Technologies for water hazard prevention and control in burnt rock aquifers within concealed burnt areas

Burnt rocks are extensively distributed in northwestern China, featuring well-developed pores and fractures and abundant water, emerging as primary aquifers in this region. The burnt rocks in concealed burnt areas in this region show inconspicuous surface remains, complicating their identification. Penetrating burnt rock aquifers in coal mining will lead to water hazard and destroy water resources in these aquifers. To prevent and control water hazard in burnt rocks within concealed burnt areas and preserve water resources in burnt rock aquifers, this study analyzed the distributions of burnt rocks in China and the effects of water in them on coal mining. Furthermore, it delved into technologies for the exploration and water hazard control of burnt rocks in concealed burnt areas and conducted exemplary application. By combining the field monitoring data, it analyzed and evaluated the performance of water hazard control and water resource preservation in the concealed burnt area on the south flank of the Ningtiaota Coal Mine in Shaanxi Province. The results are as follows: (1) China’s burnt rocks are primarily found across the northern region bounded by the Kunlun-Qinling-Dabie mountains. Among them, concealed burnt rocks, covered by Quaternary unconsolidated strata, are primarily distributed in the northeastern Ordos Basin and on the southern margin of the Yili Basin. (2) The burnt rock aquifers and weathered bedrock aquifers in the concealed burnt areas are almost directly connected and integrated, exhibiting intimate hydraulic connections. (3) The measures to prevent and control the water hazard in burnt rocks principally include setting up coal pillars for water containment in burnt rock aquifers, draining the accumulated water in burnt rock aquifers, and cutting off water via grouting curtains. Grouting curtains allow for effectively mining coal resources overlain by burnt rock aquifers, removing the water disaster threat from burnt rocks, and preserving precious groundwater resources in burnt rock aquifers. (4) By pinpointing concealed burnt areas and drilling grouting holes, burnt rock aquifers in the concealed burnt areas can be isolated as several water-bearing bodies, thus cutting off the hydraulic connections inside and outside a grouting curtain. This approach can remove the threat that burned rock water poses to mining faces and preserve the water resources within burned rocks. (5) Water hazard control was conducted for burnt rock aquifers in the concealed burnt area where mining faces S1232 and S1233 of the Ningtiaota Coal Mine are located, reducing the water inflow to below 20 m³/h during coal mining and ensuring the safe coal mining of the mining faces. Furthermore, the water level decreased inside the grouting curtain and gradually increased outside the curtain, effectively preserving the water resources within burnt rocks.