Experimental Study On The Failure Mode And Evolution Process Of Barrier Dams In Bailong River Basin

Geological disasters are serious in mountainous areas in China,especially in the western strong earthquake area.Due to the narrow river channels in the canyon area and steep slopes on both sides of the canyon,under the action of rainfall and earthquakes,it is easy to induce landslides,collapses or mudslides,and block the river channels to form barrier dams.Because of its special material composition and loose structure,once a barrier dam breaks,it will cause floods or debris flow,forming a chain of geological disasters,and its hazards present a chain-like amplification effect,which will affect the lives and properties of people in the surrounding and upstream and downstream areas.It is very difficult to collect information about the failure process in real time due to the sudden formation process of the dam and the short burst process of the dam,as well as the numerous influencing factors of the dam.As a result,the study on the evolution process of the dam burst has become a difficult and hot spot in the global research on geological disaster prevention and control.This study takes the landslide-type barrier dam formed in Wudu Goulinping,Longnan City,and the debris flow-type barrier dam formed in Sanyanyu,Zhouqu as the research objects.They are both located in the Bailong River Basin,a highincidence area of geological disasters in our country.Based on similar principles,the use of the physical model experiment of the flume has carried out the study of two types of barrier dam failure modes,failure characteristics and evolution process.Based on data collection,filed survey and indoor and outdoor water and soil mechanics parameter testing,the flume model experiments of landslide type and debris flow type barrier dam failure has carried out under different control factors such as dam particle grading,flume slope,upstream water flow and initial water content of the dam.The failure modes and main evolution processes of landslide-type dams and debris flow-type dams are discussed.And the differences in the failure process and characteristics of the two types of dams are compared and analyzed.With the help of modern sensor monitoring technology,the influence of different control factors on the burst process of the dam body is analyzed.The amplification effect of the peak flow rate of the failure and the change process of the failure flow under different control factors are analyzed,and the evolution process and law of burst of landslide and debris flow type weir dam are deeply revealed.This will provide scientific basis and technical support for the monitoring,early warning and emergency response of the failure.The main conclusions are as follows:(1)Through the experiment on the failure of the Goulinping landslide-type dam,it is found that there are two modes of failure: overtopping failure and failure of the dam slope on the back of the dam body.Through the experiment of the Sanyanyu debris flow dam,the failure form of the dam burst is overtopping failure.(2)Through the analysis of the experimental process of overtopping failure,the process of overtopping failure can be divided into three stages: the collapse slowly develops to the through phase,at which time the collapse flow slowly increases(phase I),and the collapse accelerates the erosion phase,at which time the collapse flow increases rapidly(Phase II)and the water-sediment balance phase,at this time the outburst flow drops(phase III).(3)In the process of dam break,the key physical parameters such as pore water pressure,water content,matrix suction and the impact force sensor in the end of the tank are constantly changing,and there are obvious differences in sensor changes under different dam break modes.The change of various parameter inside the dam is related to the change of the soil structure inside the dam.Through the comparative analysis of pore water pressure and water content data,the process of water change in a barrier dam can be divided into four stages: water infiltration stage,soil saturation stage,soil strength reduction stage and dam failure stage.(4)From the analysis of the change process of barrier dam failure flow under different control factors,and discusses the influence of each factor on the failure process.The peak failure flow rate decreases with the increase of the particle size D50 of the dam and the increase of the upstream water flow.The peak failure flow rate decreases with the increase of the flume slope.The peak flow rate of the breach increases with the increase of the initial water content,the rate is positively nonlinear,and the rate of increase is getting faster and faster.