Quantitative risk assessment for viable infrastructures subjected to rockfall: analyses of social and economical consequences

In quantitative risk assessment, the accurate prediction of the possible consequences represents a challenging aspect. Public Administrations and private owners often face difficulties in defining risk management plans, priority of interventions, and in allocating resources for mitigation works. Predicting and assessing geohazards and their effects is thus becoming urgent to create safe and resilient infrastructures, settlements and working places. Depending on the element at risk, different consequences can be considered. For infrastructures, damage analyses can be related to different aspects: social, e.g. people involved, physical, e.g. damages on the structure, economic, e.g. connected to activity/traffic interruption, and environmental, e.g. related with flora and fauna preservation. Dealing with rockfall hazard, the present work investigates social and economic damages for viable infrastructures, e.g. high traffic roads or mountainous roads, often unique access route to remote areas. In previous works the Authors have developed an event-tree based risk assessment method to evaluate the social risk, expressed as the annual probability of having at least one victim on a road subjected to rockfall. In the present work the method is enhanced, addressing the aspects due to road closure and the economic damages. Depending on the type of infrastructure, the traffic demand and capacity, the location of the damaged part within the transport network, and its resilience, the economic risk can vary. In mountainous area the case in which two locations are connected by alternative routes all affected by rockfall hazard is possible. The closure of one of them causes a rerouting of the traffic. Beyond the economic damage, the alternative routes suffer for an increase of exposure to the hazard, hence an increase of the social risk. The method is fundamental for risk management as it provides a decisional basis for policy-makers and public Authorities.