The quantification of risk in terms of loss of lives represents the essential parameter to manage rockfall risk in urbanized areas. Rockfall barriers are among the most adopted structural mitigation measures. Despite their wide use, the partial safety factors design approach is not able to guarantee a specific failure probability and, consequently, to assess the precise risk reduction. To tackle all these issues, a quantitative risk assessment method for infrastructures and a time-integrated reliability design approach for rockfall barriers developed by the Authors are combined in a unique framework to quantify risk reduction. The former computes the risk as annual probability of having at least one fatality; the latter allows defining an annual failure probability for a given product in a given site. Merging these methods, the evaluation of risk reduction in case of barrier installation or the definition of the required performances, are defined. An example of application is provided.
Among natural hazard, rockfall represents one of the most dangerous phenomena, due to its unpredictability and high kinetic energy involved. Rockfall can affect public infrastructures and villages in mountain environment, as well as workers in particular contexts, e.g. open pit mines (Scavia et al. 2020). As a consequence, a quantification of the risk has become an urgent issue for public administrations and road infrastructure management bodies, to properly manage the risk, predisposing effective mitigation plans and prioritizing the interventions. Generally, the quantification of the risk is required in terms of annual probability of fatalities (Mignelli et al. 2012).
To achieve such goal, an accurate hazard analysis represents the starting point. Once the possible initiating events are identified and characterized in terms of magnitudes and associated return period, i.e. detachment probability, one or more initial realistic scenarios have to be defined, from which propagation analyses have to be performed (Moos et al. 2022). Rockfalls can indeed differ in both released and arriving block volumes, according to the occurrence of fragmentation processes.
Once defined possible released scenarios, propagation analyses have to be performed and the hazard computed (Crosta et al. 2015, Farvacque et al., 2021). Finally, selected the element at risk, the consequences, i.e. the damages, have to be quantified for each scenario.
