F. Baillifard

The effect of weathering on Alpine rock instability

Weathering affects joint or fault gougematerial in the Swiss Alps, leading to the formation of smectite, which changes the mechanical properties of fault gouge and degrades slope performance. Analysis of recent rockslides in gneissic rocks in Switzerland indicates that accelerations of movements are linked to precipitation, without the development of excess pore water pressure. Processes such as weathering and crushing induce soil-like behaviour of the infilling material and explain rockslide movements induced by water seepage in both fault and joint gouges.

Velocity Prediction on Time-Variant Landslides Using Moving Response Functions: Application to La Barmasse Rockslide (Valais, Switzerland)

Landslides are complex natural systems with non-linear and time variant response to a given input rainfall rate. Although landslide response (e.g. rate of displacement) is normally assumed uniform along time for a constant input (e.g. rainfall rate), we show how the use of adaptive moving windows for parameter’s calibration may lead to a better prediction of the displacement rates. The model is based on the computation of the displacement rates at each time lapse (e.g. one day) as a convolution of a given response function times daily rainfall. The response function was deduced from physically based infiltration laws, being the values of their parameters optimized in order to minimize the error between the real observations and the modeled velocities. The model was then applied to a long-term landslide deformation time series at La Barmasse landslide (Valais, Switzerland). Model performance was significantly improved using moving windows, showing the modeled rates of displacements close resemblance to real observations.