Study on the overburden failure features and microseismic measurements in non-pillar gob-side entry retaining by roof cutting

In order to further study the failure law of overburden after the mining of non-pillar gob-side entry retaining by roof cutting technology, taking the S1201-II working face of Ningtiaota Coal Mine as the engineering background, physical similarity simulation and numerical simulation research methods are used. Combined with on-site microseismic monitoring technology, a microseismic waveform data library is established. With continuous mining of the working face, the evolution of overburden mining induced cracks and stress spatial distribution features at different stages of non-pillar gob-side entry retaining by roof cutting are studied. The periodic crack law of the overburden in the working face has been obtained. The research results show that the height of the overburden cracks during the initial pressure on the working face is about 57.6 m, the height of the middle crack zone before cutting is 95.5-96.1 m, the crack mining ratio is 23.8-24.0, the height of the edge side cracks is 105.9-106.4 m, and the crack mining ratio is 26.4-26.6 m. After the roof cutting, the final development height of the crack zone on both sides of the working face is about 104.3-105.2 m, with a crack mining ratio of 26.1-26.3. Due to the continuous compaction and closure of the overburden layer, the final development height of the crack zone in the middle of the working face is 94.3-95.2 m, with a crack mining ratio of 23.6-23.8. When the roadways are in the excavation and cutting stages respectively, there is basically no change in the displacement of the roof. When it enters the sinking and roadway formation stage, the displacement value of the roof continuously increases. After the completion of roof cutting and pressure relief, the peak support pressure on the side of the roadway increases, indicating that the span of the working face further increases after the cutting seam, and the inclined support pressure continues to increase. The pressure relief effect of the working face roof is significant, and the roof produces a large-scale stress release phenomenon. A microseismic monitoring system is installed in the working face, and it is found that there is a strong correlation between the periodic occurrence of microseismic events and the periodic pressure of the working face. The development process can be divided into the budding stage, development stage, and climax stage. Further comprehensive analysis can be conducted to obtain the periodic crack evolution law of the overburden.