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Underground Lifelines
| Article
# : |
18847 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
12 / 1991 |
3,036 Words |
| Author
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A.R. Hogan
A.R. Hogan is an independent science writer based in
Hyattsville, Maryland. He is also a contributing editor to the
monthly space magazine Ad Astra. |
Those who take tunnels for granted as just long, mundane tubes to travel through just haven't dug deeply enough into the subject to fully appreciate the wonderful versatility of tunnels.
Tunnels not only efficiently move our highways, railways, and subways through mountains, beneath cities, and under rivers and harbors, they also bring us potable water, carry away storm water and sewage, deliver hot water and steam to heat buildings, act as conduits for gas and electric lines, house power-generating stations, and give us access to veins of precious metals and fuel ores, such as gold and coal.
"Most people don't think about tunnels much. Tunnels tend to be out of sight and out of mind except when you're in one or if you're where they come out of the ground," says Hawaiian tunnel builder John Critch field, a civil engineer with the Seattle-based engineering-architecture firm Parsons, Brinckerhoff, Quad and Dougals, Inc. "Few people realize how much sweat, danger, money, time, skill, and ingenuity it takes to create a tunnel."
There is no such thing as a plain "tunnel," because all tunnels have an inherent function. Tunnels are classified according to use, and their names imply their function. There are canal tunnels, railroad tunnels, subway and vehicle tunnels, as well as tunnels for water, sewer, drainage, pedestrians, and power.
In addition to use, tunnels are also classified as to the type of ground in which a specified as the type of ground in which a specific tunnel will be built. There are four basic types of tunnels:
-Soft ground tunnels are dug through sand, clay, loose gravel, and wet ground and must be sturdily shored up.
-Rock tunnels are drilled and blasted through solid rock.
-Underwater or subaqueous tunnels usually go through mud and require extra-strong support to withstand the heavy burden of mud and water overhead.
-"Cut-and-cover" trenches are the most easily made because they entail just digging a deep trench, building a tunnel, and covering it with dirt.
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