Response of acoustic emission and vibration monitoring data during rock block collapse in the tunnel: Small- and large-scale experiments study

Block collapse is a common disaster in the jointed rock mass of tunnels and usually involves two typical evolution stages: rock bridge breakage and rock block instability. The evolutionary characteristics of mutation induced by the gradual failure of rock mass are the mechanical basis for monitoring and assessing disasters. In this study, an acoustic emission (AE)-vibration joint monitoring method is proposed to fully investigate the two failure stages based on the disaster mechanism. It is critical to reveal the evolution law of AE and natural frequency infor-mation in block collapse. Small-scale shear tests on rock specimens are conducted to investigate the rock bridge breakage stage, while large-scale physical simulation tests are performed to investigate the block instability stage. During rock bridge breakage, AE exhibits a clearer signal response to the internal rock fracture than the natural frequency and captures brittle failure under low-and medium-stress conditions. The natural frequency exhibits a significant signal response under low-stress conditions during the block instability stage. Under me- dium-and high-stress conditions, the signal becomes less sensitive. Under low-stress conditions, the natural frequency of the block gradually decreases with increasing free surface, implying that the stability of the block declines. The natural frequency decreases with the decreasing stiffness of the block, which is a vital precursor to the early warning of block collapse disasters. Additionally, AE is the primary indicator in the rock bridge breakage stage, while natural frequency is the primary indicator in the rock block instability stage. From the perspective of technological innovation in underground tunneling, AE-Vibration joint monitoring prompts a new idea to evaluate the stability of key blocks in tunnel construction safety applications.