Geological and numerical models as a tool to manage landslide risk: the Passo della Morte case study (UD, Italy)

In the northern Italian Alps, along the Tagliamento River valley (46 degrees 23'49 '' N, 12 degrees 42'51 '' E), a large deep-seated landslide affects a road tunnel near "Passo della Morte", along National Road 52 "Carnica". Several secondary phenomena are developing on the unstable slope, as rock block slides and shallow debris slides. This work focuses on the creation of a geological and numerical model able to simulate the displacements of two adjacent and partly superimposed shallow landslides, which are damaging the east entrance of the tunnel. In fact, field surveys and long-term monitoring allowed the geometries and the kinematics of the landslide bodies to be defined with great detail. In this phase, a numerical model is needed in order to evaluate the effectiveness of possible structural mitigation works. The complexity of the landslides dynamics and the different rates of activity suggest to set up a 3D model rather than a 2D one, using the commercial software FLAC3D. A helicopter-borne Light Detection And Ranging (LiDAR) survey allowed to rely on a 1 m Digital Terrain Model (DTM) for surface topography, while several boreholes equipped with inclinometers supported the definition of a 3D sliding surface. However, the high resolution of the input data collides with the necessity of reduce computational time to an acceptable level, thus an interpolation of the spatial data was almost compulsory. Anyhow, the calibrated model of the "Passo della Morte" landslides, obtained with filtered data, is the starting point for the simulation of different types of possible countermeasure works designed to mitigate landslide risk.