Abstract：Jinping II Hydropower Station，located in Sichuan Province，is the biggest station at the Yalong River. In the excavation course of the second layer of the underground powerhouse，serious local instability problems arise at R0+263 of the upstream side wall with the characters of deformation more than 20 mm and deformation rate of 3.4 mm/d. So，a new way integrating theoretical analysis and field engineering control is put forward. In the first phase，mechanical parameters of surrounding rock are identified；and engineering control methods are given. In the second phase，monitoring data and mechanical behavior of surrounding rock during excavation are analyzed；and the reinforcement scheme and reinforcement parameters are suggested. Finally，the instability problem is solved completely. The practice indicates that the method combining the real-time dynamic feedback analysis，multiform measurement information and theoretical analysis with engineering control together is very useful to deal with local instability problem in underground engineering. At the same time，the physical effect of anchor bolts which improve the mechanical strength of surrounding rock is certified according to the comparison of equivalent mechanical parameters of surrounding rock after reinforcement of anchor bolts.
