Using expert-opinions, retro-analyzes and experience feedback to risk-analysis and risk-hierarchization: application to the Lorraine ferriferous basin (France)

The dramatic events noted on the Lorraine iron-ore basin at Auboué and Moutiers in October 1996 and May 1997 recall that “La Nature a horreur du vide”. During the exploitation period of the iron ore, the Operator had undertaken protection procedures by using the “rooms and pillars method”. However, in many cases this method that consists in leaving a network of pillars to support the weight of the overlying grounds, assured only a short-term stability. Thus, the extraction of the ore has certainly an impact on the surface that can appear in various phenomenological forms: progressive such as subsidence, or abrupt such as collapse. These surface observations can cause some irreversible damages to people and constructions. Prevention of risk and protection and information of people lies to the Government when the Operator is defaulting. In this context, the analysis and the hierarchization of the risk are strongly dependent on the management of the complexity due to: the incomplete nature of information available (plans and archives); the state of knowledge on the rupture mechanisms of the mining work and on vulnerability of constructions; and the importance of strategic and space-time aspects. In this paper, we propose a method for risk-analysis and risk-hierarchization, using: the information collected on the various incidents and accidents (retro-analyzes); the individual and collective knowledge of the implied actors (expertise) and the experience feedbacks.