Conference Paper Water migration into underground cavern considering stress and temperature dependent permeability of fractured rocks

Akm Badrul, Alam  ,  Fujii, Yoshiaki  ,  Aramaki, Noritaka  ,  Kaneko, Katsuhiko

14p.47 , 2017-01-10 , 岩の力学連合会
Water migration is an important factor in sealability of underground radioactive waste disposal (URWD) and is significantly controlled by permeability of rock. The permeability of rocks varies with various factors including stress and temperature. The rock stress changes by excavation of caverns for URWD and rock temperature changes by decay heat. The temperature change induces thermal stress. Water migration (flow in and out of URWD) should be therefore evaluated considering the effect of stress and temperature. In this regard, a series of triaxial compression tests was carried out under confining pressure between 1 and 14 MPa at 295 K and 353 K, and the permeability under residual strength state was measured as input data for the water migration calculation with a 2-D elastic FEM for a simple URWD cavern in a fractured rock mass. Three rocks (Shikotsu welded tuff, Kimachi sandstone, Inada granite) are considered for the experiment to cover wide range of physical properties of rocks. Several new indices are also correlated with the post-compression permeability to show how well it can be predicted. The equations for the stress and temperature dependent permeability of fractured rocks are proposed. Fluid inflow was calculated with a 2-D elastic FEM for simple underground nuclear waste cavern with or without considering the stress and temperature dependency as an example to show the effect on water inflow. The results showed that water inflow became smaller considering the dependency. This could contribute for optimum design of underground cavern. The effects of temperature becomes slightly smaller by representing the permeability of fractured rock with indices than that of average effective stress (AES). Further consideration should be done because the effects of temperature can be clearly seen in the indices-permeability plots and the new indices were almost not effective to improve the approximation for the granite.

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