| Research for underground cavern surrounding rock stability with large span and high side-wall under complex geological conditions, is an important geological engineering issue for survey, design, construction and operation of hydraulic and water-power projects.Our home and abroad schollars have established a relatively perfect suit of theory system for apprising wall roak stability, based on their abundant engineering practices and studies. However, there's still a lack of some systematic evaluation methods during our practice work,especially for project like Nuo zhadu which requires high side-wall and large span. After getting a comprehensive analysis of in-situ investigations and former findings in Nuo Zhadu, the author establishes complex rock mass model by accurate description of its conditions. Then following basic methods for evaluating he stability of underground cavern group's surrounding rock,And combining whole deformation with local blocks stability evaluation, the author developes the systematical engineering evaluation method for large-scale underground cavern group's surrounding rock stability and surpport programme. The findings can be obtained as follow:(1) Systematical method is developed for evaluating the stability of large-scale underground cavern groups,and local Surrounding rocks under complex geological conditions.The paper not only completely appraises the stability of large-scale underground cavern groups and diversion generating system under a variety of conditions.but also puts forward suggestions about optimization of protection measures based on the stability of the cavern Surrounding rocks conditions as well as the possible deformable unstable mechanism.(2) Geological conditions of underground cavern in the engineering area were investigated, and it is considered that formation of the rock mass in the region suffered from complex structural change. The region presented faults and joints, where scales of F1 and F3 are the largest. considering the bounds of F1 and F3,The left bank of the Nuo zhadu can be divided into three engineering geological areas. The comparing indicates that area C is the optimal position for underground cavern group.(3) Latest findings about rock mass classification are applied to grade the rock mass of the cavern area and the engineering area in the left. On the basis of monitoring data, mechanical parameters are analyzed by the method of inversion. The results and monitoring data are well matched. (4)By means of collecting and analyzing each construction and their different groupings of Nuo Zhadu underground cavern, the author confirms the instable blocks,protential instable blocks, as well as the stochastic ones. Based on these datas The authour quotes the block theory together with time-vector method,and adopts SASW to analyze and summarize the surrounding stability of the underground caverns. Furthermore, he mainly focus on the forming system of the differrend blocks, and their stability in the caverns.This series of study supplied a complete basis of evaluation for caverns'sectional stability and supproting design.(5) Based on the conceptual model of rock mass structure in the engineering area, Flac3D is used to simulate stress, strain and plastic zone distribution after the underground cavern is excavated and also Summarize these datas systematically.And the analyzed resault provides the basical information and theoretical foundations.(6) In terms of the above study results, supporting parameters are put forward according to the possible destabilized mode of cavern Surrounding rocks and general characteristics of NATM and NTM. Numerical simulation methods are used to simulate strengthening mechanism and effects. And the actual excavation results reveal that.After supported surrounding rocks are stable enough for satisfying requirement of the underground cavern groups. |
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