Difficult cases of excavation and basics of large-scale cavern construction

Seven difficult cases encountered during the excavation of large-scale caverns are explained: (1) the conditions of these cases, (2) the adopted countermeasures, and (3) the causes of difficulties. The major cause of problems was due to the weak geological condition that was hard to predict. Therefore, information-aided construction is indispensable to constructing large-scale caverns. By analyzing the measurement results during the excavation of the caverns the followings were revealed: (1) the most important point in designing is to pay attention not to stress but to the deformation of the rock mass; (2) the amounts of deformation of rock mass structures vary depending on the kinds of the surrounding rock masses even if the rock stress and the deformability of the rock masses are the same; and (3) in the case of jointed rock mass a rock mass structure becomes larger, the rock mass may sometimes behave as an anisotropic body.