The mountains in the Swiss Alps are frequently subjected to extreme weather conditions, with periods of freezing temperatures, snow-melting, intense rainfall and temperature variations. These dynamic processes result in mass movements, such as rockfalls and landslides which endanger settlements and infrastructure.
In a research paper during the author’s doctoral thesis at ETH Zürich, the mass movements, in a scree slope at the Meretschibach catchment, canton Valais, south of Switzerland at an elevation between 1840-1910 m.a.s.l. were monitored and characterised, the objective was to provide information for the prediction of potential landslides jeopardising the village of Agarn located at 637 m.a.s.l. and their 720 inhabitants.
The events of mass movements in the Meretschibach reported in the area since the year 2000, were mostly debris flow type: 2 events in October 2000, 31 July 2002, 21 May 2003, 19 August 2003, 29 July 2008, 20 July 2014, 28-29 July, 2014. Additionally, in 2012 data provided of movements recorded by satellite InSAR were of 0.5 m/year at some places in the slope, which was of concern for the community, due to the vicinity to an active channel that is known for having led to extensive debris flows reaching the valley below in the past.
The research question was assessed by means of a long-term soil instrumentation and monitoring, subsequent site characterisation including field and laboratory testing, and the numerical and physical modelling testing program. The project in alpine location represented several challenges for instrumentation and data collection techniques. The site was monitored through a three years field campaign, providing information of soil volumetric water content and soil temperature. A geophysical survey was performed alongside the monitoring to define bedrock depth. Additionally, the data were complimented by precipitation data from two meteostations.
Next to the information collected from the long-term field monitoring and soil characterisation, a schematic ground model was developed and modelled in physical and preliminary numerical simulations of surficial landslides induced by rainfall infiltration. The slope stability analysis was conducted in terms of soil depth to the bedrock, slope geometry and intensity of rainfall infiltration.
The study concludes from the hazard point of view, that the scree slope studied is unlikely to experience a significant slope failure that could endangered the village of Agarn, this due to the well drained conditions, shear strength of the gravel and the limited soil thickness (1-3 m). However, a surficial landslide could be triggered in locations where the bedrock is shallow, or at steps in the bedrock. A combination of local erosion and soil saturation under a critical rainfall intensity would lead to slope failure and mass movement due to loss of effective stress of the gravelly soil. An important aspect is the data collected during the monitoring, und their use as an input for future studies and early warning systems development. Furthermore, this information can help to understand the seasonal response of scree slopes in other locations, under similar seasonal conditions in Graubünden.
IBAR is also currently conducting studies on natural hazard protection and infrastructure with sustainable building materials that can help make slopes and infrastructure structures safe in the canton of Graubünden. These include: "Slope stabilization with wood wool fascines" and "Special anchors for avalanche and rockfall protection." The latter is suitable for use on higher steep slopes, where damage and erosion from rockfall or avalanches are to be expected.
The knowledge gained at the Meretschibach in terms of alpine slope stability, plus the motivation and competences at IBAR can be applied to solve similar problematics in alpine slope stability in Graubünden.