Results from in-situ monitoring of displacement, bolt load, and disturbed zone of a powerhouse cavern during excavation process

摘要

Continuous monitoring during the construction of the project demonstrated that the design of the cavern was done successfully and the surrounding rock of cavern was stable. The maximum deformation of cavern surface is less than 6 mm after 840 days. The deformations of surrounding rock generally reached stable states after the cavern excavation was finished. The principal and secondary factors affecting deformations of the surrounding rock are spatial and temporal effect, respectively. The excavation for a different stage in the same section played an important role for the deformations of the surrounding rock of the cavern. The effect of neighbor domain excavation in a different section on the deformations of the surrounding rock for the measurement section is secondary. The three-dimensional excavation effect on the deformations of the surrounding rock for the measurement section is far less than the ones of the same section excavation in the measurement section. Soon after a certain rock volume was excavated at the face of the cavern, a support system consisting of shotcrete and rock bolts was added and convergence control devices were installed. The maximum convergence value of the cavern is less than 2.5 mm after 1 month. The deformation of cavern sections may not simply be a result of the two-dimensional deformation, but can be influenced by stresses released from neighboring sections. The monitoring results show that the average disturbed zone around the cavern is less than 3.5 m. The design of rock bolts with a spacing of 1.5 m, diameter of 28 mm and length of 6-8 m is safe and reasonable. The domain reinforcement with rock bolt is two times larger than that of the average disturbed zone. The rock bolts reached the stable rock mass within 2.5-4.5 m. The maximum bolt load value is less than 40 kN after 120 days. The load of rock bolt is caused by the released stress of rock mass by step excavation. The maximum stress of rock bolt is 65 MPa. The strength of rock bolt is assuring. The in-situ measurement results show that the time-dependent effects on deformation and convergence are very secondary for cavern in hard rock mass and can even be ignored.