Using Water Injection to Prevent Shaft Failure in the Jining No. 3 Coal Mine, China

Water injection into aquifers is a new approach for preventing shaft failure by stabilizing water levels. A series of injection tests was performed in the Jining no. 3 coal mine. Injection flow rates decreased over time as the water injection channels were blocked. Groundwater elevations in four observation boreholes and strain variations in the alluvial strata and shaft walls were analyzed to assess the effect of water injection on shaft failure and determine a preventive injection rate. The groundwater elevations in the observation boreholes decreased and the compressive strains in the alluvial strata and shaft wall increased overall over time. Although the water injection effect has weakened in recent years, it has still effectively slowed the increase of compressive strain in the shaft wall compared with conditions before water injection. We determined that the total and average injection rates for the four boreholes need to be approximately 20m(3)/h and 5m(3)/h, respectively, to maintain groundwater elevations and stabilize strain in the shafts. Measures such as oscillating pressurized water injection or increasing the number of injection boreholes could be used to increase injection flow rates and prevent shaft failure.