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Brief

Journal of China Coal Society, the 1st in the field of mining engineering, promotes the development of coal theory and practice, as well as academic exchanges at home and abroad to accelerate the transformation from scientific research to real productive forces. It is supervised by China Association for Science and Technology and sponsored by China Coal Society. Launched in 1964, it aims at providing key topics of coal scientific research and mining development. Its scope covers coal geology, geochemistry, geophysics, mineralogy and coal seam formation and evolution; petrophysics of coal; organic matter-rich shales, including mineralogy, formation, transport and storage of gases in coal and shales; unconventional energy systems (e.g. oil shales, shale gas, and other carbon-based fuels); ore deposits of materials and rare metals in coal and coal-bearing strata; and groundwater management. The journal is included in CA, JST, EI, CSCD.
Editorial Board

Editor-in-Chief
Liu Feng

Associate Editor
Fan Baoying, Xu Shengyang, Zhu Shuangcheng

Behavior of strata movement in coal mining

QIAN Minggao;XU Jialin

Journal of China Coal Society,2019,Vol 44,No. 04

Coal mining involves extracting the resources from the earth. It will disturb the strata in the mining area, which inevitably causes strata movement and the change of stress and fracture fields, thus affecting safety and environmental problems such as the occurrence of ground pressure, groundwater loss and surface subsidence. Therefore, mining-induced strata movement and its influence on safety and environment are the basic scientific problems of coal mining. The understanding of these laws will improve the scientific nature of coal mining. Because of the complexity of strata movement, however, there are still several issues to be addressed. This paper introduces the mining-induced strata movement of block structure, which is followed by the review of advances and outstanding issues in the influence of strata movement on longwall face support, mining-induced fractures evolution, groundwater, surface subsidence, and mining-induced stress field. It is found that mining-induced strata movement is a combination of stress concentration caused by the span of thick and hard strata and the mechanical behavior of the rock blocks associated with the breakage of the strata. During the collapse of thick strata and the corresponding rock block movement, the characteristics of sudden changes and discontinuities typically occur. In such a process, a structure that can sustain large deformation may be formed after the rock blocks are hinged. The “R-S” stability of the structure causes significant influence on such phenomena as the occurrence of ground pressure, mining-induced fractures and surface subsidence. Mining-induced strata movement is like a “black box” system. Currently, it is just explained from the aspect of control principles and reaches the level of a “gray box” system. Therefore, strata control refers to “macroscopic” control in many engineering cases. The Voussoir Beam model has established longwall support theory and the estimation principle of support working resistance. In a general case, the support resistance that is determined as the weight of the overburden with a thickness of 4–8 times the mining height could meet the safety requirements of most mining projects. Specially, eight times should be chosen for the longwalls with a large mining height or a thin immediate roof, a shallow cover depth, or the support-crushing risks. As for some particular conditions, however, support crushing cannot be avoided by the single measure of increasing support resistance but should be combined with other engineering precautionary measures. According to the stability of rock blocks of overburden key strata, three types were proposed to characterize surface subsidence for varied alluvium conditions in different areas of China. It is suggested that subsidence types should be considered during the subsidence prediction, control and selection of reclamation methods. The presence of key strata and the corresponding breakage characteristics play a vital role in the distribution of mining-induced stress. At present, the prevention of accidents caused by stress concentration is harder than that of methane accidents. With this in mind, it is suggested that only test-style mines could be established in the areas with tectonic stress concentration or a large depth. This paper points out the direction for the study of strata movement and the corresponding influence on safety and environment in the coal mining industry.

Analysis of mesoscale in spontaneous combustion of coal: From macro-model of representative elementary volume scale to micro-model of pore scale

LIANG Yuntao;WANG Shugang;JIANG Shuang;HU Peiyu;LIN Qi;SONG Shuanglin

Journal of China Coal Society,2019,Vol 44,No. 04

The spontaneous combustion of coal has obvious mesoscale characteristics. The application of the mesoscale science and theory to correlate the microscopic reaction mechanism with the macroscopic properties of the spontaneous combustion of coal contributes to the in-depth study in the field of the spontaneous combustion of coal. Firstly, the physical process and the mathematical concept of the coal-pile level in which the mesoscale Ⅱ exists are made clear. The differences and interrelationships between the three scales of single coal particle, particle cluster and coal pile are explained in detail. Specifically, multi-scale simulation depends on the reasonable information transfer among scales, which is mainly realized by the upscaling method in the study of the spontaneous combustion of coal. From the point of view of mathematical modeling, it is pointed out that the essence of a coal particle cluster is the representative elementary volume (REV) of a coal pile. The REV-scale simulation, whose minimum unit is an REV, is based on macro-model, which ignores the structural changes in the cluster. Correspondingly, the pore-scale simulation, which considers the interaction of individual coal particles inside the REV, is based on a micro-model. Secondly, based on the definition of an REV scale, the governing equations, including continuity, momentum, energy, and concentration equations, which consider the effects of the transient porosity and high-temperature radiation, are built and the corresponding solving method is briefly described. Besides, it is pointed out that the parameters including porosity, permeability, and heat transfer coefficient should be obtained from the pore scale simulation. Thirdly, the Lattice Boltzmann equations of pore scale simulation are discussed. A sample is employed to illustrate the procedures for the 3D digital reconstruction and the extraction of the REV. Finally, based on the constitutive relation of parameters between different scales, the upscaling method for obtaining parameters, such as porosity, permeability, inertia coefficient, and convective heat transfer coefficient in macrocontrol equation, from the pore scale is proposed, which realizes the information transmission from the pore-scale simulation with a micro-model to the REV-scale simulation with a macro-model mathematically. Consequently, the multi-scale physical and mathematical modeling from a pore scale to an REV scale is completed.