Surface collapse control under thick unconsolidated layers by backfilling strip mining in coal mines

Surface subsidence induced by mineral extraction from underground mines can significantly affect the ecological environment and human life. Surface collapse is extremely hazardous and typically occurs without warning. In China, numerous surface collapses have occurred during mining operations in coal mines located under thick unconsolidated layers. Via analysis of the stability of the bearing structure (arch structure in unconsolidated layers and key strata in rock strata) based on their effects on strata movement, our study reveals the formation mechanism of surface collapses and the roles played by two critical parameters: mining length and mining height. It is speculated that the bearing structure cannot be self-stable and will collapse during longwall mining with increasing mining length and mining height. As a result, the ground surface will collapse on the longwall face gob accompanied by the failure of the bearing structure. With these risks in mind, this study proposes a backfilling strip mining method via determination of the appropriate longwall face length and mining height to guard against bearing structure failure and thus avoid surface collapse. A field trial of the technique was conducted at a suitable Chinese coal mine located under thick unconsolidated layers. The maximum surface subsidence observed was only 0.369 m, which is 92% less than the subsidence in longwall face (LW) 3A04. No surface collapse occurred during the mining process. Thus, our results indicate that the proposed technique can successfully prevent surface collapse during longwall mining under thick unconsolidated layers.