An excavation slope in left abutment trough of Xiluodu arch dam has 380 meters or so. In order to ensure safety of the excavation slope, the designed excavation and reinforcement process of the slope is simulated systematically with self-developed 3D elasto-viscoplastic finite element method (FEM) analysis program based on the model of reinforced jointed rock masses. Distribution patterns of displacements, stresses and point safety factors of the rock slope and reinforcement effects under tectonic initial geostress field are analyzed and the slope stability is evaluated in each excavation step. The simulation results show that displacements of the excavated slope between 470 meter and 400 meter in elevation are relatively bigger and its yield zone extends deeper into the mountain body in the designed excavation and reinforcement scheme. Supplementary reinforcements with some pre-stress cables are suggested for strengthening the excavation slope from 470 meter to 400 meter in elevation. The numerical simulation results show that the new reinforcements help improve the stability of the excavation slope in left abutment trough and ensure the safety of the slope.
The Xiluodu Hydropower Project is an extreme project in China and its installed capacity is 12.6 MW, which locates on the upper reaches of the Yangtze River. The dam type is double-curvature arch dam and its maximum dam height is 278 meters. Its plan and section X-X in left bank are presented in Figure 1. Figure 1(b) shows lithological characteristics of rock masses and distributions of dominant texture planes in left bank. The rock masses mainly have four rock types according to weathering degrees: II, III1, III2, IV1. The dominant texture planes mainly include three strain-slipzoneinlayers and two joint sets. The strain-slipzoneinlayers are C7,C8,C9. Occurrences of such texture planes are presented in Table 1. After completion of excavations, the final excavation slope in left abutment trough of Xiluodu arch dam has more than 380 meters height, and its spatial shape is very complicated. Because the physical and mechanical parameters of rock masses are usually weakened for exploding construction, failures of the excavation slope are likely to occur.
In order to ensure the stability and safety of the excavation slope, many supports should be utilized to reinforce the slope in a construction period, which are pre-stress cables, pre-stress bolts, systematic bolts, etc.. Which position should be reinforced, and how many bolts and cables should be adopted are focuses of engineering design and construction. Unsuitable reinforcement measures and reinforced locations will not prevent slope from instability effectively and only increase engineering investments. Consequently it has a great significance to study excavation slope stability and reinforced effects of corresponding reinforcement measures with computer aided simulation technologies before the slope excavation (FENG Xue-min, WANG Wei-ming, et al., 2004)
Finite element method has gained popularity in analyzing geotechnical problems for fewer assumptions and more powerful functions (Chen, S.H., Egger, P.,1999; Chen Sheng-hong, Qing Wei-xin, Shahrour Isam, 2007). The excavation and reinforcement process of rock slope can be simulated conveniently by finite element method with suitable constitutive models of geomaterials.