Determination of the hydraulic conductivity components using a three-dimensional fracture network model in volcanic rock

Abstract

Accurate prediction of the pathways as well as the leakage rates of contaminated material from the underground storage facilities is one of the important tasks to protect the environment from the impact of such facilities. In particular, predicting the pathway and travel time for any radioactive nuclides escaping from an underground nuclear waste repository to the biosphere is one of the most critical factors for the performance assessment of the repository. Radioactive nuclides released from a repository are dissolved by groundwater in saturated rock mass. In the case of crystalline rock, it is normally assumed that the rock matrix is impermeable and groundwater flow is only allowable through fractures. Thus, the generation of an actual fracture network is essential for the accurate prediction of the flow path and travel time of groundwater. In order to predict the groundwater flow path more accurately, the anisotropic hydraulic conductivity should be considered. It takes, however, time and efforts to determine the anisotropic hydraulic conductivities of a site from in situ tests. In this study, a method to calculate the anisotropic hydraulic conductivities from the fracture network realized based on the in situ condition was suggested. The following two steps were suggested to realize the three-dimensional fracture network representing in situ conditions. The fracture network can be generated by using the stereographic net of the fracture data obtained from the borehole logging and the surface survey. Through this fracture network generated, an effective hydraulic conductivity tensor corresponding to the in situ hydraulic conductivities could be determined.