Structural Health Monitoring of a Road Tunnel Intersecting a Large and Active Landslide
Dealing with engineering structures that are not easily replaceable requires frequent assessment of the damage state of the construction in order to estimate its durability and reliability. The procedures that allow damage to be detected and identified are broadly defined as Structural Health Monitoring (SHM). In this work, a SHM network has been deployed in a road tunnel that intersects a massive landslide, whose movements are causing the formation of cracks along the tunnel lining. The
... lining. The monitoring system measures in real time the displacements across major cracks and the rotation of the tunnel segments; data are gathered and made easily accessible through a web-based platform. The mechanisms by which the tunnel deforms under the landslide-induced stress have been defined through the analysis of three years of monitoring data. The factors triggering an increase in deformation rates and causing damage to the structure have also been investigated. This evidence will support the design of mitigation works to extend the life-span of the tunnel. This paper describes a real-time monitoring network deployed in 2014 in a road tunnel in Italy where cracks are developing at its intersection with the slip surface of a large landslide. Study Area In the northeastern Italian Alps, in the upper valley of the Tagliamento River, a narrow gorge called Passo della Morte (46 • 23 49.7" N, 12 • 42 45.7" E) is affected by several slope instabilities. The main valley road, a national road following the Italian classification, has to cross the area since no other route is possible due to the constricted geomorphological setting. In Passo della Morte, four landslides have been investigated through monitoring and modelling for more than a decade since their movements are interfering with the road network [13, 14] . Also the damming of the Tagliamento River due to a secondary landslide may occur  . The largest landslide is a 24 × 10 6 m 3 block slide  that accounts for a large portion of Mount Tinisa's (2120 m a.s.l.) southern slope, covering an area of about 400,000 m 2 . The Landslide The block slide develops between 970 m and 640 m a.s.l.; on the eastern side, its boundary coincides with a small stream called Rio Verde (Figure 1 ). The dynamic of the landslide is determined by the presence of rigid dolomitic rock masses over more plastic clay-rich units and it is closely controlled by the structural setting of the area. Likely, in its first stages of evolution, the landslide moved in an eastern direction as a sackung and then subsequently evolved towards the south, heading to the valley bottom. The scarp of the first movement phase coincides with the SE-NW fault connected with the Alpine overthrusts of the area.