Rain-induced slope instability is a significant natural hazard in Switzerland, Slovenia and elsewhere in Europe. This contribution was prepared especially for the 12th Šuklje Symposium, and recognises that landslides occur both in mountain regions as well as in lowland regions during and following extreme-rainfall conditions. The Institute (and Professorship) for Geotechnical Engineering at the Swiss Federal Institute of Technology (ETH Zurich) has been engaged over several years in projects concerned with the characterisation, monitoring and modelling behaviour of slopes in mainly granular porous media across the full range of altitudes in Switzerland. A link is made to the doyen of the Šuklje day and then three case histories are presented and discussed to demonstrate the principal reactions to seasonal rainfall. A small slip was released in two of these cases and the "triggering" factors have been investigated and are discussed in this contribution. It transpires that the mode of inslope drainage influences the way in which the ground saturates and hence the volume of the potentially unstable ground. Simple stability analyses using limit equilibrium and soil parameters that have been amended to account for unsaturated soil behaviour were found to function well for slopes in largely granular media.

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After an extreme rainfall event in May 2002 a series of landslides occurred in Ruedlingen in Canton Schaffhausen, North Switzerland. A 38° steep slope has been chosen in this area beside the river Rhine to carry out an artificial rainfall experiment to investigate the dependence between rainfall, suction, saturation and shear resistance. Two sprinkling experiments were conducted to represent an extreme rainfall event, the second of which resulted in failure of 130 m 3 of the slope. Several cycles of wetting and drying were applied to the soil and suction and volumetric water content were measured at different depths in three locations of the slope, by which in-situ Water Retention Curves (WRC) can be derived. The WRC of an undisturbed sample was also determined from laboratory test. The in situ and laboratory WRCs are compared in this paper and the differences will be discussed.@en

A landslide triggering experiment was carried out on a 37°- 40° steep forest slope in North-East Switzerland by sprinkling water artificially to represent an extreme rainfall event. This project is part of a multidisciplinary collaboration, which includes geotechnical engineering, hydrology, hydrogeology, forest engineering, geophysics and photogrammetry. A three dimensional model of the ground was developed from non-invasive geophysical surveys, insitu probing, combined sprinkling and dye tracer tests and shallow test pits. Laboratory tests were carried out on undisturbed samples under various degrees of saturation This paper mainly focuses on the characterisation of the site.@en