A long-term field study for the investigation of rainfall-induced landslides

A two-year monitoring experiment has been conducted on a slope in shallow weathered soils overlying sandstone bedrock in Toessegg, Switzerland. Water balance and suctions were measured, together with the meteorological inputs, in preparation for predicting environmental effects on slope stability. Electrical resistivity tomography proved particularly helpful in establishing the spatial distribution of soil layering, with clayey sand overlying silty sand and bedrock. This paper describes monitoring of the field measurements, and shows that the double layer causes a bi-seasonal response, with the smallest 'factor of safety' after the wetter winter months.