Mechanism analyses and evaluation methods of schistose dangerous rock mass in cavern

There are many dangerous rocks in the Changyu ruins park, which will be the hidden hazards to serious safety. 12 schistose dangerous rocks are found. Its structural characteristics and formation mechanism are different from those of the common and dangerous rock mass. On the basis of detailed field investigation, the W42 dangerous rock is calculated by FLAC numerical simulation as an example, and the stress characteristics and unloading effect of the schistose dangerous rock mass are analyzed. It is found that the unloading effect is mainly influenced by the surrounding rock within 3 m of the excavation face. With the fracture mechanics method, the relationship and the influence law between the stress intensity factor K_I and primary fracture dip angle α, initial fracture fracture angle θ₀, initial fracture length c are analyzed. The results show that the fracture of rock mass is more likely to crack when the crack angle θ₀ is about 78°. It is close to the inclination of the structural plane of the W42 dangerous rock. The stability of the W42 dangerous rock is analyzed using the stability formula. These laws can reasonably explain the formation mechanism and structural characteristics of schistose dangerous rock masses. They also explain the regional joints tendency to be steep or upright.