DEVELOPMENT – BRIDGE 12 (Step 1.2.6.1 and 1.2.6.2)
Bridge
12 (uploaded
Bridge 12 is the rail-over-rail bridge, and, unless
anyone tells us differently, we believe it to be the only standard gauge
rail-over-rail bridge in preservation.
That is to say, both ‘under’ and ‘over’ routes are in preservation. There is of course the famous bridge on the
Dduallt spiral on the Ffestiniog, but this is narrow gauge, and in any case, is
a post-preservation artefact. There was
also the Swansea Vale Railway which had a bridge under the main line near
Pentrechwith but, sadly, this railway has closed. So, so far as we are concerned the
rail-over-rail bridge is something special.
Not only is the bridge probably unique, but it has
been difficult to manage its restoration.
Indeed there were faint-hearts on the railway who said we should demolish
it, but bulls have been grabbed by the horns, funds have been found and the
bridge has undoubtedly returning from dereliction. Bridge 12 has an important role to play in
both the extension to Blaenavon (High Level), (Step 1.2) – trains must run under
it to reach Blaenavon, and in the Big Pit branch project (Step 1.5) where it
will provide a route for the branch trains back to the yard and a
footpath/viewing platform for visitors who want to see trains on our ‘main
line’.
The limited range of funds available for the
extension work meant that initial work on the bridge would be confined to
making the bridge safe only for trains to pass under it. However, now that
funds for the Big Pit branch have been secured, work has finally started on
repairing the wing walls and reconstructing the main deck so that trains can
pass over it.
This bridge is somewhat different from the other
bridges and the repair work was awarded to a different contractor. The contract was let on
Images
and captions (uploaded
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Early
February brings inhospitable conditions.
The bridge in seen in the centre of the picture. The 3 ¾ mile milepost appears directly under
the arch. 1984 14 Feb 09 |
The
contract called for PBR to lift the rails and sleepers on the bridge. This was small beer to our intrepid PWay
team, who had done the job a few days earlier. The situation was made complicated since a
set of points lay on top of the bridge and it was important that the
sleepers, fittings and rails were all marked so that they would go back precisely in their original
positions 1988 14 Feb 09 |
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Looking north
into the yard it is easy to see the rails diverging from the position of the
points. The points are on the south
side of the bridge, the northern half once also carried a line of rails, but
is currently unused 1992 14 Feb 09 |
Looking
back the other way, in the general direction of Big Pit, it is possible to
see that the bridge, in comparison with those on the main line, is very wide,
and unlike those single line bridges is supported by three rather than two
longitudinal girders 1995 14 Feb 09 |
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A thaw
brings better conditions, but there is still substantial snow on the distant
Blorenge mountain. This shot was taken
a little further back than the image above it. The crossing in the foreground once led to the second
line of rails across the bridge. There
are no plans to re-instate it 2009 17Feb 09 |
Once the
contractors has scraped off the ballast it soon became clear that there had
been widespread failure of the bitumen waterproofing, and as a result a large
fraction of the timbers had rotted beyond redemption, and would need
replacing. 2105 9 Mar 09 |
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Meanwhile
the abutments, especially on the Furnace Sidings side of the bridge needed
extensive re-setting and pointing. The
deck under the bridge was intended to
provide a stable platform for subsequent scaffolding, additionally, the
fast-running stream that flows under the bridge had to be protected from any
lead-based paint chippings or dust which might contaminate the water
supply. The scaffold tower provides
access to the abutment and wing walls on the 2144 24 Mar 09 |
A week
later the scaffolding which supported the crash deck underneath the main span
was up, ready for initial work on the steelwork. The triangular section of the wing wall in
the centre of the picture had been largely re-pointed, but the area in the
upper centre had bulged and had to be removed and re-set. It may just be possible if your monitor has
sufficient resolution to see the numbering on the stonework, to ensure things
went back in their proper place! 2185 3 Apr 09 |
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After the
shock of the condition of the decking timbers, a second even more serious
shock unfolded as the twenty or so steel cross members were seen to be in very
much worse condition than an initial inspection had revealed. At first only one cross members was
earmarked for replacement. As the true
condition was realised, the number of girders to be removed increased, and
here we see the second being cut from the overall assembly. 2219 6 Apr 09 |
Cambrian’s
workers, on the left, continue work on the masonry. More than mere re-pointing is this, as
massive stones and large quantities of soil are moved around. On the right Cambrian’s sub-contractors
inspect the parlous state of the cross girders 2259 9 Apr 09 |
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On the
downside north wing wall the bulging masonry has been re-set and
re-pointed. It just remains for the
heavy capstones to be re-set. 2367 28 Apr 09 |
The need to
fit scaffolding on this bridge, the nearest to the yard at Furnace Sidings,
effectively maroons everything south of it – including the other bridges and
the station at Blaenavon (High Level).
