Causation And Stability Of Xiaocaizigou Landslide In Huzhu County, Qinghai Province

Xiaocaizigou Landslide is located in Xiaocaizi Ditch-on the west bank ofShatangchuan River of Weiyuan town，Huzhu County，which is in the Huangshui Valley，Qinghai Province. Xiaocaizigou Village is located on the ancient sliding body. In the recentyears, greater losses of lives and properties were caused by frequent activities of the front oflandslide, and the Landslides is raised the risk of instability. The methods of remote sensinginterpretation, field investigation, engineering drilling and laboratory test were used in thispaper to preliminary investigate the morphology and deformation characteristics of thislandslide, and engineering geological characteristics of Neogene mudstone were revealed.The original slopes and landslides computing model were established by restoring theoriginal slope terrain of landslides. The formation process of Xiaocaizigou landslide isinversed by limit equilibrium method and numerical simulation, and the stability of thesliding body is analyzed. The main understanding and results are achived as follows.(1)Xiaocaizigou Landslide is a large translational deep mudstone landslide. It is1000mlong,1200m wide, and the main sliding direction is near southeast, the area, averagethickness and volume of sliding body area are120×104m2,45m and5400x104m3. Thelandslide rock is Neogene mudstone, which is constituted of hard calcareous mudstone withthin soft mudstone. The slide wall and leading edge of landslide are surrounded by XiaocaiziDitch and its tributary. The sliding body can bo divided into three levels. The structure of theI sliding body is complete. The II and III sliding body were severely damaged. And severalsecondary slip zone were distributed in sliding body. The III sliding body is in the left front ofthe II sliding body, which is accounts for only about a quarter of the II sliding body.(2) A weak interlayer is existed in the slope. The sliding body slided along the weakinterlayer and formed the slip zone. There is a significant difference of the physical andmechanical properties bettween the weak interlayer and its upper and lower rock. Thesaturated strength of the non slip zone is significantly lower than the natural strength. Bycontrast, the slip zone was charactered with lower strength, larger water-sensitive, strongerabsorbent, weaker permeable, biger expansive and more easy softening.(3) The cause of the original slope instability are valley incised, weathering and frostheaving etc. The main controlling factor is the weak interlayer. The inducing factors is water.The formation process of landslide is summarized as5stages: incised and unloadingrelaxation, cracking and creeep, instability and buckling failure. (4)At present, the I sliding body is basically stable; the II sliding body is stable under thenatural condition, but may be instability under a rainfall or long-term irrigation. Thedeformation is serious in winter and flood season, and the main instable part is the secondaryslip zone and the disturbance layer above.