Issues North of Newcastle - Plessey Viaduct - 09/10 (onwards)

[Deepgreen]

Shows why they have issues


Is it going to withstand that? Can’t see pax being happy taken over that.

99.9% of them will have no idea. The others will either be nervous or confident that it's safe.

Not really a surprise but LNER staff being briefed today that the repair is going to take multiple weeks

Does that mean 'several'...?

 

[glasgowniteowl]

Does that mean 'several'...?

From what my friend told me its more than a couple of weeks but less than several months, multiple was the term he said was used when he was told

 

[Nicholas Lewis]

From what my friend told me its more than a couple of weeks but less than several months, multiple was the term he said was used when he was told

Need to scaffold that side on bridge 4-5 days, prepare the structure and then rebuild 7-10 days, 2 days to reinstate the track add in 2-3 days to sort site access and some contingency and 3/11 becomes potentially feasible if its 24hr working.

 

[najaB]

Engineering question, and one that I know might be impossible to answer, but would I be correct in the assumption that the parapets aren't structural to the viaduct itself? In other words, the structural part of the viaduct is flat topped and the parapets were built on top of that.

 

[Bletchleyite]

Engineering question, and one that I know might be impossible to answer, but would I be correct in the assumption that the parapets aren't structural to the viaduct itself? In other words, the structural part of the viaduct is flat topped and the parapets were built on top of that.

I believe so yes, the parapets are concrete and obviously retrofitted when you look at a photo of it (e.g. post 116).

 

[HurdyGurdy]

Engineering question, and one that I know might be impossible to answer, but would I be correct in the assumption that the parapets aren't structural to the viaduct itself?

If you study civil engineering your degree course will hardly mention masonry arches at all, so even well qualified engineers nowadays use the term 'parapet' fairly loosely. But my interpretation is that on a masonry bridge or viaduct a parapet is a non-loadbearing wall or barrier.

Many masonry arch railway bridges and viaducts were built without parapet walls and had railings or other barriers added at a later date. From the photos posted on this thread, it looks to me that Plessey viaduct is one of those. So I would not describe the part of the structure which has collapsed as a parapet. To me it's part of the spandrel wall, which supports the backfill above the arch(es) right up to track level, so definitely is structural and loadbearing.

 

[swt_passenger]

If you study civil engineering your degree course will hardly mention masonry arches at all, so even well qualified engineers nowadays use the term 'parapet' fairly loosely. But my interpretation is that on a masonry bridge or viaduct a parapet is a non-loadbearing wall or barrier.

Many masonry arch railway bridges and viaducts were built without parapet walls and had railings or other barriers added at a later date. From the photos posted on this thread, it looks to me that Plessey viaduct is one of those. So I would not describe the part of the structure which has collapsed as a parapet. To me it's part of the spandrel wall, which supports the backfill above the arch(es) right up to track level, so definitely is structural and loadbearing.

Makes it rather incredible that in that earlier Twitter feed NR’s PR people refer to the parapet having “moved”, and then there’s a rather worrying implication that they were unable to “quickly move the parapet back to its original position”. Are we supposed to believe all this heavy stuff just sits there unsecured, held in the right position by its own weight?

They're not engineers though, just PR people - and I wonder if they intentionally lose detail in the process, to try and sound reassuring…

 

[HurdyGurdy]

Are we supposed to believe all this heavy stuff just sits there unsecured, held in the right position by its own weight?

Not just by its own weight, but a masonry arch supports the imposed load (dead and live) because its elements stay in compression. Similarly, a masonry wall can be loadbearing.

 

[swt_passenger]

Not just by its own weight, but a masonry arch supports the imposed load (dead and live) because its elements stay in compression. Similarly, a masonry wall can be loadbearing.

Sorry I meant only the bit that NR claims to have “moved” (I’m assuming sideways), - surely the idea that if it moves you can just move it back seems to be a major simplification?

 

[ItsGrimUpNorth]

It's just as well that Morpeth signal box is still open as it's on its door step to arrange SIMBIDS. Soon Morpeth, Alnmouth and Tweedmouth will all be on Tyneside IECC.

Apologies for going off topic, do you know when this is planned for? Thanks!

 

[HurdyGurdy]

Sorry I meant only the bit that NR claims to have “moved” (I’m assuming sideways), - surely the idea that if it moves you can just move it back seems to be a major simplification?

As mentioned by several members upthread, what NR posted on X oversimplifies and plays down the extent of the damage shown in the photos.

 

[DelW]

Engineering question, and one that I know might be impossible to answer, but would I be correct in the assumption that the parapets aren't structural to the viaduct itself? In other words, the structural part of the viaduct is flat topped and the parapets were built on top of that.

There wasn't normally a slab or equivalent at track level, though there might be transverse tie rods. Normally once the arches were complete, and probably while they were still supported by centering, the spandrel walls (side walls) were built up to track level, then upwards as parapets. The volume above the arches and between the spandrels was backfilled to support the track. Sometimes viaducts with structural problems have been retrofitted with slabs at track level to relieve loads on the masonry.

Sorry I meant only the bit that NR claims to have “moved” (I’m assuming sideways), - surely the idea that if it moves you can just move it back seems to be a major simplification?

I took "moved" to have been a less scary euphemism for "fell off into the valley", but I may be wrong. The possibility of pushing a parapet that had moved back into place does seem unlikely even if it hadn't fallen off completely.

 

[HurdyGurdy]

probably while they were still supported by centering, the spandrel walls (side walls) were built up to track level, then upwards as parapets.

Once everything was backfilled and built up to track level there would inevitably be a displacement of the arch(es) and spandrels when the centering was struck. Anything previously built straight or level would then appear to sag. So usually the centering would be struck before topping off the spandrels and laying a straight or level string course or coping. If required, the string course would be the footing for the parapet wall.

