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在美国,无论井工开采或露天开采的煤矿,到处可见。关于多层煤开采中不利的地面控制问题在过去已广泛讨论过。由于缺乏
There are many coal mines in the United States whether it is mined or mined open-pit. The issue of unfavorable ground controls in multi-layer coal mining has been extensively discussed in the past. Due to lack of