Numerical analysis of mechanical behavior of anisotropic rock mass was carried out using some practical data obtained before and during excavation of a large scale underground cavern, Bunsui 1st power station. The large cavern was planned in a place where well-developed pelitic schist dominated and the sheet-like grains were inclined to open along the schistosity. To design the reasonable rock support system of the large cavern and ensure the stability during the excavation, the mechanical anisotropic properties should be quantitatively estimated by the appropriate analysis method. There are several analysis methods which can consider discontinuity of rocks. But no one other than the Multiple Yield Model (MYM) cannot consider both strength anisotropy and deformation anisotropy. In this article the applicability of the MYM to the pelitic schist was examined by laboratory experiments and in the actual excavation phase.

The results of the step-by-step stability analysis using the accumulated data were reflected to optimize the rock support system. The construction has now successfully completed without any severe troubles but with large displacements due to the rock anisotropy.


To excavate a large cavern in well-developed anisotropic rock mass such as the pelitic schist, it is important to evaluate the mechanical properties of the anisotropic rock. And the appropriate numerical analysis method is also important to secure the mechanical stability during the excavation. Accurate prediction of the rock mass behavior is required using results of the geological investigation.

There are two analytical methods which can deal with discontinuity of rocks. One is the equivalent continuum analysis method such as MBC. In the method the discontinuity of the rock is expressed using the constitutive law with the equivalent elasticity coefficients. The other ones are the discontinuous models such as DEM and DDA. They express the discontinuity as the geometric distribution of the different materials. However, these methods can not consider both the strength anisotropy and the deformation anisotropy efficiently. Authors considered the schistosity of the pelitic schist as potential discontinuity in the MYM which is one of the equivalent continuum analytical methods.

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