Risk Assessment Of Individual Landslide

Landslide is an important hazard of the geological disasters, It is not only a threat to humans, but also serious destructions to the environment, resources and property.Around the world, there are tens of thousands of casualties and10billion dollars economic losses caused by landslides and the secondary disasters. The tenet of landslide hazards research is how to reduce the economic and casualty losses triggered by landslides.From the early1950s, we began the systematic researches and engineering management of landslide in our country. The theoretical level of landslide research has being dramatically improved, and the technical level of management measures has also being continuously improved by combining with a lot of engineering examples. Because of the large expend of landslide treatment project,we can only choose the landslides of big harmfulness and serious loss for management, in spite of the growing funds from the national and local investment year by year. The current management measures still cannot reach the purpose of effective governance for some landslide of big volume and thick body.Meanwhile, recently in southern China,a lot of landslides, collapse and debris flow disaster caused by the extremely rainy weather and thus caused serious losses were also a wake-up call for us. Though the theoretical research and treatment level of landslide hazard have gradually increased, the casualties and economic losses didn't have a significant reduction.Therefore, with the actual needs of the disaster prevention and reduction works, we should break through the current research of the stability, mechanism and control measures of landslide, reasonably determine and evaluate the impact scale of landslide disaster on life and property by using the risk evaluation theory and method, to provide technical support for economic and effective emergency mitigation measures and disaster optimization decision management.In the landslide risk research field, the large scale spatial landslide risk evaluation has been deeply and detailed carried out at present time. Some academic institutions in the mainstream countries or regions have successively published a series of research plan, technical guidance or even laws in spatial landslide risk evaluation and management. While, it is still deficit in the research of the small scaled monomer landslide risk evaluation. A part of foreign scholars have worked on the idea of single landslide evaluations, evaluation systems, relevant techniques and methods, but there are still many problems to be settled as to the establish of the evaluation model, such as the quantitative relationship between the structures damaged conditions during the landslide deformation period and the characteristics and magnitudes of deformation, the quantitative ascertain of the vulnerability of the disaster body taking into account of landslide velocity and impacting force, the evaluation of the indoor population vulnerability and so on, especially on the calculation of fragility of destroyed body and the destroy intensity of the disaster in the vulnerability assessment.This thesis has developed the monomer landslide risk evaluation from two aspects as theoretical model and practical analysis. Based on the widely accepted definitions of landslide risk evaluation, the model of hazard assessment and vulnerability analysis is deeply researched. Taking the Zhaoshuling landslide in Three Gorges reservoir and E1.Picacho landslide in El Salvador as examples, analyze landslide risk evaluation model during the deformation stage and slide stage separately, and it accomplished the research and practice of the monomer landslide risk evaluation system and model. Through the above research, the main achievements and conclusions in this thesis are as follow:(1) Taking consideration of the uncertainty of the physical and mechanical parameters of landslide and their triggered factors, doing the research of landslide failure probability.Landslide failure probability can efficiently represent the landslide hazard. Many uncertain factors contribute to the uncertainty of landslide failure. In one hand, the uncertainty of physical and mechanical parameters of landslide materials play dominate role in that. In the other hand, we cannot ignore the other triggered factors and their occurred probabilities. This article mainly concerns the effects of rainfall and summarizes the rainfall threshold of landslide at home and abroad. The method of choosing decent extreme value date and the distribution curve of common extreme value frequency are also summarized. Besides, the paper gives overviews on the calculation method of K. Person â…¢distribution curve, exponential distribution curve and Gumbel distribution curve. Finally, the paper proposed a calculation method of landslide failure probabilities concerning the occurred probabilities of extreme rainfall.