| 5.12 Wenchuan County earthquake triggered many avalanche, landslides and other secondary geological disasters and loosening crack, multiple potential landslides and geological disasters was developed in the loose mountain. What'more, the geologic hazards make a serious threat to the county. In this paper, we used the landslides and geological disasters in Wenchuan County as the research target, and we not only have had an analysis to the development formation mechanism, influencing factors, and distribution of avalanche and landslides Meanwhile, we analyzed the stability of avalanche with the method of stereographic projection method and limit equilibrium and get the stability of landslides with the limit equilibrium method. From a different point of view to analyze the selection of slump-type disaster prevention program, and to the avalanche and landslide of Jiangsheba dam 1 # and the typical landslide of Qingtushan disaster cause study, analysis of, and then carry out prevention measures. The study on the formation mechanism and stability of the disaster has important practical significance to ensure the safety of Wenchuan County, The results obtained from the study as followed:(1) The development of avalanche and landslides distribution in Wenchuan County was found out based on the field investigation and analysis :①The avalanche and landslide mainly spread along the Minjiang River valley, with the elevation of 1300 ~ 1600m;②the avalanche mainly formed in the slope of 45 ~ 60°, and landslides with the slope of 25 ~ 35°or 40 ~ 45°;③avalanche disasters mainly distributed in the east, southeast, south, northwest slope aspect;④avalanche disasters, are mainly happened in limestone or diplomatic limestone strata, and landslides are mainly exist in Quaternary loose deposit;⑤avalanche hazards are mainly formed in the forward, reverse and oblique slopes.(2) There are 36 new geological disasters triggered by earthquake in the hit area including 16 avalanche, accounting 88.89% of total hazards, 5 new landslides,representing the total number of 71.43%.Meanwhile, all of the unstable slopes are triggered by the 5.12 Wenchuan Earthquakes. New avalanche and landslides in earthquake occurrence in the same time. Therefore, the Wenchuan Earthquake has a strong impact on the avalanche and landslide.(3) There is several failure modes of avalanche in the study area, such as the mode of dump, sliding, falling and debris flows occurred along the slippery slope. And the Landslide deformation and failure model are translational and over-style respectively. Disaster types of slope deformation and failure mode have a significant relationship with the structure type. The main influence factors of landslides are topography, litho logy, geological structures, earthquake, rainfall, human engineering activities.(4) Using stereographic projection method and limit equilibrium to analyze the stability of landslide disasters we got the relevant results show that the stability of avalanche disasters is poor and most of that are unstable and less stable, such phenomenon show us that there is a great possibility of avalanche in the future, followed by the steady-state and less stable. It is prone to have a avalanche hazard with the rain and other unfavorable factors or in the poor stability segment of slope. Will event of failure more likely or there is lots of local poor stability of the slope, prone to avalanche hazard.By using the method of geologic analysis and limit equilibrium to analyzing the stability of landslide hazard, the result shows us that a good stability was in the study area. For instance, the two potential unstable slopes of Shidai Square and the 1 #, 2 #, 3 # potential landslide of Aba Sichuan are all less stable now, but under the control of the action of rain, earthquakes and other unfavorable factors, the stability has reduced and the slope is easy to unstable.(5) The study of the Jiangsheba 1 # dam avalanche disaster show that:①W1 ~ W9, W1, W2, W5 were all in a stable state, and the rest dangerous rock were unstable;②Referred to X1 ~ X4, X3 unstable slopes was stable in all condition, and X1, X2 are unstable under the condition of rain and earthquake, X4 is unstable in heavy rain, and rain with seismic conditions;③D1 ~ D5, the stability of tD4 debris is poor and it is less stable under the natural and heavy rain condition, rest of the other accumulation body are stable, occasionally, some stone will rolls down along the slope from time to time. Combination of the slope deformation and failure disaster situation, disaster basic features, topography, hazardous objects and harm, stability, etc to taking into account of landscaping elements, 1 # avalanche of Jiangsheba Prevention Project should adopt the solution of drainage with excavation and SNS retaining initiative wall fence and retaining wall(and SNS retaining passive wall fence).(6) We can draw some conclusions of Qingtushan landslide as follows: The landslide is an old-style large-scale landslide with translational style. And the factor of rainfall has a strong influence on the stability. The different sliding surface of the landslide all are stability under the first condition. In the secondary slip plane, the secondary slides are in a less stable under the second and third conditions. Although the overall stability of the landslide is stable, but it is also requires using the engineering control measures.By using analysis software of Finite Element, we know the stress situation landslide under the condition 1 and condition 2. The result shows that the landslide deformation zone is consistent with the geological model, and the deformation of landslide is as the same as the actual situation. At the same time, we make an analysis on the landslide displacement and stress conditions under the second condition, by using sliding pile and anchor. The two kinds of programs can be effective control of landslide deformation and improve the stress state of decline through analysis, but the lattice cable project in terms of prevention effect is better than the pile area with cable.
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