Study on mechanism and response of fracture and movement of the far-field high-position hard-and-hick stratum

Mastering fracture and movement of far-field high-position hard-and-thick strata plays an important role in safety prevention and control of disasters including severe surface subsidence and strong mine seismic events. The fracture mechanical model of high-position hard-and-hick strata is established based on the panels 2201 and 2202 in Yingpanhao Coal Mine. The fracture and movement of the Cretaceous sandstone formation and its influencing factors are analyzed by using the theory of Vlasov thick plate, which is verified and analyzed by surface subsidence and microseismic events. The conclusions are as follows: ① In view of the occurrence characteristics of Cretaceous sandstone group that is far away from the coal seam, with large thickness and good integrity, a high-position hard-and-hick strata fracture mechanical model is established. And the critical mechanical conditions for the first fracture of high-position thick-and-hard rock stratum are calculated by Vlasov thick plate theory. ② With the increase of tensile strength, the fracture overhang length of hard-and-hick stratum slowly grow, linearly grow, and exponentially grow; As the thickness of the stratum increases, the fracture overhang length of the thick and hard rock stratum increases exponentially; With the increase of the overhang length along the dip (width of panel), the fracture overhang length of thick and hard rock stratum increases first and then decreases. ③ During the extraction of panel 2201 in Yingpanhao Coal Mine, the hard-and-hick stratum did not break; And when the panel 2202 advanced about 960 m, the vertical “O-X” fracture occured; When the panel continues to advance about 188 m, the hard-and-hick stratum breaks periodically. ④ The monitoring results of surface subsidence show that the surface subsidence value of panel 2201 is small as a whole, and there are many small energy micro-seismic events. The surface subsidence of panel 2202 has experienced slow subsidence, rapid subsidence and stable stages in turn, and the frequency of high-energy mine seismic event has increased significantly. The location of the high energy mine seismic events and the area of the maximum surface subsidence are highly coincident, both in the O-X break area; The surface subsidence velocity reached the maximum of the 9.87 mm/d at 960 m away from the setup room, inducing the “6·8” strong mine seismic event. The above phenomenons verified the correctness of the far-field thick and hard rock stratum fracturing behavior. The research results of this paper have guiding significance for the study on the fracture of thick and hard rock stratum and disaster pre-control under similar engineering geological conditions.