Italian guidelines for the risk classification, safety evaluation and monitoring of existing tunnels: An overview

The Italian transport network had a great expansion after World War II and a great number of tunnels were built. After 70 years, those tunnels are approaching their design lifetime. With more than 9000 tunnels extended for 2600 km of underground structures on the Italian national territory, the correct manage- ment of this asset is challenging, especially in the context of a complex road network. To provide an integrated method to monitor and plan the maintenance actions for the different stakeholders on a national scale, a Guideline for the risk classification, safety evaluation and monitoring of existing tunnels has been implemented by the Italian Superior Council of Public Works and is now mandatory for roadways tunnels in Italy.The guidelines are structured in 5 levels with progressively increasing levels of knowledge requirements and detail of the investigation, where level 0 is dedicated to a census of all the available infor- mation about the tunnel, level 1 is dedicated to the inspections that have to be carried out with the help a specifically designed defect catalogue. Then, accordingly to the data collected, in level 2 a classification to prioritize further investigations, standard maintenance procedures, or ad hoc designs is regulated through a series of logical operators to ensure that the same classification procedure is used for all the tunnels in the national territory. This last level is subdivided into 6 fields with regard to specific critical phenomena that may lead to a risk to the proper functioning of the tunnel. Then, levels 3 and 4 are respectively dedicated to preliminary and accurate safety evaluations, while the last level regulates the maintenance of tunnels of stra- tegic interest for the nation. In this paper, a detailed discussion of the structure of the guidelines and about their application is presented.