The underground powerhouse of Baihetan Hydropower Station are the largest underground caverns under construction in China. The buried depth of the left bank underground powerhouse cavern is about 270~300 m, the right bank is about 420 ~ 500m, and the measured maximum stress is about 31MPa. The stability of the surrounding rockmass of the underground caverns is also controlled by the large gentle dip faults, such as C2 and C4. During the excavation of the caverns, the spalling and high stress failure were observed in the top arch and side wall. The depths of excavation damage zone is 1~3 m and the local position is about 4m.The multi-point displacement meter monitored more than 50cm displacement in the roof arch near C4. The time dependent rockmass rupture and deformation was also observed on the roof arch when the excavation was stopped for about 13 months. In this paper, we systematically analyze the problems of high stress failure, bulking deformation, large deformation caused by faults and time effect of subcritical crack propagation in the construction of Baihetan underground powerhouse caverns.

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