Development and Occurrence Mechanisms of Fault-Slip Rockburst in a Deep Tunnel Excavated by Drilling and Blasting: A Case Study

In this work, an extremely intense fault-slip rockburst case, with a local magnitude of 2.3, observed in a deep tunnel in southwestern China was introduced as a case study. The rockburst caused a large economic loss and delayed the construction schedule for nearly 2 months. In-situ failure analysis, geological surveys, and microseismic (MS) monitoring were carried out to study the development and occurrence mechanisms of fault-slip rockburst. The fault-slip rockburst occurred in the hanging wall of a structure plane with dark green filling material and the rock mass slipped along the structure plane. It shows characteristic of intermittent occurrence, which results in great psychological pressure on workers. The dominant frequency of the rockburst MS event during the fault-slip rockburst is 13 Hz, which shows that the fault slip rockburst can be captured by the MS monitoring system. Extremely intense MS activity was recorded during the rockburst. The development and occurrence processes of the fault-slip rockburst were studied using this MS information. The stress evolution during the rockburst was studied by analyzing the dynamic stress drop. For the evolution mechanism of the fault-slip rockburst, many tensile fracture events occurred during the development stage, and a few shear fractures, corresponding to structure plane dislocation, occurred before the occurrence of the fault-slip rockburst. The presence of a large natural structure plane resulted in a higher stress and crack extension, and reduced the length of the penetration path, resulting in a stronger destructiveness. The results can be used for the further research on fault-slip rockbursts and planning appropriate warning and mitigation measures.