Special Geological Environment Of Bank Slope And Underground Engineering About Pingtou Hydroelectric Station Of Meigu River

Nowadays, with the increasingly close relationship between underground engineering of human beings activities and the geological environment of slope, the structure of slope has a significant impact on the underground engineering. As the process of the natural evolution of the slope is affected by many external factors, some complex structure and phenomenon are formed in the internal slope. The past engineering practice shows that neglect of the slope analysis and research about structure of projects often leads to serious engineering geological problems and even catastrophic consequences. Therefore, the activities carried out underground engineering must pay attention to the analysis of the internal structure of slope, combining with underground engineering activities and the geological environment of slope.The study area is located in the slope of Pingtou Hydropower Station lied in the Meigu valley, where a typical forward and layer structure slope consists of the thick Dengying Formation dolomite. However, during the excavation of the tunnel, it reveals the existence of a series of special geological phenomenon in the internal structure of slope, leading to a major engineering geological problem and a significant adverse effect of the underground engineering during the safe construction of the works. This paper is divided it into two parts, the deformation and failure phenomenon of the deep bedding bank slope and the deep karst sandification of dolomite. Moreover, the two types of special geological phenomenon are systematically studied.Based on the investigation of a number of chambers excavated in the bank slope, on the one hand, the structural type, spatial distribution characteristics and macro evolution model of the karst sandification of dolomite are investigated and discussed, and the micro mechanism and evolution of model are also described by test. On the other hand,by the analysis of the deformation and failure phenomenon of deep space structure of the bank slope, not only the genetic model of the deep landslide brought by bedding structure of the bank slope is demonstrated but also the stability of the present situation is analyzed. In addition, through systematic research of the special geological phenomenon and the interaction with the underground engineering, the feasibility of the requirements of underground engineering of the hydropower station is proposed. The research work on this paper and results achieved are as follows:(1) Based on a survey of a large number of excavation chamber, the development characteristics of the karst sandification of dolomite is analyzed. The macro structure of dolomite sandification is compartmentalized. The concept of the rock structure classification of dolomite sandification is put forward. Macro evolution of it as light-middle-strong-destructive the four-stage evolution model is defined. Furthermore, by analyzing the law of spatial distribution of karst sandification phenomenon, the relativity between the dolomite sandification phenomenon and the influencing factors is discussed,such as lithology, groundwater, geological structure of bank slope, the regional valley geomorphology and so on.(2) By analyzing of the structure and composition of karst sandification material, the article considers that it has a typical structure of matter as bedrock - dissolution layer of sandification– clay. Based on geochemical method, each layer is selected to analyze migration regularity of chemical composition during the karst sandification. It is considered that during the karst sandification of dolomite, the evolution process begins from forming of dolomite sand because of bedrock dissolution. Then a direct sedimentation of clay mineral formed by the groundwater rich in Si,Al,Fe,Mn forms or by the metasomatic dolomite, finally resulting in the clay soil interlayer.(3) Base on the study of macroscopic karst sandification phenomenon and the study of microcosmic-test about the structure of karst sandification of dolomite, the characteristics of microcosmic corrosion about dolomite are controlled by the types of dolomite diagenesis and mineral microstructure of dolomite. It is considered that development degree of karst sandification about primary dolomite and its constructive classification of microstructure is obviously lower than that of secondary dolomite's.(4) By using high rock pressure permeability test, the regularity of rock permeability about the types of dolomite in the Dengying Formation is described. It also demonstrates that the rock pore structure and its permeability is controlled by mineral type of dolomite and its microstructure features. Through analysis and comparison, it is showed that the rock permeability gradually decreases by the variation of the granular structure, sand cutting texture and microcrystalline structure which mineral composition is homogeneous. Regularity of permeability about dolomite is simulated under the condition of bank slope is unloaded. Moreover, the basic distribution regularity of macroscopic karst sandification and its impact of the control mechanism are described.(5) The detailed investigation and analysis on the interior deformation and damage of bank slope, and the basic character of interior ancient landslide is described based on the damage presentation, material composition and space shape, etc. Furthermore, the hydraulic and boundary conditions causing bank slope fail are inverted by analyzing the 3D wedges. It is inferred that the slope fails along the deep slope by heavy storm, with tailing edge cracked.(6) The main influence and controlling factors on the deep bank slope landslide's formation is analyzed. The bank slope's evolutionary significance about thick overburden layers of bank slope's surface is analyzed under the glacial periods climate. The bank rock mass's karstification and the landslide damage's relationship are described. During the process of deeply deformation damage about bank slope, it is considered that the glacial periods climate, the groundwater and the karstification are important influence of the land slope's evolutionary.Due to the wide distribution of dolomite in the southern region of China, the special geological phenomenon occurred within the internal bank slope of the research area is not isolated, as for the different structure types of bank slope composed of dolomite. It should be consistent to regional structure and quaternary climate evolution of the background, and may have some representative characteristics and typical significance. Therefore, it provides useful experience and reference for developing human engineering activities in the similar geological environment of the slope. So it provided a reference for reference example works for the human condition developments in the similar geological environment of the slope.