(2) Individual landslide vulnerability analysis considering intensity of slope hazard and susceptibility of elements at riskBased on the systematic summary of research status of vulnerability assessment model in domestic and international field, this paper discussed the key issues existing in vulnerability calculation, proposed the quantitative assessment model for landslide vulnerability analysis accordingly. Starting with the internal and external causes of landslide risk effects, this model takes both susceptibility of elements at risk (S) and intensity of slope activity (I) into account, elaborates the indexes, concepts and correspondence of S and I. Susceptibility of elements at risk (S) describes the self-characteristic of elements at risk, points out that it's only proper to quantify indexes of S after considering the different internal factors and types of elements at risk. As the external factor, intensity of slope activity (1) puts the hazard scale and intensity into consideration, divides the landslide movement process into deformation stage and failure stage, proposes corresponding indexes and assessment model for various time scale and intensity degree, having the mechanism and criterion of landslide movement effect considered of.(3) Susceptibility assessment model of elements at risk for individual landslide vulnerability analysisAfter analyzing the mechanism of landslide movement effect, susceptibility assessment of elements at risk builds the appropriate model picking the indexes which are representative of the elements characters. Different types of elements at risk should be distinguished to ascertain the susceptibility indexes. As to the quantitative susceptibility indexes of buildings, structure type, the ratio of the useful life and design life, maintenance conditions and the angle between the direction of the landslide forces and the axis of building are chosen, while the health status of the population, age composition and the condition of disaster warning systems are provided for the quantitative susceptibility indexes of people. Generalized formula for deciding the susceptibility indexes of age composition are proposed, underlined by analyzing statistic data of all ages mortality rate of different types of geologic hazard.(4) Constructing a model to evaluate the hazard intensity of individual landslide vulnerabilities evaluation in deformation stage.The hazard intensity evaluation model of landslide in deformation stage is successful constructed base on the failure modes of deformed landslides and analysis of hazard bearing body loss effect, this evaluation model aim to the whole buildings in the areas affected by the landslide deformation. The evaluation factors mainly include3aspects (landslide surface deformation, displacement rate and landslide depth). The paper calculates the additional internal force of reinforced concrete frame structure and masonry structure in the condition of landslide surface deformation. Assuredly, the limited force the two structure types can bear should be also calculated. The ratio of additional internal force and limited force will reflect the damaged intensity of buildings affected by the landslide surface deformation. Secondly, the calculation equation of landslide speed strength indicators is created according to the landslide speed threshold related to the buildings limited damaged status. Lastly, the ratio of landslide thickness and building foundation depth represent the building stability effected by the spatial distribution of landslide hazard.(5) Establish the evaluation model of landslide effect intensity during failure stage for individual landslide vulnerability assessmentOnce landslide failure, during landslide's movement along the terrain in valleys, it will cause a very powerful impact, which has a strong threat and destructive power on the buildings and people within influence areas. Therefore, if you want to establish the evaluation model of landslide effect intensity, you should first calculate the movement process under the control of terrain after landslide failure. In this paper, on the basis of concluding the calculation methods of sliding distance, we put forward the kinematics model about three dimensional landslide sliding process calculation based on finite volume method, considering the different expressions of sliding friction corresponding to different rheological properties of interlayer of surface loose deposits and slide mass material during landslide movement process, acquiring the results of landslide sliding distance, sliding speed and sliding body thickness by three dimensional calculation, providing the basis for evaluation of landslide effect intensity during failure stage.The objects for Vulnerability evaluation during landslide instability phase include buildings and people. Owing to different failure mechanisms of moving landslide to these two elements at risk, the selections of intensity index corresponding to these elements are also different. For buildings, this paper simply modeled reinforced concrete frame structure and masonry structure, then through analysis of stress and deformation to the structure model and repeated computations, established a calculation model under the limit horizontal impact force to the structure. Based on the foregoing calculations, selecting the ratio of landslide body impact force to limit horizontal impact force of buildings and the ratio of sliding body thickness to buildings'upper structure height as hazard intensity index, founded a quantitative evaluation model. For people, starting with the difficulty escaping from the threatening scope, we took into account landslide speed, depth and impact zone's width. By analyzing statistics data about sliding velocity and the corresponding to different casualties in history landslide hazard examples, confirmed speed threshold for people escaping landslide, proposed calculation formula of landslide speed intensity index for personnel.