Large-diameter gas extraction borehole is considered an effective method by which to realize coal mine methane exploitation and outburst prevention. Efficient gas extraction can be achieved by selecting the right borehole parameters. In this paper, by comparing several conventional objective weighting methods, the PCA was used to assign the weights to the research indices, the optimization objective was reduced from multi-dimensional to one-dimensional with the help of the gray correlation analysis. The study of gas extraction effect under different borehole parameters based on the response surface model. Numerical simulations were used to analyze the mixed volume of gas extraction, the pure volume of extraction and the concentration in the upper corner after extraction under different schemes. Finally, a genetic algorithm degree model was used to solve the solution and determine the optimal arrangement of borehole parameters. The study shows that (1) the weight shares of borehole stratum, borehole diameter and borehole spacing were 0.385, 0.285 and 0.33, respectively, in the reduced dimensional analysis of the PCA. (2) Using the results of improved gray correlation analysis as a comprehensive evaluation value to measure the effect of gas extraction, the optimal range of the model was 28–30 m borehole level, 190–210 mm borehole diameter and 5.5–6.5 m borehole spacing. (3) Using the genetic algorithm to solve the model, we obtained the borehole layer 28.79 m, borehole diameter 199.89 mm, borehole spacing 5.76 m. The borehole gas extraction effect was good under this parameter. The extraction mixed volume was 129.8 m³/min, the extraction pure volume was 9.16 m³/min, the upper corner concentration was 0.52%, and the prediction accuracy of the model was 97.8%.

This work focused on the insufficient or excessive pressure relief in large-diameter pressure relief by drilling. The influence of large-diameter pressure relief by drilling on the 6307 working face of the Tangkou coal mine on the roadway deformation was taken as the research background, with numerical simulations, indoor experiments, and on-site applications used. The influence of pressure relief drilling on roadway deformation was studied to propose segmented reaming pressure relief. The influences of parameters (e.g., reaming diameter, reaming depth, and borehole spacings) on the evolution characteristics of segmented reaming cracks and pressure relief were further investigated. The results showed that segmented reaming pressure relief reduced the roadway deformation and the peak elastic energy of coal in the impacted hazard area and improved the energy accumulation of the surrounding rocks of the roadway. The effect of segmented reaming pressure relief was positively correlated with the diameter and length of the reaming section; it was negatively correlated with borehole spacings. The optimized segmented reaming parameters of the 6307 working surface of Tangkou coal mine are as follows: the optimized reaming diameter of 240 mm, the reaming section depth of 15 m, and the borehole spacing of 1.6 m. Field tests proved that the optimized segmented reaming technology can improve the deformation of the surrounding rocks of the roadway and construction.

Deep mining has started in the Huaibei mining area, and the serious threat of high confined water on the floor to the coal seam is gradually increasing. Based on the deep confined water mining project at working face II633 of the Hengyuan coal mine, this paper theoretically analyzes the damage depth of the floor and the risk of water inrush from the floor. The best proportion of grouting materials was quantitatively optimized by indoor experiments, and an industrial field test was conducted to judge the grouting effect. The results show that the failure depth of the bottom plate calculated by theoretical analysis is 31.73 m; a single factor test and a response surface optimization design method determined the best value of each index: water cement ratio 0.8, bentonite 2%, water reducer 0.6%, sodium silicate 2%. The damage depth of the bottom plate after grouting is 18.83~20 m, according to the field monitoring by the strain method. The optimized slurry significantly reduces the damage depth of the floor, ensures the safe and efficient mining of the coal seam above the high–pressure water, and has a high reference value for the safe mining of the coal seam under similar geological conditions.