Removal is planned before the weekend 27/28 June – a month after the
blockade caused by the remaining bridges had been lifted. On the left is the decking over the stream,
whilst on the right, the milepost seen in the first image of this series is
seen. The sleepers were replaced by
PBR just days before the bridge was handed over to Cambrian. The gradient beyond the scaffolding has
been measured as 1 in 24 – and on a steep curve to boot! 2376 28 Apr 09 |
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Heavens –
what’s going on here? Amid ear splitting
noise, and under supposedly dust proof sheeting the grit blasters get to
work, cutting back the rust to reveal the true state of the steelwork 2382 1 May 09 |
A camera
held at arms length and through a small hole in the ‘tent’ reveals the inferno
inside. The vague shadow on the left,
with air hose at the back is human – we think. 2383 1 May 09 |
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As the dust
settled the full extent became clear, as can be seen in this view of the
south east corner of the deck. The cross
girders on the ‘rail’ side (that is, the south side) of the bridge were
essentially beyond redemption. On the
‘path’ side (the north side), one or two girders would need replacement. At this stage it was considered wise to
‘future-proof’ the bridge by replacing ALL the cross-girders despite the fact
that such a move would increase costs.
This was more than just a matter of cutting out all the cross-girders
and replacing them – there would be nothing to hold the side girders up –
hence the need for the safety chain. 2408 3 May 09 |
If that
were not enough the middle longitudinal girder had both twisted and moved and
it was necessary to jack it up and build new
pedestals upon which the middle girder could sit. Problems were also found on the outside
longitudinal girders, which were to be patched. In the event the patches (one inside, one
outside so that with the original plate, a sandwich was formed were made to
the full dimensions of the original.
This was true ‘battleship engineering’ in the old style. We cannot imagine this bridge failing in
the next century. In this view of the 2472 30 May 09 |
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In the
south-west corner, all the old girders had been removed. Apart from the safety chain, one of the two
temporary cross girders are in place, with one of the new substantive
cross-girders in the foreground.
Welding of steel is a well known science these days, but welding to wrought
iron still demands specialised materials and welding techniques. 2799 9 June 09 |
The repair
of this bridge has brought forward a number of unexpected challenges, each of
which has in turn demanded changes in planning and approach. In mid-June we’re on the final furlong the
way forward now clear to see. The
steelwork needs painting, and the deck need renewing, but the end is in
sight. The smiles on the steelworker’s
faces are testimony to the fact that the finish line is near. 2820 15 June 09 |
We anticipate only one further report on this
bridge. By the weekend of 27/28 June,
the steelwork will be painted (this was, in fact, completed on 20 June), the
wooden deck installed and the scaffolding under the bridge, which has hampered
work on the track and at Blaenavon (High Level) station will be removed. At this stage PBR will be able to lay the
track on the bridges further down the line, complete its track renewal program
and finally get to Blaenavon (High Level).
Back on Bridge 12, there will be outstanding masonry work to complete,
as well as the sub-base to be laid on the new wooden deck, which in turn will
allow PBR to relay the rails and points.
The
final fling! (uploaded
After late June the bridge made steady progress to
the final completion of the contract.
The important dates were 25 June when the crash deck and scaffolding was
removed. This step finally allowed
trains south of the bridge, and it was only a few days late that our PWay team
had re-laid the rails on Bridge 13, and were making progress on Bridge 14. Progress to 25 June had, taken rather longer
than expected (by about a month), but in the grand scheme of things, this delay
was largely absorbed. What we got was
much more than intended, and by about 8 August the remaining physical work on
the bridge, which was mainly confined to the deck was complete. The requirement for comprehensive
documentation, and inspection by third parties took a little longer, but by 24
August the contract was complete and the final payment made. PBR’s PWay team still have to replace the
points and track on the bridge, but, all in all, a very satisfactory
outcome. Following completion of
gritblasting and installation of new beams, the steelwork was painted with
specialist paints. In the case of
bridges, the primary purpose of painting is to maintain a waterproof layer and
to prevent corrosion – also looked very smart too.
