Coal Wall Instability Evolution Law of Large Mining Height Face in Steeply Dipping Hard Roof Soft Coal Seam

The coal wall of large mining height longwall fully mechanized face in steeply dipping coal seam has poor self-stability and high probability of instability, which is likely to induce secondary hazards such as support instability and flying gangue once catastrophic occurs, increasing the difficulty of surrounding rock control and production risk. Coal wall disaster prevention and control can improve the productivity of this type of face, and this is based on the sufficient understanding of damage patterns such as internal and external dispersion of coal wall pressure, deformation, and displacement; in order to clarify the coal wall dynamic failure law of large mining height face in steeply dipping coal seam, numerical calculation, field measurement, theoretical analysis, and other methods are comprehensively applied to the study. The results show that the coal wall bearing of large mining height face in steeply dipping coal seam is distributed asymmetrically, the stress concentration position in the upper and middle part of the face is closer to the coal wall than the lower part, the stress concentration degree is also larger than the lower part, and the stress concentration coefficients from upper to lower are 1.37, 1.50, and 1.29, respectively. Soft coal wall bearing is mainly dispersed in the shape of “X†in its interior, forming intertwined pressure increasing and unloading zones, and most of the pressure increasing zones are at the edge of the outer end of the pressure relief zone, compression-shear type is the main failure form of the coal, and the middle and upper part of the coal wall in the height direction is easy to break and cause disaster. The coal wall of steeply dipping face partitioning migration features is obvious, and vertical displacement within 3.77 m from the coal wall is lower > middle > upper; after 3.77 m, it is upper > middle > lower; horizontal displacement is middle > upper > lower; coal migration volume in the middle region of the face is largest; and the coal wall instability has high frequency, wide influence area, and alternating evolution law.