Investigation, monitoring and modelling of a rapidly evolving rockslide: The Mt. de la Saxe case study

During the last decade, a large rockslide along the NW slope of the Mont de la Saxe (Courmayeur, AO—Italy) showed a significant increase in the rate of activity in conjunction with snow melting periods and more recently with important amount of rainfall. The ca 8 mm3 rockslide affects a heavily tectonised and intensely fractured mass of black schists, for a surface area of about 150,000 m2. The rockslide failure surface is typically located at depths of 60–80 m b.g.l. Because of the highly valuable exposed elements regional authorities commissioned a comprehensive ground investigation and monitoring campaign, as well as theoretical and numerical analyses, in order to assess slope stability conditions, the possible evolution and the suitable stabilization and mitigation countermeasures. Here we present the recent rockslide evolution till spring 2014 when a major seasonal reactivation of a 400,000 m3 mass occurred. Finally, with the aim to develop a possible tool for displacement prediction, the results of a series of 1D visco-plastic simulations are presented, discussing the possible role of each of the main controlling factors (e.g. groundwater recharge and piezometric level oscillation, rock degradation). .