Quantitative assessment of the residual risk in a rockfall protected area

Abstract

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d'Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d'Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10 −4 to 9.1×10 −7 and the societal risk from 1.5×10 −2 of annual probability of loss of life to 1.2×10 −5 .

Integrating rockfall risk assessment and countermeasure design by 3D modelling techniques

“…The physical vulnerability of human life to rockfalls is very difficult to estimate since there is a lack of damage statistics, and none of the few published studies expressed it in the form of vulnerability curves Hungr et al, 1999;Corominas et al, 2005). For the present purposes, we assumed that the vulnerability of persons inside buildings (i.e.…”

“…Thus, rockfall protection through both structural and landplanning actions is an important issue for administrators and stakeholders in rockfall prone areas (Raetzo et al, 2002; Correspondence to: F. Agliardi (federico.agliardi@unimib.it) and Corominas et al, 2005;Jaboyedoff et al, 2005;Straub and Schubert, 2008;Fell et al, 2008). 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.…”

“…Moreover, rockfalls are rare and strongly spatially distributed processes, characterised by complex dynamics and interaction with structures. Thus, 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. Nevertheless, few researchers applied risk analysis to the design and evaluation of rockfall protection measures (Bunce et al, 1997;Hungr et al, 1999;Corominas et al, 2005;Straub and Schubert,1060 F. Agliardi et al: Integrating rockfall risk assessment and countermeasure design We integrated all the relevant stages of the rockfall protection process in a comprehensive approach which takes advantage of 3D mathematical modelling, providing useful insight and tools for the analysis of rockfall processes and related risks Crosta and Agliardi, 2003;Jaboyedoff et al, 2005;Frattini et al, 2008).…”

Analysis of Potential Rockfalls on a Highway at High Slopes in Cold-Arid Areas (Northwest Xinjiang, China)

“…Rockfall influence area zonation can help engineers to select effective mitigation measures against rockfall to avoid casualty and property losses [44][45][46]. Perret et al mentioned that according to the total kinetic energy, the rockfall influence area could be classified into the low-intensity zone, medium-intensity zone and high-intensity zone [47].…”

GIS-based predictive models for regional-scale landslide susceptibility assessment and risk mapping along road corridors

“…In the recent literature, quantitative risk assessment procedures, attempted to estimate the risk in terms of annual probability of loss of life of occupants of vehicles impacted by falling boulders, have been developed (Corominas et al 2005;Pantelidis 2011;Ferlisi et al 2012;Mignelli et al 2012;Stock et al 2012;Budetta et al 2016). The risk assessment in probabilistic terms requires the analysis of (1) the probability of occurrence of a rockfall event with a given magnitude, depending on the rockfall frequencymagnitude relationship and triggering event frequencies, (2) the probability that a boulder reaches the element at risk depending on the propagation process along the slope and mobility of element at risk, (3) vulnerability which depends on rockfall intensity and characteristics of exposed assets and (4) economic value of elements at risk, in terms of damaging of road and vehicles, interruption of traffic and loss of life (Corominas et al 2005;Agliardi et al 2009;Mavrouli & Corominas 2010;Ferlisi et al 2012;Wang et al 2014). Among the different types of landslides (Varnes 1984), rockfalls are generally characterized by small size, but by relatively high magnitude due to the high falling velocity of boulders and accordingly by greater impact and damaging potential on elements at risk, especially those mobiles (vehicles).…”