Study On The Mechanism Of Landslide In Boli Village Yanyuan County Sichuan Province

At about 5:40 a.m.on July 19,2018,a huge landslide geological disaster occurred in Boli village,Taozi Township,Yanyuan County,Liangshan Prefecture,Sichuan Province.The landslide damaged rural roads,bridges,rivers and woodlands.The direct economic loss is estimated to be 30 million yuan.After the landslide,through UAV aerial photography,field investigation,3D modeling and data access,the engineering geological conditions of the landslide area are summarized,and the development characteristics of the landslide are analyzed.Combined with its failure characteristics,the formation mechanism of the landslide is analyzed by using numerical simulation software.On this basis,the scientific basis is provided for disaster prediction,disaster avoidance and mitigation in the region,which has important significance for reducing the loss of people's lives and property Social significance.The main research results are as follows:(1)The elevation of the back edge of the landslide is 2652m,the elevation of the front edge is 2342m,and the elevation difference between the front edge and the back edge is 310m.The overall plane shape of the landslide is crescent shape.The slope is about 8-40 degrees,the main sliding direction is 300-338 degrees,the Northwest southeast direction is 1360m long,the Northeast southwest direction is 340m-810m wide,the landslide area is 58.6×10~4m~2,the thickness of the landslide is 3.0-40m,and the total volume of the landslide is 1791×10~4m~2The slope material is mainly composed of argillaceous gravel,which is a super large gravel soil landslide.(2)The plane shape of the ancient landslide is a kind of distribution with the long axis of NNW,and the landslide presents a steep and gentle turning point in the longitudinal direction,with an overall slope of about 6-35 degrees.The landslide area is about 248m long in NW-SE direction and 803m-1010m wide in NE-SW direction.The elevation of the rear edge is 3106m,the elevation of the front edge is 2305m and the height difference between the front and rear edges is 801m.The total area is about 203.2×10~4m~2.The maijiaping fault is the main controlling factor for the formation of the landslide.It is speculated that the ancient landslide occurred two-stage sliding.(3)Boli landslide belongs to the old landslide revival,and its revival is mainly affected by long-term rainfall,geological structure of ancient landslide,regional fault activity and favorable landform conditions.The slip zone of the ancient landslide is a weak intercalated zone of purple red tuff formed during the continental eruption of Emeishan basalt.The slip zone is close to the underlying bedrock.The loose layer of the landslide accumulation above the slip zone is very thick,and it is easy to slide again along the existing slip surface under the influence of rainfall,earthquake and other factors;Maijiaping fault crosses the middle part of the landslide.The rock mass in the fault zone is broken and argillized seriously,and the structural plane of rock stratum is developed.Under the long-term water erosion and weathering erosion,the loose material in the fault zone is prone to unstable sliding;Three high-order scarps developed on the terrain before the landslide formed a good free condition for the landslide,which provided a strong terrain condition for the start-up of the landslide;On the one hand,the long-term rainfall accelerated the downcutting erosion caused by the flood rising in Taozigou,on the other hand,the infiltration made the rock and soil of the sliding body saturated,increased the volume weight of the sliding body,reduced the cohesion and internal friction angle of the sliding surface.(4)Boli landslide is a super large multi-level composite landslide induced by rainfall,which has the deformation characteristics of multiple,The sliding from the front edge to the middle of the landslide has the step by step traction characteristics,and the sliding mass at the rear edge has the characteristics of front edge free traction and rear edge pushing.The sliding degree is divided into five times along the sliding direction.After sliding,the terrain can be divided into five stages.