ICGCM Papers:
Chinese Mining Practices and Solutions
 
 
Safe Mining Evaluation of Coal Seam between Abandoned Upper and Lower Room-and-Pillard Mines
35th International Conference on Ground Control in Mining
Safe Mining Evaluation of Coal Seam between Abandoned Upper and Lower Room-and-Pillard Mines
by
Guorui FengJinwen Bai, Taiyuan University of Technology, Taiyuan, ChinaYi LuoJian Yang, West Virginia University, Morgantown, United StatesMin Zhang, Research Center of Green Mining Engineering Technology In Shanxi Province, Taiyuan, ChinaYujiang Zhang, Taiyuan University of Technology, Taiyuan, China
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Chinese Mining Practices and Solutions
[Author] Guorui FengJinwen Bai, Taiyuan University of Technology, Taiyuan, ChinaYi LuoJian Yang, West Virginia University, Morgantown, United StatesMin Zhang, Research Center of Green Mining Engineering Technology In Shanxi Province, Taiyuan, ChinaYujiang Zhang, Taiyuan University of Technology, Taiyuan, China
[Abstract] 
Key Conclusions:
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The middle residual coal seam No.7 with ULPM in Baijiazhuang coal mine is selected as the research object. According to the occurrence and mining conditions, the influence of ULPM on vertical stress evolution is studied and the maximum distribution range of vertical stress is determined with numerical simulation. Then, theoretical model is established based on Elasticity-Plasticity Mechanics theory. The edge stress field of upper-lower pillar mining workface is analyzed and the damage scope of upper-lower interlayer is calculated. Results show that: (1)The vertical stress distribution is gradually evolving from initial balance to wave balance in the mining process of lower coal seam No.8: the central axis of coal pillar is stress concentration zone and the central axis of pillar mining area is stress reduction zone. It gradually converted from initial wave balance into new wave balance in the mining process of top coal seam No.6: the degree of stress concentration and reduction of the coal pillar and pillar mining area will be further enhanced. (2)The theoretical damage scope is consistent with maximum distribution range of abutment pressure: the damage height of lower coal seam No.8 is less than the thickness of lower interlayer, while the damage depth of upper coal seam No.6 is more than the thickness of upper interlayer. (3)The middle residual coal seam No.7 is in the damage scope of upper pillar mining, which will lead fracture-developing, fragmentation-distribution and poor stability of upper interlayer. (4)The stability of upper interlayer should be paid more attention in the mining process of residual coal seam No.7 and the reasonable support measures should be taken timely to ensure safety mining.
Key Findings:
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(1)The influence of ULPM on vertical stress evolution was explored. (2)The maximum distribution range of vertical stress after ULPM was determined. (3)Theoretical model of edge stress field in upper-lower pillar mining workface based on Elasticity-Plasticity Mechanics theory was established. (4)The damage scope of ULPM on upper-lower interlayer was calculated. (5)The safety mining of middle residual coal seam was evaluated.
Objective of the Paper:
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(1)Explore the influence of ULPM on vertical stress evolution and determine the maximum distribution range of vertical stress after ULPM; (2)Calculate damage scope of ULPM on upper-lower interlayer and evaluate safety mining of middle residual coal seam.
Problem Statement:
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Strata behavior in recovering middle residual coal seam with upper and lower pillar mining(ULPM) is obviously different with the one in upward mining to recovery residual coal seam, pressure-relief mining of protective coal seam, distressing mining of high burst liability coal seam and close distance coal-seam mining, which is shown as the following ones: (1)The stress environment of rock strata around middle residual coal seam has changed after UPLM, which may exacerbate rock strata’s deformation and failure. What is worse, the support crushing accident, roof cutting accident, roof-fall accident and rib spalling accident may happened regularly, which will bring difficulty for safety support of roadways and surrounding strata. (2)The integrity and continuity of middle residual coal seam may be damaged after UPLM, which may hinder the arrangement of workface and excavation of roadways. (3)The fracture develops well in rock strata around middle coal seam under the combined action of multiple mining influence and residual coal pillars. Water flowing channel and gas diffusion channel may be formed, which may generate water-flooding and methane-accumulation threat for safety mining of middle residual coal seam. (4)The residual coal pillar may be temporary state of stability after UPLM. However, shear slip, gravity slide, caving slip and other creep ruptures in coal pillars may occur with the coupling impact of long-term concentrated stress, mine water erosion, spontaneous combustion and the influence of middle coal seam. The shock and failure wave of instability can transfer, diffuse and spread to contiguous coal pillars, which may lead domino instability of coal pillar. As a result, the rock strata may collapse a large area due to the loss-support of coal pillars. (5)The domino instability of coal pillar may cause surface subsidence when the depth of the coal seam is shallow, which may damage the surface buildings and roadways. …… Therefore, it is necessary to evaluate the influence of ULPM on rock strata’s stress distribution, fracture development, moving deformation, structure evolution and damage scope, which can make a solid theory foundation for the safety mining of middle residual coal seam.