Abstract: In order to address the difficulty and low success rate of conventional stress detection methods applied to jointed and fractured rock mass, we found that the method of strain relieving in the bottom of borehole is applicable and we employed this method to the columnar jointed rock mass of the dam foundation of a hydropower station. Through this method, we obtained the plane stress of the jointed rock mass and the three-dimensional stress state from three boreholes in different directions. The stress results transformed to the borehole coordinate system were close to the test results of single borehole stress, verifying the calculation results. In conclusion, the method of strain relieving in the bottom of borehole could be well applied to the stress measurement of fractured rock mass such as columnar joints.

Key words: hydropower station, jointed rock mass, in-situ stress, borehole bottom strain relieving method, three-dimensional stress state