Erosion de la couche supérieure des sédiments cohésifs : caractérisation et propriétés

Titre de la revue : Journal of Hydraulic Engineering Volume : 133 N° : 9 Pagination : 1087-1091 Date de publication : 01/09/2007

A recent paper (El Ganaoui et al. 2004) reported an experimental protocol used to analyze sediment properties. This protocol identified for both freshwater and marine sediments a surface layer with specific dynamic properties (critical erosion shear stresses in the range 0.025 - 0.05 N m-2) and a second layer with critical erosion shear stresses about ten times larger. The present work compares these former results with the work of Pilotti and Menduni (2001) who extended the applicability domain of the Shields diagram to very fine particles. The surface layer is shown to consist in fine and unconsolidated sediments that behave like non-cohesive material while the second layer is characterized as being cohesive. This is similar to the two-layer concept of the sediment interface already discussed in Thomsen and Gust (2000) but for aggregates. It is shown that the surface layer is mainly representative of recent deposits of suspended particles. This points out the existence of a fluffy layer of fine sized particles resting near the bed, with specific erosion characteristics, which has to be considered separately when studying sediment properties.