Engineering Geological Research On The Jinsha River Valley Section Of The Yunnan-Tibet Railway

The Yunnan-Tibet railway is one of the most important planning railways of China. And it has been aparted to several subsections and each subsection will be constructed individiualy. The Jinsha River valley, which is on the route of the Lijiang– Shangrila subsection and the geological conditions are comparatively complex. How to bridging over and where to locate the bridge are the key issues which restrict the railway orientation. Therefore, this study selects the Jinsha River valley as the study area and applies multi-subjects theories and methods to assess the Jinsha River valley geological conditions, and analyses the slope stability of the potential bridge location as well.Based on the analysis of the regional geological background, this paper reviews the features of the neotectonic movements and main active faults in the study area, and reveals that the Zhongdian fault and the Longpan-Qiaohou fault are the main active faults which to some extent affect the Jinsha River Bridge project. The analyses of the topography features, geological and hydrogeological conditions and the Geo-hazards distribution of the whole study area indicates that the engineering geological conditions of the Xialuoyu Bridge near the Shangxiakou of tiger leaping gorge is relative better. This paper lucubrate the stability of the high slopes of the valley and the Lengdu complex slope body which affect the bridge safty. Engineering geological analysis and the elastic-plastic finite element simulation results indicate that: 1) There is plastic zone in the left valley bottom slope with the effects of gravity and earthquake, and there is small plastic area at the lower part of the right valley loose debris; 2) When the portential downriver reservoir were on the high water level, the plastic location concentrates in the left side at the vicinity of the same hight of the water level. The Lengdu complex slope body can be divided into three parts: the slope section from the ShangriLa No.3 high school to the estuary, the ancient landslide section from Changsheng to Hezan, and the bedrock section at the Northeast of Shibuge. The author calculates and analyses the stability of the ancient landslide section from Changsheng to Hezan using the Swedish slice method, Janbu method and the simplified Bishop method, with the conditions of the current status, earthquake, water storage and rainfall. The quantitative calculation results show that the ancient landslides is stable and of high reliability with the safty coefficient of 1.257 ~1.413 in current status, and the stability decrease to 0.929~ 1.043 and 0.960 ~ 1.315 under the condition of rainfall and 7 ~ 9 degree earthquake, while the safty coefficient turn to 0.861 to 0.960 under the combined of earthquake and rainfall, and this means unstability. In order to validate the above mentioned results, the slice numerical solution method and the Monte-Carlo simulation method were combined to calculate the stability of the Changsheng-Hezan ancient landslide. The above calculation and analysis reveal that the selected location of Xialuoyu Bridge is appropriate with respect to the engineering geological conditions.In order to guide the railway planning and engineering geological survey, this paper carry out the engineering geological condition zonation assumed the Jinsha River Bridge location were decided, Applying Analytical Hierarchy Process and GIS, which base on the platform of MapGIS 6.7 and ArcGIS 9.1. And terrain slope, engineering geological rock groups, slope structure, the Geo-hazards distribution, earthquake peak acceleration, active fault, tiny physiognomy, human activity, rainfall(main differences in vertical), and the distance to the drainges were selected as indices and quantified with expert opinions for the zonation. According to the GIS calculation, the study area is divided into 4 engineering geological classes: best, better, middle and poor. According to the zonation, the Xialuoyu Bridge mainly bridge over the better engineering geological area and the middle engineering geological area, which proves that the former analysis and calculation are reasonable. The techniques and methodology used in this study can be referenced when studying the similar engineering geological subjects in other regions.