| Zipingpu hydraulic key project is located at Shajinba reach, upriver of Minjiang River, being built for agricultural irrigation and civil water supply. It also has integrative benefits such as preventing flood, generating electricity, environmental protection and tourism. The project is 156 m dam height, 877 m normal impounded level and 760 MW installed capacity. Minjiang River benches almost conversely in Shajinba reach and makes the right bank a thin and weak ridge, which is a syncline geological structure. All of the hydraulic structures are arranged in the right bank and four underground seepage tunnels are arranged parallel in horizon, and the axle wires intersect with syncline axis almost perpendicularity, and with rock formation obtusely. Complex underground tunnels are formed under such formidable conditions, and each of seepage tunnels crosses nuclear of syncline and comes up against interlaminar sharing disturbed belt at different footage. Complex geological environment and concentrated arrangement of underground seepage tunnels in the project show great threaten to the safety of construction and operation.Taking aim of stability analysis and assessment of surrounding rock mass of underground seepage tunnels in the right bank of Zipingpu hydraulic key project, the paper bases study on exhaustive geological conditions research of the region and definite quantity and half definite quantity description and analysis of geoenvironmental properties of main discontinuities in underground seepage tunnels. Making use of abundant field investigation and statistic data, it systematically studies developmental and engineering geological features of discontinuities in surrounding rock mass, and divides structure types according to discontinuities engineering geological grading standards of Zipingpu hydraulic key project. Based on them, structural model of rock is built up. Quality classification and assessment of surrounding rock mass with four classification systems is carried out according to study on features of discontinuities. Engineering geological classification system, Hydroelectric Standard of RR.C (HC), Geomechanics System (RMR)and Q system a re chosen for quality classification and a ssessment o f surrounding rock mass of underground seepage tunnels in the right bank o f Zipingpu hydraulic key project. On the basis of site mechanical and physical tests, mechanical parameters of surrounding rock mass are brought forward, and comprehensive assessments of surrounding rock mass is carried out. With extraordinarily long and densely covered discontinuities in sand rock, blocks are easily formed in surrounding rock mass because of discontinuities combination. Stability of potential blocks at different constructional position surrounding rock mass is calculated and sensitivity to influencing factors of the blocks in surrounding rock mass is analyzed using software SASW, which is compiled by the National Laboratory of Geological Hazard Prevention and Geological environment Protection, Chengdu University of Technology. In the process of calculating, influence of distance of discontinuities, shearing strength of discontinuities, groundwater and horizontal shock-resistant coefficient on stability of b locks i s also e valuated, and influence o f blocks on regional stability analysis and a ssessment of surrounding rock mass of underground seepage tunnels is synthetically evaluated. Based on the former study work, two geo-mechanical models are separately set up , one including a single tunnel and the other including two tunnels, and numerical simulations are accomplished based on 3D-FEM analyticalprocedure (3D-). From the results of numerical simulation, distributing characters of stress and strain field of surrounding rock mass under gravity is analyzed, which presents the effect of quality of surrounding rock mass, construction order and interactions of adjacent underground runnels while being constructed simultaneously. Impact of interlayer shearing belts on surrounding rock mass stability of underground c...
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