ABSTRACT
When mining close-range coal seam with the purpose to improve the mining efficiency and reduce environmental problems caused by underground coal mining, the lower coal seam should exploited first. An upper roadway should set in the coal seam or rock at the overburden. As is shown in Figure 1, the upper roadway is in the middle of the lower coal seam, and it has a parallel position to the bottom roadways (Du et al. 2014). Drilling with long diameter should be drilled from the upper roadway to the lower gob areas, and drillings are used for the transporting of the slurries of the solid wastes. For the length limitation of the
1 INTRODUCTION
Though nowadays the mining height of coal mine in China has reached hundreds of meters, coal mining would still cause many environmental, ecological and even social problems, like surface subsidence, damage of the vegetation, bad ecological environment, et al. (Donggan et al. 2011, Bhuiyan et al. 2010a, b). Technologies like mine land reclamation, turning subsidence areas to pounds, soil reconstruction, et al. could repair the damaged land to a certain extent, but the mentioned methods could not kill or reduce the environmental problems caused by coal mining from the root (Shrestha & Lal 2011, Doležalová J et al. 2012, Borůvka L et al. 2012, Bograd et al. 2012). Meanwhile, underground coal with stone heads would make a lot of coal gangues left on the ground. Most of the hillocks contained many harmful heavy metals, and the weathering of the hillocks would release dusts to the air and would cause air pollution (Petsonk et al. 2013). Given many of the east cities’ air quality in China are poor, the control of the hillocks was taken into the agenda gradually (Cheng et al. 2011). The strategy that mining first and repairing second would not only cause the waste of manpower, material resources and financial resources, but also could be not sure that the ecological environment could be repaired as it was for the repairing work could not be done immediately (Meredith 2007). Thus, mining technology should be improved to reduce the environmental damage induced by underground coal mining. Generally, mining with stowing chooses
drilling diameter, pure solid wastes are not suitable for stowing through the drillings. So the coal gangues should be broke into micro pieces and mixed with fly ash, cement, additive, water, et al. The mixture is full of liquidity, and it will be transported to the lower gob by pipelines. After mining and stowing the lower coal seam, the upper coal seam should be exploited when the stowing body is steady. The stowing work in the upper coal seam could be either backfilling or the same technology as the lower coal seam did. If an upper stowing roadway was used for the upper coal seam, cost of production may increase. While if the coal seam bearing huge gas, the upper roadway for exhausting gas and the upper roadway for stowing could be merge to one roadway. In this case, the production cost could be reduced.
