Experiment on prevention and control of coal wall spalling in three soft coal seam working face

Broken coal and rock reinforcement technology is an effective means to prevent “three soft” coal seams from falling. Based on the background of safe mining in “three soft” coal seam, this paper studies the working face slope mechanism, indoor mechanical experiment of broken coal rock reinforcement, numerical simulation of working face coal wall reinforcement and evaluation of working face coal wall reinforcement effect through theoretical analysis, mechanical experiment, three-dimensional FLAC calculation and on-site detection, determines the mechanical strength of modified coal rock reinforcement and the evolution law of surrounding rock, and carries out on-site grouting reinforcement and grouting parameter test. The comprehensive research shows that the coal wall spalling is closely related to supporting pressure, basic roof movement, mining height, coal and rock fissures, coal quality and other factors, and the closer the coal wall is to the roof, the easier it is to spall, and then the maximum deflection ωx and the maximum rotation angle φmax of the coal wall are obtained. The strength of coal and rock strengthened with 30% reinforcement materials is 6.4 times and 6.6 times higher than that of raw coal, respectively, and the brittleness characteristics are obvious. Under the condition of equidistant grouting spacing, the optimal grouting pressure is 10 MPa. After grouting, the distance between the peak of abutment pressure stress and the coal wall is shortened by 40%, and the plastic zone in front of the coal wall is reduced by 33.33%. The experimental results of grouting reinforcement were applied in areas with serious spalling. After 30% of the reinforcement material was injected into coal under the pressure of 10 MPa (pneumatic grouting), the slurry formed a “grouting material-coal seam” combination in the coal wall, and the coal wall changed from soft and broken to the overall flat state. The lowest diffusion radius of slurry reached 4 m, and the average spalling amount of coal wall remained within 0.3 m. The support met the initial supporting force requirements, and the coal wall was deformed.