Comparing rockfall hazard and risk assessment procedures along roads for different planning purposes

Abstract

Hazard and risk assessment procedures of different types of rockfall were analyzed to compare their outcomes when they are applied to the same case study. Although numerous methodologies are available in literature, rockfall hazard and risk analyses are often limited to standard estimations, affected by a margin of uncertainty, especially when relevant engineering projects are about to be realized. Based on the design purpose, different types of approaches can be chosen among the qualitative and quantitative ones available in literature, which allow different levels of analysis. One of the main criticisms related to rockfall events is the risk affecting linear structures, such as road or railways, due both to their strategic relevance for trade and communications and to the great entity of the exposed value (traffic units) traveling along them. In this perspective, a comparison between the qualitative method known as Evolving Rockfall Hazard Assessment (EHRA), the semi-quantitative modified Rockfall Hazard Rating System (RHRS) and the quantitative Rockfall Risk Management (RoMa) approach is herein commented according to a practical application to a case study. It is the case of the rockfall threat along slopes crossed by a strategic road connecting two of the most known spots of eastern Sicily (Italy), at the Taormina tourist complex. Data were retrieved from both recent literature and technical surveys on field. Achieved results highlight how the approaches are affected by a different level of detail and uncertainty, arising also by some necessary assumption that must be taken into account, especially when mitigation measures or territory planning have to be designed. Achieved results can be also taken into account for similar studies worldwide, in order to choose the most suitable procedure based on the design purpose. This is indeed crucial in the perspective of the optimization of time and economic resources in the territorial planning practice.