| Affected by special geological and topographical conditions, geological hazards have frequently occurred, especially in mountain town area, pose great threats to peaple’s lives and property。As progress for mountain towns move, the the growing demands for geological hazards assessment and risk assessment will increase., At present, the research on the hazards assessment and risk assessment in small and middle scale mapping are well developed, but for large scale is insufficient. Taking the Yangjiao Town area in Wulong County Chongqing City as a study case, this thesis studys the hazards’runout characters and motion range of unstable rocks which have different failure patterns, aims at carry out a new method for geological hazards assessment and risk assessment based on runout analysis. Several results and conclusions from this research are assembaled as follows:1. Based on detail field investigation, the development features^failure patterns and their formation mechanisms of the geological hazards in the area of Yangjiao Town are studied. There are two types geological hazards:landslide and unstable rocks in the Yangjiao Town area, According to the shapes, features of main structural planes and signs of deformation, the failure patterns may be divided into four types which are apparent dip slide, slide collapse, topple and rockfall; The main influence factors are slope structure, lithological combination, rock mass structure, karstification and mining activities and so on.2. The runout analysis of large unstable rocks of different failure moods are studied based on numberical modelling and empirical model, and get the runout characters and motion range.For the Daxiang unstable rock the failure pattern of which is long run-out landslide-debris flow, the DAN3D code is adopted to forward-analysis of the Daxiang unstable slope, to predict the dynamic characteristic of long run-out landslide-debris flow in different rainfall intensities conditions; For the Guanyindong unstable rocks the failure pattern of which is rockfall, the methods of combination of3D software Rockfall Analyst and2D software Georock2D is adopted to study the dynamic characters and motion range; The experiential model is used to calculate the the maximum distance and runout range of formative accumulation.3. When water level fluctuation periodically in Three Gorges reservoir, landslides in the range of backwater area are influenced periodically. Select the typical engineering geological profileof Yangjiao landslide, on the basis of the saturated-unsaturated seepage theory, the method of limit equilibrium method, in order to analyze details about the transient seepage field and corresponding stability change rule. The calculating results shows that, for all the analytical working conditions of water level fluctuation, the landslide stability coefficient is bigger than1.1, which means that the Yangjiao landslide group is in low danger.4. On the basis of the caculate results of the runout mechanism and motion range, combines the analyst of the hazard-affected bodys, we study the geological hazards assessment. Based on the runout prediction of all the unstable rocks, the runout range of different rainfall conditions is overlayed in the ArcGIS environment. The hazards zone is devided into three classifications which are high danger zone, medium danger zone and low danger zone. By comparison with the geological hazards zonation gained by using information value method, we find the hazard zonation result based on the methods of runout analysis is more suitable.5. Based on the hazards zoning map, according to the type and distribution of construction land and the the extent of the possible damage, the standard for risk assessment is made, so we obtain the risk zonation for geological hazard in Yangjiao Town area, and the preventing countermeasures are put forward. Then, we propose the geological hazard risk assessment method based on landslide runout analysis, which is apply to mountain town area. |
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