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The aging of gypsum in underground mines |
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| Authors: | Christophe Auvray Franoise Homand Claudia Sorgi |
| Institution: | a Laboratoire Environnement Géomécanique et Ouvrages, Ecole Nationale Supérieure de Géologie, Institut National Polytechnique de Lorraine. Rue du Doyen Marcel Roubault, BP 40, 54501 Vandoeuvre-lès-Nancy Cedex, France b Institut National de l'Environnement Industriel et des Risques. Direction des Risques du Sol et du Sous-sol, Parc Technologique Alata, BP 2, 60550 Verneuil-en-Halatte, France |
| Abstract: | The aging properties of gypsum extracted from two underground mines in France (Livry–Gargan and Grozon) have been highlighted by means of observation performed using scanning electron microscopy on samples taken along horizontal boreholes drilled through to the middle of several pillars. The aging process is exhibited by the presence of traces of dissolution (edges of the dissolved crystals, corroded crystalline surfaces, important intra- and intercrystalline space). These dissolution figures decrease in number and in intensity from the wall heading towards the middle of the pillar. The “older” pillars display a greater number of dissolution traces than the “more recent” pillars. Then, the role of the aging has been assessed by determining various physical and mechanical parameters on cylindrical samples of 38 mm in diameter and 76 mm in height, machined from the set of drilled boreholes. The following parameters have been quantified: density, grains density, total porosity, porosity accessible to water, intrinsic permeability to nitrogen, velocity of ultrasonic compression and shear waves, dynamic Young's modulus, dynamic Poisson's ratio, uniaxial compressive strength and static Young's modulus. Significant variations in parameter values between the wall and the middle of the pillar were recorded and recognized as being strongly correlated with the intensity of dissolution traces, and hence with gypsum aging. |
| Keywords: | Gypsum Underground mine Aging Physical and mechanical parameters |
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