Deformation And Stability Analysis Of Outlet Section Of The Discharge Tunnel Of Pubuguo Hydropower Station

Many large scale hydropower stations of our country are built in gorges among high mountains. High hydraulic head, large-discharge, huge power of flood discharge are notable characteristics of these water powers. The operational safety of earth-rock dam, or even the whole hydraulic project, is directly influenced by discharge tunnel. Pubugou hydropower station, located in Hanyuan county, Sichuan province, has 3300MW power capacity, and 5060Mm3 total storage capacity. The project is built for electricity generation, flood control, sand barrage, etc. The maximal height of the vertical core-walled rockfill dam is 186m. The free-flow discharge tunnel, whose form of section is circular arch and straight wall, is located in granite rock below underground workshop of left hillside.Because the minimal thickness of the right side of tunnel is only 10m and the height of the left side of the tunnel is over 100m, the surrounding pressure distribution at the discharge tunnel of Pubugou Hydropower Station is much unbalanced. The unbalanced pressure of the tunnel and the stability of the slope during the course of excavation are studied using nonlinear finite element method (FEM). The nonlinear model strictly simulates the overall geological condition, such as fault and fissures, the tunnel's section form and various schemes of construction. The stability of the slope, under deformation of excavation and the unbalanced stress of the tunnel, is evaluated and appraised by point safety factor distribution.The major works of this thesis are as follows: (1) Using AutoLISP andFortran, a 2D mesh generation program is developed to achieve automatic node coding and obtaining the information of element and corresponding material.(2) The unbalanced stress state and stability of the slope before excavation are calculated and analyzed. (3)Stability analysis of surrounding rock and slope, and appraisal of structure safety are carried out, under the conditions of support or non-support, with lining or without lining. (4)The stress state of 1.5m thick lining is compared with that of 2.0m thick lining. (5)By degrading rank IV surrounding rock to rank V rock, the sensitivity of slope stability to mechanical parameter is also checked.It's recommended to reinforce the slope before excavation, to bolt and to shotcrete in time during excavation, and to excavate the lower-half of tunnel after bolting and shotcreting of the upper-half, and to make the second shotcrete lining as early as possible. These suggestions have been adopted in practice.