Study On Risk Assessment Of Unstable Rock Masses On Intrusive Rock High Slope Of Jiexu Hydropower Station In Tibet

Unstable rock masses collapse has made many research results as a hot spot inthe field of emerging engineering geological disasters for the last30years. Especiallyin the big national strategy of "West-East power transmission project", unstable rockmasses collapse has got many geological experts&scholars’ attention and a thoroughresearch, because it has become the large main types of geological hazards in theconstruction of hydropower facilities in the western mountain areas. But the researchalso did not form a complete set system, particularly the progress of risk assessmentresearch was very slow. Therefore, in this paper, based on mentor’s "The dam slopestability research project of jiexu hydropower station in Tibet"(unstable rock massestopic), with jiexu hydropower station as an example, to start from the formationenvironment and development characteristics of unstable rock masses in the high andsteep slope of intrusive rock with deep understanding of the specific geologicalenvironment background of the formation and development of unstable rock massesdistribution. Against its risk control factors study, at the same time, according to therisk assessment definition, feature, combined with the affected body to select the keyfactors and establish a risk of unstable rock masses evaluation system, based on themathematical method. It can be a certain try and push on risk assessment for one kindof specific geological background of unstable rock masses, and can be put forwardcertain guidance for the subsequent construction of the project, has a practicalsignificance. In this paper, research work is as follows:(1) First of all, on the basis of the unstable rock masses related research at homeand abroad, summarizes the domestic and foreign scholars for unstable rockdevelopment formation condition and the research content of risk assessment, lay thefoundation for the subsequent chapters in this paper.(2) To investigate and study the development of geological environmentbackground and the developmental characteristics of unstable rock masses in thestudy area from the perspective of engineering geology, find out the development ofdangerous rock masses distribution, and summarizes some engineering geological conditions and the relationship between the risk of dangerous rock.(3) Comply with universality, dominant and operability principles, fromtopography and geomorphology, main structure characteristics, the main inducingfactors and other factors to choose10factors to establish evaluation index set: theslope height and angel; Master structural plane obliquity, connecting rate and aperture;rainfall, earthquake and human engineering activities; vegetation effect, threat objectlevel.(4) By the expert opinion, literature summary and combining the developmentdegree of the unstable rock disaster in the study area, so on the actual situation, thedangerous level of unstable rock mass is divided into three degrees: high risk(Ⅰ),medium risk (Ⅱ), small risk (Ⅲ), and gives corresponding line scoreⅠ=(60,100),Ⅱ=(30,60) Ⅲ=(0,30), with the influence on the selection of the unstable rock riskindex factors for membership function classification by using the traditional halftrapezoid fuzzy distribution method.(5) Using analytic hierarchy process (AHP), for the purpose of risk assessment,topography and geomorphology, main structure characteristics, the main inducingfactors, other factors as the criterion layer, belonging to10secondary indexes forchild rule layer, the hierarchical model is established. Through calculation,10factorscorresponding weights were0.33,0.67,0.297,0.538,0.165,0.581,0.11,0.309,0.25,0.309.(6) In determining the impact factor based on membership function and weightdistribution, using the weighted model of fuzzy comprehensive evaluation to Jiexuhydropower station dam site area,3pieces of typical unstable rock masses for caseanalysis, for reasonable evaluation of the qualitative factors in the process,introducing of paper work for impact factor classification,3pieces of typical unstablerock masses’(W3, W5, W6) results were82.588(Ⅰ),74.062(Ⅰ),52.353(Ⅱ). Theresults obtained well with the slope stability research evaluation of Jiexu hydropowerstation.(7) Using the studied fuzzy evaluation model of this paper to all the mainunstable rock masses in the study area, the result shows that there are23unstable rockmasses belong to high risk,20unstable rock masses belong to medium risk.5of total43unstable rock masses in evaluation appear inconsistent, the other38evaluations areconsistent. The reliability can reach above88%, and verified in this paper, theproposed risk index system of influence, membership function and the correctness ofthe impact factor weights.