A new type of Ordovician limestone karst water inrush from the floor of old goaf: formation mechanism and the prevention and control technology

The Ordovician limestone water inrush accident occurred in the small coal-pit area in Xin’an Mine of Hebei Fengfeng mining area on October 25^th, which resulted in the production level being flooded, with the coal mine shut-down. Specifically, the accident cause was analyzed, and the concept of Ordovician limestone karst water inrush from the floor of old goaf was proposed, with its difference from the connotation and denotation of water inrush from the old goaf or floor water inrush accidents induced by mining summarized. Then, the water inrush mechanism based on the dynamic evolution of stored energy release from the confined water of Ordovician limestone in shallow old goaf floor was revealed. Based on the evolution history of regional Ordovician limestone karst, flow field analysis, numerical simulation, and engineering disclosure by exploration and treatment were performed to determine the distribution pattern of strong runoff zone of regional Ordovician limestone karst in the mine field. Thus, a karst hydrodynamic field model was established, and the artificial intelligence and deep learning methods were applied to invert the “10·25” water inrush time and spatial location in Xin’an Mine. In response to the characteristics and treatment difficulties of water inrush from the coal mine goaf floor, a “Trinity” technology system, with the integration of flow field targeting, exploration and treatment combination, and joint treatment of new and old water inrush points, was proposed for preventing and controlling water inrush from the coal mine goaf floor. Through the three stages of treatment, the three old water inrush points with a total water inrush of 1 080 m³/h and the new stable water inrush point with an inrush of 3 600 m³/h were completely blocked. In addition, the original normal water inrush of the mine was decreased from 2 040 m³/h to 1 020 m³/h. Generally, the treatment result is better than the expected.