Study On The Complex Geological Condition And Its Control Of Dam Project Stability In Yangfanggou Hydropower Station In YaLong River

Yangfanggou hydropower station is the fifth cascade station in the middle reach of Yalong River. The power is at the stage of feasibility exploration now, and is proposed to be double-curvature arch dam. The safety and stability of the dam is important, because if it crashes, there will not only be economic losses, but also threat the safety of lives and the property of millions of people downstream. Domestic and international experience shows that the success of dam construction depends largely on the basis stability. Due to adverse geological and environmental conditions, in international, there are many painful lessons, such as France Malpasset Arch Dam,Xiuwen Arch Dam of China, etc.Therefore, it is practical significance for dam contribution to systemly summariz the factors that affect the stability of the dam or dam shoulders and to evaluat the stability of abutment anti-sliding.According to the domestic and foreign reports on dam destroy incidents, the factors of the dam instability accidents mainly include the destroy of dam foundation, bad geology conditions of dam shoulders, the submergement of flood through the top, the slope collapse of internal and external reservoir, seepage of groundwater and the change of temperature. A arch dam characterized by transferring most loads to both river banks predominates in all events of losing anti-sliding stability due to bad treatment of abutment. Under the situation that geology environment in dam site area is relatively complicated, the major factors proposed influencing the anti-sliding stability are as followings: lithology, rock mass structural planes, groundwater, crystal stress. After cutted by structures, rock mass will be of no continuity and heterogeneity, the strength properties and the deformation of rock mass will be significantly deduced and the ability against weathering and groundwater effect of rock mass will be significantly weakened too. So rock structure is the main factor controlling abutment anti-sliding stability. The research on their engineering geological characteristics holds an extremely important role in the stability analysis.In order to analyze the stability of anti-sliding of arch dam's abutment, detailed study has been put on the geological characteristics of rock mass structure of dam site, and we know that faults in site area are mainly in steep angle. Fault plane outspreads mostly less than 1km except the controlling fault F2 of 1 ~ 2km. The character of the fault zone is the development of brittle tectonite, such as foliated tectonite, fault breccia fault gouge, multiple tectonite and so on, which show the multistage characteristics of the fault activity. Fractures develop randomly on the left and right bank abutment, preferred orientation of which changes with the bank and elevation. Fractures are mainly of steep angle with the strike of NNE and NWW. Compared with the NNE-trending dominant fractures, NWW-trending fractures outspread longer in space.Through special field investigation and indoor data analysis on different scale faults and bedrock fissures going against with arch dam stability, slipping and sideslip surface boundary of sliding block are distinguished. Considering that the characters of slipping surface and sideslip surface crack boundary are different in different parts, parameters are assigned based on segmentation and partition, and meanwhile, the shear strength parameter and the analysis of bedrock fissures which are the possible boundary of abutment instability block are combined in the parameter assignment. Finally, possible combinations of boundaries and anti-sliding stability of Yangfanggou dam abutment rock mass are evaluated using rigid limit equilibrium analysis method. The anayalsis results indicate that the anti-sliding stability of daganagshan dam abutment can meet the need of the design of arch dam.