Progress,practice and scientific issues in steeply dipping coal seams fully-mechanized mining

The steeply dipping coal seam belongs to the coal seams with complex mining conditions,which is wide- spread in western China. Its development plays an important role in regional economic development. Due to the strata movement is complex and the working space is limited,it makes the fully mechanized mining difficult under the occur- rence condition in steeply dipping coal seams. Some scholars and engineers have studied the mining methods,ground control theories and equipment of the steeply dipping coal seam since the 1980s in China. Up to now,it has made great improvement in theories,technologies and equipment,and has built a relatively complete research system. This paper systematically reviewed the state of art,field experiences and key scientific problems that need to be solved in the fu- ture from three aspects. In this study,following main conclusions can be drawn:① China first proposed the concept of steeply dipping coal seam (inclination ranging from 35 to 55 degrees) and its engineering interpretation. However,the inclination range of steeply dipping coal seam should be extended with the increase of equipment ability and mining methods in recent years. Since the 1990s,a lot of breakthroughs were made on ground control theories and key technol- ogies,a great progression was made on protective methods for dynamic hazard and mining equipment was developed for inclined working face,etc. ② Except for the fully mechanized mining technology gradually matures in medium thick- ness coal seam,the fully mechanized mining technology in the thick coal seam with large mining height,and the fully mechanized caving mining in extra thickness coal seams,the fully mechanized mining technology using pseudo-inclined working face in thin coal seams also have made some breakthroughs in field. However,there are still many “bottleneck problems” that need to be solved from a scientific perspective in the future. ③ Although there are good feedbacks,the study also needs to be strengthen on the following aspects in the future:mechanical properties and quantitative charac- terization of overburden after coal mining,the influence of surrounding rocks mechanical behaviors after coal excava- tion on working face and its control,multi-dimensional interaction and multiple objective stability control for “support- surrounding” rocks system in longwall face,and the generation,motion and damage of separated blocks in working face and corresponding protective principles. Finally,some revolutionary mining methods,new technol-ogies and equipment should to be proposed to achieve a safe and green mining in the steeply dipping coal seam mining.