Integration of protective mining and underground backfilling for coal and gas outburst control: A case study

Abstract

Mining protective coal seams is an effective approach for coal and gas outburst control, but a large amount of gangue is usually produced when mining a thin protective seam and dealing with the gangue can be a challenging task. In the paper, a novel integrated mining system by extracting two panels simultaneously was demonstrated in the 12th coal mine of the Pingdingshan coalfield: one panel was mined in the thin protective coal seam, and the other one was mined in the protected coal seam. The thickness of the protective seam was only 0.8 m, but the mining height reached 1.8 m, indicating that there was about 1 m thick roof stone being mined. An underground coal preparation plant was built, and the mixture of coal and gangue from the protective panel was sorted underground. The sorted coal was delivered to the surface stockpile, while the waste rock was directly backfilled into the gob of the panel in the protected coal seam. Thus, waste rock did not need to be lifted up to the surface, which can reduce material handing cost and minimise mining footprint on the surface. In order to prevent the migration of pressure relief gas into the working areas of the protective coal seam, the main reasons causing gas exceedance in the upper corner of U-shaped ventilation system were investigated, and then the Y-shaped ventilation system and various gas extraction boreholes were implemented to effectively control the pressure relief gas. Numerical models were developed to assess the effect of applying gob backfilling during the extraction of two panels in parallel. The results show that the gob backfilling can reduce the surface subsidence and horizontal movement, which is very helpful for the protection of ground water and surface infrastructures.