 

[snowball]

Many masonry arch railway bridges and viaducts were built without parapet walls

A bit like Pontcysyllte, where there is nothing on the non-towpath side of the canal to stop a person falling off a boat and 120ft down.

Are open boats allowed?

 

[alf]

It appears there is at least one & a half metres of ballast sitting atop the viaduct at the collapse point. Is that normal?
At 1.5 tonnes a cubic metre of dry compressed ballast that is a load over & above track & train of almost 11 tonnes per meter length for the double track. Over the length of a 23 metre coach that is 253 tonnesover the width of the viaduct. Then there is the coach weight of 40 tonnes plus the rail & sleeper weight.
That is an amazing extra load. And is based on the ballast being dry.

I bet the 1840 engineers did not calculate for anything like this massive dynamic load downwards & a vector of it sideways into the ballast holding walls.

 

[HurdyGurdy]

Are open boats allowed?

Yes. Standing at the tiller of a traditional narrowboat, should you trip over your shoelace, there's nothing between you and the drop.

<checks shoelaces>

 

[najaB]

Just came across this document, seems like it might be interesting reading: https://www.networkrail.co.uk/wp-co...-report-Spandrel-Walls-Managing-the-Risks.pdf

 

[DelW]

Once everything was backfilled and built up to track level there would inevitably be a displacement of the arch(es) and spandrels when the centering was struck. Anything previously built straight or level would then appear to sag. So usually the centering would be struck before topping off the spandrels and laying a straight or level string course or coping. If required, the string course would be the footing for the parapet wall.

Yes, good point. IIRC from my bridge building days, we always struck the deck soffit supports before finally levelling in the coping formwork for exactly that reason.

 

[Trestrol]

Apologies for going off topic, do you know when this is planned for? Thanks!

Not sure but I think after the reprieve of Tyneside IECC and it's upgraded to a mini ROC it won't be long. Although all three NML boxes have had new panels. With the expansion of the operating floor there was also talk of moving stuff from York ROC. York ROC is very crowded as it was underestimated the size of the equipment in the equipment room would take. When York IECC moved to the ROC the only thing that moved were the workstations. All the equipment is still in the IECC as there's no room in the ROC. This of course didn't stop NR property coming round trying to flog the land off.

 

[Craggle]

New user here, this happened very close to where I live and I usually walk the dog along the riverside path under the viaduct. Saw this sign this afternoon in Plessey Woods country park, informing said path is shut giving a finished date of 27th November. It's a council sign so make of that what you will.

 

[TrackLad]

The structure is listed and details of strengthening works as well as cross sections of the original construction are available on the planning portal.

 

[Nicholas Lewis]

The structure is listed and details of strengthening works as well as cross sections of the original construction are available on the planning portal.

Good find. So the concrete walkway lintels were added back in 1978 and then in 2014 permission was sought to strengthen the walkways due to

The most recent detailed structural examination report for the structure has highlighted that the precast concrete walkway units on the structure are showing signs of outward lateral movement and it is recommended that stitching bars are installed through the walkway units to restrain this movement.

Also cross section of bridge provided


So with those rods tying it all together if the top started to overturn it could take a fair part of the structure with it compounded by the supporting safety barrier tying it altogether longitudinally

 

[HurdyGurdy]

Good find.

Excellent. It clarifies the construction. Apart from the walkway with handrail and the original vertical dowel bars fixing it into the plinth and copings, you can see the reinforced concrete lining of the arches.

The section shown must be at the crown of the arch, where the angled 1500mm long stitching dowels are fixed into the voussoirs, which are the external face elements of the arch rings. The dead load of backfill holds the arch ring in compression. If the dowels were the same length at a section further from the crown of the arch, they would only penetrate the plinth, copings and spandrel wall. These are not held in the same compression, so will have a more limited resistance to overturning and support less vertical and/or lateral load on the overhanging walkway.

Overturning of the spandrel wall is one of the modes of structural failure described in the document found by @najaB, upthread.

 

[GuyGibsonVC]

The SIMBID running between Plessey and Morpeth is scheduled to continue until 04/11/23 and the speed over the Down on the viaduct is 50mph.

The independent coffee shop in Morpeth station has endured quite a torrid 18 months with weeks of industrial action, engineering blockades and now this!

 

[Starmill]

The actual viaduct and the track bed is solid and safe.

Indeed - they're just as safe as the hundreds of other similar railway bridges that go through the same regime of inspection and maintenance.

 

[Amlag]

Indeed - they're just as safe as the hundreds of other similar railway bridges that go through the same regime of inspection and maintenance.

AND with the added safety hazard of the damage being caused by roots of increasingly large bushes and trees growing in their structures.

 

[PM77]

When York IECC moved to the ROC the only thing that moved were the workstations. All the equipment is still in the IECC as there's no room in the ROC. This of course didn't stop NR property coming round trying to flog the land off.

Not entirely true. When the IECC moved to the ROC the IECC part went with it, although on a more modern compact system. Some interlockings have been migrated into the ROC and more are planned to go next year.

 

[Narrowgauge725]

My daughter has just crossed southbound and took a video, there's obviously lots of activity in the field leading up to it. Her quote is that "it is off putting"

 

[najaB]

Her quote is that "it is off putting"

Yeah, that would be slightly disturbing for those sitting on the left-hand side of the train.

 

[Senex]

There was an item on BBC Look North yesterday evening (https://www.bbc.co.uk/iplayer/episo...-north-east-and-cumbria-evening-news-10102023 - about 6 minutes in) which gave a clear and concise explanation of what's happened and wht is going on. The NR spokesman was Paul Rutter, whom I take to be one of the senior engineers dealing with it all — certainly miles away from the sort of PR waffle the TOCs generally seem to offer.