Reform and prospects of mining technology for large inclined coal seam in China

The steeply dipping coal seam is one of the main forms of coal storage in China. It is widely and regionally distributed. According to incomplete statistics, twenty-six provinces, autonomous regions and municipalities directly under the central government are involved in the mining of such coal seams, with abundant reserves, large production and high production concentration in the central and western regions. It shows diversity and complexity in terms of the conditions of existence, with different regions having different coal formation periods and different tectonic control processes, forming diverse and complex mining conditions and giving rise to different mining technology requirements. The mining of steeply dipping coal seam is technically difficult. The asymmetry of the movement and damage of the peripheral rock in the mining area affected by the inclination angle of the coal seam is obvious, and the difficulty of the stability control of the support system and equipment, the matching and coordination of the “three machines”, the layout and support of the mining roadway, and the safety guarantee of the “human-machine” environment at the working face has increased significantly, which seriously restricts the safe and efficient mining of the mine. This has seriously restricted the improvement of safe and efficient mining. The regional economic demand for the mining of steeply dipping coal seam is strong. This kind of coal seams and the production of more concentrated areas are mostly seen in the coal industry-based resource cities, the economic structure is relatively single, the safe and efficient development and utilization of coal resources for the regional energy supply, people’s livelihood, economic stability has the role of the bottom of the pocket, the demand is urgent. For a long time, mining technologies for the steeply dipping coal seam changes focus on solving the “difficult” and “need” contradiction. In the coal mining methods and techniques, strata control theory and technology, complete sets of equipment development and application of the three aspects of continuous improvement, innovation, development, to achieve the transformation from non-mechanized to fully-mechanized mining, the level of safety and production efficiency has increased dramatically, the personnel labor intensity has decreased dramatically, and the operating environment has improved significantly. In the mid-1990s, Lvshuidong Coal Mine of Sichuan Coal Industry Group Limited Liability Company successfully realized longwall fully-mechanized mining in steeply dipping coal seam with medium mining height for the first time, breaking through the "forbidden zone" in this filed. Under this demonstration, the three pioneering engineering practices of longwall fully-mechanical mining of steeply dipping coal seam with thick mining height, steeply dipping coal seam with large mining height, and longwall fully-mechanical mining of steeply dipping coal seam with thin mining height in pseudo-inclination have been successful successively, which innovated the non-linear limiting arrangement of the working face and the way of adjusting the slanting, established a multi-dimensional interactive control mode of the system stability of the “bracket-surrounding rock”, and researched and developed the “support and stability and heavy weight, high-strength and light-weight, safe and reliable, and matching synergistic” complete set of equipment of the working face, which has achieved good results, and the scope of application of the comprehensive mechanized mining technology has further been widened. At the same time, there are still many key scientific problems and technical bottlenecks that need to be broken through in the mining of steeply dipping coal seams, resulting in a large gap between the intelligence level and that of the flat/gently inclined coal seams. Research on the mining dynamics of coal and rock bodies in inclined bedded coal beds, revealing their control mechanisms on the disaster of the surrounding rocks in the mining field, and realizing quantitative characterization need to be further strengthened. It is necessary to further clarify the multi-dimensional dynamic process and law between the system of “rock-bearing structure - mining equipment group”, improve the theoretical and technological basis of “multi-dimensional dynamic multi-objective synergistic control of equipment and surrounding rock”, and realize the transformation and application of the technology. On the basis of breakthroughs in scientific issues, we will carry out systematic technological innovation and research and development of coal mining methods, mining techniques, rock formation control, and complete sets of equipment, so as to crack the bottleneck of the constraints on the double enhancement of “safety and efficiency” in the mining of steeply dipping coal seams, and make the upper limit of the inclination of the steeply dipping coal seams for comprehensive mechanized mining extend upward under the prerequisite of reliable technological safeguards, so as to lay the foundation for the realization of automated and intelligent mining.