(6) Proposing vulnerabilities evaluation model of persons in the room based on the buildings vulnerabilities.Vulnerabilities of person in the room can be directly affected by the structure type and their vulnerabilities. Buildings vulnerabilities reflect their deformation or damaged extend. However, buildings'structure influence the degree of difficulty of people's escape and persons'safety due to the drop of building elements when serious deformation happens. It can be easily found that people in different building types are damaged differently when lava flows or earthquake make them topple down. Therefore, vulnerabilities calculation model of person in the buildings related to the buildings'vulnerabilities is created by analyzing a great deal of date between the rate of casualties and building types from literatures.(7) Risk assessment study during landslide deformation stage, taking Zhao Shuling landslide in Three Gorges Reservoir area as an exampleThrough analyzing the basic geological data, exploration data, soil test data, the displacement monitoring data, rainfall data and hazard-effected elements'field survey data of Zhao Shuling landslide in Ba Dong County Three Gorges Reservoir, a case study is made by adopting the landslide risk assessment model during deformation stage mentioned above. Based on the statistical analysis of rainfall monitoring data in Ba Dong County from January1980to June2010, this paper introduced the method to calculate frequency distribution curve parameter for maximum cumulative rainfall of five days, ten days, twenty days and thirty days in four stages, and then optimized the value of parameter. Besides, by calculating the probability of multi-day cumulative extreme rainfall distribution adopting Gumball distribution curve in Ba Dong County, we obtained rainfall intensity of different stage, different accumulative rainfall days and different return period. Based on the rainfall conclusion and landslide stability method, the paper calculated landslide's year failure probability with the combination of two kinds of rainfall intensity and water level. Secondly, landslide disaster vulnerability assessment was made for the operation conditions of larger failure probability. Based on the field investigation data of elements at risk, we acquired vulnerability evaluation index's values; Then made numerical simulation of landslide deformation under calculation conditions adopting FLAC3D, based on the surface displacement data from simulation results, calculated building's structure additional internal force on deformation landslide, combining with sliding speed and the depth of sliding body from simulation results, completed the calculation of disaster effect intensity index, obtained vulnerability distribution map of buildings on the landslide; Based on landslide failure probability and landslide vulnerability assessment, the risk assessment of buildings was given. Owing to Zhao Shuling landslide's stability state being better now, year failure probability under calculation conditions is2.18%, building vulnerability's values range only from0.00to0.15, consequently, the economic risk value under calculation conditions is low, only Y49,200.(8) Risk assessment study during landslide failure stage, taking El Picacho landslide in El Salvador as an exampleThe application of risk assessment model during landslide failure stage is explained in El Picacho landslide, the emphasis of calculation is vulnerability assessment during landslide failure stage. First of all, according to remote sensing images of landslide sliding track and survey data of sliding distance and thickness of accumulation bodies, validated landslide kinematics calculation model mentioned in this paper, the results show that sliding path and sliding distance gained by model calculation have a good agreement with the actual situation, only in open area without lateral slope, the width of landslide impact area between calculation and actual situation is different, therefore the simulation result of landslide impact influence scope was safer.Adopting the kinematics model mentioned in this paper, we calculated landslide sliding distance, sliding speed, sliding body thickness and width of sliding path in the same research area under other eight conditions, confirmed the limit horizontal impact force to buildings within landslide impact influence area, completed disaster effect intensity evaluation of buildings and people during failure stage. Then counted the attributive characteristics of elements at risk within landslide impact influence area, based on the vulnerability assessment model mentioned above, we acquired vulnerability evaluation index's values. Based on the index values and GIS, we obtained vulnerability distribution map of outside personnel, buildings and indoor personnel. The results show that under moving landslide's giant impact energy, the people within landslide influence scope have a high vulnerability, whose values are greater than0.4. About64%of the buildings are the highest level of vulnerability, especially the buildings close to the landslide source area or the center of landslide accumulation area. Compared with outdoor personnel, indoor personnel's vulnerability is smaller; this suggests that buildings have protective effect on indoor personnel. Finally, according to the vulnerability assessment results and qualitative landslide probability, we got the landslide risk results during landslide failure stage under different conditions.