Background The burnt rock formations in the Yushenfu mining area are widely distributed, predominantly developing along rivers and gullies. These formations are characterized by well-developed pores and fractures, with water-bearing capacity ranging from weak to extremely strong, exhibiting significant heterogeneity. They pose serious threats to roadway excavation and longwall mining in both the same coal seam and underlying seams.
Methods To effectively prevent and control water hazards associated with burnt rock formations and mitigate related risks, a combination of methods—including field investigation, statistical analysis, chronological testing, exploration and analysis, in-situ experiments, demonstration applications, and monitoring analysis—was employed.
Results and Conclusions The study analyzes the distribution characteristics of burnt rock in the Yushenfu Mining Area, investigates the micro- and meso-scale structural features, as well as the water-filling characteristics and hazard formation mechanisms, and develops key technologies for water hazard prevention and control. Demonstration applications and performance evaluations were also conducted. The results indicate that burnt rock formations in the Northern Shaanxi coal base are mainly distributed along both sides of the Tuwei River, Kuye River, Wulanmulun River, and their tributary gullies, covering an area of approximately 787 km and affecting roadway excavation and mining operations in dozens of coal mines. Vertically, the formations can be classified into four types: coal ash, fused rock, sintered rock, and baked rock; horizontally, they can be divided into three zones: the outer fully burnt zone, the central mixed burnt zone, and the inner burnt boundary zone. Burnt rock exhibits extensive development of cavities, fractures, and pores. The internal flow channels are well connected, forming effective seepage pathways. These formations receive recharge from atmospheric precipitation, pore water in Quaternary sandy layers, and weathered bedrock water, leading to three types of water hazards: lateral seepage through excavation-induced fractures, vertical seepage from the roof via mining-induced fractures, and lateral seepage through mining-induced fractures. Based on continuous boundary detection of burnt rock, key prevention and control technologies have been developed, including coal pillar water isolation, surface borehole grouting curtain for partitioning and interception, and surface two-dimensional combined gravity-driven direct drainage. These technologies have been successfully applied in multiple coal mines, such as Nanliang, Ningtiaota, and Zhangjiamao, achieving significant results. It has effectively eliminated the threat of burnt rock water hazards, liberated substantial coal resources, and enabled the protection and utilization of water resources within burnt rock formations.
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