• 标题：Prevention and Control of Water Inrushes from Subseam Karstic Ordovician Limestone During Coal Mining Above Ultra-thin Aquitards
• 关键词：China;Directional borehole;Grouting;Hydrogeological condition;Water inrush coefficient;Transient electromagnetics
• 作者：

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Horizontal directional drilling technology was used to prevent and control water inrushes from the Ordovician limestone strata at the Sangshuping coal mine in the Hancheng mining area by drilling and grouting the contact zone along the top of the aquifer. Considering the hydraulic conductivity of the floor failure zone, we used the modified water inrush coefficient method to estimate the critical thickness of Ordovician limestone that had to be grouted. We carried out directional borehole exploration from both ends of the mining face and combined the results with borehole water pressure tests to determine appropriate grouting techniques and parameters; we then analysed the effectiveness of the grouting. 3-D seismic and ground transient electromagnetics (TEM) were used to detect areas of anomalous resistivity and geologic structure in the mining area, while DC and TEM geophysics were used to detect water-bearing areas ahead of the roadway. After the roadway was developed, TEM, DC resistivity sounding, and audio-magnetotellurics were used to explore water-bearing areas under the roadway and the mine floor. Radio waves were used to detect the structure of the mining face and changes in coal thickness. Finally, based on the results of exploration, an inspection program was devised using conventional boreholes supplemented by directional boreholes to comprehensively evaluate the feasibility of mining under pressure. The study showed that the failure depth of the floor was 15 m and that the top of the Ordovician limestone was no longer water-bearing and was now a relative aquitard. The water inrush coefficient was reduced to less than 0.073 MPa/m, which will ensure safe mining and extend the lower limit of safe mining in the area. This provides a technical reference for prevention and control of Ordovician limestone water disasters in similar coal mines.