Brimstone wrote:

As was done during the building and extending of every deep
tube line on the underground since the 1920s. Build the
junction round the existing tunnel whilst allowing the service
to continue running.

That is not possible at Heathrow, as Richard J. has indicated
elsewhere.

Basically, the ground is so unstable and poor that if a traditional
step-plate junction were built, the tunnels could collapse. Thus a huge
cofferdam is needed to enclose the site of the junction.

I highly doubt that TfL wanted to do this in the first place, but they
would rather close the loop than risk a collapse and entrapment of a
service train with hundreds of passengers.

Which is preferred?

Brimstone wrote (I've repositioned his comment):
Mait001 wrote:
It is also the complete lack of foresight and advance preparation
when building the original line, and then the T4 line that irks me.

Whilst I don't disagree with you basic premise, it has to be said
that the site for T5 has been moved IIRC.

Yes, the design of T5 was changed, which meant that the straight section
of the T4 loop that could have accommodated a station was not in a
suitable place. In other words, people did their best to show foresight
and advance preparation. You would have done better within the
available budget, I assume?

Let me give you an example. In the late 1960s/early 1970s, my
father was a civil engineer working for the London Borough of
Hounslow. He was responsible for rebuilding Stanwell Road, a road
connecting the Great South West Road to the cargo area of Heathrow
Airport. At the time, there were vague rumblings about building a
rail link to Heathrow from Victoria. In the end, it was abandoned
because it would have cut through Buckingham Palace Garden.

With that possibility in mind, however, he ensured that there were
culverts, diverted drainage etc., and indeed an opening beneath
Stanwell Road (that is there, unused, to this day) so that this
could have been used by the railway line if ever it was built.

So, on the basis of "vague rumblings", extra costs were voluntarily
incurred by L.B. Hounslow, including a bridge under Stanwell Road large
enough for a 2-track railway apparently. That perhaps explains part of
the large debt that Hounslow council taxpayers are still having to pay
the interest on.

--
Richard J.
(to e-mail me, swap uk and yon in address)

"Richard J." wrote in message
k...

There are some details in this month's Modern Railways
(page 52). The ground at the junction site consists of
water-bearing gravel, and conventional techniques to
build a step-plate junction would risk a collapse of the
existing tunnel. "At the site of the existing junction,
the ground is being opened up for the construction
of a big coffer dam extending 25 metres down. ...
Once complete,this box will then hold the junction."
TBMs will drill towards the site from the T5 end,
but the final breakthrough will be done outwards from
the box. Then they have the task of restoring the
concrete aircraft taxiway over the box. In
the circumstances, 20 months seems reasonable.

Did I fall asleep at LURS in November, or was this
important information omitted from the talk on the T5 extension?

Omitted, I believe.

If I'm understanding this correctly, this info seems to significantly reduce
the wastage involved in building a step plate junction which will never be
used as a junction, but doesn't seem to completely eliminate it.

--
John Rowland - Spamtrapped
Transport Plans for the London Area, updated 2001
http://www.geocities.com/Athens/Acro...69/tpftla.html
A man's vehicle is a symbol of his manhood.
That's why my vehicle's the Piccadilly Line -
It's the size of a county and it comes every two and a half minutes

"Mait001" wrote in message
...

That is called foresight and forward planning that is so patently missing
now.

I don't agree. Many modern schemes have passive provision, or more, for
other schemes. In fact, the existing Heathrow Express has a junction which
was built for the T5 branch, although this will not be used.... and the
Piccadilly T4 loop has a straight bit beneath where T5 was planned, although
this will also now not be used.

--
John Rowland - Spamtrapped
Transport Plans for the London Area, updated 2001
http://www.geocities.com/Athens/Acro...69/tpftla.html
A man's vehicle is a symbol of his manhood.
That's why my vehicle's the Piccadilly Line -
It's the size of a county and it comes every two and a half minutes

TheOneKEA wrote:
Brimstone wrote:

As was done during the building and extending of every deep
tube line on the underground since the 1920s. Build the
junction round the existing tunnel whilst allowing the service
to continue running.

That is not possible at Heathrow, as Richard J. has indicated
elsewhere.

Basically, the ground is so unstable and poor that if a traditional
step-plate junction were built, the tunnels could collapse. Thus a
huge cofferdam is needed to enclose the site of the junction.

I highly doubt that TfL wanted to do this in the first place, but they
would rather close the loop than risk a collapse and entrapment of a
service train with hundreds of passengers.

