Study On The Regionalization Of Debris Flow Danger Degree In The Area Along G212 In Longnan

The 212 national highway (G212) (Lanzhou-Chongqing) is a main stem connecting northwestern region to southwestern region of our country. The mountains area along G212 in Longnan is one of the most famous area for debris flow. The disaster has affected traffic seriously, which is blocked 25 days averagely per year. It has greatly hampered the economic development of Longnan. Therefore, in order to ensure proper construction and safe running of the planning G212, it is necessary to have a study on the regionalization of debris flow danger degree in the area along G212 in Longnan.The research area locates in the northeastern fringe area of hai-Tibet plateau, drape strip of west Qinling, and it is also just at the crossing of north-south and west-east structure strips of our country. Complicated geological structure, stagger faultages, fragmentized rock, intense new structural activities, mass and concentrative rainfall, asymmetric vegetation coverage and improper human activities provide necessary preconditions for debris flow disaster. First, through consulting plenty of reference books and field research, this thesis analyzes the engineering geological environment of the research area thoroughly, including: geological structure, stratum and lithology, engineering geological rock team, terrain and physiognomy, new structural activities, rainfall, vegetation and human activities etc.Second, by investigating typical debris flow gullies and linking the engineering geological environment, we analyze spatial and temporal characteristics of the debris flow distribution synthetically. Debris flows mainly exist in the Bailong River, Min River(the first-level branch of Bailong River) and Beiyu River. The distribution characteristics of time are discussed from three aspects: daily period, month period and age period. Among of them, debris flow appears in July and August in the light of month period.Third, we ascertain the principle and method of this regionalization, and filtrate eight regionalization factors by summarizing research achievements of foregone geological disaster regionalization and considering actual condition and engineeringobjective, these factors includes: rock and soil characteristics, the distance from falutages, seism, gradient, relative altitude, rainfall from May to August, soil using and vegetation coverage, We obtain values and proportion of these factors by using expert system. Then, we collect data of reasoning and characteristic factors and digitalize them, plot grids. On the basis of GIS, we process spatial analysis, confirm index and compartmentalize grades, then obtain the regionalization result after overlapping all factors and uniting grids. .Finally, using the debris flow distribution picture of the research area, we process reliability analysis through studying several typical debris flow gullies. The conclusion shows that the result coincides properly with actual conditions. The study will have some instructional meaning on how to choose route and establish approaches and measures to deal with a geological disaster.