Study of the state of rock masses and linings within the Grand-Saint-Bernard Tunnel

Italy is today one of the world's leading countries in the field of tunnels and underground construction. The development of the Italian motorway network was concentrated in the 1960s and 1970s; by the end of the 1970s, approximately 70% of the tunnels in the current ASPI network were opened to traffic. After the tragic accidents that occurred in the Mont Blanc and Gotthard tunnels, the main European countries took a series of legislative actions focusing on the problem of tunnel safety. Thanks to the important work carried out by the Superior Council of Public Works, the Guidelines concerning the classification and risk management of tunnels were published on 23/08/2022. The tunnel surveillance system includes inspections, the execution of diagnostic investigations as well as the installation of continuous and permanent instrumental monitoring systems, which make it possible to achieve an adequate state of knowledge of the work. Following the acquisition of an adequate initial state of knowledge of the tunnels, the subsequent investigations and their periodicity must be foreseen within a specific surveillance plan that covers the maintenance and control activities following any restoration work carried out. The objective of this essay is the analysis of the tensional state of stress within the Gran San Bernardo rock mass and the Gran San Bernardo tunnel lining, including the analysis of the degradation phenomena affecting the tunnel lining. Measurement campaigns were carried out in order to create a mapping of the current state of the tunnel. In the light of the results obtained an assessment of the tunnel is then created . The Guidelines introduce a risk-based classification of the tunnels, by means of the class of attention, calculated with a general multilevel approach, from which derives the need for a safety assessment, whether limited to possible disruptions of a local nature or referring to the global behaviour of the work, which must be followed by the programming of the interventions and surveillance plans that are recognised as necessary.