Continuous geotechnical monitoring for alert thresholds and hazard management

We present the case study of the Valle Boidi landslide. This is a complex and compound landslide affecting the Alice Bel Colle municipality (Piedmont, Italy, 786 inhabitants). This landslide has been subjected to repeated reactivations on April 1969, March 1970 and august 1974. To provide a reliable monitoring and early warning system and to properly design structural countermeasures a multiparamet-ric geotechnical borehole DMS system (patents and trade mark CSG srl, Italy) was installed on June 2010. The DMS column includes 25 Biaxial Inclinometric modules, 1 Piezometric Sensors and 25 Temperature Sensors, for a total active monitored length of 25 metres. The DMS modules are connected between them by special 2D flexible joints that allow strong continuous adaptability to bends and twists of the borehole, whilst maintaining rigorously the orientation with respect to a reference system. The DMS system is active in continuous with automatic download and sms/direct call in case of events more than the thresholds defined. On March 17th 2011 the DMS system recorded a sharp displacement at 16-18 m of depth, reaching on the 24th a cumulative displacement of 5 mm. The event was detected in real time and the sliding zone identified allowing to analyze the kinematics and the triggering factor. On May 2011 two more columns, each one 25 meters in length, were installed to implement the Early Warning system. A weather station was also installed to detect the site specific correlations between displacements and rainfall and the delay time between perturbation and reactivation. This system allows the management of the monitoring and early warning system directly by the technical personnel Alice Bel Colle municipality.