Systematical Engineering Geological Study On The Stability Of Surrounding Rock Mass With Large Span High Side-Wall Underground Caverns And Their Support Proposals

Evaluation of underground cavern surrounding rock stability with large span and high side-wall under complex geological conditions is an important engineering geological issue for survey, design, construction and operation of hydraulic and water-power projects. Based on plenty of engineering practices and studies, the scholars have established a complete suit of theory system for appraising wall rock stability. However, evaluation methods of wall rock stability in underground cavern groups with high side-wall, large span and intersect caverns are required for actual projects such as Nuo Zhadu. On basis of comprehensive analysis of plenty of in-situ investigations and former findings in Nuo Zhadu, the author established complex rock mass model by accurate description of rock mass conditions. Then following basic methods for evaluating the stability of underground cavern group's surrounding rock combining whole deformation with local blocks stability evaluation, the author developes the systemantical engineering evaluation method for large-scale underground cavern group's surrounding rock stability and surpport programme. The findings can be obtained as follows:(1) Systematical method, which can evaluate the stability of large-scale underground cavern groups and local Surrounding rocks under complex geological conditions, is developed. The paper completely appraises the stability of large-scale underground cavern groups and diversion generating system under a variety of conditions, and puts forward the suggestion about optimization of protection measures based on cavern Surrounding rocks stability conditions and 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 structure in the region suffered from complex structural change. The region presented faults and joints, where scales of F₁ and F₃ are the largest. The left bank of the Nuozhadu can be divided into three engineering geological areas considering the bounds of F₁ and F₃. The comparing indicates that area Cl is the optimal position for underground cavern group.(3) Based on rock mass structure research, spatial plane relationship is utilized, and idea from point to plane is adopted, eventually three dimension distribution characteristics of the structure plane have been studied.(4) Latest findings about rock mass classification are applied to grading 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 were well matched.(5) With the prototype of underground cavern groups at Nuozhadu, modeling technique of complex rock mass is used, and numerical simulation is adopted in order to study the effect of the controlled structure plane on the engineering. The results show that main caverns should be more than 80 meters distance from first-order structure plane when underground caverns are designed. Big included angle between the structure plane with different altitudes and the cavern axis helps enhance the stability of the Surrounding rocks, and second-order structure planes with middle included angles adversely influence deformable stability of the Surrounding rocks.(6) The authour developes the evaluation method of surrounding rock block stability in underground caverns with large span and high sidewall. Movable blocks in the caverns can be divided into complex...