Research The Sediment Incipient Motion And Flocculation Based On Rheological Characteristics

In this paper,the rheology method has been used to study the sediment incipient motion and flocculation.The Rheometer MCR302,were used to study the relationship between sediment physical properties and rheological parameters.Samples were mainly collected from the Yangtze Estuary and the Chongming Island.With the relationship between rheological parameters and sediment incipient motion,the relationship between sediment physical properties and threshold shear stress was obtained.Combined the rheological experiment with scanning electron microscope photographs,the structure of suspended sediment under different flocculation conditions were analyzed.Draw the following conclusions:(1)Sediment in low salinity conditions,salinity has a great influence on the viscosity of sediment.The viscosity change under the combined effects of water content and salinity is complex and can be discussed in two stages.Under low water content and the salinity is lower than 0.5‰,the viscosity increase with salinity.And when the salinity is higher than 0.5‰,the viscosity of the sediment decreases with the increase of the salinity s.Clay content affects the rheological characteristics of cohesive sediments.As the clay content increases,the viscosity value increases and the yield stress increases.When the water content is lower than 37%,there is much influence of the water content on the initial structure of viscous sediment.The initial structure tends to be more unstable with high water content the.The moisture content is the main factor affecting the rheological characteristics of sediment.When the water content is higher than 37%,the threshold shear stress is low.The higher water content is,the more closely the viscous sediment is in a flowing state.(2)The results of amplitude sweep show that the sediment viscosity and structural strength both increase as the increase of salinity.The increase of clay content will cause the sediment viscosity and fluidity to increase and structural strength enhance.The increase of water content leads to the viscoelasticity and structural strength decrease,and fluidity enhance.The effect of salinity on the sediment yield stress is small.As the salinity increases,the sediment yield stress increases first and then decreases,the maximum of yield stress occurs at a salinity of 0.5‰,and the range is within ±4%.With the change of clay content,the yield stress shows a bimodal trend.The water content has much influence on the yield stress.The yield stress shows a trend of increasing first and then decreasing with the increase of water content.It fits to an exponential distribution.The yield stress increases with the increase of water content when the water content is lower than 28%.The yield stress decreases with the water content increases,when the water content is greater than 28%,t.When the water content is greater than 37%,the yield stress deviates from the exponential distribution.The threshold shear stress shows a tendency of increasing first and then decreasing with the increase of water content.The critical value of water content is 28%.Based on the research of the correlation between sediment physical properties and yield stress,a formula between the water content and the threshold shear stress has been proposed.(3)The presence of organic matter will affect the cation's promoting effect on flocculation.Inorganic flocculation structure has higher shear strength than organic flocculation structure,and strong thixotropic recovery.The presence of cation can promote the recovery of organic flocculation structure.The flocculation will affect the incipient motion of sediment particles.The larger the size of the flocculation structure is,the more difficult for the sediment particles to incipient motion.The sediment particles are more difficult to incipient motion under the effect of organic flocculation than the inorganic flocculation.The organic flocculation structure is larger than the inorganic flocculation structure.Cationic species have an impact on flocculation,and lower cations have a stronger effect on flocculation than high cations.The effect of saltwater on flocculation is stronger than that of ferric chloride in the inorganic flocculation,and the shear strength of the flocculated structure is higher,the shear strength is increased by 34.4%.The shear strength of the sample added with ferric chloride solution was higher than that of the sample added with water,with an increase of 14.6%.During the shearing process,the large flocculation structure is destroyed,gradually forms a dispersed structure,the shear strength is reduced,and the dynamic equilibrium is reached under long-term stable shear failure,and a new flocculation structure formed again after 45 min.