In message
,
lonelytraveller writes

The post office railway is disused.

Why didn't they just widen the tunnels and reuse them for Crossrail,
instead of digging hugely expensive new ones?

It's not deep enough - the Post Office Railway is on average 21m below
the surface, although the stations are virtually at basement level (and
so the tunnels also have steep 20% gradients either side of stations).
Crossrail in the central area is up to 36m below the surface. Also, the
Post Office Railway doesn't have a straight enough alignment - it runs
north of Oxford Street, curving up to Wimpole Street and then coming
back south before the big loop up to Mount Pleasant.

It is a shame, though, that it hasn't been put to some good use since
its closure.
--
Paul Terry

"Paul Terry" wrote in message

In message
,
lonelytraveller writes

The post office railway is disused.

Why didn't they just widen the tunnels and reuse them for Crossrail,
instead of digging hugely expensive new ones?

It's not deep enough - the Post Office Railway is on average 21m below
the surface, although the stations are virtually at basement level
(and so the tunnels also have steep 20% gradients either side of
stations). Crossrail in the central area is up to 36m below the
surface. Also, the Post Office Railway doesn't have a straight enough
alignment - it runs north of Oxford Street, curving up to Wimpole
Street and then coming back south before the big loop up to Mount
Pleasant.

Also, the big cost with Crossrail will be the huge stations more than
the tunnels. Re-using the PO railway would not help reduce this cost,
but would probably make it worse.

On 26 May, 07:18, Paul Terry wrote:
It's not deep enough
Deep enough for what?

the Post Office Railway is on average 21m below
The circle line is only on average around 9m below the surface, so the
PO railway is more than twice as deep.

the stations are virtually at basement level
That's hardly a bad thing. Less distance from the surface is greater
convenience for passengers trying to access it.

the Post Office Railway doesn't have a straight enough alignment - it runs
north of Oxford Street, curving up to Wimpole Street and then coming
back south before the big loop up to Mount Pleasant.

Straight enough for what? The curves are fairly gentle, even though
the tube itself copes with curves like those at Shepherd's Bush, and
the PO railway is close enough to oxford street at all the stations.
It doesn't need to hug oxford street when its not at a station, not
that the current Crossrail's Hanover Square and Dean Street Stations
are on Oxford Street either.

As for the loop at mount pleasant, its a comparatively small thing to
dig a new bypass around the loop than it is to dig an entirely new
route across the whole of london. Besides, mount pleasant /
clerkenwell / essex market could do with a tube station, the met and
thameslink lines run through it but don't stop.

On Wed, 26 May 2010 04:56:23 -0700 (PDT)
lonelytraveller wrote:
As for the loop at mount pleasant, its a comparatively small thing to
dig a new bypass around the loop than it is to dig an entirely new
route across the whole of london. Besides, mount pleasant /
clerkenwell / essex market could do with a tube station, the met and
thameslink lines run through it but don't stop.

I would imagine that by the time you've stripped out all the tracks, cables
and tunnel lining so you can enlarge it you've probably spent more time and
money than you would if you just bored a new tunnel. Tunnels arn't dug with
picks and shovels any more - a TBM won't care if it has to dig the whole
tunnel itself or theres a small tunnel already there , it will take more or
less the same time. The only difference will be in the amount of spoil
needing to be carried away. Plus why inflict a windy route on a new
rail line when for high speed it needs to be as straight as possible.

B2003

In message , d
writes

Tunnels arn't dug with
picks and shovels any more - a TBM won't care if it has to dig the whole
tunnel itself or theres a small tunnel already there , it will take more or
less the same time. The only difference will be in the amount of spoil
needing to be carried away.

Which reminds me that there were several proposals to use the Post
Office Railway to remove spoil from the central area. I haven't heard
anything more of the suggestion, though.
--
Paul Terry

On 26/05/2010 15:04, Paul Terry wrote:
In message , d writes

Tunnels arn't dug with
picks and shovels any more - a TBM won't care if it has to dig the whole
tunnel itself or theres a small tunnel already there , it will take
more or
less the same time. The only difference will be in the amount of spoil
needing to be carried away.

Which reminds me that there were several proposals to use the Post
Office Railway to remove spoil from the central area. I haven't heard
anything more of the suggestion, though.

Wouldn't it be easier to remove the spoil by the Crossrail tunnels they
had just dug?

In message , Basil Jet
writes

On 26/05/2010 15:04, Paul Terry wrote:

Which reminds me that there were several proposals to use the Post
Office Railway to remove spoil from the central area. I haven't heard
anything more of the suggestion, though.

Wouldn't it be easier to remove the spoil by the Crossrail tunnels they
had just dug?

The idea was to use the PO Railway to remove the huge amounts of spoil
from the shafts and station boxes that are currently being dug. The
actual tunnel boring is not due to start until late 2011 but when it
does, the spoil from that will indeed be removed by rail through the
tunnel itself.

Apparently the idea of adapting the PO Railway for spoil transportation
was considered by the Crossrail board, but rejected for a number of
fairly obvious reasons, so lorries are being used instead at the moment.
--
Paul Terry

On Thu, 27 May 2010 02:09:07 +0100, Basil Jet
wrote:

On 26/05/2010 15:04, Paul Terry wrote:
In message , d writes

Tunnels arn't dug with
picks and shovels any more - a TBM won't care if it has to dig the whole
tunnel itself or theres a small tunnel already there , it will take
more or
less the same time. The only difference will be in the amount of spoil
needing to be carried away.

Which reminds me that there were several proposals to use the Post
Office Railway to remove spoil from the central area. I haven't heard
anything more of the suggestion, though.

Wouldn't it be easier to remove the spoil by the Crossrail tunnels they
had just dug?


Not necessarily. In most tunnelling projects you have conflicting
movements of excavated spoil coming out and lining segments going in,
with workers going in and out. If the spoil comes out via a separate
route, it reduces conflicts and might improve progress.

On Wed, 26 May 2010, d wrote:

Tunnels arn't dug with picks and shovels any more - a TBM won't care if
it has to dig the whole tunnel itself or theres a small tunnel already
there

Yes it will - TBMs are built for digging through clay, gravel, and the
like. Sticking a bloody great cast-iron pipe like the PO railway end-on in
its way will completely bugger it.

tom

--
uk.local groups TO BE RENAMED uk.lunatic.fringe groups

On Wed, 26 May 2010 20:41:10 +0100, Tom Anderson
wrote:

On Wed, 26 May 2010, d wrote:

Tunnels arn't dug with picks and shovels any more - a TBM won't care if
it has to dig the whole tunnel itself or theres a small tunnel already
there

Yes it will - TBMs are built for digging through clay, gravel, and the
like. Sticking a bloody great cast-iron pipe like the PO railway end-on in
its way will completely bugger it.


But you wouldn't do that. Tunnel miners would dismantle the segmental
lining of the smaller diameter tunnel, ring by ring, a short distance
in front of the main tunneling shield. The shield would then move
forward, excavating as it went, and the new, larger diameter lining
would be installed at the rear of the shield.

This is all routine tunnelling work. The only complication is the
need to stop any excavation of the larger diameter tunnel while miners
dismantle the lining of the smaller diameter tunnel. But that would
happen simultaneously with the building of a ring of new lining, so it
wouldn't actually need to stop progress.

However, what would kill the idea stone dead is that the PO railway
tunnel is on the wrong alignment and is far too shallow for Crossrail.
Also, it is only one tunnel and Crossrail needs two. You cannot build
one alongside because the ground at that depth is almost certainly now
peppered with bearing piles for buildings that have been built since
the PO railway.

So, a complete non-starter.