On Tue, 9 Oct 2007, lonelytraveller wrote:

If you hollowed out the existing station and put in a downward-sloping
track at a gradient of 1:30 (generally considered the practical
maximum, i think), you could drop

But if you did that, you wouldn't have Cannon Street Station, meaning
that the Commuters all pile off the trains at whatever the next station
is - presumably Bank, which would be a disaster in terms of how busy
that station is already.

You'd add more exits and passageways when you added the platforms.

You might need to demolish No 1 Poultry, but it's a horrible building anyway.

Its not such a problem - the bottom 2 floors worth of basement are
isolated from the rest of the building with a concrete slab in between -
they did that so that archaeologists could get down there while they
were building the building above them.

Ah, interesting.

But, if you were heading in that direction, you'd run straight into the
Waterloo & City line platforms, travelator, or the passenger tunnel
between the Waterloo & City platforms and the Central Line.

Yes, you'd have to get deep enough to pass under those. Getting past the
District line is going to be interesting too.

When DLR extensions have been suggested in the past it is usually
mentioned that the Bank of England vaults are in the way too!

The vaults thing is a red herring when it comes to the NCL, though -
there have been serious proposals from the time it opened up to the
1960s to extend it southward, and none of those had any problem with
vaults.

(from the north) I'd assume it would be fine until you actually reach
Bank station - at that point, if you turn right, you hit the (former)
Midland Bank HQ (now some other bank's important building) vaults,
unless you make it a 45 degree turn. The alternative is to pass through
the slight gap between the central line and the ticket hall, over the
northern line, and then turn right. You can't really head straight on,
because there are loads of vaults around there. The DLR platforms are to
the west of the Northern line ones, rather than directly below,
presumably to help avoid undermining them, or the buildings above -
anything any higher would thus need to be to the east, which basically
means you end up heading more towards Monument, not Cannon street, and
there are quite a few listed churches in that direction, as well as
office vaults, that you wouldn't want to interfere with.

I believe the plan for extensions of the line beyond Bank has always been
to make it really deep, so it's below any of this stuff.

tom

--
It is a laborious madness, and an impoverishing one, the madness of
composing vast books. -- Jorge Luis Borges