Research On Basic Characteristics Of Cohesive Sediment In Estuary

The muddy estuary and coasts which are composed of cohesive sediment spread over the world and also take on widespread distribution in China, the cohesive sediment possess flocculation which is not presented by non-cohesive sediment, the complexity of cohesive sediment movement is due to the flocculation of fine particles in estuarine and coastal environment .In view of the basic characteristics of cohesive sediment, three aspects of research are made in the paper:In the first part, a laboratory study is presented on the setting velocity measurements of natural muds. Natural mud dredged from Haihe River is tested in the laboratory using settling measurement instrument at different slit concentration and salinity .The test results show:①the settling velocity in still water have close relation with the slit concentration; The settling velocity can reach a peak value when the slit concentration is 40 kg/m3.②the salinity is also one of the influencing factors, the general settling velocity law is that the settling velocity increases along with the increasement of salinity at low salinity due to the enhancing flocculation; settling velocity decrease along with the incressement of salinity at relative high salinity due to tiny dispersion of flocs.In the second part, a laboratory study is present on rheological measurement of natural moods from Haihe River and Hangman Sea using NXS-11A viscometer. Flow curves of moods under different shear rates are recorded and experimental data are analyzed using the Bingham and power-law model. The research show:①The Bingham model fails to describe the structural change at low shear rates while the power-law model gives better description of the shear-thinning behavior at low shear rateγ< 20s?1.②We also can point out that mud samples with high density or high sediment content display some viscoelastic properties atγ< 20s?1. The complicated rheological behavior atγ< 20s?1 indicates that mud can undergo dramatic structural changes in response to shearing.In the third part, in order to make good understand of complicated viscoelastic characteristics at low shear rates the dynamic rheological measurement is made using CVO rheometer which is produced by Bohlin. And the strain amplitude is controlled between 0.005 and 0.1. The test results show that the complex number shearing module G * decrease along with the increasement of strain amplitude while the viscosity module G′′increase to the peak value then decrease .And elastic moduleG′decrease along with the increasement of strain amplitude.