| With the rapid development of China’s economy and a mass of construction of infrastructure, which is especially widely known for the implementation of Western Development Strategy, the water conservancy and hydropower engineering, railway transportation, oil and gas and many other construction projects in western China have brought about serious challenges that rock mechanics engineers and engineering scientists are now faced with. It is bound to carry out large-scale excavation and construction when it comes to the building of large underground caverns in alpine valleys. During construction, engineers will inevitably encounter problems like a lot of hard and soft rock layers parted by each other, and massive unloading rock formed by excavation. These rock excavation and support structure problems have become one of core issues for construction and design as well as safe operation. The choice of what measure is taken to solve engineering problems has great impact on engineering cost and rock stability. For these large-scale rock mass deformation control and insurance of the stability of underground caverns and other technical problems, it is urgent to carry out research on mechanism and related supporting of rock mass deformation caused by excavation unloading. The study of excavation and supporting of comprehensive control of the super large underground cavities and high slope is as a key research item of12th Five-Year Plan of National Energy Technology ", released at the end of2011by the National Energy Board. So this paper has a certain forward-looking.This paper focuses on the key technical issues on stability of surrounding rock of underground powerhouse of Shuibuya plant. Through research about the factory rock geology, plant engineering properties of rock, the main plant rock stability of measures to deal with the soft rock, and advanced safety monitoring and dynamic feedback optimization research, following key findings are obtained:(1) Through the classification method of "Engineering rock mass of combination", the quality level engineering division of the complex problem of Shuibuya layered rock mass is solved. It provides a new way to think about rock mass quality classification. After the research of plant and rock mass deformation, geological characteristics of plant and engineering characteristics of rock generalization are determined.(2) Rock around underground space is divided into four types:relatively homogeneous rock, the medium thick rock, thick rock, soft and hard-and-white composite thin-bedded rock and soft rock shear zone. Deformation modulus and shear strength parameters of the four categories of rock are also obtained. Plant trait characteristics of soft rock and rock failure modes as well as a variety of weak levels of shear strength parameters are obtained at the same time.(3) According to the stratigraphy, lithology conditions, combined with the power plant operational requirements and results of numerical analysis, it is determined to control the stability of surrounding rock of underground plant in the upper wall of soft rock (p1q3) by using of advanced soft-rock style closed ring beam support structure. This ensures the plant’s rigidity and integrity of the upper rock as well as the force transmission between upper and lower parts of soft rock, preventing soft rock extrusion. At the same time, making use of closed ring beam confining pressure on the formation of soft rock so that soft rock formations remains in original stress state, thus maintaining the carrying capacity of soft rock and fully making use of carrying capacity of it. Keep supporting isolated pier of soft rock to control the stability of underground powerhouse soft rock bottom wall (p1q3, saddle seam and Huanglong shear zone). The piers play a role of supporting lower side walls of the underground powerhouse, limiting plant wall deformation, and effectively reducing the height of full-face excavation of the plant and limiting the rebound deformation of bottom soft rock.(4) After the2D and3D numerical simulation of the upper and lower part of the plant of soft rock with different treatments and surrounding rock of different support schemes, the soft rock treatment scheme and its surrounding rock support parameters are Verified and optimized.(5) Through analysis of important and difficult aspects of various parts of the underground plant construction, principles of construction process control are determined. Also proposed is the layout of temporary and permanent monitoring devices. Dynamic researches are done on underground plant construction period and stability evaluation as well as prediction and optimization of feedback. The processes of excavation for the construction of a plant, optimization of soft rock dealing as well as parameters for support are proposed.(6) Basing on the actual disclosure of geological conditions, combined with the optimization of safety monitoring and feedback of research results, dynamic optimization is implemented for the procedures of construction of the underground plant, excavation methods, support parameters, design and information construction. |
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