Tunnel
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A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each
Tunnel in Col du Galibier, France
Tunnel in Fort de Mutzig, France
Decorated portal to a road tunnel in Guanajuato, Mexico
Utility tunnel for heating pipes between Rigshospitalet and Amagerværket in Copenhagen, Denmark
Tunnel construction
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Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length a
Tunnel
…first artificial tunnel was constructed in Babylon, in about 2200 B.C. This was built to join the temple of Belos with the palace with the aid of the cut and cover technique. Some of the earliest tunnels used by humans were paleoburrows excavated by prehistoric mammals…
Tunnel Construction
Cut-and-cover construction of the Paris Métro in France
A workman is dwarfed by the tunnel boring machine used to excavate the Gotthard Base Tunnel (Switzerland), the world's longest.
Illowra Battery utility tunnel, Port Kembla. One of many bunkers south of Sydney.