Abstract
Precipitation, together with erosion and earthquakes, have been recognized as the main triggering factors of shallow landslides. However, there are relatively few well-documented cases where direct relationships could be established between occurrence and features of shallow landslides, the rainfall characteristics (e.g. intensity, duration) and water retention curves. A field experiment has been performed on a steep forested slope located on the east-facing banks of the river Rhine in Ruedlingen, northern Switzerland. The aim of the experiments was to study the triggering mechanisms of the landslides induced by rainfall. The pore pressure and the degree of saturation, which are linked through the water retention curve, represent two of the main variables affecting the mechanical behaviour of unsaturated soils, and their relationships to rainfall are complex. The difference in the determination of water retention curves at different scales are analysed in this paper for Ruedlingen soil together with their effects on mechanical behaviour at multi-scale.
Highlights
Rainfall induced landslides are one of the major natural hazards in Switzerland [1,2-3,4]
The curves obtained for depths of 120 cm and 90 cm in cluster 1 show air entry values of around 2.2 kPa, which is lower than that implied by the laboratory water retention curves (WRCs)
The depth of failure and the pore water pressure acting on the slope are fairly well predicted by the limit equilibrium analyses, which account for an apparent cohesion dependent upon suction and saturation degree and have been extended to a lateral limited slide
Summary
Rainfall induced landslides are one of the major natural hazards in Switzerland [1,2-3,4]. The slope stability depends directly on the distribution of water and of the pore pressure inside its mass These factors are affected by the hydraulic properties of unsaturated soils, such as the water retention curve and the hydraulic conductivity function [e.g. 7-8]. A landslide triggering experiment was carried out near Ruedlingen in North East Switzerland, on a slope overlooking the river Rhine, in autumn 2008 and spring 2009. This attempted to replicate the effects of a heavy rainfall event from May 2002, in which 100 mm rain fell in 40 minutes [9], causing 42 superficial landslides. HM behaviour observed in situ and in the laboratory are compared, highlighting common trends and discrepancies in preventing shallow landslides being induced by rainfall
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