Water inrush and environmental impact of shallow seam mining

Shallow seam mining is very common in China for enhancing coal recovery. However, this may cause a series of severe problems in environment and mining safety in some cases, because the alluvium aquifers are directly above the shallow coal seams. Some typical water and sand inrush incidents resulting from shallow mining in China are analyzed. Based on in-situ observation, the mining-induced strata failures are investigated. The height of the fractured zone decreases as the size of the outcrop pillar or mining depth decreases. The spatial distributions of the failure zones in the shallow mining have specific features compared to the deep mining. These provide an advantageous condition for the shallow mining under alluvial aquifers. Optimal designs for outcrop pillar sizes are also given in different hydrogeological conditions for environment friendly and production-safe mining at shallow depths. According to in-situ mining experiments in several coalfields, technical measures for shallow mining are presented. These primarily include the lift mining for thick seams and reduction of the thickness of extraction in the first lift, short-wall mining, and detection of faults and other potential hazards prior to mining.