Background  Water hazards in coal seam floors represent a core challenge restricting the exploitation of deep coal resources in North China-type coalfields. As coal mining extends to greater depths, previous studies and experience exhibit limited applicability in the pattern classification, mechanism interpretation, and prevention and control of water hazards in thick floor aquicludes. Therefore, there is an urgent need to make breakthroughs and improvements in these three aspects.

Methods  Using several methods, including case-based induction, theoretical analysis, numerical simulation, and technical summary, this study developed a classification system based on parallel multiple criteria for floor water hazards by combining available water hazard patterns and representative cases of water inrushes. Based on a review of classical mechanisms behind water inrushes, this study systematically expounded on the disaster-causing mechanisms underlying water inrushes from thick floor aquicludes using the circular hole model in an infinite elastic plate (also referred to as the elastic circular hole model). In combination with numerical simulation, these mechanisms were further supplemented from a dynamic evolutionary perspective. Based on the derived disaster-causing mechanisms, the prevention and control system for water hazards from thick floor aquicludes was improved.

Results Regarding water hazard patterns, this study developed a four-level classification system based on parallel criteria, i.e., the mechanisms and dynamic sources of water inrushes, as well as geological structures (including their types and characteristics). The mechanisms underlying water inrushes were classified into two general categories: the holistic failure of thin aquicludes and fracturing-induced water uplift of thick aquicludes. For water inrushes from thick floor aquicludes, the rupture process of defects in the floor was characterized using the elastic circular hole model. Accordingly, the distributions of the defect rupture pressure and fracture reopening pressure were proposed to serve as indicators for characterizing the floor state in the full spatiotemporal domain. Under the condition of thick floor aquicludes, the disaster-causing mechanisms of two water inrush subcategories, i.e., those with dynamic sources of mining pressure combined with water pressure (for intact aquicludes and aquicludes bearing faults, collapse columns, folds, and fractures) and merely water pressure (for equivalent homogeneous thick aquicludes), were elucidated. Besides, a water hazard prevention and control system incorporating six major links was organized. Based on mechanisms underlying water inrushes from thick floor aquicludes, this study refined eight specific tasks of three links in the system, namely exploration and evaluation, engineering prevention and control, and monitoring and early warning.

Conclusions  The four-level classification system provides a basis for the multi-perspective categorization of water hazard patterns. The elastic circular hole model enables the systematic analysis of mechanisms underlying water inrushes from thick floor aquicludes, overcoming the limitation of conventional models, each of which corresponds merely to a single pattern and mechanisms of water hazards. The controlling effects of the defect rupture pressure and fracture reopening pressure on the fracturing-induced confined water uplift are clarified, facilitating a shift from a static to a dynamic perspective in understanding the mechanisms behind water inrushes. The improved water hazard prevention and control system provides theoretical and methodological support for preventing and controlling water inrushes from thick floor aquicludes in the case of deep coal mining above confined aquifers. Overall, the results of this study provide a systematic basis for the prevention and control of water hazards in coal seam floors, holding significant theoretical and practical implications for enhancing the prevention and control level of water hazards in coal mines and ensuring the safe exploitation of deep coal resources.