ABSTRACT
Rock-drilling surveys are useful in predicting geological conditions ahead of tunnel faces, especially in areas with complex geological structures at active plate margins, as in Japan. For the Otonaka Tunnel in northern Hokkaido, weak heterogeneous ground conditions comprising microdiorite and serpentinite were visualized in three dimensions through numerous drilling surveys that yielded the drilling energy, slime content, and color of return water. The boreholes also served as injection sites for ground stabilization, allowing excavation to be completed safely with effective auxiliary construction methods. In future the labor should be reduced by setting drilling energy thresholds and organizing the data for automatic visualization.
