Monitoring of large slow rock-slope deformation interacting with hydroelectric plants through Robotized Inclinometer System

Large slow rock-slope deformations as Deep-seated Gravitational Slope Deformations (DsGSDs) are widespread phenomena in alpine territory and many times interact with in-frastructures with more or less severe damage. DsGSDs show very slow displacement (mm to cm per year) with movement that may last for long period through a progressive failure comparable to a slow creep, with a corresponding large cumulative displacement over the time. Despite the slow-moving deformation, considering their long-term evolution pro-longed and continuous, DsGSDs may represent a natural hazard able to affect anthropic infrastructures. Hydropower facilities, e.g. dams and penstocks, can be particularly sensi-tive to the evolution of these phenomena, mainly related to their complex behavior char-acterized by different kinematics and spatial and temporal evolution trends, which can re-sult in a progressive damage of these strategic infrastructures. In the Aosta Valley (West-ern Italian Alps), DsGSDs affect about 13% of the entire regional territory, interfering with many hydropower plants. Among them, two relevant cases are those of the penstock of the Perrères hydropower plant (Valtournenche) and the Beauregard dam (Valgrisenche), both located in correspondence of two major active DsGSDs associated to secondary mi-nor landslides. In order to improve the comprehension of DsGSDs evolution, a robotic in-clinometer system was used to acquire automatically deep-seated ground deformation in boreholes. This system, independent from the length of the borehole, allows to measure horizontal deep displacement using a single inclinometer probe managed by a robotic sys-tem. This innovative instrument combines the advantages of traditional manual measure-ments (one standard biaxial probe, double readings, 50 cm step) with a robotized approach to improve quality of results in terms of revisiting time, repeatability and accuracy. Over-all, the implemented system represents a useful and innovative instrument for surveillance along sensitive sections of hydropower facilities for a better risk assessment and mitigation strategies implementation.