The Research Of Large Scale Landslide Risk Assessment Method Based On GIS

Landslide geological disasters occurred frequently in our country, since the 21 st century, frequent seismic activity and the urban construction will bring more severe human engineering activities and extreme rainfall conditions, etc. That have been exacerbated the occurrence of landslide geological disasters, putting forward new challenges for disaster prevention and mitigation strategy. The traditional monomer and mechanism analysis of landslide engineering cannot satisfy largely the social demand of disaster prevention and mitigation. The means which the world has been advocated of disaster prevention and reduction is the research of regional landslide hazard and risk assessment, making research from a single landslide flood gestation genes to the regional landslide hazard assessment, prediction and risk management direction. Through the technical method of the danger of regional landslide geological disasters study, we recognized that the study method for large regions of the small scale was relatively mature and the research for large scale degree of small area was relatively insufficient, thorough system of large scale evaluation methods needed to be strengthened.In view of this, it is discussed firstly the key theory and technology of landslide-prone evaluation in this article, analyzing the different levels of evaluation,servicing to different evaluation objects, elaborating systematically the mapping methods and processes of risk assessment with large scale, to analyze the plasticity and applicability of evaluation with different methods, respectively using grid unit and geomorphic unit as evaluation unit, with infinite slope of static safety coefficient method and weighted information content method, evaluating landslide liability of the study areas on the basis of high resolution DEM data. Following, it is considered the induced factors included earthquake, rainfall. The landslide disaster risk assessment of Puge county based on the improved model of Newmark introduced in detail how to use the method to carry out operation steps and evaluation method of landslide disaster in the mathematical statistics tools of ArcGIS and Excel. Making the large scale regional landslide prone to risk assessment studies true. Based on the above research, the following main achievements and conclusions was made in this paper:（1）Through based on the detailed investigation and summarization of landslide disaster, hazard inducing environment and formation mechanism of Puge county, it is summed up the development landslide in the region has the following characteristics:（1）the rock zone of sliding body wall after a steep cliff;（2）the ancient landslide of the history from leading edge to trailing edge gradually creep landslide deformation in the body or shallow surface deformation;（3）the central deep cataclastic rock landslides.（2）A variety of factors controlled the landslides distribution situation of study areas. First of all, the landslide geological disasters near 800 meters along the fault zone of wood river and black river development intensively, and the development density is maximum; Secondly, landslide development is controlled by the stratum lithology. It is mainly in the group of Jurassic and Triassic ginkgo bay（T₃bg）, yi door group of Jurassic(J_1-2y), new schiscosomiasis of Jurassic（J₂x）, late pleistocene diluvium(Qp^3-4pl), the holocene residual slope sediments(Q_h^dl+cl), accounts for 79.2%of the proportion of the total in the study areas. Third, the distribution of landslide controlled by slope structure is not obvious, developed both the reverse slope and the consequent slope.Fourthly, the relation between landslide disaster and human engineering activities, the geological disasters landslide within 100 meters apart from the road is more frequent. The number of developmental disasters were 14, with bigger landslide development density. Fifthly, more development slope of landslide geological disasters is between 20 ° 40 °, account for 73% of the total number of landslides.（3）Nine evaluation factors included choosing density, DEM, slope landslide development, formation lithology, structure, river water system, vegetation type, slope structure, human engineering activities established evaluation index system of geological hazards in the study areas. Using the analytic hierarchy process to determine weight, through the method to calculate the information quantity,completed preliminary liability assessment in the study areas. On this basis, it is summed up the existing deficiency and improved the method. Taking Puge county as an example, it introduced the study on the method of geological disaster risk assessment analysis in detail based on the improved model of information rights slope unit, and then made grid unit and geomorphic unit as evaluation unit, using the static infinite slope safety coefficient method to evaluate the liability in the region.（4）Through making the grid unit and the geomorphic unit as the evaluation unit,basing on comparison and analysis by the method of information rights and infinite slope of static safety coefficient method to geological disasters in the study areaevaluation, it got the following conclusions: for the district with the evaluation of large scale degree of small area, based on the evaluation results of geomorphic unit is superior to the evaluation results based on the grid unit, with the quantitative method of evaluation results is higher than the evaluation results based on the information method. It put forward the suitable optimization method for the sites with liability evaluation of large scale degree of small area. It is "infinite slope of static safety coefficient method based on the slope unit".（5）In view of the basis of the advantages and disadvantages of slope unit and grid unit division method in the evaluation of large scale landslide liability, it put forward the application of large scale landslide risk assessment with Newmark evaluation model, and introduced the operation steps and analysis method of the Newmark evaluation model using in ArcGIS.（6）Combined with the research methods of risk assessment technology,considering the inducing factors for earthquake of landslide geological disaster risk assessment, and implement the assessment of regional landslide from prone to risk.Taking Puge county as an example, the demonstration study, and drawing the zoning map of landslides geology disaster risk in the study area, it can be divided into four levels: high risk zoning, middle risk zoning, low risk zoning, extremely low risk zoning.（7）On the basis of existing logging data and the evaluation result of the liability of Puge county, it assigned the landslide instability of spatial probability of Puge county. It used the Gumbel frequency distribution curve to fit the frequency of the occurrence and the return period of annual rainfall in Puge county, and evaluated risk prediction research for 5,10, 20, and 30 years of rainfall return period, getting the zoning map of 10-year rainfall landslide disaster risk in Puge county, to achieve the long-term evaluation of landslide hazard prediction.