"Howard Berkowitz" wrote in message
...
In article , (Al Dykes)
wrote:



Some people might do well to look at the geology of Syria. The flatter
parts are generally sandstone or an equivalent crumbly rock that won't
support tunneling much deeper than irrigation. A start was once made on
a Damascus subway, but apparently abandoned because every tunnel would
have to be steel- or concrete-lined.


As is every tunnel on the London Underground, except for some of the
older tunnels were cast iron segments or brick linings are used.

The more mountainous areas are karst, which does tend to have natural
caves, but doesn't lend itself enormously to tunneling. Serious deep
excavations, like Cheyenne Mountain, are granite or similar hard rock.

You may wish to think again

London is built on clay, I guess that means you think they couldnt
possibly build the London Underground

The sea bed under the English Channel is made of soft chalk.
Somehow though they managed to build a tunnel under it.

The technical breakthrough that makes tunnelling in soft
materials isnt exactly new . The use of a tunnelling shield
and brick lining dates in modern times was introduced
by Marc Brunel but the technique seems to have been known
to the Romans.

In the middle east the techniques for building extensive
underground tunnels have been know since antiquity.
The network of irrigation tunnels in Iran are known
as the qanat and in Arabia they call them the falaj.

Keith