Val Genasca landslide (north Italy): an example of the methodolog used for the identification of the landslide main features and its monitoring

Abstract

The Geological Monitoring Centre supervises deformations in some major landslides in the Lombardy Region (Italy). This article aims to present the methodology used to increase the knowledge about the landslide of Genasca Valley, located in the municipality of San Giacomo Filippo (Sondrio), and to monitor its evolution. The approach to the problem has been developed through the implementation of various activities in different stages.The monitoring activities started in summer 2010 with a cognitive monitoring based on distometric measurement, periodical topographic and GPS measurement. The slope areas (30.000 square meters) in movement were defined thanks to these activities and to the geological survey.Second step was the set up of a real time monitoring with a meteorological station, three wire extensometers and one automatic topographic system. A geophysical investigation and three drilling boreholes were made to increase the knowledge of the subsurface.Inclinometric casing and piezometric pipe for periodical check were placed in the two drilling boreholes out of landslide (above 10 meters upper the main scarp). A differential multiparametric system (DMS) for the depth monitoring inclinometric and piezometric was installed in the borehole at the landslide centre.In order to minimize the costs of the DMS column we designed a particular configuration (alternation of sensors module with a sterile module), that didn’t allow a direct correlations between the surface and depth movements but it has however allowed the precise identification of the shear band and the movements quanti cation.In the meantime the University of Milan made a modeling of the collapse in order to verify spread models and propose preliminary warning thresholds.This monitoring network has permitted to acquire and analyze data collected for more than three years. During this period Val Genasca landslide showed 7 different accelerations with static period intervals. Last acceleration, dated winter 2013/14, showed a 5 meters displacement, measured on the surface along the maximum displaced vector.The data analysis showed that the shear band affected a thickness of about 15 meters and permitted to estimate in about 500.000 cubic meters the landslide volume in movement. The topographic data allowed to define a kinematic motion of a typical rotational slip with the values of lowering higher in areas near to the main scarp compared to those positioned in the lower part.