Risk Assessment And Early Warning Of Individual Landslide

Landslide, which is a major hazard of geological disasters, is not only a threat to humans, but also to the environment, resources, property, etc.. In the world, thousands of casualties and hundreds of billions dollars of economic loss are caused by landslides and their secondary disasters of every year. How to reduce the economic and casualties loss caused by landslides is the purpose of landslide research. China is a country with frequent and variety geological disasters, including landslide, collapse, debris flow and so on. National geological disaster survey results show that, more than 400 counties are troubled by the potential geological disasters, and more than 10,000 villages are threatened by landslides, avalanches, debris flow and other disasters.The proportion of landslide disaster accounted for more than 65% in China, while average annual economic loss is more than 2 billion RMB. Therefore, faced with the practical needs of disaster prevention and mitigation, we should break through the current research of landslide stability, the mechanism and control measures, and apply the risk assessment methods to identify and evaluate the impact scale the landslide hazard to life and property, to provide technical support for the cost-effective mitigation measures and disasters optimization decision-making management.Landslide risk assessment and management started relatively late in China in addition to Hong Kong, which shows a big gap with the developed countries. There are no relevant technical guidelines available at present. Moreover, after the sudden catastrophic geological disasters, Such as the "5.12" Wenchuan earthquake in Sichuan in 2008, the "8.7" Zhouqu catastrophic debris flow in Gansu in 2010 and the"1.11" landslide in Zhenxiong, Yunnan in 2013, the geological safety issues of post-disaster emergency, disaster evaluation and long-term recovery and reconstruction became new challenges for risk assessment and management. Therefore, combined with the international experience and the actual demand of geological hazard prevention and mitigation in China, one of the urgent tasks is to develop the geological disaster risk management guidelines suitable for China.In this paper, the Tangjiao landslide in the Three Gorges Reservoir was taken as an example to make the hazard assessment and vulnerability assessment of the individual landslide. Then the risk of lives and economic was assessed. Based on the risk acceptance criteria of lives in China, the risk level of the Tangjiao landslide was determined. Based on the landslide deformation mechanism and the comprehensive consideration of the various factors, the landslide displacement was predicted based on the artificial intelligence models.Based on the above researches, the main results of this paper are as follows:(a) The individual risk acceptance criteria and the F-N curve of the social risk acceptance criteria were established. Different risk acceptance criteria of various disasters were summarized, then the risk acceptance criteria of lives in China was studied, including the individual risk and social risk induced by geo-hazards and landslide in China. The individual risk acceptance criteria of geo-hazards in China were: the acceptable criteria is 1×10-6 each year, while the tolerable criteria is 1×10-4 each year; the acceptable criteria of landslide in China is 1×10-7 each year, while the tolerable criteria is 1×10-6 each year. Based on the ALARP criteria method of the social acceptance risk research, statistical analysis of the deaths in the geo-hazards and the total population in China were made comprehensively in this paper, and the social risk acceptance criteria of geo-hazards in China were obtained. At last, the F-N curve of the social acceptance criteria of geo-hazards and landslide in China were proposed.(b) The failure probability calculation of various deformation modes of the Tangjiao landslide under different conditions of rainfall and reservoir water level. Based on the deeply analysis of the engineering geological conditions of the Tangjiao landslide and its characteristics of the surface displacement, the groundwater and the influencing factors, and combined with the feature of the macro-deformation, the landslide deformation mechanism and deformation partition were determined. Based on analysis of the main triggers (rainfall and the reservoir level fluctuation), the hydrologic boundary conditions of landslide hazard analysis was determined and the failure probability under different conditions were calculated, respectively.(c) The calculation of the velocity, the submerged volume and the generated waves of the Tangjiao landslide. Based on the calculation theory of the velocity, the submerged volume, the height of the first wave, the propagation distance of the wave, and the height of the propagation wave, the triggered waves were calculated and analyzed respectively, which made the hazard assessment of the reservoir landslide more complete.(d) The vulnerability of the element at risk of the reservoir individual landslide was studied, and the risk acceptable level of lives was evaluated as well.In this paper, the author studied the vulnerability composition, the investigation and classification of the element at risk, the risk evaluation of lives, the economic valuation and the vulnerability assessment of the element at risk on the landslide and within the influence area of the waves. The landslide deformation was divided into two stages for the vulnerability assessment, including the deformation stage and the failure stage, then the vulnerability of lives and economy were evaluated respectively. The vulnerability of the dam, the shipsides, the residents and buildings along the bank within the influence area of the generated wave were evaluated respectively, which completed the vulnerability assessment of the element at risk of reservoir landslide.Risk assessment results show that, if the Tangjiao landslide fails under the most dangerous condition(175m→145m+heavy rain occurred every 50 years), the smallest individual risk of which is 7.2×10-4 each year. The risk of lives on the landslide is larger than the tolerable criteria, therefore, measures should be taken to achieve an tolerable even acceptable risk.(e) The forecasting and early warning of the individual landslide based on the landslide displacement prediction. The accurate prediction of landslide deformation plays a significant role in the early warning of the individual landslide, which can reduce the loss of economic and casualties caused by the landslide.Three artificial intelligence models were chosen in this paper to predict the surface displacement of the leading part of the Tangjiao landslide, including the BP neural network model, the support vector machine model (SVM), and the Extreme Learning Machine Model (ELM). Landslide displacement is controlled by the triggers and the landslide evolution state together, therefore, seven factors, such as the rainfall, the fluctuation of the reservoir level and the pre-displacement, were adopted to establish the prediction model. The results show that, the ELM model shows great result in the smooth stage, it also performed effectively in the most critical stage of landslide early warning, which is better than the SVM model and BPNN model. The prediction result of the ELM model can better reflect the response relationship between the main factors and the deformation of the Tangjiao landslide, so as to predict the development trend of landslide displacement more accurately. Therefore, based on the landslide deformation mechanism and the comprehensive consideration of the various factors, the proposed ELM model can better reflect the key role of the dynamic factors to the development of the landslide deformation, which is an effective method for landslide displacement prediction.