Characterization of Fracture Distribution Based on Borehole Geophysical Logging and Comparative Assessment of Outcrop Distribution Characteristic

Site characterization is essential for the safe disposal of high-level radioactive waste. This study investigates fracture distribution characteristics in granite site using borehole geophysical logging, supported by surface outcrop data. Site investigations were conducted to assess the number, orientation, and dip of fracture sets at depth, with emphasis on low-, medium-, and high-angle fractures. The results show that while fracture patterns observed at the surface generally continue at depth, differences in dip direction may occur. Notably, low-angle fractures observed in shallow zones are less frequent at greater depths, consistent with the evolution mechanisms of granite plution. In particular, high-angle fractures become dominant around depths of 500 meters, a typical target depth for HLW disposal. These findings highlight the importance of integrating surface and subsurface data to reduce uncertainty in deep geological environments. Comparative analysis with other granite study sites further supports the reliability of fracture characterization through borehole data. The study underscores the need for detailed geological investigation when evaluating candidate sites for HLW disposal in Korea.