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Rôle du transport particulaire lié à la déstructuration de gypses poreux dans le développement de cavités de dissolution

Abstract : The north-eastern suburbs of Paris are most prone to sinkhole development due to the natural dissolution of gypsum rocks in contact with groundwater flow. This dissolution induces a loss of solid material creating underground voids that can lead to surface disorders. A release of grains and their transport by the flow could very strongly increase the growth of the cavity compared to considering only the dissolution. Gypsum samples with different porosity and content of insoluble impurities were used to quantify experimentally the respective role of dissolution and particle transport processes in the formation of cavities in gypsum horizons. Rotating disk experiments allow us to determine the kinetic rate model parameters of each sample by measuring the electrical conductivity of a solution up to saturation. The results were analyzed according to the initial solution, the temperature as well as the texture of the facies and the roughness developed during dissolution. As a result of this roughness, dissolution is dominated by diffusive transport in the boundary layer. The effective dissolution rate values are found between 2 and 12 mg/m²/s, depend on the insoluble content and their distribution, and therefore lower than the dissociation rate of the gypsum mineral. The lowest values refer to the matrix textured gypsum with insoluble content that serves as coating for the gypsum grains. The impact of erosion and particle transport related to gypsum dissolution was determined by controlled leaching tests involving a collection of the released grains. For each gypsum facies tested, the particular flux is found low composed mostly of insoluble grains. The distribution of insoluble at the interface is found to have a large influence on the dissolution.To extend these results to in situ conditions, the influence of the groundwater composition and the mineralogy of the insoluble particles was studied from geochemical simulations and validated with water analyses during and at the end of the rotating disk experiments. These findings were applied on two sites to evaluate an effective recession rate using the measured or estimated porosity and insoluble content of a natural gypsum and the groundwater saturation index obtained from its chemical analysis.
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Submitted on : Thursday, July 28, 2022 - 10:43:13 AM
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  • HAL Id : tel-03739757, version 1

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Imen Zaier. Rôle du transport particulaire lié à la déstructuration de gypses poreux dans le développement de cavités de dissolution. Ingénierie de l'environnement. Université Paris sciences et lettres, 2021. Français. ⟨NNT : 2021UPSLM064⟩. ⟨tel-03739757⟩

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