新汶矿业集团华丰煤矿四层煤分层开采，长期以来全部采用金属菱形网作假顶。

There are four layer coal in Huafeng coal mine of Xinwen coal group company, it is mined layer by layer, artificial roof is used by diamond metal net over a long period of time.

youdao

新汶矿业集团华丰煤矿四层煤分层开采，长期以来全部采用金属菱形网作假顶。

There are four layer coal in Huafeng coal mine of Xinwen coal group company, it is mined layer by layer, artificial roof is used by diamond metal net over a long period of time.

youdao