Hydrogeological condition evaluation and water hazard control for mining above the confined aquifer in No. 5 coal seam of Dongdong Coal Mine

This study addresses the water inrush threat during mining above the confined Ordovician limestone aquifer in the floor of No. 5 Coal Seam at Dongdong Coal Mine, aiming to provide technical support for safe mining under complex hydrogeological conditions. By establishing a "multi-dimensional, full-coverage" detection technology system, methods such as 3D seismic and electrical joint exploration, along with in-seam wave detection, were used to precisely identify the distribution of weak zones in the coal seam floor. A quantitative risk assessment was conducted by combining the water inrush coefficient method with the vulnerability index method, dividing the mining area into three grades: safe zone, buffer zone, and forbidden mining zone. A comprehensive water hazard control technology plan integrating "advanced detection + sectional dewatering + dynamic monitoring" was implemented. Results showed that the floor water pressure at the 50112 working face decreased from 0.58 MPa to 0.23 MPa (a 60.3% reduction), and the water inflow was 65 m³/h, a 45.8% decrease compared to predictions. At the 50122 working face, the area of anomalous electrical resistivity decreased from 25% to 18%, and the average monthly microseismic events were reduced by 65.2%. This technology effectively controlled the risk of floor water inrush, reduced the water control cost per ton of coal from 18.6 RMB to 12.7 RMB, achieved an early warning accuracy of 92%, and avoided economic losses of approximately 28 million RMB, providing an effective solution for mining above confined aquifers under similar conditions in the Weibei Coalfield.