Empirical investigation of friction weakening of terrestrial and Martian landslides using discrete element models

Abstract

Understanding what controls the travelling distance of large landslides has been the topic of considerable debate. By combining observation and experimental data with depth-averaged continuum modelling of landslides and generated seismic waves, it was empirically observed that lower effective friction had to be taken into account in the models to reproduce the dynamics and runout distance of larger volume landslides. Moreover, such simulation and observation results are compatible with a friction weakening with velocity as observed in earthquake mechanics. We investigate here as to whether similar empirical reduced friction should be put into discrete element models (DEM) to reproduce observed runout of large landslides on Earth and on Mars. First we show that, in the investigated parameter range and for a given volume, the runout distance simulated by 3D DEM is not much affected by the number (i.e. size) of grains once this number attains ~ 8000. We then calibrate the model on laboratory experiments and simulate other experiments of granular flows on inclined planes, making it possible for the first time to reproduce the observed effect of initial volume and aspect ratio on runout distances. In particular, the normalised runout distance starts to depend on the volume involved only above a critical slope angle > 16–19°, as observed experimentally. Finally, based on field data (volume, topography, deposit), we simulate a series of landslides on simplified inclined topography. The empirical friction coefficient, calibrated to reproduce the observed runout for each landslide, is shown to decrease with increasing landslide volume (or velocity), going down to values as low as 0.1–0.2. No distinguishable difference is observed between the behaviour of terrestrial and Martian landslides. Electronic supplementary material The online version of this article (10.1007/s10346-019-01140-8) contains supplementary material, which is available to authorized users.

Is the Grain Size Distribution a Key Parameter for Explaining the Long Runout of Granular Avalanches?

“…A common characteristic among these events is their large mobility, exceeding the prediction of simple frictional models (Corominas, 1996; Davies & McSaveney, 1999; Heim, 1932; Hsu, 1975; Legros, 2002) and emphasizing their hazardous perception when interacting with infrastructure, communities, or other land masses (Cabrera et al., 2020; Froude & Petley, 2018). The proposed mechanisms behind this large mobility are varied, including excessive reductions of the flow basal friction, for example, the formation of an air cushion (Shreve, 1968); size segregation (Iverson et al., 2010; Roche et al., 2011); a series of interactions that weaken the collective shear resistance, for example, fluid, air, or fines fluidization (Collins & Melosh, 2003; Kent, 1966; Hsu, 1975); self‐lubrication (De Blasio & Elverhøi, 2008; Goren & Aharonov, 2007); dynamic rock‐fragmentation (Davies & McSaveney, 2009); and volume‐induced frictional weakening (Borykov et al., 2019; Lucas et al., 2014). Despite the variety of explanations, the causes of the large mobility in granular flows remain an open and scenario‐dependent discussion, demanding a systematic validation of the aforementioned mechanisms.…”

Deep-seated gravitational slope deformation scaling on Mars and Earth: same fate for different initial conditions and structural evolutions

“…It was shown that landslide volume is one of the factors that control landslide propagation (McEwen, 1989;Lucas et al, 2014;Johnson and Campbell, 2017) when the slope angle of the propagation plane is steeper than ca. 20 • (Farin et al, 2014;Borykov et al, 2019), whereas it has no influence for more gentle slopes. This dependency of landslide propagation on slope, and indirectly on volume (and friction), initially identified in lab- oratory experiments (Farin et al, 2014) could be adequately documented by natural examples thanks to some very large Martian landslides (Johnson and Campbell, 2017;Borykov et al, 2019), much larger than any terrestrial landslide, which help populate the landslide dataset for voluminous landslides that propagate on nearly flat surfaces.…”

“…20 • (Farin et al, 2014;Borykov et al, 2019), whereas it has no influence for more gentle slopes. This dependency of landslide propagation on slope, and indirectly on volume (and friction), initially identified in lab- oratory experiments (Farin et al, 2014) could be adequately documented by natural examples thanks to some very large Martian landslides (Johnson and Campbell, 2017;Borykov et al, 2019), much larger than any terrestrial landslide, which help populate the landslide dataset for voluminous landslides that propagate on nearly flat surfaces. Similar to landslides, DSGSD occurs on mountain slopes that are much smaller on Earth than on Mars, and at the first order, their origin may be similar.…”

The Basal Friction Coefficient of Granular Flows With and Without Excess Pore Pressure: Implications for Pyroclastic Density Currents, Water‐Rich Debris Flows, and Rock and Submarine Avalanches

“…Interestingly, a similar conundrum has confounded the pyroclastic flows community for decades (Hayashi & Self, 1992; Kelfoun, 2011; Lube et al, 2019; Wilson, 1980). Notably, for both debris flows and pyroclastic density currents, large L/H require lowering of the effective basal friction coefficient as noted in many depth‐averaged studies (e.g., Charbonnier & Gertisser, 2009; Charbonnier et al, 2013; Lucas et al, 2014; Ogburn & Calder, 2017) or even in discrete element modeling (Borykov et al, 2019). Phenomenologically and mathematically, the low effective basal (also called wall) friction can be produced by either lowering the effective normal stress or reducing the friction coefficient for both landslides and pyroclastic density currents (Breard et al, 2017; Pudasaini & Miller, 2013).…”