The Baihetan hydropower plant is one of the most important backbone energy points of power transmission from west to east in China’s energy layout. In the initial stage of hydropower plant construction

some in-situ stress data were obtained by using conventional methods. However

with the continuous excavation of underground cavern

significant brittle failures caused by high stresses were observed in the surrounding rock. Therefore

the study on the stress field of surrounding rock mass is highly important for the long-term stability control of underground caverns. The borehole wall was scanned by the high-precision ultrasonic downhole television imaging system to obtain the logging image

and the widths of breakouts WBO was extracted by WellCAD software. The stress polygon based on Mohr-Coulomb criterion and Anderson theory and the breakout failure method based on Wiebols-Cook criterion were integrated and utilized to limit the estimation of stresses value

the characteristics of rock mass stress field in the project area were analyzed. The results show that the orientation of the maximum horizontal principal stresses in the engineering area was about N30.15°E

and the magnitudes of the major principal stresses were Sh=11.62±0.34 MPa (horizontal minimum principal stress)

SV=14.45±0.33 MPa (vertical principal stress)

SH=25.88±5.61 MPa (horizontal maximum principal stress) respectively. This stress state is favorable for the strike-slip faulting(Sh