Abstract:
This study investigates the differential mechanical response of fully mechanized coal mining and continuous mining versus continuous backfill technology under thick coal seams and fault structures, and to clarify mechanisms of preventing coal bursts under mining disturbances. The
1301 working face of Gucheng Coal Mine was used as a case study. This study uses theoretical derivation to research the stability of the bottom coal and the characteristics of fault slip under disturbance effects for both ming methods. We established mechanical models for bottom coal and faults, revealing their respective disaster mechanisms. This study proposes the impact danger coefficient of bottom coal
η and the fault instability evaluation index
I, comparing their variations under the two mining technologies and revealing the essence of internal differences. Finally, validation is carried out through microseismic measurement results. The study shows that the mechanism of impact ground pressure under dynamic loading disturbance, associated with the bottom coal instability, occurs when the horizontal stress of the bottom coal exceeds its critical structural stress, leading to impact destruction in the excavation roadway. The mechanism of impact ground pressure under mining disturbance with fault instability type is that the rock mass at the fault bends and sinks, superimposing self-static load to form a high static load, combined with the action of horizontal stress, accumulating substantial elastic potential energy, causing a local adjustment of the stress field in the fault, thereby unlocking and activating it. The impact danger coefficient
η is negatively correlated with the thickness of the bottom coal. Under thick bottom coal conditions, the impact danger between the two mining technologies is insignificant. The risk difference increases exponentially with decreasing bottom coal thickness and increasing mining length, indicating that under conditions of thin bottom coal and long mining distances, the continuous mining with backfill significantly reduces the intensity and dynamic load disturbances during the key layer rupture cycle of the roof of the working face, thereby significantly reducing the impact risk. The instability evaluation index
I significantly increases proportionally with the fault dip angle, and the risk difference between the two technologies tends to moderate in the far field of low-dip faults, while sharply increasing in the adjacent area of high-dip faults. This indicates that continuous mining with backfill technology can effectively weaken the superposition of the mining stress field and the fault structural stress field in the nearby area of high-dip faults, thus inhibiting the shear slip of coal-rock bodies at the fault and reducing elastic energy release. The risk difference shows a slight increase with decreasing distance to the fault, but linearly increases with the increase in dip angle, indicating that the dip angle
θf of the fault has a more sensitive impact on the risk difference of the two mining technologies. In the initial stage of mining, the average energy of single microseismic events in each branch roadway increases marginally. The frequency of microseismic events in the near field of the fault significantly increases compared to the far field, and increases stably in high-energy events; instead, microseismic events are released progressively as 'high frequency and low energy,' reflecting the suppression effect of the continuous mining and continuous backfill technology on dynamic load transmission and energy accumulation under complex geological conditions.