Numerical model for assessment of subsidence due to dissolution of salt, application to Nancy Basin (East of France)
Résumé
Medium and long term evolution of mine works in salt is difficult to assess because of the complexity of the involved mechanisms. The stability of an underground mine depends mainly on the mechanical stability of its structures: roof, wall and pillars. The evolution of this stability in time depends on the material mechanical behavior (creep, aging, etc.), but also its specific developments (dissolution of salt, damages, etc.), phenomena that are not independent but interact. The intrusion of unsaturated water or brine from "salty groundwater" at the interface between the covering layer and the salt layer is an important element in assessing the long-term stability of closed salt mines and, more generally, the long-term stability of the ground. Such phenomenon has been observed in the Nancy Basin (Lorraine region in the East of France) where brine percolates since several years through an access shaft in a salt mine. It is therefore important to specify the current operation of this groundwater system, characterized also by significant subsidence in this area bringing about growing societal concerns. In order to analyze the kinetics of dissolution of salt inducing the phenomenon of subsidence, a numerical model is implemented to simulate the circulation of water between the salt layer and the impervious layer and calculate the dissolution rates and mass fluxes. Then the evolution in space and time of the geometry of voids created at the interface salt / ground by dissolution and circulation of brine is assessed to estimate the movements induced at the surface. A reverse analysis is performed by comparison of results with subsidence measurements, to adjust the groundwater transport model parameters.
Domaines
Sciences de la Terre
Origine : Fichiers produits par l'(les) auteur(s)
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