Visualization analysis of potential fracture in overburden strata induced by longwall coal mining

Abstract

The condition of overburden strata is a key problem relative to the safety of underground mining activities. However, the invisibility of it poses significant difficulties for on-site monitoring. Accordingly, a multi-indicator visualization analysis method for strata fracture was proposed in this study. Deformation localization features of overburden strata were visualized from the perspective of energy release. Taking high-pressure events in mining face as a clue, combined with seismic energy, frequency and other indicators, the potential fracture and its development process were analyzed. The following results were obtained: (1) The clustering of seismic events dynamically progresses with the advance of mining. Significant differences in seismic clustering features were observed during mining, which reflects the influences of nearby goaf, changes in strata structure, specific geological structures, and self-fracture. (2) Before high-pressure events occurs, seismic events tended to cluster in a certain zone, exhibiting significantly higher frequency and energy compared with the other zones. Through incremental analysis, the potential strata fractures that cause high-pressure events can be identified. (3) The development of strata fracture not only progresses along the mining direction, but also in the vertical direction relative to the mining. In the initial stage, the fracture region was concentrated behind the mining face and on the side of goaf. As mining progressed, influenced by structural damage, the fracture region gradually shifted towards the front of the mining face and extended towards the coal seam side. (4) In the early stage of mining, fracture primarily occurs in the low-lying strata. In the mined-out area, the suspended section of the lower-level strata experienced fixed beam fractures initially, gradually shifting the fracture layer upwards. Simultaneously, in front of the mining face, the fractured strata became cantilever beam structures, leading to periodic fractures occurring ahead of the mining face.