Which is preferred?

My response was made before Richard J's appeared on my server. He has
answered the question that I've been trying to find the answer to.

John Rowland wrote:
"Mait001" wrote in message
...

That is called foresight and forward planning that is so patently missing

now.

I don't agree. Many modern schemes have passive provision, or more, for
other schemes. In fact, the existing Heathrow Express has a junction which
was built for the T5 branch, although this will not be used.... and the
Piccadilly T4 loop has a straight bit beneath where T5 was planned, although
this will also now not be used.

And away from Heathrow, the Jubilee line has provision for an eastwards
branch to Thamesmead at North Greenwich; the DLR has provision for
future stations at Connaught Bridge, Thames Wharf (on the new LCY
branch) and also I believe even in the tunnel to Bank for an underground
station to replace Tower Gateway, which was originally going to be
closed in favour of Bank, but DLR decided operationally that it was too
useful to close. Plus the CTRL works incorporate provision for
Thameslink 2000 by building a new link from St Pancras to the GN lines
out of King's Cross.

So I agree with John; planners still take into account future
possibilities, but whether those possibilities change or not is a
different issue. No-one can predict the future!

--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London

John Rowland wrote:
"Richard J." wrote in message
k...

There are some details in this month's Modern Railways
(page 52). The ground at the junction site consists of
water-bearing gravel, and conventional techniques to
build a step-plate junction would risk a collapse of the
existing tunnel. "At the site of the existing junction,
the ground is being opened up for the construction
of a big coffer dam extending 25 metres down. ...
Once complete,this box will then hold the junction."
TBMs will drill towards the site from the T5 end,
but the final breakthrough will be done outwards from
the box. Then they have the task of restoring the
concrete aircraft taxiway over the box. In
the circumstances, 20 months seems reasonable.

Did I fall asleep at LURS in November, or was this
important information omitted from the talk on the T5 extension?

Omitted, I believe.

If I'm understanding this correctly, this info seems to
significantly reduce the wastage involved in building a step plate
junction which will never be used as a junction, but doesn't seem
to completely eliminate it.

I'm not sure why you say it will never be used as a junction. When T5
is open, the trains that run via T4 will join the eastbound T5-T123
track at the new junction. There may also be a connection from the T4
loop to the westbound T123-T5 track, which I guess wil be rarely used.
Is that what you were referring to?
--
Richard J.
(to e-mail me, swap uk and yon in address)

"Mait001" wrote in message
...

I have just read the TFL leaflet "Heathrow by Tue"

Rats, my plane leaves on Monday.

--
John Rowland - Spamtrapped
Transport Plans for the London Area, updated 2001
http://www.geocities.com/Athens/Acro...69/tpftla.html
A man's vehicle is a symbol of his manhood.
That's why my vehicle's the Piccadilly Line -
It's the size of a county and it comes every two and a half minutes

In article , (Dave Arquati)
wrote:

John Rowland wrote:
"Mait001" wrote in message
...

That is called foresight and forward planning that is so patently
missing now.

I don't agree. Many modern schemes have passive provision, or more,
for other schemes. In fact, the existing Heathrow Express has a
junction which was built for the T5 branch, although this will not be
used.... and the Piccadilly T4 loop has a straight bit beneath where
T5 was planned, although this will also now not be used.

And away from Heathrow, the Jubilee line has provision for an eastwards
branch to Thamesmead at North Greenwich; the DLR has provision for
future stations at Connaught Bridge, Thames Wharf (on the new LCY
branch) and also I believe even in the tunnel to Bank for an
underground station to replace Tower Gateway, which was originally
going to be closed in favour of Bank, but DLR decided operationally
that it was too useful to close. Plus the CTRL works incorporate
provision for Thameslink 2000 by building a new link from St Pancras to
the GN lines out of King's Cross.

So I agree with John; planners still take into account future
possibilities, but whether those possibilities change or not is a
different issue. No-one can predict the future!

The world is littered with provision made for schemes that never came off.
How many single track railway lines had enough land bought for future
doubling that never happened, for a start?

--
Colin Rosenstiel

In article ,
(John Rowland) wrote:

"Mait001" wrote in message
...

I have just read the TFL leaflet "Heathrow by Tue"

Rats, my plane leaves on Monday.

But mine goes on Wednesday. We're back on January 3rd, though.

--
Colin Rosenstiel