Evaluation of the impact of a cavity upon an earth dike (analytical and numerical approaches): Application to the Val d'Orléans area (France)

Abstract : The objective of this thesis is to study the interaction mechanisms between a cavity resulting from a karst collapse and a fluvial dike. The question that arises here is to evaluate the potential role of cavities beneath the dikes and their impact on the dike stability in normal and extreme flood conditions. Therefore, the first main point of the present work is to create a method to assess the influence of a dike on the stability of a cavity beneath it. Thereafter the second main point is to evaluate the stability of the dike slope when a cavity appears underneath without taking into account the collapse of the cavity. To achieve the objectives of the thesis, the dike effect on the cavity stability was investigated by studying the influence of the cavity location relatively to the dike and the interaction mechanisms, in the way to prioritize the geometric and geotechnical parameters for a better evaluation of the risk of dike failure. Numerical and analytical approaches were used. An application is described based on the in situ observations and data for the Val d’Orléans area (France). This area is protected against the Loire’s floods by 52 km of earth dikes (levees), in this area, more than 600 karstic sinkholes from 0.5 to 20 m diameter have been identified. The first results of the analytical method show that the cavity instability can significantly increase when the cavity is located under the centre of the dike, and this can affect the stability of the dike when the cavity is sufficiently close to it. We also show that there is a significant effect of the cavity on the dike slope stability, especially in the saturation state (i.e. during extreme floods): cavity collapse can then contribute to dike collapse. A nonlinear numerical modeling (2D and 3D) was used to validate the analytical approach, and to highlight the influence of the different geometrical and geotechnical parameters of the dike and the cavity. The results of the numerical modeling confirmed those of the analytical method. As operational conclusion, the results of the analytical model can be used to help assessing hazard due to the dike collapse taking into account the likelihood of an existing cavity, its position and diameter, and the thickness of the alluvium layer, regarding the data from the Val d’Orléans area
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Rafid Alboresha. Evaluation of the impact of a cavity upon an earth dike (analytical and numerical approaches): Application to the Val d'Orléans area (France). Other. Université de Lorraine, 2016. English. ⟨NNT : 2016LORR0025⟩. ⟨tel-01752229⟩

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