Abstract
Abstract. To date, many rockfall hazard assessment methods still consider qualitative observations within their analysis. Based on this statement, knowledge and expertise are supposed to be major parameters of rockfall assessment. To test this hypothesis, an experiment was carried out in order to evaluate the influence of knowledge and expertise on rockfall hazard assessment. Three populations were selected, having different levels of expertise: (1) students in geosciences, (2) researchers in geosciences and (3) confirmed experts. These three populations evaluated the rockfall hazard level on the same site, considering two different methods: the Laboratoire des Ponts et Chaussées (LPC) method and a method partly based on the "slope mass rating" (SMR) method. To complement the analysis, the completion of an "a priori" assessment of the rockfall hazard was requested of each population, without using any method. The LPC method is the most widely used method in France for official hazard mapping. It combines two main indicators: the predisposition to instability and the expected magnitude. Reversely, the SMR method was used as an ad hoc quantitative method to investigate the effect of quantification within a method. These procedures were applied on a test site divided into three different sectors. A statistical treatment of the results (descriptive statistical analysis, chi-square independent test and ANOVA) shows that there is a significant influence of the method used on the rockfall hazard assessment, whatever the sector. However, there is a non-significant influence of the level of expertise of the population the sectors 2 and 3. On sector 1, there is a significant influence of the level of expertise, explained by the importance of the temporal probability assessment in the rockfall hazard assessment process. The SMR-based method seems highly sensitive to the "site activity" indicator and exhibits an important dispersion in its results. However, the results are more similar with the LPC qualitative method, even in the case of sector 1.
Highlights
Rockfall instabilities are a major hazard for people, human activities and infrastructure (Bell and Glade, 2004; Moreiras, 2006)
The methodology proposed by the Laboratoire des Ponts et Chaussées (LPC) method is somehow classical and follows the following steps as previously described: 1. a literature review, which avoids repeating studies or investigations already done; 2. an historical review, which makes an initial zoning of hazard levels, taking into account past events; 3. a geomorphological analysis, during which the level of the rockfall hazard is assessed
The novel experiment developed in this paper had the goal of statistically evaluating the influence of the level of expertise and the choice of the method used for the rockfall hazard assessment
Summary
Rockfall instabilities are a major hazard for people, human activities and infrastructure (Bell and Glade, 2004; Moreiras, 2006). The PPR (Plans de Prevention des Risques Naturels Previsibles) in France (Besson et al, 1999) and the cartes de dangers in Switzerland (Leroi et al, 2005) evaluate the hazard level in affected zones, according to a predefined set of hazard classes. Based on this hazard maps, different areas are identified: areas where construction is restricted, areas where a monitoring system or a protection system is required for reducing the risk and areas where no restrictions apply for constructions (Fell et al, 2008). Because of the implications in the territory management, the rockfall assessment must be as accurate as possible (neither underestimated nor overestimated) and reliable
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