Development of downward compact conical-ended borehole overcoring technique for rock stress measurement

In order to determine complete in-situ stress at great depth with high accuracy, down ward compact conical-ended borehole overcoring (DCCBO) technique, which is one of stress relief methods, was developed. DCCBO technique can be applied to a water-filled vertical borehole. In a shallow in-situ test, a measuring system consisting of a bonding device, a cleaning system and a multi-channel data logger were verified to work well in a water-filled borehole with cuttings on the bottom. Thus, we confirmed the usability of DCCBO technique.