Study on the formation mechanism of rock bursts during coal seam mining with a competent main roof

Abstract

During the extraction of coal seams with competent and strong main roof strata, the collapse of the immediate roof is often insufficient to fill the mined-out void, resulting in the main roof being suspended over a wide area. The suspended main roof bears the overburden pressure from the upper rock layers, leading to significant stress concentrations around the boundaries of the goaf, which become potential weak zones. As the void expands, the increasing stress may exceed the strength limit of the main roof rock mass, causing brittle failure and a sudden, large-scale collapse, known as a mine seismic event. In this study, FLAC3D software and the mechanical parameters of rock masses at the Vàng Danh coal mine were used to develop a numerical model to investigate the formation mechanism of mine seismic events under varying thicknesses of strong main roof rock. The results indicate that mine seismicity occurs primarily when the thickness of the competent main roof is less than 15 meters, and when three failure zones (Zone I, II, and III) in the roof of the working face become interconnected. At that point, the entire main roof block collapses into the mined-out area, triggering a mine seismic event. Furthermore, the study reveals that the thickness of the main roof is inversely proportional to the onset time of seismic events, and directly proportional to the intensity of smaller seismic disturbances.