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The coal seam gas development in closed gob zone is still in the exploratory stage in China, and potential evaluation and sweet spots selection are the key issues. This paper establishes a complete evaluation system for selecting sweet spots for closed gob methane extraction with surface wells in the Tiefa mining area to reduce the blindness of area selection. The one‐vote veto system, the comprehensive evaluation index system, and the AHP‐entropy combined weight model are used to screen and evaluate the closed gob zones in the Tiefa mining area. A total of twenty evaluation units are evaluated and the development potential of which is classified as three levels by the optimal segmentation method. The relationship between the results of the assessment and the closed gob methane resource is also discussed, as well as the combined weight distribution coefficient. The results show that the development potential of the block cannot be estimated simply by the closed gob methane resource because the consistency between the comprehensive evaluation value and the closed gob methane resource is poor. The size of the combined weight distribution coefficient has little effect on the comprehensive evaluation values and only affects the ranking of evaluation units in a small range. [ABSTRACT FROM AUTHOR]

The coal production exploited from extra‐thick coal seams accounts for 45% of China's total coal production. With large coal output, the extra‐thick coal seams require that the chamber section be more than 100 m2. In case of parting (the noncoal rock, usually mudstone, sandwiched in the coal seam) in the extra‐thick coal seams, the integrity of the coal seams will be damaged and the large‐section chamber is extremely easy to occur rib spalling and roof leakage, which will increase the chamber's supporting difficulty. To solve such problems, this paper took the electromechanical chamber in Tashan Coal Mine as the engineering background and analyzed the deformation and failure characteristics of this chamber surrounding rocks by the numerical simulation method during the excavation process. The results indicated that the failure areas of surrounding rocks were mainly in partings, chamber ribs, and chamber dome with the failure depths of 15 m, 10 m, and 5 m, respectively. Based on the obtained deformation and failure characteristics, the supporting method of grouting integrated with high‐strength bolts and anchor cables was put forward. The grouting method was firstly used to improve the integrity of the chamber surrounding rocks, and the high‐strength bolts and anchor cables were used for supporting. Then, the supporting parameters of the bolts and anchor cables and the grouting parameters were optimized by the numerical simulation method. The optimized parameters were applied in the electromechanical chamber in Tashan Coal Mine, and the on‐site chamber ribs lateral displacement and roof separation amounts were only 0.018 m and 0.012 m, respectively, indicating that the surrounding rocks were controlled effectively. [ABSTRACT FROM AUTHOR]

Due to the complex geostress and mining conditions in the coal seam with depth of 800 m, stability of surrounding rock for gob‐side entry retaining is very difficult to achieve. In this paper, we firstly propose an innovative bolt‐grouting controlled roof‐cutting for gob‐side entry retaining (BCR‐GER) approach for deep coal mines. Secondly, a mechanical model of "surrounding rock‐supporting body" for BCR‐GER is constructed, which consists of coal wall, roadside props, and gangues in gob (the whole supporting body). Thirdly, the key parameters (ie, cutting height, cutting angle, grouting cable length, and row of roadside props) are designed. Finally, field practice was applied at the No. 31120 haulage roadway of the Suncun coal mine in China, and in situ investigations were conducted for verification. Field measurement results show that maximum convergences of roof‐to‐floor and side‐to‐side were 264 mm and 113 mm, respectively. What is more, the maximum support resistance of roadside props was reduced by approximately 58%. The deformation and failure of surrounding rock were effectively controlled, and the pressure on roadside props was greatly reduced. This research fully considers the bearing properties of gangues in gob, eliminates the secondary disasters caused by borehole blasting, and provides guidance and reference for deep surrounding rock control of the same or similar gob‐side entry. [ABSTRACT FROM AUTHOR]