Th Preliminary Study On The Stress Of Flow With Hyper-Concentration On The Condition Of Stationary And It Effect On The Floog Of Weihe River

The middle and lower reaches of Weihe River is the political, economic and cultural center of Shanxi province. In recent years, small discharge but large flood disaster prevails due to the heavy siltation at the downstream channel of WeiHe River and to the characteristics of hyper-concentration sediment flow, which constrains the development of economy in this region. And as a part of Yellow River regulation, the study of the causes that lead the river channel be in shrinking has been carried out by many institutions while widely regards are given to the river as it is a typical type of hyper-concentration flow with exiguous sediment particlesThis thesis associated with the studying subject, the mechanics of channel shrinking and its influences on the situation of flood control at the downstream channel of Weihe River, investigates the main cause from which the flood transmitting time becomes longer than before and the channel deforms fiercely. The results suggest that it is the static shearing stress of a hyper-concentration flow, a character of the flow. This static shearing stress is the stress appearing when a hyper-concentration flow is in the rest state. Only few people made a systematic research in this field except for professor Cao Ruxuan who did a few researches on it when she studied the density current. Researches have been taken to the relationship between the stress of hyper-concentration sediment water and its time of resting by the combination of experiment and practice analysis in this thesis. The major contents and the studying results of this work are listed as follow.1.Through the analysis of observed data, the conclusion is drawn to be that a flood with hyper-concentration of sediment containing a certain amount of small particles induces integral depositing easily at riverbed and the sides of river channel, and such integral depositing is one of the major cause that help river shrinking.2.The causes of the flood transmitting time being longer are enlarging of Bingham yield stress, rivershrinking, river slop flatting, high crops at riverbed, and the static Bingham yield stress is one of the major affecters.3. Experiments had been made with depositing pipe and electronic balance to find how the rest shearing force (τ_静) varies when the time spent on the sample water resting is becoming longer and longer. Three kinds of silt size grading and eighteen groups of silt-laden suspending liquid were used in experiment with depositing pipe, and other twelve groups with electronic balance.4. The experiment results indicated that when the fine particle silts accounted for some a percentage, its flow pattern would change as a function of time, and the static shear forceτ_静, became bigger than the Bingham yield stressτ_ B That theτ_静increased with the time was also found, but the speed of this increase became close to zero when the time was longer enough.5. The Static stress is not only related to the time of resting but also correlated negatively with sediment diameter, and positively with sediment content.6. In the past, the judgment for water with hyper-concentration of sediment going on flowing is thatτ_ B less thanτ_ 0. Based on the experiments and analysis of field observations, the judgment has changed asτ_静less thanτ_ 0 rather thanτ_ B less thanτ_ 0.