Study Of Sediments' Response To The Hydrodynamic Action On The Tidal Flat Of Yellow River Mouth

The dissertation is sponsored by the project of National Nature Science Foundation Project Formation and Failure of Hard Crust on the Subaqueous Delta of Yellow River(Contract No: 141720888), and its aim is to research the process of sediment' development under the effect of hydrodynamic action. In the past, scholars believed that the composition of sediment was decided by hydrodynamic action, while the effect of hydrodynamic action after the deposition was often ignored. In this dissertation, the variation of sediment's composition and microstructure is analyzed and explained from the angle of the different hydrodynamic action. There are five chapters in this dissertation. First, the situation overseas in the responding field is summarized, and the clew is put forward; Then the characteristics of typical tidal sediment is analyzed. In the third chapter, the variation of sediment due to different hydrodynamic action is discussed and the sediment's evolve is studied through the physical simulation in the fourth chapter. In the last, the conclusion and some problem are put forward. Around Yellow River Delta, we chose several lithosomic bodies formed in different time, like Dawang, Guangligang, Diaokou and Xintan. At the positions, test line and typical site were arranged, and disturbed and undisturbed samples were collected, and gained the character of silt on the surface and hard crust, besides this, the variation on the depth and space of laminate soil was also got. Diaokou was chosen to carry out more work, since the silt on the surface develop better and its hydrodynamic difference is more typical than other places. In Diaokou, test lines were arranged on both strong and weak sides, disturbed and undisturbed samples were collected in 1999 and 2002 respectively, the depth of the silt and the strength of the underlying sediments were tested along the lines. From the above work, the sediment's characteristic of composition and microstructure along the horizontal and erect profiles were gained atboth strong and weak hydrodynamic action sides. After all those in-situ work, the physical simulation indoors was carried out to deepen the knowledge of sediment' variation, and the granular composition, microstructure, physical and strength indexes were got. On the basis of the above work, the following conclusions were drew:1.There is some possible connection between silt on the surface, subtle lamination and hard crust, which shows the effect of hydrodynamic action.2.Under the effect of strong hydrodynamic action, the grain fractal dimension and the content of fragment mineral fall along the test line; while on the side of weak hydrodynamic action, the law is contrary. At the depth profile, grain fractal dimension appears dispersedly at the strong side, on the contrary, it is increscent at the weak side; The content of subtle objection and the existing mode change regularly, while at the opposite side, this law is not clear. The variation of mineral is not remarkable at both sides.3.The variation law does not change with the time of hydrodynamic action. But its duration can lead to the uniformity of grains.4.Physical simulation shows that the grain will move and swivel under the effect of hydrodynamic action, and this will help the grain arrange along some direction. The consolidation and drain will be accelerated due to the hydrodynamic action, and these process can make the sediment tighter and stronger; in addition, the sediment's strength rises with the strength and duration of hydrodynamic action.In this dissertation, two new points are got: There is some possible connection between silt on the surface, subtle lamination and hard crust; The variation law does not change with the time of hydrodynamic action. But its duration can lead to the uniformity of grains.