The Columbia Encyclopedia, Sixth Edition
tunnel underground passage usually made without removing the overlying rock or soil. Although tunnels are approximately horizontal, they must be built with sufficient gradient for proper drainage. Tunnels may be ventilated by shafts leading to the surface or by exhaust fans at the ends. Design and Construction Techniques Methods of tunneling vary with the nature of the material to be cut through. When soft earth is encountered, the excavation is timbered for support as the work advances; the timbers are sometimes left as a permanent lining for the tunnel. Another method is to cut two p... Read more
tunnel underground passage usually made without removing the overlying rock or soil. Although tunnels are approximately horizontal, they must be built with sufficient gradient for proper drainage. Tunnels may be ventilated by shafts leading to the surface or by exhaust fans at the ends. Design and Construction Techniques Methods of tunneling vary with the nature of the material to be cut through. When soft earth is encountered, the excavation is timbered for support as the work advances; the timbers are sometimes left as a permanent lining for the tunnel. Another method is to cut two p... Read more
Bibliography
See T. M. Megaw and J. V. Bartlett, Tunnels (1981-82); B. Stack, Handbook of Mining and Tunnelling Machinery (1982); Approaching the 21st Century (1987).Author not available, TUNNEL., The Columbia Encyclopedia, Sixth Edition 2008
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