Research on exploiting residual coal around final end-walls by highwall mining system in China

To improve the resources' recovery ratio and the economic benefits of surface coal mines, we present a residual coal extraction technology from final end-walls with highwall mining system in China. Based on MarkBieniawski formula and tributary area theory, the evaluation methodology of highwall mining parameters under the thick cover was given. Furthermore, the pillar design chart in the highwall mining system under the thick cover was also concluded. In order to examine the rationality of the pillar design with the presented methodology, numerical simulation was also carried out. The outcome shows that it will require a larger pillar width with the thickening of the cover; hence, the recovery ratio will decrease correspondingly. To improve coal recovery ratio, the backfilling technology should be considered under the thick cover. According to two-dimension numerical simulation results, the calculated methodology for pillar stability of highwall mining system under the thick cover presented in this article is acceptable. It also found that keeping the pillar width-to-height ratio above 1 is a key measure to maintain the pillar stable and integral under the thick cover. Meanwhile, it can be concluded that the bigger safety factor is demanded for roof of openings under much thicker cover and higher stress ratio. In other words, the highwall mining system is feasible to extract the residual coal around end-walls in Chinese surface coal mines. Thus, not only coal recovery ratio can be improved but also can increase the production life of surface coal mines in China.