Abstract
Abstract. Rockfall risk analysis for mitigation action design requires evaluating the probability of rockfall events, the spatial probability and intensity of impacts on structures, their vulnerability, and the related expected costs for different scenarios. These tasks were integrated in a quantitative risk assessment procedure supported by 3D rockfall numerical modelling performed by the original code HY-STONE. The case study of Fiumelatte (Varenna, Italy), where a large rockfall in November 2004 resulted in 2 casualties, destruction of several buildings and damage to transportation corridors, is discussed. The numerical model was calibrated by a back analysis of the 2004 event, and then run for the whole area at risk by considering scenarios without protection (S0), with a provisional embankment (S1), and with a series of long-term protection embankments (S2). Computed impact energy and observed damage for each building impacted in 2004 were combined to establish an empirical vulnerability function, according to which the expected degree of loss for each element at risk was computed. Finally, costs and benefits associated to different protection scenarios were estimated, in order to assess both the technical performance and the cost efficiency of different mitigation options.
Highlights
Rockfalls are widespread phenomena threatening human beings and causing significant damages to structures
A Quantitative Risk Analysis (QRA; Corominas et al, 2005; Fell et al, 2005) for these processes should be based on sound modelling of rockfall processes
We showed that integrating advanced process-based modelling techniques in a physically sound quantitative risk assessment framework can provide tools to overcome some of these difficulties, even when considering long runout landslides with a complex dynamics as rockfalls (Agliardi and Crosta, 2003; Crosta and Agliardi, 2004)
Summary
Rockfalls are widespread phenomena threatening human beings and causing significant damages to structures. Rockfall protection includes different tasks, namely: rockfall risk assessment for land planning and prioritization of actions; identification of mitigation options able to achieve a specified risk reduction; and evaluation of their cost efficiency to optimise budget and design. Accomplishing these tasks involves evaluating: (1) rockfall hazard over the affected area; (2) the distribution and intensity of impacts on exposed structures; (3) the vulnerability of impacted structures; (4) the expected cost of specific risk scenarios; and (5) the efficiency of mitigation options. Most rockfall protection studies have been aimed to susceptibility or hazard assessment (Pierson et al, 1990; Cancelli and Crosta, 1993; Mazzoccola and Sciesa, 2000; Crosta and Agliardi, 2003; Budetta, 2004; Guzzetti et al, 2004; Jaboyedoff et al, 2005; Frattini et al, 2008), while the design of structural countermeasures (e.g. barriers, embankments, rock sheds) is usually based on empirical criteria (Ritchie, 1963; Fookes and Sweeney, 1976; Nichol and Watters, 1983) or numerical modelling results (Spang, 1987; Barret and Pfeiffer, 1989; Agliardi and Crosta, 2003)
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