Abstract: For The geological condition is very complex for the NJ hydropower station in Pakistan. The maximum overburden depth of the NJ TBM tunnel reaches 1900 m. Rock burst occurs frequently during tunnel excavation. Insitu stress is one of the most important factors that influence the tendency of rock burst. The shape and thickness of the core discing are analyzed to estimate the principal stress direction and magnitude of the insitu stress of the TBM tunnel. The analyzed results show that the axis of the borehole is almost parallel to one of the principal stress directions. If the gravity stress is one of the principal stress, TBM tunnel axis is the third principal stress direction. The relationship between the two principal stresses in the horizontal plane is obtained. For lateral stress coefficient between 0.8-1.5, the magnitude of the other stress is 80 MPa-110 MPa. During tunnel excavation, strong rock burst is likely to occur in regions around the arch bottom and vault.

Key words: In-situ stress, Core Discing, Principal Tensile Strength, Borehole Camera