Shear‐rate‐dependent strength control on the dynamics of rainfall‐triggered landslides, Tokushima Prefecture, Japan

Abstract

A typhoon (Typhoon No. 10) attacked Shikoku Island and the Tyugoku area of Japan in 2004. This typhoon produced a new daily precipitation record of 1317 mm on Shikoku Island and triggered hundreds of landslides in Tokushima Prefecture. One catastrophic landslide was triggered in the Shiraishi area of Kisawa village, and destroyed more than 10 houses while also leaving an unstable block high on the slope. The unstable block kept moving after the event, showing accelerating and decelerating movement during and after rainfall and reaching a displacement of several meters before countermeasures were put into place. To examine the mechanism for this landsliding characteristic, samples (weathered serpentinite) were taken from the fi eld, and their shear behaviours examined using ring shear tests. The test results revealed that the residual shear strength of the samples is positively dependent on the shear rate, which may provide an explanation for the continuous acceleratingdecelerating process of the landsliding. The roughness of the shear surface and the microstructure of the shear zone were measured and observed by laser microscope and SEM techniques in an attempt to clarify the mechanism of shear rate effect on the residual shear strength.

A characterisation of the physical properties of soil and the implications for landslide occurrence on the slopes of Mount Elgon, Eastern Uganda

“…That notwithstanding, slope failure often occurs as a result of localised deformation in a thin zone of intense shearing. Consequently, using overall stress-strain measurements may not be representative of such intense shear behaviour (Finno et al 1997;Gonghui et al 2010). 'Conditional stability' would be the appropriate description of the slopes at the supposedly stable sites, owing to the interplay of various physical, pedological and anthropogenic factors.…”

Rate-weakening friction characterizes both slow sliding and catastrophic failure of landslides

“…For the slow-moving landslide model runs, we use a larger d c that is consistent with fieldbased estimates of friction parameters on faults (35). We select μ 0 that characterizes weak, clay-rich materials (45,46,48,49) that are common to slow-moving landslides with well-developed slip surfaces (2). The shear modulus and shear wave speed are based on values measured for the Jurassic and Cretaceous Franciscan Complex, Northern California (50), a region well known for slow-moving landslide activity (5), and are notably lower than values reported for deep faults.…”

“…landslides | slope failure | rate and state friction | pore-water pressure | effective stress L aboratory experiments (1,2) and numerical models (3,4) suggest that for slow-moving landslides that persist over periods of years to centuries (5) the shear strength that resists motion increases with slip rate-a characteristic referred to as rate strengthening-whereas the opposite is true for landslides that exhibit runaway acceleration and catastrophic failure. Two primary mechanisms are invoked frequently to describe the former rate-strengthening behavior.…”

Effect of particle size and shear speed on frictional instability in sheared granular materials during large shear displacement

“…The dynamic properties and transition parameters of these phenomena are also important for better understanding the related geophysical events. Particularly, the stick-slip motion has been suggested as analogous to the phenomenon of earthquakes (Brace and Byerlee, 1966;Scholz, 2002), and also indicates some similarities to the reactivation of large landslides (Schaeffer and Iverson, 2008;Wang et al, 2010). Many recent laboratory experiments and numerical simulations have been devoting to investigating such kind of frictional instabilities (Campbell, 1990;Marone, 1998;Mair et al, 2002;Anthony and Marone, 2005;Schaeffer and Iverson, 2008;Scuderi et al, 2014).…”

“…(Terzaghi, 1950;Lambe and Whitman, 1969;Scholz, 2002). In general, these locally deformed zones are mainly composed of granular materials with a pore-fluid, where granular friction plays a significant role in dictating the diverse styles of deformation when the zones experience a shear stress (Tika et al, 1996;Wang et al, 2010;Schulz and Wang, 2014). Thus better understanding the physical processes of granular friction is not only vital for quantitative interpretation of their occurrences and characters, but also for assessing the resultant hazards (Terzaghi, 1950;Campbell, 1990;Marone, 1998;Scholz, 2002).…”