A reliability-based approach for assessing the safety of rockfall protected slopes

Rockfall is a high-energy natural hazard that poses significant threats to inhabited areas and infrastructure in mountainous regions. Rockfall net fences, or barriers, are widely used passive structural systems designed to mitigate this hazard. These devices intercept and arrest falling rocks by dissipating energy through permanent deformation. Despite their widespread use, the design of these systems is not fully codified. European guidelines recommend ensuring that the factorized capacity exceeds the increased action for both energy and height capacities. However, this approach overlooks the failure probability of the system, which is crucial for assessing risk in engineered slopes. The Authors have developed a mathematical framework to compute the failure probability of rockfall mitigation systems based on reliability considerations. Unlike other approaches, their method accounts for all potential block volumes that may reach the mitigation measure, recognizing that smaller blocks are more frequent than larger ones. The time-integrated formulation offers two main advantages: it provides the design characteristics of the protection system for a specified failure probability, and it quantifies the failure probability for an existing net fence. The present paper incorporates the variability in the capacity of the barrier into the mathematical framework. Different probability distributions associated with the system's capacity to arrest blocks or intercept rockfall trajectories were assigned, critically discussing the sensitivity of the failure probability concerning the parameters of the distributions. Examples of applications demonstrate that the method can lead to more informed management of rockfall risk in hazardous areas.