The large diameter direct drainage borehole is used to strengthening mine drainage capacity, to ensure coalmine safety production.
大孔径直排孔的作用是加强矿井排水能力，保证煤矿安全生产。
The large diameter direct drainage borehole is used to strengthening mine drainage capacity, to ensure coalmine safety production.
大孔径直排孔的作用是加强矿井排水能力，保证煤矿安全生产。
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