Study On Special Fluid Dynamic Characteristics Of Barrier Lake Disaster Chain

The barrier lake is a lake formed by the natural dike.The natural dike is formed by volcanic eruption,landslides,debris flow,glacial deposit and so on,which blocks the river valley horizontally and causes the upstream section to backwater under certain geological and geomorphic conditions.When the mountain disaster chain contains the link of the barrier lake chain and the barrier lake and other kinds of disasters are linked and acted on each other,in which the evolution of the disaster has the characteristics of spatial amplification and time amplification,the disaster process of the mountain disaster chain with the chain structure is the barrier lake disaster chain.There are many barrier lakes in the eastern and southern margin of the Qinghai-Tibet Plateau.At the same time,various kinds of mountain disasters such as rock collapses,landslides and debris flows occur frequently,which is easy to form the barrier lake disaster chain and seriously affects the safety of local residents and the railway.The barrier lake is very easy to break.On the one hand,such as earthquake,collapse,landslides,avalanche,leads to the surge of the lake body,which overflows the dam crest and break.On the other hand,the structural stability of natural barrier lake dam is poor,which is easy to cause local undercutting under the action of water pressure,forming a breach and then causing break.However the collapses and landslides have the characteristics of high starting position,fast moving speed and long moving distance,and they usually move in the form of debris in the areas of high altitude and strong earthquake intensity;the clastic flow landslides entering the barrier lake in the way of similar fluid movement will form a large landslide surge,which will lead to the break of the barrier lake.It is a special hydrodynamic process in the disaster chain of the barrier lake caused by the inflow of a clastic flow landslide under the action of an earthquake.At the same time,the break of the barrier lake can cause the dam break debris flow under certain conditions,which has a fast impact speed and strong destructive force.It is another special hydrodynamic process in the disaster chain of the barrier lake.In this paper,the hydrodynamic characteristics of two kinds of barrier lake disaster chains,the surge of the barrier lake caused by the inflow of a clastic flow landslide and the dam break debris flow caused by barrier lake break are studied:1.Based on the analysis of the movement of a clastic flow landslide,we propose a method to calculate the surge height.First of all,we use the hydrodynamics method to analyze the movement of a clastic flow landslide enter into the water,and combined with the piston wavemaking principle,we put forward a calculation formula for the surge height based on the moving analysis of a clastic flow landslide underwater.Through the above theoretical analysis,we have a certain theoretical basis for the surge process of a clastic flow landslide falling into the water.At the same time,in view of the limitation of underwater motion model,a calculation method of a clastic flow landslide inflow water surge based on momentum conservation and hydrostatic pressure assumption was proposed,and experiments of the clastic flow landslide on shaking table water tank were carried out to prepare for the subsequent experiments.2.A large-scale shaking table seismic surge model experiment was carried out.Wenchuan wave(2008.5.12 Wenchuan earthquake,main frequency 2.34 Hz)was used as the source of seismic disturbance to study the characteristics of seismic surge under different initial water depth,seismic peak acceleration.We summarized the calculation formula for dynamic effect of seismic surge under different initial water depth and different seismic peak acceleration.At the same time,the conversion relationship between surge height and hydrodynamic pressure is analyzed.3.We use a large-scale shaking table experiment to analyze the surge effect caused by the comprehensive action of an earthquake and a clastic flow landslide.Based on the experimental results,this paper systematically analyzes the laws among seismic surge,the clastic flow landslide surge and the combined surge,and puts forward a calculation model of surge generated by the comprehensive action of an earthquake and a clastic flow landslide.4.First,we use Bingham model theory to analyze the section distribution rule of the overall impact force of the debris flow,and use the surface velocity of debris flow to modify the calculation formula of the super-elevation;then we change the parameters of debris flow densities,channel slopes,debris flow mud depth and obstacal front slope,and carry out twodimensional flume experiment to verify the theoretical analysis results;finally,we put forward a calculation method of the section distribution and the super-elevation of dam break debris flow,which can provide the basis for the risk assessment and prevention strategy of the debris flow disaster after the dam break.5.In view of the calculation and analysis of combined surge generated by an earthquake and a clastic flow landslide and the impact of dam break debris flow,which are two special hydrodynamic characteristics in the barrier lake disaster chain.The risk analysis and comprehensive prevention of these two special hydrodynamic characteristics of the barrier lake disaster chain are illustrated with the proposed Gongpu station project of China-Nepal railway.