Abstract
During the mining process of short distance coal seams group with high gas content, excavation of the protective coal seam will result in stress relief and fracture development which provides pathways for gas migration. Gas stored in the lower coal seam moves along the mining-induced fracture to the floor of the upper working face, which may cause the gas over-limit at the upper coal seam. This paper takes the short distance coal seams group in Xinghua coal mine as an example, theoretical analysis, numerical simulation and field monitoring are comprehensively applied to study the floor failure mechanism, pressure relief law and dynamic evolution of cracks induced by the mining of the second-right working face. The results showed that as the upper coal seam gradually advances, the pressure relief angle of roof and floor gradually decreases, and the pressure relief range and floor failure depth gradually increase. After the working face of the upper coal seam is advanced 100 m, the range of the pressure relief in the surrounding coal and rock masses approaches stable; the cracks in the shallow depth are mainly with small angles or type II shear cracks, and the cracks in the large depth are mainly shear-expansion with lager angles, and the amount of fractures in the floor reduces with the increase of the depth of the floor. It was found that the mining-induced fractures in the floor is distributed in the shape of an “O” ring, and as the working face advances, the range of this “O”-shaped crack circle keeps moving forward but the width of the crack circle is basically unchanged. Finally, the low-level drilling field was used to control the gas from lower coal seams according to the stress relief and fracture distribution law, which achieved satisfied application effect and provided guidance for mine gas extraction in similar mining conditions.
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Acknowledgements
This paper was supported by the State Key Research Development Program of China (Grant No. 2016YFC0600708), the National Natural Science Foundation of China (51804129, 51808246, 51904112), the Jiangsu Post-doctoral Research Funding Project (2019K139), science and technology projects of Monistry of Housing and Urban–Rural Development of the People’s Republic of China (2017K6004), and the Foundation of Huaiyin Institute of Technology. The authors would also like to express special thanks to the editor and anonymous reviewers for their professional and constructive suggestion.
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Zhang, C., Feng, R., Zhang, X. et al. Numerical Study on Stress Relief and Fracture Distribution Law of Floor in Short-Distance Coal Seams Mining: A Case Study. Geotech Geol Eng 39, 437–450 (2021). https://doi.org/10.1007/s10706-020-01502-3
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DOI: https://doi.org/10.1007/s10706-020-01502-3