Abstract: Safety monitoring is an important means to assess the stability safety of surrounding rock. The right bank underground powerhouse of Wudongde hydropower station is huge with three large caverns (main powerhouse, main transformer cavern, and surge chamber) parallel to each other. In order to ensure the safety stability of surrounding rock during construction, we monitored the surface and deep deformations of surrounding rock by using multi-point displacement meter, anchor stress gauge, anchor dynamometer, and joint meter. We also analyzed the displacement characteristics and deformation regularity of the three large caverns. Monitoring results show that the deformation caused by excavation is small, mainly concentrating in the shallow surface; maximum deformation of surrounding rock above the height of rock anchor beam in the three caverns is 16.43 mm. Large deformation appears at the top of the main power house, upstream side rock anchor beam and upstream side wall of tail-water chamber room. Moreover, the rapid development of deformation is greatly influenced by blasting disturbance, space effect caused by excavation, and weak geologic condition. Timely and strong support measures could limit the development of deformation.

Key words: Wudongde Hydropower Station, underground powerhouse, deformation of surrounding rock, safety monitoring, corrosion fissure