Comprehensive Evaluation of In Situ Stress in the Daning–Jixian Area and Its Control on the Distribution of Coal-Measure Gas
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Keywords:
Coal measures
Lithology
Tension (geology)
Overburden pressure
Seam spacing plays a crucial role in selecting roof bolting of the close-distance coal seam. This work utilized three methods to determine the minimum roof bolting seam spacing of the lower coal seam (LCS) entry after the upper coal seam (UCS) mining. Based on the entry of the No.3-2 coal seam (LCS) in Chaili Coal Mine in China, theoretical analysis, pull-out bolt test, and numerical simulation were performed to calculate the maximum floor failure depth of the UCS and to determine the minimum seam spacing of the roof bolting. The maximum floor failure depth of the UCS determined through theoretical analysis and numerical simulation is 3.2 m and 3.3 m, respectively. In general, the anchorage length of rock bolting is less than 2.4 m, so the minimum seam spacing is 5.6 m or 5.7 m. To further determine the anchorage performance of the roof, the pull-out test was employed on the entry roof of the LCS. When the seam spacing is no less than 6 m, the test results show that the pull-out force of the bolt is more significant than 30kN; in addition, the numerical simulation results indicate that the roof-to-floor and rib-to-rib convergence are relatively small. Therefore, the LCS entry’s minimum roof bolting seam spacing can be determined as 6 m. This study could be used to select and design roof bolting under similar close-distance coal seam conditions.
Bolting
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In order to obtain lower coal seam mining of roof breaking characteristic and the law of mine pressure appearance in the close distance coal seams, this paper takes working face 6101 of a mine as the engineering background, and studies the roof breaking characteristics and pressure law in close distance coal seam through theoretical analysis, numerical simulation and engineering verification, which provides the basis for roof control in lower coal seam mining. The results show that the maximum failure depth of 4# coal seam mining on floor is 8.28 m. The lower coal seam mining roof forms a “loose-block” structure, and the main roof fracture step distance is 44.61 m. The UDEC simulation shows that the initial weighting intensity of 6# coal seam is large, and the first weighting distance step is about 40 m. The hydraulic support with the highest working resistance should be chosen based on the roof pressure analysis, and the weighting is frequent. The hydraulic support with higher working resistance should be selected through the analysis of roof pressure, some control measures should be taken to strengthen the organization and management, and prevent the occurrence of roof disasters. The roof is effectively controlled through engineering verification. The study further recognizes the laws of mining pressure appearance in lower coal seam of close distance coal seam, and provides experience for similar mine mining.
Longwall mining
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