Tunnelling-induced landslides. The Val di Sambro tunnel case study

Tunnel excavation in mountainous or sloping regions can sometimes reactivate or accelerate landslide phenomena with a potential important impact on the stability of such constructions. The problem of tunnelling-induced landslides, that represents an important issue for many areas of the world, is very complex to analyse and demanding to solve. In addition, there are very few well documented case histories in literature. The paper presents the case of the Val di Sambro twin tunnels excavated in a structurally complex formation, in a geomorphological setting characterised by landslides of various areal sizes, whose depth was not well known before tunnelling. After a description of the main technical features of the tunnels, the geological setting and the geomechanical site conditions, the paper illustrates and comments the most significant outcomes of the monitoring system in the Southern zone of the tunnels, one of the areas where the major deformative phenomena occurred. The Val di Sambro tunnels represent a unique case study for the large amount of monitoring data collected before and during the tunnel excavation through an integrated system, consisting of various measure methods (inclinometers, piezometers, underground and surface topographic measurements, SAR interferometric technique). The combined use of surface, subsurface, underground and satellite data allowed analysing the characteristics of the landslide movements before the tunnel excavation and in relation to the tunnel construction.