| Since the beginning of this century,because of the frequent occurrence of seismic activity,the intensity and frequency level of debris flow in earthquake areas are significantly higher than it used to be.Debris flow in strong earthquake area not only has abundant provenance,low threshold value and obvious blocking effect,but also forms high-level landslide-collapse type debris flow in steep terrain valley area.It means that the material source comes from the earthquake-collapse landslide accumulations or earthquake-fractured mountains on high and steep slopes.It has extremely high gravity potential energy and strong destructive force,so it can be called high-position debris flow.The extraordinarily high-position debris flow in Sanyanyugou,Zhouqu,Gansu Province,which occurred on August 8,2010,caused1765 deaths and was the most serious geological disaster since the founding of the People's Republic of China.Therefore,this paper selects Sanyanyugou debris flow as the research object.By means of on-site detailed description,engineering geological analysis,remote sensing image interpretation and numerical simulation of the"8.8"disaster,the formation conditions and high-position disaster characteristics of Sanyanyu debris flow are studied,and a new prevention and control technology suitable for high-position debris flow in strong earthquake area is proposed.The main conclusions are as follows:1.Sanyanyu is a typical alpine gorge landform,with numerous branches and trenches,and large vertical slope gradient,which provides favorable topographic conditions for the formation of debris flow;through remote sensing image interpretation,the provenances in the area have obvious characteristics of high-position debris flow provenance in strong earthquake area:abundant sources,total amount of sources reaches 4143.92×10~4m~3,the sources of collapse and landslide type accounts for 68.28%of total reserves,sources are widely distributed,the sources of relative height difference between the ditch and the ditch is greater than 500m,accounts for 91.74%of the total reserves,with a very high gravity potential energy.2.Through field investigation,remote sensing images interpretation and other means,"8.8"Sanyanyu debris flow has a high-position start-up characteristics,the formation process can be divided into two stages:high-position collapse into water-rock flow and dynamic erosion into debris flow in the process of movement.With the action of heavy rainfall,loose material sources in the upper reaches of the basin form water-rock flow;in the process of movement,erosion of material sources in the middle and lower reaches of the basin forms large scale debris flow.Obvious blocking and collapsing effects also occur in the course of erosion.The blocking and collapsing happened three times during the movement.According to the improved formula of peak flow,the instantaneous flow rate of Sanyanyu debris flow is up to3831.14 m3/s,,the instantaneous flow rate increased by about 1800m3/s compared with the normal flow rate,and the blocking coefficient is up to 11.93.3.LS-RAPID software is used to simulate the whole process of debris flow.The results show that the maximum discharge of Sanyanyu debris flow is about 15.77m/s,and the disaster lasts about 13 minutes and 16 seconds.According to the dynamics and disaster characteristics of debris flow,a new partition method of high-position debris flow in strong earthquake area is proposed,which is high-position starting area,inertial acceleration area,dynamic erosion area and circulation accumulation area.which explains the dynamic characteristics and the disaster process of high-position debris flow in strong earthquake area well.4.A comprehensive prevention and control design model is put forward,which includes reducing debris flow erosion capacity in high-position start-up area and inertial acceleration area,reducing material sources in dynamic erosion area,increasing drainage in circulation and accumulation area,and risk management technology combined with monitoring and early warning system.The design mode successfully guided the implementation of the prevention and control project of Sanyanyu debris flow:a new type of permeable barrier structure was designed in the high-position start-up area and inertial acceleration area to intercept debris in the fluid and resist the impact of huge blocks to reduce the erosion capacity of debris flow;a high-standard gravity barrier dam was designed in the dynamic erosion area to intercept the remaining substances in the fluid and control the starting of the material source;a multi-section drainage system with graded protection is adopted in the circulation and accumulation area,and the main stream and the multi-section can protect debris flow in a once-in-a-hundred-years.The monitoring system aims at early warning of high starting area to get adequate emergency escape time,combined with the compound drainage system,a comprehensive risk prevention and control system is formed to minimize the disaster risk of debris flow.5.Reinforced concrete Pile-Beam structure,a new type of permeable barrier structure,fully exerts the self-bearing characteristics of megalithic accumulation,and remarkably improves the ability to resist the impact of debris flow.The results of finite element numerical simulation show that the coupling of megalith accumulation and Pile-Beam composite structure produces the arch ring effect before pile,which can directly reduce the impact load of subsequent debris flow on the structure and make the structure stress more uniform. |
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