Research on rock burst generation mechanism and three-level collaborative control technology of multi-key strata narrow coal pillar

Taking the 11–3106 working face of Menkeqing Coal Mine as the research background, a fracture model of the structure covered by thick and hard overburden at the 11–3106 working face was established. The mechanism of rock burst in the open roadway of narrow coal pillar with multiple key layers under the deep thick and hard roof mining condition with high strength was studied. The three-level collaborative pressure relief prevention technology of “drilling, blasting and pressuring” was proposed and applied in the field. Seismic CT, microseismic monitoring, support pressure monitoring and surface subsidence observation were used to verify the effect of pressure relief. The results show that there are high and low key layers overlying the working surface of 11–3106. When the two key layers break, the overlying rock may move in a wide range, and the surrounding rock of the open roadway is greatly affected by the dynamic load disturbance. The low bearing capacity of the narrow coal pillar makes the overburden load transfer to the solid coal side of the roadway and the stress increase on the solid coal side, which is the main area of impact initiation. Under the superposition of the lateral fixed abutment pressure and the mobile abutment pressure of the working face, the stress concentration degree of the solid coal side increases continuously. Affected by the periodic breaking of the hard roof, the “dynamic and static” loading is easy to induce the impact of the open roadway. Hard roof is not only the high static load source in the 11–3106 working face system, but also the source of strong dynamic load outside the system. For the prevention of rock burst at the 11–3106 working face, the measures should be taken from three aspects at the same time: ① the coal body is weakened to form a buffer and isolation zone for impact; ② the low pre-cracking roof is weakened to reduce the density of coal rock mass and destroy the energy storage conditions inside and outside the system; and ③ the high pre-cracking roof is artificially induced to break the key layer in the middle and high levels. The three-level collaborative pressure relief prevention and control technology of “drilling, blasting and pressuring” was developed. After the on-site implementation, the impact dynamic load caused by the breaking of high and low thick hard roof was reduced, the stress concentration in the high stress zone in the coal body was weakened, the high energy microseismic events were significantly reduced, the surrounding rock activity during the mining of working face was reduced, the compressive strength of working face roof was reduced, and the ground settlement value was increased by 200%. The results show that the three-stage coordinated pressure relief of “drilling, blasting and pressuring” has a good effect of “energy release and impact reduction”, which can provide a reference for the rock burst prevention and control of narrow coal pillar working face under similar thick hard roof conditions.