A study on the law of overlying strata migration and separation space evolution under hard and thick strata in underground coal mining by similar simulation

Fracture of the hard and thick key layer can easily cause dynamic disasters, such as the rock burst and mine seismicity, which seriously threatens the safety of underground coal mining. To analyze the characteristics of overlying strata fracture and law of evolution of separation fissures under hard and thick strata in underground coal mining, and further reveal the process of the occurrence of dynamic disasters, the fracture characteristics of overlying strata during underground coal mining were analyzed via similar simulation in this study. The characteristics of surface movement and deformation before and after the fracture of hard and thick strata were then discussed based on the law of overlying rock displacement. Finally, the development law of separation fissures under the hard and thick strata was revealed. Results show that the key stages of overlying strata movement during underground coal mining are immediate roof fracture, main roof fracture; main roof cycle fracture, and hard and thick rock fracture, respectively. Before the hard and thick strata are fractured, as the key layer, bearing the weight of the overlying strata and the overburden strata subsidence is small. The developmental height of the separated stratum stops at the bottom of the hard and thick strata, and the separated stratum stays in an unclosed state for a long time, which provides the incubation space for the accumulation of gas and water in the strata. After the hard and thick strata are fractured, the subsidence of the overlying strata increases dramatically, and the separated stratum is closed rapidly, inducing gas outburst, water inrush, dramatically surface subsidence, and other disasters in the working face. The research results of this study are of considerable significance to the safe mining of working face under similar geological conditions.