5. Subsidence Prevention by Controlling Groundwater in Coal Mines

Huangsha Mine of north China adopts the multi-level development method with production levels at − 280 level and − 500 level. The average water flow in the mine is approximately 3.5 m³/min. A water inrush incident occurred in 2011 at the bottom of the − 280 level, and a large volume of groundwater flowed into the mine from the Ordovician limestone underlying the goafs. The peak water flow exceeded 400 m³/min, which was greater than the drainage capacity. The working face level was completely flooded as well as the pump house at the − 500 level. In response to the water inrush, the drainage capacity of the mine increased significantly by installing large-capacity submersible pumps to control the rate of the groundwater level rise. A concurrent grouting program was implemented to fill the goafs and cut off pathways from the water sources to the mining area and the water passageways between Huangsha Mine and the neighboring mines. The water inrush and engineering activities associated with the grouting program caused significant groundwater level fluctuations, which are contributors to collapse pits or subsidence depressions on the ground.