The mechanism of rock burst and the field response in the coal mining face under the influence of an acute-angle syncline

Rock burst has long been a significant issue for mining safety. Its initiation mechanisms and response characteristics often show unique features in special geological structures. When the working face advances at an acute angle to the syncline direction, the spatial relationship between the syncline axial and wing sides changes, leading to more complex mechanisms for the rock burst and strong mining pressure. Based on the differences in the cross-section of the working face before and after an acute-angle syncline, the dynamic and static load characteristics and failure risk of coal and rock layers in different zones were analyzed. The corresponding mechanisms of rock burst and the main controlling factors were revealed. A relevant field case was selected, and the site response pattern of the acute-angle syncline working face (ASWF) was obtained. The following conclusions were drawn: Two modes of failure instability and risk zones for induced rock bursts exist in the ASWF rock layers, resulting in the conventional tectonic stress affected zone (CTSAZ) at the syncline axis and the large deflection unstable structure zone (LDUSZ) at the syncline wings. Stress is abnormally concentrated in the rock layers at the syncline axis. The residual energy from structural movements in the wing rock layers results in a larger initial deflection. These factors increase the likelihood of rock bursts occurring along the syncline axis and at the front and rear wing tips within the working face area. The 307 working face of a certain mine was selected as a typical case for analysis. The occurrence of the rock burst microseismic event is located in the risk zone of the rear wing of the syncline. Among the three risk zones, the frequency of microseismic energy is relatively high, with large energy events concentrated. Monitoring of mining pressure indicates that support pressures exceeding 40 MPa are concentrated, which is significantly higher than in other areas. The research findings assist in risk assessment under similar geological conditions and facilitate the implementation of effective measures to mitigate key controlling factors.