Experimental Study On Critical Condition For Viscous Debris Flow Blocking River

Debris flow is a common natural disaster in mountain areas of china, it's a kind of solid and liquid two phase fluid containing mud, sand and stone. Debris flow has the characteristics of sudden eruption, rapid movement and short duration, and is turbulent and laminar flow.Debris flow carries a lot of sediments and stones. In the debris flow,the content of solid matter sometimes exceeds the amount of water, which often occurs suddenly and lasts for a short time. Debris flow is a common natural disaster in mountainous areas. The debris flow is extremely destructive, which destroys all the buildings,roads and bridges along the way, flooding farmland, forests and rivers, causing great damage to the national economy. Debris flow is known to contain a large number of solid matter (especially large size particles), when it enters the main river, debris flow changes the composition of the main river water and local boundary conditions, The topographic condition of the debris flow is changed, and its movement is affected by the resistance of water flow, The moving route of debris flow will change, and siltation will occur near the entrance, If the main river hydrodynamic conditions and debris flow is relatively weak, it is possible to block the main river. In the last ten years, due to frequent earthquakes and extreme weather in China, the secondary disasters caused by debris flow blocking the river has become an important field of geological hazard prevention and control.At present, there are three kinds of research methods for debris flow blocking the river. First, through the laboratory flume experiment to study the correlation factors,we can get the river blocking discriminant. The two is to analyze the existing river blocking events through statistics, and get the relevant statistical model. Three, the theoretical mechanical model is established by theoretical analysis. The current research methods have their own advantages and disadvantages. As a whole, the following problems exist:The discriminant factor is selected to consider incomplete or duplicate selection; Previous studies have not quantitatively analyzed the results of damming the river, the discriminant calculation results are mainly qualitative; related research on fluid properties of debris flow disaster in the utility of the lack of.In this paper, the factors that affect the damming of the debris flow are simplified by using the mass analysis, and the influencing factors are simplified into four dimensionless parameters: Volume factor V, single wide flow ratio R,yield stress factor?, inflow angle factor (p, control variables through the flume experiment,combined with field data, the conclusions are as follows:(1) The accumulation dam of debris flow with large yield stress is better to resist the main river's disturbance and shock resistance, which is beneficial to the blocking river. On the contrary, it is not conducive to blocking the river.(2) After the debris flow flows into the main river, the total amount of debris flow must reach a certain standard before blocking the main river. This amount is related to the depth and width at the confluence. Smaller river bed capacity and larger amount of debris flow are beneficial to the blocking river.(3) Debris flows with large single width can move longer distances in the width of the main river, and the formation of the accumulation dam will impede the movement of the main river flow, resulting in upstream backwater. The debris flow with small single width flow not only has limited movement distance in the width of the main river, but also is difficult to form a dam with enough scale and strength.(4) When the debris flows into the main river at an acute angle, the main river flow can easily erode and transport debris flow fluid, It is not conducive to blocking the river; When the debris flows into the main river at an obtuse angle, a large number of debris flow deposits at the confluence,it's difficult to handle and erode, this is conducive to the occurrence of damming the river.(5) Through simplified the influence factors into dimensionless parameters ? V,r,J, using flume experiment control variable to get off factor. The final formula was obtained: P=r0.9×V×r1.1J0.78, When P?0.93 , debris flow may cause full block;When 0.6 ?P < 0.93 , debris flow may occur most block;When the 0.32?P<0.6,the debris flow may cause partial blockage; P<0.32,debris flow caused by the possibility of blocking the river is lower.