Similar material simulation test study on evolution law of overburden fracture based on microseismic monitoring

In order to study the evolution law of overburden fracture in the “three-soft” coal seams, physical simulation experiments were used, combined with microseismic monitoring instruments and pressure sensors, to study the distribution characteristics of the microseismic events in the mining face and their relationship with the variation law of floor pressure, and the overburden characteristics of fissure evolution were analyzed. The research shows that: during the recovery of the model, a total of nine times of periodic pressure occurred, and the step distance has obvious pattern of large and small. After the sixth pressure, the cavity was closed and the fracture zone no longer developed upward. After that,the fracture zone only occurred laterally with the recovery; the evolution of overburden cracks during mining was a complex energy release process. The frequency and energy of microseismic events increase from the initial mining stage to the fourth cycle of pressure, and reach the peak value after the fourth pressure. After the sixth pressure onset, the cavity was closed and and the vertical fracture gap basically stopped to develop upward. After that, the frequency and energy of microseismic events decreased;the variation law of floor pressure and the variation law of energy frequency of microseismic events were basically the same, but the pressure data changed. The zoning is more obvious and has hysteresis, and the fluctuation range of microseismic events is larger than the fluctuation range of pressure;Both the change of fracture density and the change of energy frequency of microseismic events increase first and then decrease. But the two changes are in the process of increasing. Based on the simulation results and on-site drilling and peep monitoring, the gas enrichment area of the overlying strata was determined. According to this research result, the high-level boreholes were arranged for gas drainage. The gas enrichment has been well controlled, ensuring the safe and efficient production of the working face.