| At8:20on January11,2013, a catastrophic was triggered in Zhaojiagou,Zhengxiong county, Yunnan. It involved68persons of14housesdamaged, resulting14houses damaged and48buried. This disaster event is a influential and majorgeological disaster event,which caused heavy casualties. This landslide occurred inthe winter of little rain, not in the time-flood season that geological hazard easy tohappen. So the landslide formation mechanism attracted many attentions fromrelevant departments and many scholars.This paper regards Zhajiagou landslide as research object, which analysed thebasic characteristics of landslide based on the field investigation work. It analyses themajor factor about inducing instability of landslide, conbining the experient result ofsoil mass physical and mechanical properties. The paper obtain mainly followingknowledge and achievement:(1) The length of Zhaojiagou landslide is about900m,. The width of the leadingedge of landslide is about100m. The width of central landslide is about250m. Thewidth of the tralling edge of landslide is about110m. The average thickness ofaccumulational soil is about1~3m. The total volume of slidig mass is about40×104m3. The tatal area of landslide is approximately0.11square kilometre. The overalllandslide terrain is steep-flat-steep from from the top of the mountain to the foot. Theslope where the landslide happened develops two levels of erosion platform. It’s areverse slope.(2) Based on the movement and accumulation characteristics of ZhaojiagouLandslide, landslide is divided into the region of source,the region of circulation andaccumulation, the region of accumulation into the disaster, the region of accumulationis subdivided into3district according to the difference of the region ofaccumulation‘s characteristics of deformation and failure.The back of the sourceregion appeared a three prism notch after the landslide,the water flow outcontinuously from fracture of the posterior wall’s bedrock; the feature ofgeomorphic’s deformation is various in the region of accumulation,including the mounds forest, scraping band, the accumulation of gravel strip, the lateral accretionridge,the tensile berm, the dual structure of accumulation and so on. Theaccumulation from the region of source moved to the disaster area through thecirculation-accumulated area.(3) The conditions of Zhaojiagou landslide formed include the followingaspacts.Firstly, the special terrain of landslide formed good water storagecondition,providing favorable conditions for landslide instability;secondly, thetectonic stress field and the unloading effect of the formation process of the slopetrigger the back scarp of the slope fracture development, providing the groundwaterflow channel;thirdly,the weak intercalated layer on the dip slope provides basicconditions for the formation of the sliding zone;finally,rain and snow and bedrockfissure water infiltration triggered the starting of the landslide.(4) Physical and mechanical properties test show that the existence of clayminerals in the sliding zone make the soil of sliding zone hydrophilous easily andswelling in water-dying shrinkage. It make the soil of sliding zone softening easily,which is the root reason of instability.(5) The attenuation of the strength of the soils in sliding zone is very obviousduring the softening process of groundwater, the test value of soil’s strength when it issaturated for20days is substantially lower than the natural state.The calculations oflandslide’s stability shows that the stability coefficient of landslide is close to1whenthe sliding soil is saturated for six days,and the landslide is into an unstable state. Themain predisposing factor of landslide’s initiation is a significant attenuation of theshear strength in slip zone caused by the local stagnant water in the upper section ofthe slope,and this is because of the rain-snow weather and bedrock fissure water’sinfiltration.(6) Based on the analysis of the landslide instability process, combinedengineering geological conditions and the deformation of slope geological mechanicsmodel, the geological model of zhaojiagou landslide is “creep-cracking”. Thedeformation and failure process of landslide is divided into three steps:1. Under thecondition of rain and snow, the soil of landslide absorb water and the shear strengthdecrease. The back of landslide appeared cracks.2. With infiltration of rain、meltedsnow and bedrock fissure water, the water stay the upper of slope and creep shearzone appeared the sliding zone.3. When sliding resistance is more than sliding force,the slope start to become instable. (7) A two-dimensional Seepage numerical simulation analyses the landslide inthe long process of the change of seepage field under the condition of rainfall, theresults show that the continuous rain make the underground water level of the slopefoot has obviously rised, slope toe pore water pressure increases,slope stability isreduced over time,the stability coefficient of the decline has lag, performancing forthe stability drop dramatically after snowmelt or rain stopped for a period of time.Rainfall caused slope overall stress increases, the landslide, the trailing edge and theslope toe maximal shear strain increases. Strongly weathered rock permeabilitycoefficient and the initial water head has a certain influence on underground waterlevel. |
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