On Sun, 7 Jun 2009, Paul Scott wrote:

"Tom Anderson" wrote in message
rth.li...
On Fri, 5 Jun 2009, Tom Anderson wrote:

On Thu, 4 Jun 2009, John Rowland wrote:

Tom Anderson wrote:

Or, of course, you could dive, and build some platforms in tunnel.

And sever the Regents Canal?

Underground locks.

I had a bit of a look to see if there was such a thing as an underground
lock, and i couldn't quite find any, although i did find an underground
inclined plane:

http://www.d.lane.btinternet.co.uk/canal2.htm

Does anyone know of an actual underground lock?

No, but this might help. Depending on the required gradient on the
tracks, you could conceivably cross the canal on the near level,
traditionally this would have involved a swing bridge. However a 'drop
lock' (or sump lock) has been provided for the Forth and Clyde
restoration to allow the canal to effectively burrow under a road, the
same could be done under a railway:

http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm

Ah yes, i'd forgotten about that. That's a fine bit of engineering!

Although now i come to look at it, i'm not sure the canal needs to be
interfered with at all. I make it 2200 feet from the buffer stops to the
canal; if we take 960 feet for platforms (enough to hold 12 cars of class
172 - not that you'd use diesels in a tunnel, but it's indicative), that
leaves 1240 feet, which at a gradient of 1:30 is enough to dive 40 feet.
That's not as deep as a normal tube line, but it's deep enough to fit in
under the existing platforms, although it might have to be built as
cut-and-cover.

If that gradient is too steep, you could shorten the platforms, make them
deeper, or push them further towards Marylebone Road under the station.

tom

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