noun
face; working face
Mining term for the exposed surface of a mine or tunnel where excavation is actively taking place.
坑夫たちは切羽で石炭を掘り進めた。
The miners dug coal at the working face.
切羽の状態を確認してから作業を始める。
We check the condition of the face before starting work.
坑道 refers to the entire mine tunnel or gallery, while 切羽 specifically means the active excavation face at the end of the tunnel.
Compound of 切る (kiru, 'to cut') and 羽 (ha, 'wing' or 'edge'), here meaning the cutting edge or face of a mine. The reading は for 羽/端 is an older nominal form.