Research On Mechanism Of Deji Gully Debris Flow Formation And Prevention Scheme

Debris flow is a fluid composed of solid and liquid,which has the characteristics of fast flow velocity,short occurrence time and strong destructive force.Once debris flow occurs,it will damage traffic facilities,ecological environment and local people's life and property safety.Debris flow disaster has become a natural disaster that can not be ignored in mountain areas.The debris flow of Deji gully poses a serious threat to people's life and property safety and economic construction and social development of Niedang town.According to incomplete statistics,Niedang town Deji ditch's mudslides disaster's outbreak since the 80s of 20 century,a total of 20 households are affected,of which a total of 5 households in the village houses were completely destroyed,so did the basin units,and State Road 318 was interrupted several times,and so much economy serious losses.Therefore,the research of Deji gully debris flow formation conditions and mechanism analysis has important significance,the corresponding control measures is also put forward.This paper takes Tibet Niedang town's debris flow in the northwest side as the research object,through field geological investigation and theoretical calculation analysis of debris flow parameters and Deji gully debris flow formation mechanism was studied,and combined with the risk evaluation thought,using Arcgis software to carry out the debris flow hazard,vulnerability and risk assessment in the region on this basis,comprehensive prevention plan is put forward.The main understanding is as follows:?1?The field geological investigation,topography,lithology,geological structure of the study area were analyzed:regional mountain is high,rolling,a primary watershed is NNE,small watershed of the main area is nearly East-West or west south,regional stratigraphic lithology is mainly Cretaceous;Department of the Tang Jia group?K₁t?,Quaternary and magmatite zone;and faults are North East,North West,north-south and east-west distribution of four groups.?2?The main source of Deji of the solid material of debris flow ditch?residual slope sediments,colluvium?and supply?slope erosion,lateral erosion,collapse and gully bed propose four?,landform?erosion,erosion and deposition of mountain mountain valley landform?,watershed distribution is analyzed.The formation,circulation and accumulation process of the debris flow gully are studied.The characteristics of the debris flow gully are summarized,that is,the loose material on the slope is rich,the potential collapse distribution of the gully and bank is dense,and the channel siltation is serious.?3?Detailed calculation and analysis of debris flow characteristics of fluid Deji through field investigation data?including debris flow fluid density,peak flow,flow rate and the maximum amount out?and DEJI debris flow dynamics?including the impact force of debris flow,drop height and bend high?.?4?To investigate the formation of debris flow ditch DEJI terrain?gullies,topography,gully valley slope characteristics,channel characteristics?,source reserves?eluvial material storage,colluvial storage,gully side erosion material storage,channel deposit,storage?water source conditions?valley rainfall characteristics,surface runoff characteristics,critical rainfall,snowmelt?:Deji gully narrow longitudinal gradient,to promote the mixed water and sand flow and debris flow;the total reserves of solid debris source is 696.25×10⁴ m³;the critical rainfall intensity is10.4mm for 1 hours.?5?The formation mechanism of debris flow of Deji gully is analyzed:debris flow gully catchment area is large,strong valley cutting,relative elevation and slope,steep channel gradient,funnel form single channel domain form,which provide sufficient energy for the formation of debris flow,the sand flow in the source enrichment area quickly transformed into debris flow;the channel is narrow and the longitudinal gradient,which promote the mixed water and sand flow,debris flow.Loose solids source types,eluvial colluvial slope erosion;recharge mode?including surface erosion and gully erosion?,lateral erosion,collapse and gully bed propose four,this provides sufficient solid material for debris flow of Deji ditch.In the favorable terrain and full source conditions,rainfall or snowmelt infiltration changed its original rock and soil properties,density,strength,resulting in change of pore pressure increase;water erosion and down cutting changed the original slope geometry,the slope was in a stable state gradually tends to be destroyed,i.e.the formation of debris flow?6?To establish the risk assessment model of debris flow forecast of Deji,Arcgis software was used for qualitative evaluation of the risk and danger of Deji ditch range of quantitative.The results show that the place away from the main ditch near the study area is influenced by the debris flow impact,moderate or high risk area,and relatively far away from the main channel basically not affected by debris flow,low risk area,in the debris flow and debris flow area near high risk area;study of regional debris flow ditch the risk range are relatively large,basically in the above 0.25km²,the No.3 and No.4 gully catchment area,in the loose valley is abundant,the larger gap,the risk range of debris flow gully,relative to the No.2 more.The topography and motion characteristics of debris flow based on the partitioning of the debris flow risk,according to the DEM model,the quantitative calculation of debris flow vulnerability,using Arcgis software,based on the material and economic vulnerability of the fitting formula,the evaluation factors for grid computing,and vulnerability zoning of debris flow.The hazard and vulnerability zoning of the results of the grid computing,the composition of Deji debris flow risk zoning map.The results show that the bare land is the low vulnerable area,and the cultivated land is the middle vulnerable area;the area near the main ditch is generally the middle and high risk areas,while the far away from the main ditch is the low risk area.?7?According to the important degree and level of security threats,different object Deji gully debris flow management position,combined with the feasibility of the project,take security measures are as follows:in consideration of proposals,topography,debris flow characteristics and traffic conditions and construction conditions,the recommended general idea for"the overall governance project management mode to block,dredge auxiliary",namely the rataining dam?9 dams,part of solid material of debris flow is blocked?and afforest?soil?and drainage engineering?excluding solid material,to prevent debris carrying?channel source on the road below the residents.The calculation and checking of dam project shows that the verification results meet the design requirements.