Risk Assessment And Early Warning Study Of Perilous Rocks And Slopes In Yuntai Mountain Scenic Region

The Yuntai mountain scenic region is the main component of Yuntai mountain World Geopark of China. The unique geological relics, ecology and cultural connotations in the scenic region have attracted over five million. tourists come here for tour, relaxation and vacation. However, a certain amount of perilous rocks and slopes are found in Yuntai mountain scenic region. Their occurrences are caused by the complicated geological conditions and the combined impact of tectonic activity, geologic agent and human activities. It would be quite dangerous for tourists to the region once the collapse of the perilous rocks or landslide of the instable slopes take place. Selecting the perilous rocks and slopes as research object, the paper carried out the stability analysis and risk assessment and put forward safety treatment measures on them based on the investigation of geological environment conditions. The paper has established the early warning system for the disasters of the perilous rocks and instable slopes based on rainfall amount in Yuntai mountain scenic region. The main results of the paper show as follows:A large number of fracture structure, fracture cleavage and joints, especially the two-group vertical joints destroyed the integrality of the rocks and cut them into blocks under the influence of neotectonics. The perilous rock mass(perilous rock zones) and instable slopes ultimately occurred in Yuntai mountain scenic region under the combination influence of outer dynamic geological process and human activity.There are 86 perilous rocks in study area based on the investigation and analysis of the scenic region. The qualitative determination of engineering geologic analogy shows that three are 37 perilous rocks in unstable situation, and others are currently overall stable. The quantitative stable evaluation of static analysis indicates that most of them are stable in the natural condition, only a few are much unstable. There are 83 slopes in study area including soil and rock slopes formed under the natural condition and human factors. The qualitative determination of engineering geologic analogy shows that 36 slopes are in stable situation, 30 slopes are basically stable and 17 slopes are unstable.The field rockfall experiments indicate that six kinds of principal factors have important influence on the possibility of disaster forming of perilous rock. The weight value of these six kinds of principal factors can be obtained based on the AHP. That is A={the length of slope, the gradient of the slope, the shape of rockfall, the mass quality of rockfall, the distance(the bottom of the slope to footpath), the condition of the slope}={0.295,0.098,0.034,0.135,0.404,0.034}. The quantitative evaluation method of the possibility of disaster forming of perilous rock has been established in the paper.The risk assessment of geological disasters in hazard and vulnerability shows that there are 39 perilous rocks in high-risk situation, 15 in moderate-risk and 32 in low-risk situation. There are 22 high-risk slopes, 22 moderate-risk slopes, 39 low-risk slopes in Yuntai mountain scenic region. The high-risk perilous rocks and slopes must urgently be treated; the moderate-risk perilous rocks and slopes can be suspended to treatment. The low-risk perilous rocks and slopes have weak danger to tourists and staff of the region without strong external factors triggered.Prevention and controlling measures for perilous rocks and unstable slopes are put forward according to their characteristics and geological environment. The main measures used for perilous rock treatment include careful removal, supporting prevention, anchoring, guniting, pointing for drainage, building slope protection, active and passive SNS(Safety Netting System) and so on. The main measures used for unstable slope treatment include the bulkhead or brick wall of slope protection, supporting prevention wall on the free face, guniting, impact resistance wall and passive SNS(Safety Netting System) and so on.The statistical analysis on geological disasters for nearly 10 years indicates that there is a quite positive relationship between the frequency, the scale of the geological disasters of perilous rocks and unstable slopes and rainfall in Yuntai mountain scenic region. That is means that the more plentiful the rainfall was, the more frequently and the greater scale the geological disasters of perilous rocks and unstable slopes occur. The safety measures should be taken as follow on the basis of rainfall amount: When it has small or moderate rain on weather forecast(the rainfall amount is from 0 to 25 mm among 24h), the staff of the scenic region should pay attention to rainfall information and patrol middle-high risk geological hazard points. While weather forecast suggests that it has heavy rain(rainfall amount is between 25 and 50 mm among 24h), the staff of the scenic region should release the geological disaster early warning and start contingency plans based of rainfall information. The middle-high risk sections should be restricted or protected to pass. While the storms or heavy storms will visit the region(rainfall amount is more than 50 mm among 24h), the staff of the scenic region should release the geological disaster warning and close middle-high risk sections, meanwhile, the dangerous case should be eliminated and the tourists should be taken to safety place.