Normal Stress‐Dependent Frictional Weakening of Large Rock Avalanche Basal Facies: Implications for the Rock Avalanche Volume Effect

Abstract

To explore the mechanism behind the volume effect of rock avalanches observed in field data, a series of rotary shear tests were conducted at a shearing velocity of 0.87 m/s and varying normal stress levels (from 0.29 to 1.85 MPa) on soil collected from the basal facies of the Yigong rock avalanche in Tibet, China. This experimental study reveals that (1) as normal stress increases, the steady state apparent friction coefficient (μss) of the soil decreases, indicating a normal stress‐dependent feature of μss; (2) the higher the normal stress, the lower the decay rate of μss; (3) water vaporization induced by frictional heating is commonly observed in the tests accompanied by large decreases in μss, and excess pore pressure is generated in the shearing zones of the samples due to vapor accumulation; and (4) with increases in normal stress and decreases in soil permeability, an increasing feature of excess pore pressure is reached. Based on the experimental results, we propose that the coupled effects of water vaporization induced by frictional heating in avalanche basal facies and depth‐dependent permeability of avalanche basal facies should be contributed to the volume effect of rock avalanches.

An Empirical Power Density‐Based Friction Law and Its Implications for Coherent Landslide Mobility

“…This may have affected its runout behavior as different evolutions of the friction coefficient may be associated with different thicknesses. Experiments have indeed demonstrated the control of normal stress on the friction coefficient as well as on the velocity‐dependent behavior in a wide range of stress and velocity (Boneh et al, 2013; Scaringi & Di Maio, 2016; Wang et al, 2018). Using a single parameter, a PD ‐dependent law can incorporate both the velocity‐dependent and normal stress‐dependent behaviors while tracking the evolution of the landslide movement through time.…”

“…By fitting experimental data, Mizoguchi et al (2007) obtained an exponential‐decay equation for the friction coefficient of shear gouge: where μ p and μ ss are the peak and steady‐state friction coefficients, respectively, d is the shear displacement of the specimen, and D c is the slip‐weakening distance. An exponential decrease of μ ss with the shear velocity (velocity‐dependent law) was observed, yet some experiments also identified a similar dependence on the normal stress (Boneh et al, 2013; Wang et al, 2018). Therefore, μ ss can be generally expressed as where ξ represents either the velocity ( v ) or the normal stress and A , B , and C are fitting parameters.…”

“…where μ p and μ ss are the peak and steady-state friction coefficients, respectively, d is the shear displacement of the specimen, and D c is the slip-weakening distance. An exponential decrease of μ ss with the shear velocity (velocity-dependent law) was observed, yet some experiments also identified a similar dependence on the normal stress (Boneh et al, 2013;Wang et al, 2018). Therefore, μ ss can be generally expressed as…”

Multiscale effects caused by the fracturing and fragmentation of rock blocks during rock mass movement: implications for rock avalanche propagation

“…Many dynamic mechanisms have been proposed to explain the hypermobility of rock avalanches. Some mechanisms involve fluid media, such as air (Kent, 1966), water (Wang et al, 2002;Hungr and Evans, 2004), a fluid-like fine grain matrix (Hsü, 1975), melted rock or vapour (Habib, 1975;Goguel, 1978;Hu et al, 2018), and thermal pressurization and thermal moisture fluidization (Wang et al, 2017(Wang et al, , 2018a. Others invoke the interactions of materials in rock avalanche systems, such as shearing and impacting between a sliding mass and undulate path-generated acoustic fluidization (Melosh, 1979;Collins and Melosh, 2003), shearing between a rock mass and the ground (Foda, 1994;Wang et al, 2015), shearing between particles in the basal layer (Preuth et al, 2010), momentum transfer caused by the collisions of particles or different parts of the rock mass (Heim, 1932;Van Gassen et al, 1989;Miao et al, 2001), and dispersive pressure caused by dynamic fragmentation (Davies et al, 1999;Davies and McSaveney, 2009).…”

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

“…These hypotheses include bulk fluidisation or lubrication by air, gas, water, ice, heating or acoustic waves (see, e.g. references in Shreve 1987 ; Goren et al 2010 ; Ferri et al 2011 ; Bulmer 2012 ; Liu et al 2015 ; Mitchell et al 2015 ; Charrière et al 2016 ; Johnson et al 2016 ; Wang et al 2018 ), or the presence of an erodible bed (e.g. Mangeney et al 2010 ; Crosta et al 2009 , 2015 ; Iverson et al 2011 ; Farin et al 2014 ).…”