Rock avalanche deposits store quantitative evidence on internal shear during runout

Abstract

We investigated the quantitative effect of internal shear on grain breakage during rock avalanche runout, by means of 38 ring‐shear experiments on identical sand samples at different normal stresses, shear strains and shear strain rates. We compared sample grain‐size characteristics before and after shearing. We found that grain size decreased with increase in normal stress and shear strain. Reduction in grain size was inferred to occur through grain breakage associated with grain interactions in strong force chains during strain. The results were consistent with observations of both inverse‐grading structure in deep rock avalanche exposures, and fining and grading of particles with increasing rock avalanche travel distance. Our study suggested that with appropriate calibration, variations in grain‐size distributions within a rock avalanche deposit would provide quantitative information on the distribution of internal shear during its runout.

The Monitoring-Based Analysis on Deformation-Controlling Factors and Slope Stability of Reservoir Landslide: Hongyanzi Landslide in the Southwest of China

“…The majority of the deformations occurred during the declination of the reservoir water level, and no large deformations were observed when the reservoir water level remains stable or increases. Similar observations were also made by previous studies [12][13][14][15][16][17][18]. Due to the extensive deformation of the Hongyanzi landslide, a multiparameter monitoring program was conducted on the Hongyanzi landslide to advance the understanding on the deformation characters and its major influencing factors.…”

Internal Erosion Controls Failure and Runout of Loose Granular Deposits: Evidence From Flume Tests and Implications for Postseismic Slope Healing

“…In our tests we see the small, erodible soil fraction playing a fundamental control on the failure mechanism and runout of flow‐like landslides in loose deposits. Under the same hydraulic boundary and e s , coarse‐only deposits are much less susceptible to failure, while deposits with significant small‐sized fraction (8%–25%)—that can be produced, for instance, by large rock avalanching with intense distributed fragmentation (Dufresne & Dunning, ; M. Zhang & McSaveney, )—can fail dramatically and exhibit fluidization and long runout. The proportion of small erodible particles correlates positively with the runout distance but negatively with the landslide‐triggering rainfall threshold (the rainfall duration, in this case).…”

Shear‐Rate‐Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels

“…Their shear zones have been shown to be at-or very close to-the interface between a mudstone rock layer and a weak clayey layer of the same nature, generated by weathering, softening and shearing (Zhang et al, 2016). Basal sliding can also occur along the soil-rock interface in debris flows, rock slides, and rock avalanches (Chigira et al, 2010;Fan, Xu, Scaringi, Dai, et al, 2017;Hungr et al, 2014;Hu et al, 2015;Xu et al, 2012), although shear localization in this latter typology might not be exclusive (Zhang & McSaveney, 2017). Nevertheless, observations and analyses support a velocity-weakening mechanism-of various possible origins-to explain the catastrophic failure and hypermobility of these types of landslides (e.g., Aaron et al, 2017;Alonso et al, 2016;De Blasio & Crosta, 2015;Handwerger et al, 2016;Hu et al, 2017;Johnson et al, 2016;Lucas et al, 2014;Song et al, 2016;Wu et al, 2017).…”