Study On Sediment Critical Erosion Stress On The Tidal Flat Along The Yellow River Delta

To conduct study on sediment critical erosion stress in the Yellow River Delta, study work is done sponsored by the project of National Nature Science Foundation Project"Study on Consolidated Sediment Re-suspension and Transportation in the Yellow River Estuary"(Project Number, 40876042).To obtain the surface sediment critical erosion stress of the tidal flat in the Yellow River Delta, in situ erosion experiments were conducted using a recirculate flume at eight tidal flat experiment stations along the seashore of the Yellow River Delta. Such conclusions are educed: (1)The sediment critical erosion stress in the study area varies between 0.088Pa and 0.196Pa with a variation coefficient of 0.22, and the heterogeneity of sediment erodibility is one possible cause of the formation of concaves on the tidal flat in Yellow River Delta; (2)Parallel tests show sediment physical-mechanical properties among stations also change with different extents, such as bulk density, water content, mean diameter, sand content, clay content, plasticity index, penetration resistance, shear strength and compression coefficient, which may be the direct influence factor on critical erosion stress; (3)Biological activities, especially the benthic cave animals, can decrease sediment penetration resistance and shear strength, and can also increase the seabed surface roughness, which both lower the critical erosion severely.In order to know the effect of sediment consolidation degree on critical erosion stress, study was carried out on the relationship between critical erosion stress and consolidation time. The datas shows that: (1)At the initial stage of sediment consolidation process, the critical erosion stress linearly increases with time; (2)At the later stage, critical erosion stress continues rising as penetration resistance and shear strength does, while bulk density and water content has come stable, which means the compactness is steady. It is considered that the continuous increase of critical erosion stress is strongly related with the enhancement of the cohesive force between the soil particles.To study the influence of wave loadings on sediment erodibility, simulated wave loadings were exerted to the surface sediment on the tidal flat and the development of sediment erodibility were monitored. It is found out that wave loadings can reduce the critical erosion stress. With wave loadings'continuous working, the critical erosion stress can be reduced to 0.023Pa from the original 0.086Pa, which is so weak that even the shear stress caused by simulated wave loadings can easily suspend the surface sediment.