Abstract
An appropriate layout of the first-mining working face of protected seams is key to rockburst prevention in coal seams. By taking the first-mining working face in the 2-2# middle coal seam in Hulusu Coal Mine as the background, a mechanical model for the stress distribution after mining the upper protective seams was established through theoretical analysis and in situ measurement. The problem concerning the layout of the first-mining working face in the protected seam was transformed into one concerning the optimal horizontal distance L. Furthermore, based on the theory of stress transfer within a semi-infinite plane, the distribution of the vertical stress in the protected seam was deduced, for which numerical simulation was performed. Through calculation, it is best (in terms of roadway excavation) to set L to between 50 and 75 m; the mining-induced disturbance shows the least influence on the two roadways at L = 80 to 140 m and at L = 40 to 100 m, and the influence of the remaining coal pillar on mining of the working face is the least significant. Based on the analytic hierarchy process (AHP) evaluation method, the weights of three groups of contradictory criteria and the weighted values of the peak stress under different values of L were calculated. The results show that the global stress on the first-mining working face in the protected seams is lowest at L = 60 m. The results can provide a reference for the layout of the working faces in protected seams in adjacent coal mines.
Highlights
Rock burst is a typical dynamic disaster in deep coal mining through the world and usually induces momentary gateway deformation and failure, casualties, and, more seriously, a series of secondary disasters, such as coal and gas outburst, gas explosion [1,2,3,4,5,6]
The number of the coal mines subjected to rockburst accidents in the Inner Mongolia Autonomous Region and Shaanxi Province, China, has increased year-over-year; restricted by the prevailing geological conditions in these areas and the as-formed mining layout, only local measures can be taken; consuming much resource often has little effect
Advancement in some areas is considered as the principle of preventing and controlling the risk of a rockburst in coal mines while techniques involving protective seams are effective as a means of prevention. e measure is applicable to prevention and control of the closely spaced rockburst-prone coal seams in the Inner Mongolia Autonomous Region and Shaanxi Province
Summary
Rock burst is a typical dynamic disaster in deep coal mining through the world and usually induces momentary gateway deformation and failure, casualties, and, more seriously, a series of secondary disasters, such as coal and gas outburst, gas explosion [1,2,3,4,5,6]. E stress distributions on the working faces in protected seams at different mining stages and the influence of the remaining coal pillar in the middle part were comprehensively considered On this basis, an analytic hierarchy process (AHP) method for determining the optimal horizontal distance L was proposed: this can provide information about the best layout of the first-mining working face in mines whose second coal seam is about to be mined in the Inner Mongolia Autonomous Region and Shaanxi Province. Erefore, the distribution of vertical stress within the protected seam (the 2-2# middle coal seam) can be calculated by substituting the piecewise function σy, formed by simultaneously calculating formulae (1), (3), (4), and (6), into formula (7) and setting y 24 m; the estimated function σy for the stress distribution in the protected seam is complicated and some parameters therein are difficult to determine accurately, making analysis of the optimal layout of the working face for pressure relief by peak-shift complicated. Further investigation is required and numerical simulation was used
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