GNGTS 2013 - Atti del 32° Convegno Nazionale

Mostly because of the road and rail interruption and the resulting closure, the event caused severe damages not only to the local community, but also to the national railway system, especially on Southern and Central Italy. Considerable efforts were carried by the Italian national Civil Protection Department (DPC) to tackle the emergency. Moreover, a series of actions (artificial drainages, removal of slide material from the toe, etc.) has been taking place since then, in order to mitigate the effects of the moving landslide. Notwithstanding the resulting slowdown of the earth-flow obtained, further coordinate actions are yet ongoing, in order to ensure safer conditions to the rail and road infrastructures. In this context arose the collaboration between Italian national DPC and the Institute of Methodologies for Environmental Analysis (IMAA) of the National Research Council (CNR). In the framework of the agreement between DPC and IMAA-CNR, two field surveys were carried out in the area, one in July 2011 and one in October 2012. The Electrical Resistivity Tomography (ERT) technique was adopted, in order to collect indirect information about the features of the landslide geometry. Data were acquired through a multi-electrode system using a Syscal R2 (Iris Instruments) device. The apparent resistivity data were inverted by the RES2DINV software (Loke, 2001) to obtain a subsurface image of the electrical resistivity pattern. All the ERT were placed perpendicularly to the landslide body and realized with a 5 m electrode spacing array that allowed to explore up 40 m in depth. During the first field survey, on 5th-6th of July 2011, 4 ERT were carried out in the upper- zone, whereas the 5th in the lower part, at about 530 m a.s.l. (Fig. 2). More than one year later, on 23rd-25th of October 2012, 11 ERT were realized at almost regular intervals of about 50-60 m. As explicitly required by the DPC, the attention was focused on the central part of the landslide, despite the drainage interventions, continues to move downward of some mm per day (Fig. 2). Geological setting. In the area Miocene sedimentary rocks crop out (Guadagno et al. , 2005), including: • layered limestone, calcarenite, marly limestone, marl and argillaceous marl pertaining to the Faeto Flysch Formation, Langhian to Tortonian in age (Crostella and Vezzani, 1964), • clay, argillaceous marl and fine sand pertaining to the Villamaina Unit, Messinian in age (D’Argenio et al. , 1975). Fig. 2 – Electrical resistivity tomography surveys carried out on the Montaguto landslide on July 2011 (A) and October 2012 (B). 98 GNGTS 2013 S essione 3.2