Study on Overburden Movement and Fissure Evolution Law of Protective Layer Mining in Shallow Coal Seam

Abstract

This study aims to effectively solve the problem of the destruction of the coal roof and floor overlying rock after mining the protective layer, and determines whether the gas in the protected layer can be effectively released. We do this based on the engineering background of the Weng’an Coal Mine; research and analysis of the movement of the roof and floor overlying rocks; the evolution of cracks and the pressure relief characteristics of the protected layer after mining the protective layer; and through theoretical analysis and similar simulation experiments. Through numerical simulation, it was found that the protected layer was depressurized due to the mining of the protective layer, and the decompression rate of the protected layer was 0.2–0.8. In addition, the overall expansion rate of the protected layer was greater than the requirements of the “Detailed Rules for Prevention and Control of Coal and Gas Outbursts” for coal mines, and the investigation of the residual gas pressure and content of the protected layer revealed that the protected coal seam had been mined in the upper protective layer coal face. The gas pressure dropped to 50.7% of the original coal seam gas pressure, the rate of decrease was 49.3%, the residual gas content dropped by 68.67%, and the gas concentration in the return airway was 0.31% on average, meeting the national regulations that require its value to be less than or equal to 1%. The study comprehensively demonstrates that mining of the protective layer is beneficial to the release of gas from the protected layer, and provides a practical reference for coal and gas outbursts in mines.

Experimental study on rock strata movement and stope stress distribution law under mining height regulation

“…[6][7][8][9][10] At present, there have been a lot of studies on the stress distribution law under different mining height mining conditions. [11][12][13][14][15][16] However, the studies focus on the summary of the stress distribution law after mining at a given mining height, lacking a comparative analysis under different mining heights. There are relatively few studies on how mining height affects rock strata movement and stress distribution in stope.…”

“…For non‐full coal protective layer mining, it is of practical significance to obtain the role of mining height in regulating the stress distribution in the mining field and to determine the optimal mining height to reduce the amount of rock mining 6–10 . At present, there have been a lot of studies on the stress distribution law under different mining height mining conditions 11–16 . However, the studies focus on the summary of the stress distribution law after mining at a given mining height, lacking a comparative analysis under different mining heights.…”

Overburden Failure and Water-Sand Mixture Outburst Conditions of Weakly Consolidated Overlying Strata in Dananhu No.7 Mine

“…It is considered that the easily disintegrating argillaceous rocks such as sandstone and mudstone with weak argillaceous cementation will cause water-sand inrush due to disintegration under the combined disturbance of mining and high-con ned water . Under the circumstances of multi-coal seam mining, the in uence of plastic failure zone and pore pressure in surrounding rock, development law of overburden fracture, and evolution characteristics of seepage eld in Yixin mine was determined (Liu et al, 2022). Through theoretical analysis, physical and numerical simulation, in-situ monitoring and other means, the surface subsidence of the ecologically fragile western mining area under repeated mining is predicted and analyzed.…”

Comparative Analysis of the Drainage Effect Based on Improved Hydraulic Flushing Technology

“…Compared with the above methods, protective layer mining technology was once considered to be the most economical and effective method for gas drainage in coal mines. − The China State Administration of Work Safety stresses that the protective coal layer should be mined first when a coal seam group is present . The technology aims to mine a coal seam with low gas outburst risk so as to relieve the stress and improve the permeability in the protected coal seam. , The protective layer can be divided into coal seam and rock strata according to different lithology. , According to the position of the protective layer, it can be regard as a upper protective layer, lower protective layer, , and upper protective layer and lower protective layer at the same time . The mining technology of the protective layer has been greatly recognized in practical engineering, but unfortunately, many coal seams in China that face the risk of coal and gas outburst do not have proper protective coal seam.…”

“… 30 The technology aims to mine a coal seam with low gas outburst risk so as to relieve the stress and improve the permeability in the protected coal seam. 31 , 32 The protective layer can be divided into coal seam and rock strata according to different lithology. 33 , 34 According to the position of the protective layer, it can be regard as a upper protective layer, 35 lower protective layer, 36 , 37 and upper protective layer and lower protective layer at the same time.…”