| On the harmfulness of geological disasters, the disastrous consequencecaused by landslides to human is only after the earthquake. The landslide has the characteristics of wide distribution, high frequency, fast movement and severe losses etc. In China, there are 70% areas in mountainous areas, which makes the occurrence of landslide high density, complete type, frequent occurrence, huge scale, very serious harm. Especially since the 21st century, with the large-scale development of urbanization, growing range of human space activities gradually expanded, and the growing of the degree of disturbance to the geological environment owing to human engineering activities, meanwhile influenced by the global climate change and the degree of crustal activity increased and other factors, the frequency and intensity of landslide events showed a growth trend, the caused casualties and economic losses continue to increase. According to the data released by the China’s Ministry of land and resources,10907geological disastersoccurred in 2014, China, and the disasters caused 349 deaths,51 people missing,218 people injured, the direct economic loss of 5 billion 410 million yuan; Among the geological disasters, there are 8128 landslide disasters, and it accounted for 74.5% of the total number of geological disasters. The landslides are mainly in Chongqing, Sichuan and Hunan district. It indicates that:landslide is a serious threat to human life and property safety, it destroys the environment and resources, brings huge losses to the country and the people.The frequent occurrence of landslide disaster has aroused widespread concern and attention of the international community, while prevention and reduction of disaster can reduce the harm of landslide disasters effectively in the face of this grim situation of disaster. Before this century, in order to prevent and reduce the landslide disasters, the traditional geological formation mechanism and engineering control technology are the main basis. But with the development of science and technology, the means of landslide disaster prevention and control are developed synthetically from geology, engineering management into landslide disaster monitoring and early warning, risk assessment and management and other aspects. Especially, the "landslide risk assessment and management " which is to promote and advocate in the international community has turn into one of the effective ways for disaster prevention and reduction. Research in the landslide risk assessment and management in China started late, at present the national level has not made the landslide disaster risk management into the strategy of disaster prevention and reduction, so landslide risk assessment and management research is not only a leading edge research topic, but also an important practical means of developing disaster prevention and ruduction issues urgently need to be addressed.At present, both at home and abroad, the research of landslide disaster risk in regional scale mainly has following several questions:First, for landslide susceptibility studies, in the index classification still rely on method that divided by the person who require a higher experience judgment,or in accordance with the isometric classification, have no theoretical support of scientific and rational, and it will ultimately affect the accuracy of the calculation model.At the same time, the methods of classification of landslide susceptibility mainly rely on the variety of classification methods belong to ArcGIS.With the different selection methods, then the classification results are not the same, and it increase the difference of susceptibility classification. Or in accordance with the artificial demarcation of the area of each grade accounted for the whole area percentage to the susceptibility of grading,similarly, highhuman experience is required, and there is no reasonable theory support, increasing the randomness of susceptibility classification.Secondly, for landslide hazard research,confuse the concept of "susceptibility"and " hazard ", wrong think "landslide susceptibility" is "landslide hazard", and the domestic scholars study the landslide hazard only stay in landslide susceptibility analysis. It’s just come to the spatial location of the landslide may occur, that’s spatial probability, and it does not take the time probability into account to the landslide problem, and did not fully meet the periodof landslide hazard evaluation.Furthermore, for the landslide disaster vulnerability research, the analysis of anti-disaster ability of the intensity of disasters and hazard-affected body aremostly still based on experience assignment, lack of scientific theoretical foundation, leading to vulnerability a low accuracy.Finally, for regional landslide disaster risk research, China is still in the research stage, and no large-scale, large-scale application and promotion, and lack of the support and protection of the relevant laws and regulations; at the same time, in the specific implementation process, due to the many technical problems have not been solved very well, making the credibility of the results of landslide hazard risk reduce; In addition, up to now, the landslide hazard risk management system is still not perfect, and the system of various regions and departments is not uniform.The Three Gorges Reservoir of Yangtze River area has always been the landslide and other geological disasters prone areas due to the complex natural conditions, strong human engineering activities and so on. Chongqing city, Wanzhou district is located in the confidant of Three Gorges reservoir area. The landslide development in Wanzhou district has the characteristics of high frequency and wide distribution. In view of this, this paper will start to analysis the problems from the characteristics of regional landslide development, and based on the domestic and foreign mature risk analysis method, for the problems and shortcomings raised above, to carry out thetechnology and method research of landslide risk assessment technology and management in county scale. Through the above research, this thesis has made the following results and conclusions:(1)Thisresearch will analysis the development and distribution rules of landslide disasters in Wanzhou District,then the typical landslide is taken as an example to discusses the response relationship between landslide surface displacement and the influence factors in detail, and the landslide deformation and failure mode are clarified. Through collecting the latest geological disaster investigation data ofWanzhou district, and combined with the appropriate field investigation, and do statistical analysis on regional distribution regularity and the characteristics of the development scaleof landslides in Wanzhou district. The results show, the spatial distribution of regional landslide have the characteristic of clusters, density distribution is nonuniformity, and with the increasing of the area and volume of landslide, the fewer the number of landslide distribution. Under this premise, taking the Tangjiao 1# landslide、Sunjia landslide and Dabaoliang landslide as the example, to analyze the intrinsic relationship between landslide deformation and influence factors of inside and outside from the angle of deformation mechanism, and conclude that rainfall, water level and other external factors have a greatimpact on deformation of landslide,and among them has a complex nonlinear response relationship; The internal factors of the landslide decide the general development trend of deformation, whereas the external factors such as seasonal rainfall and reservoir water level changes directly accelerated the deformation and failure of the landslides, and this is the reason why the landslide in Three Gorges reservoir show a "step type" development and evolution.