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Modélisation mathématique de la spéléogenèse : une approche hybride à partir de réseaux de fractures discrets et de simulations hydrogéologiques

Abstract : The main objective of this thesis is to provide an approach ofspeleogenesis modeling which would allow to bring new knowledge on the genesis of the Mediterranean karstic systems.Several numerical modeling approaches of speleogenesis exist. They take intoaccount physical and chemical laws for flow and dissolution in fractured carbonate aquifers. Nevertheless, the initial void networks considered by these models gene-rally do not correspond to the fracturing reality.The proposed approach aims to simulate karstogenesis in an aquifer characterizedby a fracture network, while matching field reality as closely as possible andrespecting geometrical properties. Using statistical and geometrical parameters obtained by field observations and analogical experiments, it is possible to generate3-D realistic networks in terms of the relative position of joints that control theoverall network connectivity.Once the fracture networks are generated, they are adapted and incorporated in a3-D ground water flow and transport finite element model. The flow simulationsin the fracture networks allow the determination of the spatial distribution of porevelocities for the initial configuration. This distribution, added to the distributedage of the groundwater, is used to simulate the evolution of the aperture of the different elements by the use of a dedicated empirical equation.The calibration of the empirical growth law is carried out considering initial testson single fractures, taking previous works as reference, and leading sensitivity analyses. Results of simulations taking into account a limestone matrix surrounding the conduit, and considering various values of hydraulic conductivity of the matrixand various recharge conditions, are presented.Then, results obtained considering configurations designed with a single stratum containing fracture networks are presented, considering various fracture densities,matrix hydraulic conductivities and boundary conditions.
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Antoine Lafare. Modélisation mathématique de la spéléogenèse : une approche hybride à partir de réseaux de fractures discrets et de simulations hydrogéologiques. Sciences de la Terre. Université Montpellier II - Sciences et Techniques du Languedoc, 2011. Français. ⟨NNT : 2011MON20171⟩. ⟨tel-00698665⟩

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