Reduction theory and technical system of underground coal mining

The coal mining changes the overburden boundary conditions and causes the redistribution of the in-situ stress and the deformation, movement, fracture of overburden rock. The damage conducts from the bottom to top in overburden and causes the damage of aquifers, surface appurtenances, and mining area ecosystem. Besides, while the modern mining ensures the energy demand of social development, it also causes great damage to groundwater , ecological environment and construction/construction facilities in mining areas. In order to solve the problem of large-scale coal mining damage and the safe coordination of protected objects in the mining area, based on the systematic analysis of the damage reduction mining theory and technology and long-term practice worldwide, according to the concept of “source damage reduction” and “pre-mining source control, mining optimization reduction and post-mining collaborative repair” for the entire mining process reduction, a pre-mining, mid-mining, post-mining reduction technology is proposed as the main measures for reducing mining damage throughout the entire mining process, which includes the three types and four technologies: “source reduction technology based on mining process parameter optimization, hard rock pre-fracturing-soft rock grouting modification and postmining water conduction fracture sealing and water control technology, as well as maintaining the stability of the overburden bearing structure during mining”. And the theoretical and technical system for reducing mining damage in underground coal mines has been constructed, and the focus and direction of research on reducing mining damage has also been clarified. In terms of mining damage monitoring, due to the significant spatiotemporal differences in monitoring technology, it is difficult to achieve a synchronous monitoring of surface deformation and cracks in the same space-time, as well as an integrated monitoring of multiple elements of the surface ecological environment. Therefore, it is still necessary to propose the targeted methods for correcting and processing asynchronous data from the multi-source monitoring of coal mining induced damage. In terms of damage conduction theory, based on the theory of overburden damage conduction, a mining damage field model is proposed from the perspective of energy indicators. Combined with the differences in the combination of soft-hard rock layers and the media of rock-soil layers, a unified damage field quantity and cross interface conduction theory for the multiple factor indicators of “overburden-aquifer-surface-ecology” is proposed. The 12401 longwall face of the Shangwan coalmine has adopted the measures of pre-mining parameter optimization and grouting in the caving zone during mining, the maximum surface settlement amount has been relatively reduced by 25%, and the surface cracks have been adjusted from step-like cracks to dynamic small cracks. In addition, since the technical implementation at the Shendong mining area in 2010, the vegetation coverage has increased from an average of 31% to a maximum of 74.1%.