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In order to study the coupling law of mining and gas migration in close coal seams in fault structure area, taking the coal mining face in Guizhou as the research background, the development of mining fracture field and gas migration law of No. 5 coal seam and No. 9 coal seam were studied. Based on the development of mining-induced fracture field in coal seam, the fracture distribution was binarized and quantitatively analyzed by using fractal dimension, and the gas migration law of mining-induced fractures in No. 5 coal seam and No. 9 coal seam was simulated and studied. The results show that under the condition of U-shaped ventilation, the gas accumulates seriously in the upper corner of the mining fracture field, and the gas generally floats and accumulates to the separated layer development area of the overlying strata. Due to the existence of faults, even if the mining-induced fracture field in goaf of No. 9 coal seam is within the mining-induced pressure relief range of No. 5 coal seam, the gas concentration in the mining-induced fracture field is still high, and the variation gradient of gas concentration is large. The gas will circulate actively and accumulate easily near the fault structure, and the gas concentration at the high level of the fault is slightly higher than that at the low level. The research results can provide some reference for the mining of close coal seams in the fault structure area, the comprehensive prevention and control of gas, and the safe and efficient production of coal mines. [ABSTRACT FROM AUTHOR]

Surrounding rock deformation control of gob-side coal-rock roadway in inclined coal seams (GCRICS) is a major problem in gob-side entry technology application practice. This paper describes a case study of the surrounding rock deformation characteristics and control technology of a typical GCRICS in Guizhou, China. As according to data obtained during a field investigation, the reasons for the deformation and failure of 151509 tailentry and the shortcomings of the original support scheme were analyzed. In combination with existing theory and field experience, the "anchor cable + U-shaped steel + shotcreting + grouting" (CUSG) support method was proposed. The plastic zone distribution, displacement, and stress evolution law of the roadway-surrounding rock under the four support modes were analyzed and compared by numerical simulation. The results show that the supporting effects of several support methods varied from good to poor; CUSG was the best, followed by anchor cable support, U-shaped steel support, and then no support. Based on the previous seepage grouting theory, a slurry diffusion model of hollow grouted anchor cable (HGC) was established and the calculation formulas of slurry diffusion radius and grouting time were deduced, which provided guidance for field construction. Finally, the CUSG surrounding rock control technology was applied to 151509 tailentry subsequent roadway support. Through drill holes, analysis of the surrounding rock of the non-grouting area and the grouting area was conducted. It was found that the surrounding rock of the grouting area was high in integrity and strong in bearing capacity. Throughout the excavation period to the end of roadway mining, the roadway did not have to be repaired. This case study has high practicability, high popularization value, and provides a useful reference for the engineering support design of the GCRICS. [ABSTRACT FROM AUTHOR]

In order to improve the accuracy of coal and gas outburst risk prediction for an excavation face, an outburst equilibrium equation for the excavation face was established based on the Mohr–Coulomb criterion to predict the coal and gas outburst risk for the excavation face. The numerical model was established using the COMSOL Multiphysics simulation software to explore the relationship between the initial gas emissions from the borehole and the gas pressure. Using a ZTL20/1000-Z mine flameproof prediction device, taking excavation face 9301 in the Anshun Coal Mine in Guizhou Province, China, as the research object, and taking the detailed regulations for prevention and control of coal and gas outburst promulgated by the China Coal Mine Safety Supervision Bureau in 2019 as the prediction standard for coal and gas outbursts, an experiment on the outburst risk prediction for the excavation face was conducted. The results show that the gas pressure measured in the borehole is positively correlated with the initial gas emissions, and the initial gas flow can be used as a sensitive index to predict the outburst risk of the excavation face. The initial gas flow increases as the borehole depth increases, and it tends to be stable in the later stage. The initial borehole gas flow can not only reflect the outburst risk but also reveal the possible location of the outburst, which has obvious advantages over other outburst prediction indexes. [ABSTRACT FROM AUTHOR]

As a result of the mining of a C3 coal seam in a mine in Guizhou, perilous rock masses on the surface collapsed. In this study, the stability of perilous rock masses on the surface of the coal mine before and after mining was calculated and examined, and the movement law of the overlying strata in the goaf, the movement and deformation law, and the failure mode of perilous rock were analyzed. This study provides a theoretical basis for the treatment of unstable rock and coal seam mining, and has important guiding significance for the safe and efficient production of the mine. The results show that: (1) The perilous rock is in a basically stable state without the influence of mining. Through theoretical analysis and the construction of the collapse model of perilous rock, it is judged that perilous rocks W1, W3, W4, and W7 were basically stable, perilous rocks W2 and W5 were in an unstable state, and perilous rock W6 was stable without heavy rainfall. (2) As a result of the mining of the C3 coal seam, the cracks in the upper strata began to develop to the surface, and the longitudinal separation cracks gradually appeared between the surface perilous rock and the rock matrix. Due to the existence of these cracks, the perilous rock had a downward shear force. In addition, due to the heavy rainfall in the Guizhou area, the transient saturated zone of perilous rock is expanding and the strength of perilous rock is reduced. The seepage increases the sliding force of the perilous rock and aggravates the opening of cracks at any time. (3) The stability of the surface perilous rock mass is largely affected by the mining of underground coal mines. The simulation analysis was repeated using the method of setting coal pillars. When 45 m permanent protection coal pillars are set at both ends, and 15 m local protection coal pillars are set at 60 m, the safety of coal mining can be ensured without affecting the surface and perilous rock. [ABSTRACT FROM AUTHOR]