The influence of expertise on rockfall failure probability assessment -- an original experimentation

• Published in: Natural hazards and earth system sciences 2016-01, Vol.2016 (1), p.1
• Main Authors: Delonca, A, Verdel, T, Gunzburger, Y
• Format: Article
• Language: English
• ISSN: 1561-8633; 1684-9981

To date, many rockfall failure probability assessment still consider qualitative observations into their analysis. Based on this statement, knowledge and expertise are supposed to be major parameters in the determination of the rockfall assessment. To test this hypothesis, an experiment has been carried out in order to evaluate the influence of the subjective assessment. Three populations have been selected, having different levels of expertise: (1) students in geosciences, (2) researchers in geosciences and (3) confirmed experts. These three populations have evaluated the rockfall failure probability level 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, an "a-priori" assessment of the rockfall failure probability has been requested of each population, without using any method. The LPC method has been used knowing that it is the most widely used method in France for official hazard mapping. It combines two main indicators: the susceptibility to instability and the expected magnitude. Reversely, the SMR method has been used as an ad hoc quantitative method to investigate the effect of the level of quantification within the method. These procedure has been 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 probability assessment, whatever the sector. Furthermore, there is a non-significant influence of the level of expertise of the population for two of the three sectors. 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. On the other hand, the results are more similar to the LPC qualitative method, even in the case of sector 1.