Development and application of borehole sealing technology for water-sand inrush from Ordovician limestone aquifer in coal mine

The technology for surface sand filling and underground grouting is adopted to control the karst collapse column of Ordovician limestone in Sangshuping Coal Mine. However, there are serious water-sand inrushes in three conventional inspection boreholes, so it is of great difficulty to seal them. Putting wooden wedges and reverse wire packers into the boreholes all fail. In order to solve this problem, the grouting sealing technology with pressure replacement is proposed in this paper. Firstly, water larger than the casing pipe volume is injected into the borehole to ensure a clear borehole and to avoid sand filling into the casing pipe, resulting in the sealing depth not reaching the stable rock layer below the casing. After that, a lower pumping volume is adopted to repeatedly inject cement slurry larger than the casing volume into the borehole. Finally, after the cement slurry is solidified, a small diameter bit is used to drill outside the casing to check the sealing quality of the large diameter boreholes. Three conventional inspection boreholes are successfully sealed. In the engineering practice, it is found that the water-cement ratio of the cement slurry for early grouting borehole sealing should be 1︰1, and the single setting time should be 3 to 4 days. Prolonging the cement setting time can improve the quality of borehole sealing. This borehole sealing technology is applicable to underground narrow space operation, which can prevent water-sand inrushes from the orifice, ensure the sealing quality and personnel safety, and provide a technical reference for sealing similar water-sand inrushes.