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The spatio-temporal distribution and gas conductivity of overburden fissures in the mining of shallow thick coal seams are investigated to understand the correlation between the dynamic growth of overburden fissures in the mining of shallow thick coal seams and their gas conductivity. Theoretical analysis, numerical simulation and on-site measurements were combined for the mining of shallow thick coal seams in the Chuancao Gedan Mine. The results revealed that ground fissures with dynamic changes were observed periodically as the coalface moved forward. Dynamic changes of the horizontal fissure opening and vertical deformation related to the instability motion of the loading key stratum in the overburden were observed. The coalface mined-out area was divided into the fissure initiation, fissure propagation and fissure closure zones based on the changes in the horizontal opening and the vertical deformation of adjacent rocks in the overburden. [ABSTRACT FROM AUTHOR]

Surface mining-induced fissures formed in shallow coal seam mining have serious impact on safety mining and water resources protection. This paper proposes a novel approach to study the formation mechanism and dynamic development of surface mining-induced fissures in shallow coal seam mining. This approach combines field tests, theoretical analysis, and numerical simulations based on the geological condition of shallow coal seam mining in Chuancao Gedan Coal Mine. Two typical surface mining-induced fissures, step-type fissures and collapse-type fissures, are generated in shallow coal seam mining. The fissures with large vertical throw or horizontal opening severely impact water resource protection and surface ecological environment. Surface mining-induced fissures are generated periodically and changed dynamically with the advancing of working face. The vertical throw and horizontal opening of surface fissures are changed dynamically with the movement of loading key strata. The movement forms of loading key strata determine the morphological development of surface fissures. Downward sliding movement of broken rocks causes step-type fissures, while downward rotation movement leads to collapse-type fissures. The degree of the downward sliding and rotation of broken rocks determines the vertical throw and horizontal opening of surface fissures. This paper proposes mining technologies to reduce damaging ground fissures in shallow coal seam mining and analyzes their control effects. [ABSTRACT FROM AUTHOR]

The large mining height fully mechanized top-coal caving mining technique has developed rapidly and become the most extensively used mining method for ultra-thick coal seams. The arching of coal/gangue and the drawing out of gangue are peculiar phenomena in the process of fully mechanized top-coal caving mining, which not only affects the recovery of top-coal, but also affects the quality of the coal. This paper studies the arching phenomenon in top-coal caving mining process of ultra-thick coal seam. A series of laboratory granular material simulation experiments were performing and a top-coal arching model in the framework of mechanics was established to explore the formation characteristic of arches and their effects to top-coal loss. Then the countermeasures against the arches and technology path of intelligent mining based on improving top-coal recovery were put forward and performed in practice. The results show that the recovery ratio of top-coal has increased nearly 6%, and increased the production efficiency at the same time. The research on arching mechanism and removing strategies of dynamic random arches effectively improves the efficiency of fully mechanized top-coal caving mining in ultra-thick coal seams, and provides the foundation for the realization of intelligent top-coal caving mining technology. [ABSTRACT FROM AUTHOR]