The Classification And Risk Assessment Of Perilous Rock Mass

Our country is a mountainous country, which is also one of the country where there are many collapse and rockfall distributed. With the rapid development of the state construction, the large-scale and oversize hydropower project, road engineering which are built in mountain area increase day by day, and the problems of geological hazards that follow are also increasing remarkably. So the disaster events that coused by collapse get more and more. Life and property loss coused by collapse is enormous every year in the whole country. Therefore, the frequent occurrence, the universal distribution and the severe harm of rock falling are indubitable. Especially in Western China, rock falling is one of the main geological hazards. In recent 20years, many researchers at home and abroad did plenty of researching from different aspects and got some achievements. Based on these researched results, this paper takes sample for the perilous rock mass on the high slope of the rear mountains of the underground powerhouse of Huangjinping Hydropower Station in Dadu river, to study the dangerous rock systematically. The paper did studies with different degrees from the definition, the formation condition, the influencing factors, the formation mechanism , the classification to the stability of dangerous rock mass also with the final risk analysis, and formed a more complete system . The main conclusions were represented as follows:(1) At first through introducing the status of dangerous rock mass study at home and abroad, it summarized the development situation of study on the deformation and failure mode, the stability analysis method, the risk analysis, the prevention measures and the motion path after collapse of dangerous rock mass. And established a foundation for the study of dangerous rock mass in the following chapters.(2) It introduced the engineering geological environment condition of study area detailedly, summarized the structure character of rock mass, made dominant fracture statistical on structural plane which is in study area and classified the scale and characters of structural plane, given the physical and mechanical parameters of rock and structural plane, these provided a reference for the stability analysis of dangerousrock mass.(3) The definition of dangerous rock mass was supplemented and perfected, to make it more easily in field identification. Made a detailed introduction for the formation condition and the influencing factors of dangerous rock mass, and then divided the failure Process of dangerous rock mass into three Stages which are potential dangerous rock mass formation stage (time-dependent deformation stage ) , original structure plane development stage and new structure plane formation stage (gradual fracture stage) , dangerous rock mass unstable failure stage (sudden collapse stage) .Classification of dangerous rock mass was done according to the deformation mode and the failure mode : according to the deformation mode, the dangerous rock mass was divided into creep-cracking, sliding and fracturing, buckling, dumpping pull crack, plastic flowing and fracturing, relaxed-tension crack; according to the failure mode, it was divided into collapse, slump, lateral spreads and spalling. Among them, according to the motion mode as soon as it failure and the failure mechanism, the collapse was classified into two subclasses which are falling and toppling.(4) Summarized the stability analysis methods of dangerous rock mass, and described each in detail .Among these methods, the Static—Analytical Method was given a supplement and perfection. To different failure ways, this paper puts forward the concrete qualitative and quantitative instability criterion.(5) Combined with the engineering geological condition of study area, there was a detailed analysis for the formation mechanism of dangerous rock mass in the study area. And the stability of dangerous rock mass in the study area was analyzed by using Static-Analytical method. The results showed that dangerous rock masses in the study area were basically stable or stable (individual dangerous rock mass was critical state) .In the cases of rainstorm and earthquake, the whole stability decreased , the local was not stable and unstable . By analyzing the calculation results , it indicated that hydrostatic pressure in fracture play a different part in different failure mode dangerous rock mass. And the effect on collapse mode dangerous rock masses is obvious than the slump mode.(6) The definition, basic characteristics and evaluation content of risk assessment of dangerous rock mass were presented in detail. A risk assessment system was established in this paper, the hazard analysis was done by using the Fuzzy Evaluation Method and Analytical Hierarchy Process. Then, the risk level was divided into three grades which are I,II,III, and the risk level is successively form high to low. There are eight blocks belong to I grade, seventeen blocks belong to II grade, ten blocks belong to III grade.(7) The vulnerability system of dangerous rock mass was described simply, and the vulnerability was divided into three grades which are I,II,III, the vulnerability level is successively form high to low. To make dimensionless valuation on the different grade of risk and vulnerability, finally, according to the risk assessment calculation formula , the risk assessment of dangerous rock mass in study area was done. The risk degree was also divided into three grades which are I,II,III, and the degree is successively form high to low. There are nine belong to high risk blocks, nine medium risk blocks and seventeen low risk blocks.