ABSTRACT
Rockfalls are frequent natural processes in mountain regions with the potential to produce damage. The Quantitative Risk Analysis (QRA) is an approach increasingly used to assess risk and evaluate the performance of mitigation measures. In case of fragmentation of the falling rock mass, the results of the QRA differ significantly because the number of new fragments generated increases the probability of impact while the kinetic energy of blocks and the runout is overestimated.
We have developed a procedure to account for the fragmentation, integrated in the RockGIS code (Matas et al. 2017), which is a rockfall propagation model. The procedure is applied at the Monasterio de Piedra, Spain as part of a QRA. The results show that for small-size rockfalls (<1 m3), fragmentation reduces risk to the visitors. For rockfall events >100 m3, fragmentation increases the overall risk due to the generation of multiple divergent trajectories and higher exposure of the elements at risk. For 10 m3-size rockfall events, the shorter runout and smaller kinetic energy compensates the effect of exposure. Furthermore, fragmentation makes feasible the implementation of protective measures.
