Rate, Water Pressure, and Temperature Effects in Landslide Shear Zones

Abstract

The behaviour of slow‐moving landslides is controlled by the residual strength of the shear zone. Despite their mobile state, such slides can often withstand extreme events like heavy rainfalls and earthquakes. A rate‐hardening in the shear zone is suspected to be one of the main stabilizing factors and has been well investigated, in particular for clayey soils. Soils from steep alpine landslides, on the other hand, are often dominated by silts and sands with various clay content, and while understanding of their rate dependency is less advanced, it remains critical for the reliable risk assessment. In this article, an improved ring shear apparatus is presented and applied to investigate rate, pore water pressure and temperature effects in landslide shear zones. The testing program on samples from two alpine landslides in Switzerland reveals a moderately positive rate effect explaining their mobile state. An achieved insight into the thermo‐hydro‐mechanical processes of fast shearing provides physical evidence to the widely debated hypothesis on generation of excess pore water pressure due to frictional heating. However, for the tested materials this effect only occurs after extended shearing and does not lead to a complete loss of shear strength. Based on that and the observed positive rate effects, catastrophic failure seems unlikely for these landslides. At the same time, the results suggest that for less permeable soils, frictional heating may indeed be a source of negative rate effect during very rapid shearing.

Response Mechanism of the Residual Strength to the Mesostructure of the Shear Surface in the Gravelly Slip Zone of Ancient Landslides

“…Larger particle sizes result in larger and stronger interlocked friction due to increased roughness and greater resistance to shear forces. The compaction effect of normal stress promotes particle uplift, shifting, rotating, and pulling out at the shear surface (Marc et al., 2023; Wafid Agung et al., 2004). This movement enables the clay particles to adhere to the gravel surface, creating a lubricating effect (Wang et al., 2010; Xin et al., 2016).…”