Mining collapses currently occur in Lorraine (France) above abandoned iron mines (room and pillar system). The workings exposed in this paper relate firstly to the proposition of a hydro-mechanical behavior law according to conventional laboratory tests on iron ore. This law consists in a generalization of the Mohr-Coulomb model. This generalization takes account of the active physical phenomena during a short term loading by coupling the plasticity with the damage within a hydro-mechanical framework. Moreover, in order to describe the transition from hardening to softening behavior, a deviatoric yield function with two strain hardening rules is proposed. A long-term behavior law was also proposed according to creep tests on iron ore. It consists in a three-dimensional generalization of the Lemaitre law for materials with dilatancy. In order to take account of the mutual influence between plasticity and creep, both laws were coupled. The numerical simulation of hydro-mechanical and creep tests shows a good agreement with experimental curves.
Mining collapses currently occur in Lorraine (France) above old iron mines. Over the greater part of the iron deposit, recovery involved removing the roof supports and collapsing the residual pillars. However, beneath sensitive zones, where there were houses and surface infrastructures, partial recovery methods were used since the beginning of the century and until 1980; abandoned rooms and pillars. Thus, some of these safety pillars are abandoned since 100 years. In these areas of partial recovery, collapse phenomena have occurred several times, usually owing to the failure of abandoned pillars. At first glance, the pillars could be considered as continuous, with a few fracture on a large scale.
The end of these exploitations caused the closing of drainage pumps and then upraise of karst waters that percolated down the fractures caused by mining workings. So, an important research program was set up to solve the difficulties that arise with regard to the security on the surface structures and the regional planning. This program entitled GISOS (Research Group one the Impact and Safety of Underground Works) includes studies on rocks ageing (Grgic et al. 2001), the time-dependant behavior, the monitoring by acoustic sensors (Senfaute et al. 2000), geochemistry of mine waters, and the estimation and the establishment of a risks hierarchy. This paper focuses on the study of iron ore mechanical behavior. So, in order to explain these phenomena, the iron ore constituting abandoned pillars is characterized after performing laboratory tests. Then, a theological model to predicthe short and long-term behavior is proposed.