Modelling of the drying and flooding of underground iron mines in Lorraine (France)

Mining collapses currently occur in Lorraine (France) above abandoned room-and-pillar iron mines during the transient stage of mine flooding. The mining rocks are exposed in situ to various hydrous conditions: full saturation–partial saturation (ventilation)–full saturation. In order to explain the mechanisms involved in mining collapses, we have performed one- and two-dimensional numerical simulations based on a poroplastic model and within the framework of partially saturated and continuous porous media. These numerical simulations model the hydrous cycle imposed to the rocks in these underground deep mines. It results from this hydromechanical modelling that the final stage of resaturation induces transient tensile stresses that lead to failures at the roof and at the floor of the galleries. These instabilities appear during the transient stage of resaturation only if the variation of the equivalent interstitial pressure π is important. The studied key points are the complex geometry of the model (rectangular rooms and dissymmetry of the upper and lower boundaries conditions) and the kinetics of the fluids diffusion processes that makes the reversibility very long and induces an important hysteresis in the hydromechanical cycle. The convergence measurements in an in situ experimental site, in which the flooding of the mine has been simulated, are well modelled.