Study on the failure mechanism and stability control measures in a large-cutting-height coal mining face with a deep-buried seam

Coal face spalling is a major issue affecting the safety of a large-cutting-height mining face, especially in deep mining. In order to analyze failure mechanisms and propose corresponding stability control measures in a large-cutting-height longwall face, panel 1303, with a mining depth of 860 m, which is arranged and advanced distances of 300 m and over 1000 m along the dip and strike directions of a coal seam, respectively, was selected as the engineering background. In addition to uniaxial compressive strength (UCS) tests, triaxial compression tests under different confining pressures and loading methods were carried out to investigate the deformation characteristics of the coal specimens. A mechanical model, the "coal face support roof", was established to illustrate the factors affecting the stability of the coal face. Combined with numerical simulation, the dominant factor was obtained, and the stress distribution around the coal face at different advance distances was revealed. Based on the coal face failure mechanism, the pertinent in situ measures of "manila + grouting" reinforcement technology for controlling coal face spalling were proposed. The results showed that the coal face spalling depended mainly on vertical cyclic loading and horizontal unloading in both initial and periodic weighting. In terms of deep mining, the surrounding stress distribution played a vital role in coal face failure and instability. Specifically, two dimensions of loading conditions were found in the front 3 m of the coal face, and the principal stress sigma(xx) of the coal body was significantly less than the other two principal stresses in the front 8 m of the coal face. In addition, the horizontal principal stress sigma(yy) was greater than the vertical principal stress sigma(zz). Therefore, the horizontal principal stress and strength of the coal body were the prominent influencing factors in the large-cutting-height coal face. The mining height and support system working resistance were also of great importance with respect to the stability of the coal face to some degree. Lastly, "manila + grouting" reinforcement technology proposed in this study resulted in 70-80% reduced potential for the occurrence of coal face spalling and in the degree of failure of the coal face, as well as grouting cost could be saved of 30-40% compared with pure grouting measures.