Study on dynamic subsidence mechanical model and time-space evolution law of key strata

Reasonable lag time of gob-side entry driving is the key to alleviate the mine pressure and improve the efficiency of safe mining. Based on the thin plate theory, the Maxwell model is introduced to establish the relationship between the time parameters and the migration of the key strata. The dynamic subsidence mechanical model of roof breaking is futher validated using the numerical simulation and engineering practice. The results show that the stress concentration on the upper surface of the key stratum is the key factor of rock breaking, and the mining step distance and time are linearly related to the deflection of the roof during the compaction period. The numerical simulation results show that the displacement of the key strata in the goaf during the compaction period (within 30 days) is rapidly affected by the residual mining, and the stress in the middle of the key strata in the goaf is transmitted from the center to the edge, and finally concentrated in the roof of the roadway. After stopping mining, the stress concentration in the goaf is significant in a short time, and there is still a tendency of dynamic disasters. Roadway excavation is not recommended in a short time (within 60 days). The mine pressure monitoring and microseismic data in the field proved the residual influence of mining dynamic pressure from the perspective of time and space. The microseismic events gradually developed from the deep to the shallow, which confirmed that there was a spatial and temporal evolution process from stress concentration to balance during the compaction period of the goaf. Taking the time parameter as the connection point, and combining the key stratum movement and roadway excavation time organically have important theoretical guiding significance for the selection of gob-side entry driving time.