| Landslide disasters caused serious harm to natural resources, human life and property. Historical records of landslide showed it caused significant losses to buildings, dams, reservoirs, roads, railways, rivers and lifelines, etc. With the development of human society and the change of environment, disaster losses caused by landslides continued to increase, so the research on landslide is particularly important.Since2003, the operation of the Three Gorges Dam impoundment has been started, because of the periodical fluctuation of the water level in the Yangtze River, collapses, landslides and other kinds of geological disaster increased significantly in the Three Gorges Reservoir Area. With the consummation of the geological disaster prevention projects in the second and third stage in the Three Gorges Reservoir Area, some geological hazards have been taken the appropriate engineering control measures, but there are still so many geological disaster point which need to be controlled and prevented. Wanzhou District whicn belongs to Chongqing City located in the middle of the Three Gorges Reservoir Area, and it played a key role in the prevention and control of geological disasters in the whole Three Gorges Reservoir Area. Because a lot of old deepseated bedrock landslide distributed in this region, such as the Taibaiyan ancient landslide, Caojiezi ancient landslide, Anlesi ancient landslide, Pipaping ancient landslide, Diaoyanping ancient landslide, Shuangyantang ancient landslide and Fuma ancient landslide. The distribution of rainfall in Wanzhou district is also the most dense in the Three Gorges Reservoir area, and the landslides induced by rainfall is therefore endless.The fundamental purpose of the study for landslide is to reduce population and economic loss caused by the occurrence of landslide, therefore, landslide risk analysis has become an important content of landslide research area. At present, the international landslide risk assessment and management concepts and definitions related to research and theoretical framework have been basically mature, and a series of technical guidelines, laws and regulations about landslide risk have been published. In most of case studies, the most difficult and time-consuming work in landslide risk management is to identify, understand and interpret the landslide disaster, and engineering geologist with extensive knowledge and experience are often better able to complete the work of landslide risk analysis. Such landslides geologists usually have a better understanding of landslide uncertainty and don’t unrealistically quantify it. Relative to overemphasize the importance of landslide risk quantification, it’s better to put much more effort in understanding and interpreting the geological evolution of the landslide. Thus, from the point of geology, it has practical and theoretical significance to combine the risk assessment of single landslide with regional landslide.This paper carried out the study of regional landslide risk assessment from the theoretical model and case analysis two aspects. On the basis of internationally recognized theoretical framework for landslide risk management, this paper combined the regional with single landslide risk analysis and applied the mature hazard and vulnerability assessment model for single landslide hazard to regional landslide risk assessment. This process mainly included the landslide classification and the selection for the typical representative single landslide for landslide hazard and vulnerability analysis. And then this method was promoted to the same type of landslide based on the common features. The final aim is to achieve landslide risk systematic evaluation from the point to plane. Through the above analysis and research, the paper mainly achieved the following results and conclusions:(1) On the basis of deep study on the formation mechanism of bedrock landslide, the possible deformation pattern of large landslide group was promoted and landslide hazard prediction was carried out. On the basis of summarizing the previous formation mechanism analysis of nearly horizontal bedrock landslide, numerical simulation method was used to analyze the stability and failure probability of landslide under various different conditions, identify major predisposing factors of landslide and analyze four possible deformation and failure modes of the entire landslide group.(2) Evaluation models for different types of landslides wrer proposed. Since the type of landslide at the study area is very complex, the size of landslide volume has high disparity, and the mechanism of landslide also is different, therefore, on the basis of deep analysis of historical data and formation mechanism of landslide, the landslides at the study area were divided into four types:bedrock landslide, debris landslide, shallow deformation body and unstable rock. Depending on the detail level of landslides historical data and survey data and the number of different types of landslides, respectively, qualitative and quantitative models were used for landslide susceptibility zoning, and its accuracy has been tested in full compliance with the requirements.(3) This paper considered the impact of the treatment project effectiveness to the hazard of regional landslide. The study area distributed seven old landslide groups, and the front loose deposits had serious deformation, so most of the deformation body had been treated by various treatment measures. By collecting the detailed survey and treatment design data of landslide, combining with the regional remote sensing image data, this paper tried to restore the type, manner and location of control measures for individual landslide. Through the analysis of the effectiveness of landslide treatment project and displacement monitoring data of landslide, this paper tried to have an in-depth understanding of the quality and effectiveness of various landslide control project and provide a basis for subsequent landslide hazard evaluation.(4) The remote sensing image data was used in the investigation of landslide bearing body to reduce the workload of field work, supply and perfect the spatial information of regional landslide bearing body. On the basis of detailed survey for landslide bearing body of Tangjiaocun No1landslide and Shanwanyantang landslide group, the DEM model of study area and remote sensing image data were overlaied to supply and perfect the regional landslide bearing body information, meanwhile, the landslide inventory map was added and advised again including some data about landslide control project. Through the in-depth analysis of two typical landslide bearing body, combining with regional remote sensing image data and the city plan map in this region over the past decade, the study area was divided into two blocks:1) the city center, most were high-rise buildings with reinforced concrete structures, and the population was very dense;2) suburbs, most were two-room residents with brick structure, and the population was very few. The purpose of zoning is to facilitate the assessment of the value of the regional landslide bearing body.(5) By choosing typical landslide to carry out vulnerability analysis for landslide bearing body, combining with the landslide formation mechanism and deformation characteristics, the results of vulnerability assessment for single landslide was extended to vulnerability analysis for regional landslide. Through the vulnerability analysis for Tangjiaocun No1landslide and Shanwanyantang landslide in deformation or instability phase, vulnerability evaluation index and model for different types of landslide bearing body were founded, and the vulnerability analysis for four types of landslides:unstable rock, bedrock landslides, shallow deformation body and debris landslide was finished, finally, it provided a basis for the quantification of regional landslide risk assessment.(6) Taking Wanzhou District as an example, case study for risk assessment of the different types of of landslide was conducted. On the basis of the landslide hazard and vulnerability analysis for landslide bearing body of Shanwan rock landslide, focused on the formation mechanism and distribution of bedrock landslide at Wanzhou District, bearing body vulnerability index value of this type of landslide was proposed, and the condition of the water level reduced from175m to145m adding50year return rainfall and earthquake was selected as the most dangerous working conditions for regional landslide hazard and vulnerability assessment, finally, the result was combined with the distribution map of landslide bearing body to calculate the risk value of the population and building in the instability stage of landslide. Risk assessment of unstable rock is built on the basis of statistics, and regional vulnerability assessment indicators and model for unstable rock were built on the basis of calculation for the stability factor and the maximum horizontal distance of290unstable rocks in two typical dangerous rock bands. The condition of50-year heavy rainfall plus the earthquake was selected as the most dangerous working condition to calculate the risk value of the regional dangerous rock in this working condition. Considering the similarity of deformation modes for shallow deformation body and the debris landslide, these two types of landslides were put together to conduct the landslide risk assessment focusing on the risk is to consider the risk value of the building on the stage of deformation. Finally, the results of the risk assessment which was carried out according to four types of disasters were put together to get the whole landslide risk assessment results at Wanzhou District. The results can be applied to land use planning and landslide disaster prevention planning at Wanzhou urban area, and the ultimate goal is to the loss of local people’s lives and property which was induced by the landslide development. |
PDF Full Text Request