Development and Occurrence Mechanism of Extremely Intense Rockbursts and Structural Stability Analysis of Deep-Buried Tunnel Groups: A Case Study

An extremely intense rockburst occurred in a deep tunnel in southwestern China, releasing energy approximately seven times greater than that of typical excavation blasts. This event resulted in equipment damage, support failures, and significant construction delays. Utilizing microseismic (MS) data captured by the MS monitoring system, the development and occurrence process of the rockburst was reconstructed. In conjunction with on-site damage assessments, geological surveys, and geological radar monitoring, the occurrence mechanism of the rockburst, its impact on the structural stability of the tunnel group, and its failure mechanism were analyzed. The findings are as follows: (1) the MS data recorded by the optical fiber MS monitoring system (OF-MMS) accurately captures the development and occurrence process of rockbursts, and the established classification standard for rockburst early warning levels aligns closely with the actual severity of rockbursts. (2) High-energy MS events are critical indicators for early warnings of rockburst location and intensity. When such events occur during periods without blasting activities, the risk of severe rockbursts increases. (3) Variations in the integrity of the surrounding rock influence stress transfer directions and determine the location of stress concentrations. Continuous excavation supplies stress to these concentration points, weakening the load-bearing capacity of the rock mass between the stress points and the free surface, ultimately triggering the extremely intense rockburst. (4) This intense rockburst is characterized by a mixed failure mechanism, manifesting as a wedge-shaped extrusion failure. Shear failure diminishes while tensile failure increases as it moves towards the working face. (5) Stress concentration makes tunnel group intersections more vulnerable to damage; however, the fractured rock masses near these intersections exhibit a greater capacity for stress concentration than the intersections themselves. These results can help enhance the understanding of rockburst mechanisms and the structural stability of tunnel groups, and provide valuable insights for early warning, prevention, and mitigation of rockbursts in deep-buried tunnels affected by blasting disturbances.