Study On The Geological Disaster Prediction Of Yalong River For Le’an Hydropower Station

Proposed Le，an hydropower station was situated in the southeastern TibetanPlateau, which belongs to the Western Sichuan Plateau. In these areas, the rivers ofwhich the valley slope is more than40degree was,which is the typical alpine gorgelandform.Having complex geological structure, the study area is located in the "riverof Sichuan-Yunnan block" on the north side, near the "Qinghai block". And there has27disasters including2landslides,8collapses,17debris flows through the fieldinvestigation. It is an unavoidable problem that the impoundment of thedevelopmental tendency of disaster and soil bank slope bank reengineering duringdam construction. Therefore, researches on the prediction of geological disasters haveimportant engineering practical value.On the basis of the reservoir of a hydropower station in Yalong River leanengineering geological conditions, we master the development and distributioncharacteristics of all kinds of geological disasters in the reservoir area through fieldinvestigation. And following the combination of qualitative and quantitative analysisand quantitative evaluation of thought, we make the forecast evaluation ofdevelopment trend of geological disasters in the reservoir area. Finally, to provide aguarantee for the Yalong River Hydropower Station Construction of lean constructionand operation, GIS software analysis and the analytic hierarchy process was combinedto evaluate the whole area of risk evaluation. The key contents and conclusions are asfollows:(1) Reservoir bank slopes are two main types of rock bank slope and the soilbank slope.The rock bank slopes are longitudinal and transverse valleys and its mainfailure modes are the bending and tension. The soil bank slopes are mainly debrisflows, the second are pluvial slope of talus and the least are landslides. Its failuremodes are the collapse type collapse and circular arc slide. (2) In the study area, there are two landslides, the landslide of cut brotherManasseh bead and Linda landslide. Developed in the valleys and steep and steepreverse layered slope, the failure modes are toppling deformation caused by bendingto failure. The landslide of cut brother Manasseh bead is mainly stable in Natural,rainstorm and3185m static water level condition. But it is less stable in seismiccondition. The other one, Linda landslide is stable in Natural, rainstorm and3185mstatic water level condition. And it is also less stable in seismic condition. TheSecondary Resurrection1, the Secondary Resurrection2and the SecondaryResurrection3of Linda landslide are basically stable in natural condition. But it isopposite to the Seismic condition. Because of the influence of water to landslidephysical, chemical and mechanical effects after restoring, the stability of landslidesare decreased in varying degrees in different conditions.(3)There are8collapse consisting of3large collapse3,5medium-sized collapse.The deformation and failure modes are dumping deformation. In study area thecollapses are of above35°slope, and its altitude is between3130~3250m slope.Most of them are at stable state before restoring. After water storage, the stability ofthe water level below the collapse, the stability is not affected by it. Front submergedleading to local damage, stability will decrease.(4) Being abundant with the required conditions of landform, provenanceconditions and water conditions, there are17mudslides including3giant debris flow,3large-scale debris flows and the rest are small debris flow. And it is dominated byflow gully debris flow which has the characteristics of multiple development. Thedebris flow hazard zone is low.Evaluation results of debris flow for low risk is12,accounted for75%of the debris flow gully, evaluation results for the debris flowhazard is4, accounted for25%of debris flow, and debris flow high risk does not existwithin the area.(5) There are17places predicted to be the occurrence of collapse bank. Its widthover40m is5with the total length of2120m accounting for10.6%of the length ofthe reservoir, its width over20m less than40m is6with the total length of1654m,accounting for8.3%of the total length of the reservoir bank collapse prediction, thewidth within20m is account for the investigation of pre side bank of7sections withthe total length of1846m accounting for9.2%of the total length of the reservoir.(6) Using the analytic hierarchy process, the evaluation factors of the researcharea of geological hazard risk are the risk of historical disaster (disaster pointsdensity), slope gradient, slope, elevation, the structure of the reservoir water level variation and human engineering activities. Accordingly, the weight values were0.3119,0.2266,0.1343,0.0873,0.0423and0.1976. Combined with the technology ofGIS and AHP mathematical model, the study area is divided into: high risk, high riskarea, medium danger zone and low risk area. It is showed that the geological disasterin high risk area is1.89km~2, accounting for a total area of7.6%of the study area,geological hazards in the secondary high risk area is5.82km~2accounting for a totalarea of23.4%of the study area, the geological disasters danger zone in the area of9.69km~2accounting for the total area of39.1%of the study area and nature disaster inlow risk area is7.41km~2the total area of the study area,29.9%.