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.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
Sections in this article:
- Design and Construction Techniques
- Significant Historic and Modern Tunnels
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