Author(s): Didier Marot; Alain Alexis; Jean-Pierre Bouchard
Keywords: Ultra-weak cohesive soils; Bank; Sliding; Erosion; Deposition; Dam reservoir
Abstract: In fluvial or littoral environment, submerged ultra-weak cohesive soils are characterized by a very high water content, a great spatial variability and great strains. The study of their instabilities induced by the variation of hydraulic stress requires the modelisation of coupled phenomenon: sliding, erosion and deposition. So for anticipating the impact of a reservoir emptying on the stability of submerged mud banks situated upstream from the dam, we propose a model of these coupled phenomenon. The scientific approach associates: theoretical and numerical modelisations and characterizations of sediments on the selected site. The theoretical study by the slice method allows to propose a flat sliding criteria. This criteria is validated by confrontation of height calculated with the changes of the thickness of sediment layer during partial emptying. In order to deal with the natural instability, we integrate this sliding criteria in a numerical code of erosion-deposition. In this code, hydraulic evolution and the calculation of hydrodynamic transportation of sediments are processed separately. The main originality of the numerical code comes from the calculation of the different modes of transportation: erosion, deposition and sliding. The results of the coupling of these three mechanisms are then confronted with variations of bathymetric profiles carried out on the reservoir.