Microseismic precursor response characteristics of rockburst in the super-long working face: A case study

Rockburst is one of the significant dynamic hazards of coal and rock bodies during super-long working face mining. Microseismic (MS) technology has been widely used to monitor the dynamic hazards of coal and rock bodies. By analyzing the parameters and statistics of seismic events, the level of rock burst hazard can be assessed. Then, the prevention and control measures taken in advance in the working face should be guided to reduce the impact damage. This study analyzed the precursor characteristics of rockburst MS signals in super-long working faces from spatial distribution, total daily energy, number of MS events, spectrograms, and b-value of MS signals. The results show that the MS events are mainly distributed in the coal seam roof three days before the occurrence of rockburst, the proportion of daily MS events in the coal seam roof increases, and the number of MS events shows a continuous decline. The proportion of large energy MS signals is higher than that of conventional and inclined seam workings in super-long workings before rockbursts; the amplitude of the MS signals from the super-long working face is large, the vibration duration is long (0.8–1.4 s) and the frequency is low; with the approach of rockburst, the low-energy frequency band tends to increase and the frequency decreases. The proportion of the low-energy frequency band (0–40 Hz) of the precursor of impact ground pressure is high. The main frequency of the MS signal of the super-long working face is lower than that of the conventional working face and the inclined coal seam working face when the rockburst occurs; rockburst often occurs in the b-value decreasing stage, and the number of MS events and b-value changes before the rockburst shows the same downward trend, rockburst occurs when the occurrence of the b-value is less than 0.8. The study results for the safety of the super-long working face mining back to provide a scientific basis.