Random Blocks in the Rock Mass Around the Underground Powerhouse on the Right Bank of Wudongde Hydropower Station

The geometry and stability of random blocks are fundamental to support design of underground powerhouse of Wudongde hydropower station. This paper systematically analyses the characteristics of random blocks in the underground powerhouse on the right bank of Wudongde hydropower station. Based on the theory of the general block method and data of fractures obtained from the field survey, the discrete fracture network model is established by an inverse method for identifying and analyzing random blocks. The calculation is realized for 10 times at random by GeneralBlock to reduce the influence of randomness. The results show that most of random blocks formed by discontinuities and excavations can be found in the vault of the powerhouse; for the 10 realizations, the average number of the random blocks is 414; the average volume of the blocks is 2.9m3 and the maximum volume of the blocks is 152.0 m3; the average depth of the blocks is 1.2m and the maximum depth is 8.8m. Most of the blocks are stable. Most of the unstable blocks present a failure of falling. Most removable blocks have 3 or 4 discontinuities and the maximum value is 12; fractures with west dip-direction and medium dip are the most dangerous for forming unstable blocks. Therefore, it is suggested that the anchor bolts should pierce through the fractures of west dip-direction and medium dip.