Rock burst risk in an island longwall coal face by stress field

Abstract

In many coal mines in China, skip-mining and the corner coal pillar will lead to the formation of an island longwall coal face (ILCF), which will induce a series of problems. Rock bursts pose a severe threat to miners and safe production in coal mines. Here, we used a mechanical model, theoretical calculations, seismic computed tomography, and energy density to explore the stress field distribution in an ILCF to obtain some pre-warning parameters. Based on elastic thin-plate theory, three cases of rock strata of ILCF were analysed to explore various stress fields (case 1: solid coal, case 2: two-sided goaf, and case 3: four-sided goaf). The stress reaches the peak value at the points of “a = b” in case 1, “a = 0.7b” in case 2, and “a = 1.4b” in case 3, respectively, which indicates high rock burst risk. In the case study, the test methods of seismic computed tomography and energy density were used on four ILCFs in Zhaolou Coal Mine (ILCFs 11301, 1307, 1305, and 1306). The stress field can be reflected by the three parameters: velocity distribution, velocity gradient, and stress concentration factor; and the energy density can indirectly reflect the accumulated damage of coal and rock mass and test two parameters of velocity distribution and stress concentration factor, which verifies the stress field in ILCFs, and assesses their rock burst risk.