Upward slicing longwall-roadway cemented backfilling technology for mining an extra-thick coal seam located under aquifers: a case study

Many water inrush disasters have occurred in mines that were attempting to recover extra-thick coal seams located under aquifers. This paper presents a technology known as upward slicing longwall-roadway cemented backfilling (USLCB) which can provide a safe and effective solution to extract these seams. The fundamentals of the technology are to divide a coal seam into several slices and extract each slice sequentially, from bottom to top, using longwall-roadway mining technology. Gobs are filled with cemented backfill which then act as a new floor allowing the overlying slices to be mined, similar to the overhand cut and fill method. This paper also presents the compressive properties of cemented backfill material with various mixing ratios and curing times. Moreover, a physical simulation was conducted to verify the effects of USLCB. The results of the simulation indicate that USLCB can be used to control strata movement as well as the height of the water-conducting zone (HWCZ). The USLCB was applied at Gonggeyingzi Coal Mine in Inner Mongolia, China. The results indicate that the recovery ratio has increased from 39.2 to 95%, the backfill ratio reached 95%, water inflow decreased from 245 to 120 m3/h and the maximum HWCZ was 39.2 m after extracting the entire 21 m of the coal seam. The conclusions of this research show that implementing USLCB can significantly improve productivity and safety when extra-thick coal seams are mined which are located under aquifers.