Tunnels and underground excavations Tunneling techniques
From this experience plus limited trial at the Hecla Mine in Idaho, the first major use of coarse aggregate shotcrete for tunnel support in North America developed in 1967 on the Vancouver Railroad Tunnel, with a cross section 20 by 29 feet high and a length of two miles. Here an initial two to four inch coat proved so successful in stabilizing hard, blocky shale and in preventing raveling in






































