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Ordovician limestone in North China coalfield has the characteristics of karst fissure development and strong water yield. Coal mines in North China have been threatened by Ordovician limestone water for a long time. Taking the mining of 32 coal seam in the first eastern mining area of Qianyingzi coal mine in Anhui Province in China as the engineering geological prototype, this paper uses the self-developed fluid solid coupling similarity model test device to carry out the similarity model test of overburden stress and pore water pressure response of coal mining under Ordovician limestone nappe aquifer. Based on the variation law of pore water pressure and overburden stress in a stope, it can be seen that the variation law of pore water pressure in confined aquifer is jointly affected by two factors: the vertical distance between the monitoring point and coal seam and the horizontal distance between the monitoring point and DF200 fault. According to the analysis of experimental results, the maximum height of a water flowing fracture zone in the stope is fifteen times the mining thickness. Compared with the theoretical calculation results of empirical formula, the coupling effect of seepage field and stress field and the geological structure characteristics of the stope promote the development of a water flowing fracture zone. The research results of this paper have important theoretical and practical significance not only for the safe mining of Qianyingzi coal mine but also for the safe mining of the coal mine facing the double threat of roof Ordovician limestone confined aquifer and reverse fault. [ABSTRACT FROM AUTHOR]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

Solid waste backfill mining can effectively deal with gangue and other mining wastes, as well as control the movement and damage of rock strata. In this paper, the RFPA2D rock failure process analysis software is used to study the fracture evolution and seepage response mechanism of the key aquiclude strata (KAS) under the conditions of different structural characteristics, interlayer rock thickness, and backfilling ratios in backfill mining. The simulation results show that, in backfill mining, soft rock plays a crucial role in the fracture repair of KAS with different structural characteristics. An increase in the KAS thickness from 15 to 35 m is shown to results in a continuously improved repair of KAS fractures. At the advancing distance of the working face of 50~100 m and the KAS thickness of 35 m, the minimum vertical seepage velocity of 0.06 ‐ 0.78 × 10 − 2 m / s is reached. An increase in the backfilling ratio from 45 to 80% improves the control effect on the overlying strata. A case study of backfill mining in the Wugou Coal Mine located in the Anhui Province of China was conducted. At the goaf backfilling ratio of 80%, the composite KAS's good control effect was achieved, which minimized seepage and avoided the water in rush phenomena. The above engineering application ensured the safe backfill mining of coal resources. [ABSTRACT FROM AUTHOR]