Failure mechanism of deep TBM tunnels subjected to dynamic disturbance under true triaxial unloading stress path

Abstract

The peril posed by time-delayed rockburst significantly undermines the safety of deep-buried tunnel construction and operation, with dynamic disturbance recognized as a pivotal triggering factor. Vibration monitoring of critical Tunnel Boring Machine (TBM) components and surrounding rock surfaces within TBM-constructed tunnels shows that low-frequency dynamic disturbance affects the failure behavior of excavated surrounding rock. However, the mechanism underpinning instability of hard rock under dynamic disturbance during stress adjustment in deep excavations remains elusive. To bridge this gap, multilevel dynamic disturbance experiments (A = 1 MPa, f = 20 Hz) under true triaxial loading and unloading paths were conducted. The results indicate that dynamic disturbances can accelerate the failure of granite, with its strength reduced by 10 %–12 % under the combined effects of high-stress unloading damage. These effects diminish the energy storage capacity of rock mass, thereby lowering the threshold for rockburst occurrence. The deformation rates of granite increase with each phase of σ₁ loading and σ₃ unloading. Based on real-time deformation rate observations at the final stage, critical instability characteristics are categorized into two types: stress adjustment and dynamic disturbance. With prolonged exposure to dynamic disturbance, a distinct acceleration-stabilization-acceleration (V-shaped) pattern appears in the strain rate of dynamic disturbance-induced failure. Acoustic emission monitoring demonstrates the degradation mechanism in hard rock subjected to dynamic disturbance, leading to the initiation of tensile cracks and accelerating the propagation of cracks across fracture surfaces. Ultimately, the effect of supporting stress was evaluated through comparative testing. A regulatory strategy was proposed for controlling the evolution process of dynamic disturbance-triggered rockbursts, entailing the construction of a three-dimensional wave-absorbed support system for the excavated rock surrounding deep-buried tunnels. These findings provide a valuable reference for understanding, early warning, and controlling the mechanisms underlying time-delayed rockbursts triggered by dynamic disturbances.