Concepts and operational tools for multihazard risk analysis in road tunnels. The San Benedetto event, Italy

Let's define “multihazard”: a chain of sequential events intersection, each one conditioned by the previous. The present study affords an in-depth insight into road tunnel multihazard. The paper stems from interest in analyzing the conditions of occurrence and development of two important accident events: San Gotthard (Switzerland, 2001) and San Benedetto tunnel (Italy, 2016). The first originated from the improper human behavior of a driver who invaded the opposite lane colliding frontally with another vehicle. A fire developed involving the vehicles' fuel, cargo of goods, bituminous conglomerate of the pavement and collapse of the vault concrete with eleven victims and damage to the structure. The second which occurred during the seismic activity of 2016 in central Italy (Umbria), caused the break and relative 20-30 cm displacement of two sides of the tunnel pavement. The first part of the paper deals with the study of seismic hazard conditions around the San Benedetto tunnel and fragility of concrete lining and asphalt pavement. In the second part the deepening concerns the probability estimation of a potential intersection of a seismic event with forced swerve, collision, and fire. The seismic induced break plays the role of the human factor in the Gotthard multihazard accident. The overall length of TERN Italian tunnels is greater than the one of all other countries joint lengths and for this reason, Italy can be called the Country of Tunnels. The risk of fire in tunnels in Italy must be compliant with Alarp criteria of acceptability and tolerability according to a Legislative Decree of 2006 which in turn complies with the European Directive of 2004. The quantitative and interactive “Play Gu@larp” procedure is described, which allows and support in risk-based design, reducing risk under compliance conditions.