the waves were preserved in the deposits unlike in our experiments where the erosion waves disappeared as the flow front decelerated (Figure i).…”

“…Experiments on granular collapse over horizontal and inclined erodible beds have been performed recently to investigate and quantify erosion processes [ Mangeney et al , , ; Iverson et al , ; Dufresne , ; Roche et al , ]. Mangeney et al [] have shown that erosion processes affect the flow behavior above a critical slope angle θ c that is about half the repose angle θ r of the granular material ().…”

Rock slope instability and erosion: toward improved process understanding

“…Important uncertainties relate to estimation of rheological properties and the role of intermediate storage or entrainment. Size effects critically influence the mobility of rock slope failures greater than~10 6 m 3 and topography and trajectory effects modulate runout length (Evans et al, 1989;Hewitt et al, 2008;Dufresne, 2012). However, size, topography and trajectory effects also influence smaller magnitude events and explain why deposits of different rockfall magnitudes occur in different positions (Krautblatter et al, 2012b), and thereby why most studies fail to cover the entire magnitude spectrum of rock slope erosion.…”

Link Between the Dynamics of Granular Flows and the Generated Seismic Signal: Insights From Laboratory Experiments

“…Parallel to field investigations, many scaled laboratory experiments of granular flows have been conducted since the 1980s to better understand the dynamics and deposition of landslides (e.g., see reviews; Andreotti et al, ; Delannay et al, ; GdR Midi, ). These experiments include horizontal axisymmetrical granular column collapses (e.g., Lajeunesse et al, ; Lube et al, ; Roche et al, ) and 2‐D granular collapses in horizontal (Balmforth & Kerswell, ; Lacaze & Kerswell, ; Lube et al, ; Roche et al, , ; Siavoshi & Kudrolli, ) or inclined flat channels (Dufresne, ; Farin et al, ; Hogg, ; Huang et al, ; Lube et al, ; Mangeney et al, ; Sulpizio et al, ). In particular, Mangeney et al () and Farin et al () showed the existence of a critical slope angle above which the dynamics of granular flows change dramatically.…”