Abstract
Within inshore or fluvial environments, submerged fine matter mud banks are characterized by a high water content, a great spatial variability, and a strong deformability. The study of their instabilities induced by the variation of hydraulic stress requires a coupled modeling of sliding, erosion, and deposition mechanisms. In order to predict the impact of dam reservoir emptying on the stability of immersed upstream slopes, the method of approach to the problem proposed here combines theoretical developments, numerical modeling, site observations, and measurements. First, the theoretically achieved sliding criterion is compared with unstable mud height measurements. For more accuracy in the representation of the natural events, the sliding criterion is then integrated within a numerical code which couples the computation of hydrodynamic conditions, the erosion, and deposition of mud and the banks sliding. Finally, the results of the combination of all these mechanisms are compared with the variations in the bathymetric profiles obtained on the experimental site.
Highlights
The impact of the water/soil interaction is significant on inshore and fluvial environments. Both environments are characterized by the presence of high water content fine soils and a strong deformability. These complex fine soils with great spatial variability are subjected to changing hydraulic stresses, which can be periodicdue to swell and tidesor exceptionaldue to floods, seisms or dam reservoir emptying
Dam erection slows down sediment transport and generates fine soil deposits within the reservoirs, which form submerged mud banks
The flat sliding criterion proposed here takes the specific features of high water content soils and is based on the theoretical formulation of the safety factor when the massif is submerged, partly and fully emergent
Summary
The impact of the water/soil interaction is significant on inshore and fluvial environments. Dam erection slows down sediment transport and generates fine soil deposits within the reservoirs, which form submerged mud banks. Using the observations collected on a experimental site, a flat sliding criterion for a rectangular soil sliceAlexis et al 2001͒ has been first developed This criterion suits simplified cases where both the shearplane and the water/sediment interface are parallel. Justification of assumption 1͑1͒: the profiles of total stress and undrained shear strength obtained by different researchersMekerta 1995; Alexis et al 2001͒ for this type of soil allow us to suppose the sediment massif to be homogeneous. The diffusion operator induces the conservation of mud volume Such a description implies that at each time step, under variable external conditions, the cross section tends to come back to the stability of all the segments and that no inertial effect exists in the movementslow deformation. Four configurations are possible: 1. Both segmentsi − 1 , iandi , i + 1͔ are stable: line i is defined by: ͑ 0 1 0 ͒, point i does not move
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