(2)Based on the statistical analysis method of landslide frequency ratio, the landslide index factor will be divided, and then conducting the landslide susceptibility mapping in Wanzhou area.Landslide hazard susceptibility research has very important practical significancein the landslide disaster risk management and city planning etc. In previous studies, there are few studies on the classification of index factors. In view of this, this paper take Wanzhou District where landslide disasters occurred frequently in the Three Gorges reservoiras the object of stud:First of all,5 types disaster-deducing factors(topography, basic geological, hydrological factors, predisposing factors and human engineering activities) which affect the occurrence of landslide were chosen for evaluating indicator of landslide susceptibility. The landslide area frequency ratio method was adopt to conduct the classification of the status of each index factor;Secondly, based on the historical data of 655 landslides in the whole district,the decision tree model and support vector machine modelwith the deeper study internationally were adopt to establish their respective landslide susceptibility evaluation system.Furthermore, according to the curve graph of landslide susceptibility index, obtaining the classification of the susceptibility results bythe 2 methods mentioned above and get the whole landslide susceptibility zoning map;Finally,2 models are discussed and compared from the aspects of the model results, accuracy and applicable conditions etc.The research results show that:the prediction accuracy of the decision tree model and support vector machine (SVM) model were 98.0% and 97.4%, the former prediction ability is superior to the latter.(3)Based on the results of landslide susceptibility mapping, considering the major inducing factor(rainfall), conduct the landslide hazard analysis under different rainfall return period, and it comes true that from the analysis of landslide susceptibility to the transition of regional landslide hazard assessment. Firstly, the thesis has done statistics rainfall data for 53 years in Wanzhou District, and analyzed the relationship between the annual quantity of landslide disaster and the rain data, and it is concluded that the landslide event has a significant positive correlation with the rainfall event. Secondly, using the Pearson type Ⅲ distribution function to fit the rainfall frequency curves of Wanzhou district, and obtained the rainfall intensity of 5 years,10 years,20 years and 50 years rainfall reappearing period in the study area. Then, combined with the historical landslide inventory data to count the induced landslide area of various levels of susceptibility in different rainfall return period, and then get the Spatial probability and time probabilityof landslide occurrence in each prone area. Itfinally accomplish the landslide hazard assessment under different rainfall return period in Wanzhou area.(4)Based on the quantitative analysis method,establishing vulnerability assessment model for landslide bearingbodyin Wanzhou area. And then carry out the risk assessment of the whole region.The main contents of vulnerability analysis for landslide bearingbodyincludes landslide strength and the anti-disaster abilities of bearingbody, and the former is the measurement index of comprehensive damage ability of landslide, the latter reflect ability of avoid casualties for disaster bearing bodies suffered a certain intensity disaster avoid casualties. Both of them are used to establish the quantitative evaluation model of vulnerability for landslide bearingbody in Wanzhou area,and obtained the vulnerability of buildings, roads, land resources and population vulnerability respectively. According to the statistics of distribution of the value of disaster bearing body, population density in Wanzhou region,and the regionallandslide hazard risk assessment can beput into practice. The results indicated that:landslide disaster life high risk zone mainly concentrated in Wanzhou city of Taibai subdistrict offices, Shahe subdistrict and zhonggulou subdistrict and other densely populated area; landslide disaster economy high risk areas are mainly distributed in the urban areas,streets and towns of the both sides of Yangtze river and the Zhuxiriver, and traffic construction land and other area with greater economic value.Combined with the distribution of life risk and economic risk zoning map, it obtained that the main city zone has the biggest landslide disaster risk.(5)Based on a certain landslide risk assessment criteria, the population risk and economic risk assessment of landslide disaster will be studied in Wanzhou district.The results show that the population risk only includes acceptable risk area and unacceptable risk area, in addition, the latter area, accounting for 55.01% of the area of the whole risk assessment and mainly distributing in the residential areanear the town and the coastwise of the Yangtze river and its main tributaries where the population is relatively concentrated and the landslide susceptibility is very high.Besides, the economic risks unacceptable area, which the total area of 4.78% in the study area, are mainly located in the main urban area of Wanzhou district, Dazhou town, Xiaozhou town,Baianba street and the other townwith great economic value as well as the important traffic region.The economic risks tolerable area are accounting for 2.5% of the whole study area, the distribution of such region has been rather dispersed and mainlyspread over the Longdu street and Baianba street. Thepercentage of economic risk acceptable areareachs up to92.72% and mainly distributed in the area where human engineering activities are fewer such as forestry land in the mountains and agricultural land area, etc. |
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