Study On Stability Of Tunnel-Face Slope For Intake Of Right-Bank Jinping Ⅰ Hydropower Station

In recent years, there have been increasing hydropower projects in alpine-gorge and deep-valley areas due to exploration of waterpower energy resources, and then more and more high-steep rock slopes were constructed in these areas. Various deformed-fractured phenomena, in view of complicated geological environments, were found in the rock mass of high-steep slopes, moreover, they present a series of deformed-fractured characters and refer to tremendous range, therefore, the stability is increasingly prominent for these high-steep rock slopes. In this paper, choosing tunnel-face slope at intake of right-bank spillway tunnel of Jinping I hydropower station as project background, its physico-mechanical and structural characters were summarized on the fundaments of geological environments in the dam area. The combination of sliding-failure model of rock block was analyzed, and then the limit equilibrium analysis and elasto-plastic numerical simulation analysis were carried on tunnel-face slope at intake, At last, its consequences were verified with dynamic monitoring data in the process of construction of the slope, and its stability was also evaluated. Through the researching in this paper, following conclusions and achievements are drawn:(1) There are some main structural planes that control the stability of the tunnel-face slope at intake, including: f13 fault, compressive rupture zone between strata, interlayers of weathering chlorite schist, bedding fissures and NE-direction fissures. The strike direction of strata is N28°W, and is nearly perpendicular to the main structural planes in the rock mass, like as f13 fault, compressive rupture zone between strata and bedding fissures. The probable instability modes are wedge-sliding. The combinations of instable block include: f13 fault and NE-direction fissures, patulous NWW-direction fissures and compressive rupture zone between strata, and interlayers of weathering chlorite schist and bedding fissures. (2) Through 2D limit equilibrium analysis on typical, Radiall-1, Radial2-2, Tower 0+118m and Tower 0+170m of tunnel-face slope at intake and 3D limit equilibrium analysis on combination of probable instable blocks which were formed by three cutting joint fissures, we have drawn that the stability coefficients f blocks are big after supported and it meets the demands.(3) Through 2D&3D elasto-plastic numerical analysis on process of excavation of tunnel-face slope at intake, It has been drawn that the deformation amount of slope surface is small, even taking water storage and earthquake into account, there is still no large-deformation sliding zone. Through analysis on displacement curves of observation points on slope surface of model, it has been drawn that the slope surface deformed towards inner of rock mass, and its deformation laws are consistent with displacement curves which is monitored by multi-point extensometers during excavation. Through numerical analysis and analysis on monitoring data, it has been drawn that the slope is stable after supported and support design meets demands.