| The fluid of debris flow is a three phase mixture consisting of solid matter,water and a small amount of gas.The solid material includes soil,sand,stone and so on.Driven by gravity,it moves along the hillside or valley.The characteristics of debris flow are sudden,fierce and destructive.Debris flow is a geological disaster with wide distribution and long activity time.Every year,there are different scale of debris flow disasters,which has a serious impact on people’s production and life.According to the historical data of the Boqiang gully in Xinzhou city,the eruption of debris flow in 1956,1996 and 1997 respectively.Debris flow destroyed people’s houses and flooded farmland at that time.Therefore,study the movement process,danger range and risk intensity of debris flow in the Boqiang gully has important significance for early warning and the prevention and control of debris flow disasters.At present,the related researches of debris flow have been paid much attention all over the world.One of the important directions is to apply numerical simulation to the risk zoning of debris flow.Based on data collection and field investigation,the Massflow numerical model is applied to simulate the movement process of debris flow.The numerical model is based on the continuum model,and is calculated by the finite difference method based on the derivation of two dimensional mass conservation equation and momentum conservation equation.This paper uses the Voellmy friction model according to the development characteristics of the Boqiang gully debris flow.Using thisnumerical model,we can visualize and quantify the movement process and accumulation characteristics of debris flow.According to the case of debris flow in the Boqiang gully,the debris flow disasters in 20 years,50 years and 100 years are simulated.The rainfall is43.68mm/h,47.05mm/h,59.18mm/h,and the bulk density of the debris flow is1.885t/m.The coefficient of friction is 0.3 and the turbulence coefficient is10m/s2 through numerical simulation.The above conditions are input into the numerical model to get 3 kinds of rainfall debris flow process.20-year return period debris flow,the maximum mud depth of whole basin is 2.34 m,and the maximum mud depth of Beitaifeng village is 0.8m.50-year return period debris flow,the maximum mud depth of whole basin is 2.51 m,and the maximum mud depth of Beitaifeng village is 1.2m.100-year return period debris flow,the maximum mud depth of whole basin is 2.71 m,and the maximum mud depth of Beitaifeng village is 1.5m.The velocity characteristics of 3 kinds of rainfall are basically the same.The debris flow from the slope to branched gully to the main gully,The flow rate is from small to large to small.In the process of beginning to the end of the movement,the maximum flow velocity is 20~24m/s,the maximum flow velocity in the branched gully is about 16m/s,the maximum flow velocity in the main gully is about 11m/s,and the velocity of debris flow near the Beitaifeng village is 6~7m/s.Finally,according to the mud depth and velocity under different rainfall conditions,the risk zoning of the Boqiang gully is carried out according to the criteria of the influence intensity of debris flow.According to the zoning results,the west of the Beitaifeng village and south of the Beitaifeng village are high hazard level.The east of the Beitaifeng village and the north of the Beitaifeng village are medium hazard level.According to the results of hazard zoning,it will provide some references for the prevention and control of debris flow geological hazards in this area. |
