The Study Of Shattering Mountains Landslide-Break Debris Flow Disaster Chain

The effected of Wenchuan earthquake on May 12,2008, there have been a mass of disasters such as landslides and collapses in earthquake disaster area.The most prominent are those who "hang" near the mountain ridge of the shattered mountain. Most of them are less stable to unstable, once the heavy rain, easily formed the disaster chain of shattering mountains landslide(collapse)—break debris flow,so that lead to the larger scale and activity increased of debris flow. Can't estimate the degree of harm.The Gan gully basin have heavy rain which located in An county of Sichuan Province on August 24,2009. The top of Niujing gully has occurred landslide which is the tributary of Gan gully upstream. The landslide along the channel by the high speed,then transformed into clastic flow and almost Orthogonal into Gan gully,so that plug to form a barrier dam. In the impact from heavy rain and continuous high-speed impact, caused the dam-break. Finally,triggered the outbreak of break debris flow and causing huge losses.Taking the"8.24"break debris flows of Gan gully as the study object.Through field investigation, testing,earthquake, precipitation and other related information,the paper analyzes the basic characteristics, genetic mechanism and movement characteristics of landslide—clastic flow—blocking gully and dam break—debris flow so as to provide valuable reference basis for future disaster prediction and management of the landslide—debris flow.First,this article analyzes the basic characteristics and formation mechanism with Niujing gully landslide. "5.12" Wenchuan earthquake caused the top of the mountain of Niujing gully had serious damage and shattered deformation,and "8.24" of local heavy rainfall is the main factor induced Landslide.Niujing gully is the collapse and residual soil landslide which sliding along the bedrock-cover discontinuity.It divided into sliding zone and the residual area. Currently residual area have about 240,000 m~3 loose accumulation, and is less stable.Secondly,the formation process and mechanism of landslide clastic flow, blocking gully and dam break are discussed. The formation mechanism of the high-speed landslide of clastic flow as the following stage: starting stage of shattering mountains landslide by rainfall induced—acceleration of gravity and landslide formed erosion riverbed—disintegration of high-speed impact, scraping and long-distance movement—blocking gully. Clastic flow blocking the gully and formed length about 80m, the average width of 50m, thickness of 5 - 10m of the barrier dam.The dam—breaking mode is sliding and collapse,and calculated the instantaneous peak flow.Finally, the basic characteristics,movement mechanics characteristics and harm of Gan gully was analyzed. Break debris flow outbreak after the barrier dam break, the peak flow of debris flow increased Instantaneous,and to bring a lot of material to the downstream by high-speed movement. Debris flow avoid bending but straight at lime factory of distance of about 300m,and rapid thrust down the ridge and finally stopped at a flat plot in the lower reaches.The severe is 2.05t/m~3, peak flow in the circulation area of up to 494.74m~3/s, the flow cross total of a debris flow is 35.96×10~4 m~3/s. Currently, the debris flow are in the development stage, as upstream are still a lot of loose material, easily happen slide—outburst debris flow again.