Erosion threshold of saturated natural cohesive sediments: modeling and experiments

Titre de la revue : Water Resources Research Volume : 44 N° : 11 w11434 Pagination : 18p Date de publication : 29/11/2008

Predicting the erosion resistance of saturated natural sediments requires taking into account cohesion, which results from interactions between clay particles. The current paper describes a combined experimental and theoretical examination of the threshold conditions for a mixture of clays and sands. Erosion threshold measured values are larger than those predicted from non-cohesive models. Beyond the usual dependence on grain size, a significant correlation between erosion threshold and porosity measurements is confirmed for heterogenous mixtures of grains with particle Reynolds number lower than 5, for pH values in the range 6–8 and under freshwater conditions. A model of the erosion criterion is proposed. First, a cohesion force between two spherical particles is introduced into the usual erosion criterion. This reveals a specific function of the cohesion force, called cohesion function. The force we consider is the long range van der Waals interaction. Then, multiple interactions between one particle and those surrounding it are counted and modeled on the basis of both the coordination number and the porosity. Finally, the overall erosion threshold for the sediment bed is inferred from the average of the multiple interactions over the grain size distribution. The model highlights that cohesion comes from clay particles (about 2.10−6m) and can affect the entire grain size range (from clays to sands) by means of coordination. The model relevance is assessed by comparison with experimental thresholds obtained from resuspension campaigns. The results show that the proposed cohesion model offers good agreement with experimental data.