| The debris flow in large valley of shawan is located in JinYuan township of XunDian county in YunNan province, located nearby the area of active fault with xiaojiang, located on the east side of western fault of active fault with xiaojiang. The debris flow is one of the geological hazard with a mixture of sand, stones, water and gas, found in the mountainous area. The character-istics of the debris flow are very complicated, occasional, regular, inevitable and so on. The risk and harmfulness of debris flow are also called risk and hazard degree. Risk refers to the possibility of landslide damage to the damag-ed object size；Hazard degree refers to the debris flow within the basin, it is harm to the damage of the object. Risk is inherent in debris flow, and the ha-zard degree and the harm to the location of the object in the basin and intensi-ty.For risk assessment of debris flow is an important way to research and the prevention and control of debris flow.Analytic Hierarchy Process is a kind of quantification theory ofmultivariate statistical analysis method.Combining with the actual situation of the landslide, there are three levels into the target layer, rule layer and index layer in the study, the target layer is risk assessment of debris flow; Rule layer is about on hazard factors, topography, source condition, etc; Index layer includes the loose material reserves, general average of main ditch slope, the basin area, the terrain slope, rainfall in 24 hours, the maximum relative relief, sediment supply length ratio, main channel length, watershed cutting density, main chan-nel bed bend coefficient, vegetation coverage and other factors. Through preli-minary investigation and calculation of the basic work of each factor in the in-dex layer assignment and grading, all factor scores is added up, eventually it is the end of adding.In the large valley of shawan area, geological structure is complex, lithol-ogy of stratum is complex and crushing, topography and geomorphology is co-mplex, rainfall is abundant and stronger activity in rainy season. The debris fl-ow in the vally of shawan is located on the east side of active faults, it is ab-out 1.5km faraway, the active fault is the large faults from SongMing to Can-gXi, for it is affected by active faults and role, the structure of rock mass is broken in research area, the terrain changes ups and downs greatly. The valley of Shawan is a shape of "gourd", the terrain in upstream is gentle and broad, it is channel formed a "V" shape, exposed rock surface is limestone, dolomitic limestone, argillaceous siltstone and shale, they are carbonate rocks and clastic rocks, the ditch for composition of these rocks is unstable, there are several distribution of landslide and collapse geological, they provide a good source for its formation conditions of debris flow provenance, it is an area for the for-mation of debris flow; The terrain in midstream is large cutting deeply, the terrain is very steep, the channel is narrow, exposed rock surface is dolomitic limestone and basalt, they are a group of hard rocks, the ditch and gully bed for composition of these rocks is stable, it is advantageous to the mud fluid ci-rculation quickly, it is an area for the circulation of debris flow; the terrain in downstream is flat and open, the out of vally is a shape of the fan, stack layers is very thickness in the mizoguchi, valley bed is wide and shallow, it is cutted deeply, the fluid rate of debris flow goes down sharply, it stopped flowing and was heaped up constantly, it is a area for the accumulation of debris flow.Through the investigation and analysis research and parameter calculation, the main achievements of this paper studies and acknowledge of each other for the following:(1)The debris flow in large valley of shawan has a big gully watershed area, circulation area and accumulation area partitioning feature, lay the found-ation for the debris flow formation conditions and provide Spaces.(2) Research area of strata is outcropped incomplete, lithology is some clastic rocks with argillaceous siltstone and shale, it is affected by active faults and destruction, it is crushing of rock mass and weathering, it is joint fissure development, it is conducive to the formation of source conditions.(3) Important parameters of debris flow are calculated as a result, the density γc=2.12t/m3, flow rate υc=5.05m/s, quantity of flow Qc=61.5m3/s, the overall impact F=94.42KPa, single boulder impact F=1600.00KPa.(4) The formation mechanism the debris flow in large valley of shawan is some source conditions, water conditions and terrain conditions, under the sufficient and necessary conditions for the organic combination of all three out break has the outbreak of large-scale, high frequency and velocity, the huge impact, and they carry a huge movement and the dynamic characteristics of coarse particle.(5) Results debris flow risk assessment with using the Analytic Hierarchy Process (AHP), Q=136.(6) There are some towns, villages, roads, electricity, communications, farmland,water conservancy facilities and other infrastructure in the downstream of the large valley of shawan, it has great hazard of degree this day. It will cause different degrees of damage with some forms of landslides buried (buri-ed), shock (impact), erosion and abrasion, jams and extruding channel for the harmful form of object, namely mechanism of debris flow hazards.(7) Such as three respects of source conditions, water conditions, terrain conditions, its development trend will increase on the hand of both scale and frequency.(8) The debris flow in large valley of shawan is determined to be a sha-de viscous extremely serious debris flow of gully-type with high frequence. |
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