Monitoring of the Beauregard landslide (Aosta Valley, Italy) using advanced and conventional techniques

An advanced monitoring technique, based on radar interferometry and implemented by using a ground-based instrumentation (GBInSAR) has been applied for monitoring the Beauregard Deep Seated Gravitational Slope Deformation. This landslide is located in the Aosta Valley (on the Dora di Valgrisenche river), in northwestern Italy, and impinges on a 132 m high concrete arch-gravity dam. This is recognized to have relevant implications in terms of civil protection and poses important territorial and environmental issues. The poor rock mass conditions of the left abutment slope were reported in the fifties, during dam construction. Since 2002, additional geological, hydrogeological and geotechnical investigations have underlined the presence of a deep seated shear zone up to 20 m thick, at the landslide toe. Continuous conventional monitoring over a time span of more than 50 years of both the slope and the dam has allowed to gain insights into the understanding of the behaviour of the basal portion of the slope, with very limited and uncertain point-wise displacement monitored in the upper sector. The GBInSAR monitoring technique has allowed to obtain multi-temporal surface deformations of the upper portion of the landslide, discovering the presence of a main sector in motion, previously unknown, characterized by a total displacement of 45 mm over 4 months. The results of radar monitoring have been validated by comparing with topographic measurements carried out by an automatic total station on 4 targets located at the toe of the slope.