Modification of the discontinuous deformation analysis method and its application to seismic response analysis of large underground caverns

Two modifications are made to enable the DDA method to be used to study the seismic dynamic response of underground caverns. The first modification involves setting viscous boundary conditions and the second involves inputting seismic waves from the bottom in stress way. The modified DDA code is verified by a two-dimensional continuous model. Moreover, for the propagation problem of an elastic P-wave travelling across a joint face, the numerical solution of the modified DDA is close to the theoretical solution. The modified DDA method is applied to study the seismic response of the underground houses of the Dagangshan hydropower station in Western China, and valuable results are obtained. At three intensity levels, whether the KOBE seismic wave or the artificial seismic wave, will bring about the damage of the surrounding rock masses of unsupported underground houses. Increasing the seismic intensity increases the destructive effect of the wave. The most unstable blocks are at the downstream side wall of the main machine building and tail surge chamber, and these blocks slide first during an earthquake. By contrast, with bolt supporting, the surrounding rock masses maintain stability. Bolt forces change dramatically during the first few seconds of the earthquake (about 6 s in the KOBE seismic wave and 10 s in the artificial seismic wave), and then remain stable. The bolts through the most unstable blocks experience the largest forces, which means the most unstable blocks are the most dangerous blocks during an earthquake.