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Following completion of gritblasting and
installation of new beams, the steelwork was painted with specialist
paints. In the case of bridges, the
primary purpose of painting is to maintain a waterproof protective layer and
to prevent corrosion – but there’s no denying that the finished article looks
attractive. Here we see the northern
half of the deck looking west to Big Pit.
Although there are no immediate or medium-term plans to run a track
over this side of the bridge, it was considered wise to ‘futureproof’ the
bridge by providing the potential to carry trains on two lines of rails if
they are ever needed. 2840 23 Jun 09 |
With
painting complete, the next task was to replace the wooden decking. When the old deck was stripped it was clear
that about half of the timbers could be re-used, but, once again, the
decision was made to replace ALL the timbers ,for the same reasons as given
alongside. The original but
serviceable timbers thus released will be used as point timbers around the
yard. 2843 23 Jun 09 |
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Viewed from
the edge of the site of the Up Exchange Sidings (soon to be brought back into
use in order to accommodate the Big Pit branch), a large mobile crane is
seen, dropping the new timbers into place.
The scaffolding which supports the crash deck is still in place, but,
with the deck in place, it will no longer be needed. Although
difficult to see in this scene, containing as it does a welter of different
gradients, the bridge deck slopes down to the left at a gradient of 1 in 40,
immediately reversing its slope to 1 in 40 up on the eastern abutment. The gradient underneath is 1 in 24 over a
short distance. 2851 23 Jun 09 |
Here is a
close up of new and recovered steelwork. The original plan was to replace
only one or two of the cross beams, but it soon became clear, following
exploratory grit blasting that the most economical long-term route was to replace them all. As noted above, the two outside
longitudinal beams were originally to be patched, but eventually it was
quicker, easier and better to sandwich them.
Only the centre longitudinal beam escaped largely unscathed but best
part of a week was spent jacking and packing it into position and removing a long-standing
twist. 2856 23 June 09 |
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Installation
of the deck timbers is completed. The centre beam is buried under the
timbers,in this view, looking south-west
towards Big Pit. Passengers on the Big
Pit branch will join this route from the right, whilst the route over the
bridge will only be used for shunting and for special workings The width of
the bridge can appreciated in this view – the only double track bridge on the
line. 2862 26 Jun 09 |
With the
deck timbers in place, no time was lost in removing the crash deck and the
scaffolding. A few more hours were
taken to remove the polythene sheet, ply and heavy sleepers that had been
used to protect the leat which runs through the bridge from contamination by
blasting grit, and, more seriously, from paint residue that might contain
lead. The impressive extent of the
work re-setting and pointing the masonry abutment is clear 2863 25 Jun 09 |
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Masons with
the skills to work on the heavy stones that make up bridge abutments don’t
grow on trees, and two of these three were drafted in from the deep West
Country, all three were also involved in demonstrating the variety of skills on the steel deck,
and on the special bearers required to support the deck. 2865 25 June
09 |
’Da
management’ looking very happy that the job is all but complete. There were some worrying moments, and there
were a few times during the course of the work when brows looked decidedly
furrowed! 2885 6 July 09 |
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Between the
decking timbers and the track a complex smorgasbord of materials protects the
timbers from water damage. The first layer
is heavy black sheet of some type of rubber polymer, a semi-permeable white
sheet sits on top of this. Small piles
of pea grit prevent everything blowing away.
The management of water on this sloping bridge was always difficult,
and repairing and replacing the drainage system so that it would not fail for
many years was complex. 3095 25 July 09 |
PBR had
agreed to spread the ballast, so with all the contract staff, except one
technical man drafted to ‘other duties’, we see technical input provided
through the medium of the Mark 1 shovel, whilst over 30 tons of ballast are
spread onto the eight tons of pea grit already laid. As the job moves to a
successful conclusion the ‘technical man’ looks deservedly happy. 0038 6 Aug 09 |
Postscript
(uploaded
We had thought that we need not report further on
Bridge 12, albeit aware that we had not reported on the relaying of the
rails. However a year and a month later
the situation allowed this relatively small item of work to be completed by our
own volunteers.
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First uploaded
Images and captions uploaded
Second
section uploaded