La perturbation chimico-minéralogique (Hydratation, état d'oxydation, eau interstitielle) de la zone perturbée excavée et ses relations avec la perturbation texturale et mécanique : application aux argilites des galeries de Bure

Abstract : Dehydration, oxidation, and fracturing are the three main and coupled processes underwent by Callovian-Oxfordian argillite cut by the galleries of the Laboratoire Souterrain of Meuse / Haute-Marne of Andra during the excavation. Several boreholes drilled at different times after the opening of the gallery were used to study the evolution of disturbances with time up to 18 months. Profiles of water content and isotopic analysis show dehydration at the surface of the walls of about 50%. The area of dehydration is rapidly sub-stationary because it results from a balance between the suction by the pore water and the evaporation imposed by the partial pressure of water in the air of the gallery. The disturbed area mainly affects the first 70 cm, and not exceeds 1 m 50. The oxidation of pyrite causes the formation of acid sulphate fluids which dissolve the surrounding minerals in the solution, release Ca2+, K+ and Na+ in the pore water then during the dehydration of argillite, the evaporation of the pore water leads to the precipitation of sulphate minerals mainly. The degradation of organic matter in the galleries shows a limited deterioration due to a very moderate oxidation or the slow degradation is not detectable at short times. Several experiments of equilibration between more or less oxidized samples and water were used to evaluate the impact of the presence of new-formed mineral phases (sulphates) on the chemical composition of the rehydration water. This experimental approach has been compared to results of geochemical modelling. The results obtained allow us to define geometrical, mineralogical and physico-chemical properties of the disturbed zone which could evolve thereafter during rehydration and temperature rise in storage condition.
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Olivier Belcourt. La perturbation chimico-minéralogique (Hydratation, état d'oxydation, eau interstitielle) de la zone perturbée excavée et ses relations avec la perturbation texturale et mécanique : application aux argilites des galeries de Bure. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 2009. Français. ⟨NNT : 2009NAN10140⟩. ⟨tel-01748565⟩

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