(from the article `tunnels and underground excavations`) Mining downward, generally from the surface, although occasionally from an underground chamber, is called shaft sinking. In soil, shallow shafts are ... Found on http://www.britannica.com/eb/a-z/s/73
(from the article `tunnels and underground excavations`) Mining downward, generally from the surface, although occasionally from an underground chamber, is called shaft sinking. In soil, shallow shafts are ...