underground coal mine
Technical term for a coal mine where extraction is done via underground shafts and tunnels, as opposed to open-pit mining.
There used to be many underground coal mines in this area.
Working conditions in underground coal mines were extremely harsh.
Full standard spelling for an underground coal mine.
Abbreviated spelling omitting り; less common but still encountered.
Compound of 坑内 (inside a mine) + 掘り (digging) + 炭鉱 (coal mine).