Rheological Study Of Fine Sediment In Estuary

The estuary is the junction of land and ocean,which plays an important role for material exchange.With climate changing and human activity developing,estuarine and coastal system will be affected and pattern transformation occurred.The movement of sediment is the key process,which can affect the sustainable development of ecology and environment in the estuary,like intensive erosion and the shift of estuarine turbidity maximum zone.Rheological behavior of sediment is always related to the sediment motion.Therefore,the rheological study of sediment is better for us to understand the evolution on geomorphology of estuary.In this paper,grain size,water content,sediment concentration and phase composition had been discussed in the rheological study of fine sediment.By using rheometer to establish the relationship between physical properties and rheological behavior.Through this,the boundary curve of yield stress has been given and the flow pattern transition process corresponding to the vertical sediment distribution has been summarized.The results and findings provide essential scientific bases for study of erosion and deposition processes.The main conclusions obtained are as follows:1.The yield stress decreased with the increase of water content in power function.When the water content increases by 10%,the yield stress decreases by90%.With the increase of grain size,the yield stress first increases and then decreases,the turning area is 54?79 ?m.For kaolin sediment,given the same grain size,the yield stress decreases with the increase of water content in power function,and the degree of reduction gradually slows down.The slope of curves at different grain size is the same,but the intercept is different,which means,different grain size affects the absolute value of yield stress,but it does not affect the variation range of yield stress with water content.The threshold shear stress also has a negative correlation with water content.Given the same water content,the yield stress increases first and then decreases with the increase of grain size.2.The critical sediment concentration range is determined by the transition stage from Newton fluid to Bingham fluid with the increase of sediment concentration.Sediment concentration is the main factor on the rheological parameters of Newton fluid.In the non-Newtonian fluid stage,grain size is also needed to be considered.For kaolin sediment flow,when the grain size is less than 10 ?m,the sediment concentration in transition stage is 200?600 g/L.When the grain size is larger than 23?m,the sediment concentration in transition stage is 800?1200 g/L.In the Newton fluid stage,the viscosity decreases first and then increases with the increase of sediment concentration,and the minimum viscosity appears at 2?10 g/L.After the sediment concentration is over 10 g/L,the viscosity increases continuouslyIn the non-Newtonian fluid stage,the viscosity increased both with the increase of sediment concentration and the decrease of particle size.The yield stress also increases with the increase of sediment concentration,and the increase rate has an upward turning point,the increasing rate after the turning point is an order of magnitude larger than that before.The turning point indicates that the sediment flow enters the Bingham fluid stage.The bigger the grain size is,the more difficult the turning point appears,which means fine sediment is the key factor for Bingham behavior.3.The phase composition affects the rheological properties,but is controlled by the grain size.Given the same sediment concentration,kaolin's variation range of yield stress is wider than montmorillonite's.In the range of 15?54 ?m,the difference of sediment's rheological parameters caused by phase composition increases with the increase of particle size(the difference of shear stress reaches 96% at 54 ?m),but the difference of sediment flow's rheological parameters decreases with the increase of particle size.When the sediment concentration is less than 1200 g/L,the grain size of kaolin sediment flow in Bingham fluid stage is wider(less than 23 ?m),and that of montmorillonite is less than 15 ?m.