My mind might be playing tricks but wasn't the viaduct braced/strengthened some years ago due to structural issues?
Yes. Back in 78/79 additional parapet extensions were added to provide handrails and a higher side wall (I find it amazing that structures such as these had no real side fence/protection for track workers for so many decades, or indeed that it was ever considered acceptable by those who built the structure!).
There was a project to add stitching bars to the parapet sections back in 2014, after which the viaduct was monitored for a few years but there was no movement so it was stopped. In the videos you can see some bars sticking out so I do wonder if those bars are the stitching bars. No idea though.
It begs the question - what if there were no planned engineering works and this happened during normal running of services? I dread to think about it.
It's rare that failures of this nature happen without some kind of external force or change. The change here was the removal of the track and the plant working over the viaduct. This both removed a surcharge load from the parapet bottom sections (the ballast) and also added different forces to the parapet walls due to the plant working next to it.
I believe the engineering work just uncovered it as there was a planned rerail that evening so the excavators uncovered the extent of the damage while carrying out the rerail.
It was a full renewal, not a re-rail. The whole track bed was being removed and replaced. The failure happened during that.
Interesting it says they found parapet wall had moved and they didn't have machinery to move it back. If it had they shouldn't have ripped out all the track out. Still feels like the track renewal has caused the failure even if the wall was weakened already. Also did they then to decide to demolish wall or did it collaspe.
It moved after they had started removing the track, and works stopped once the failures became apparent.
Was the sidewall accidentally ‘nudged’ / touched by an excavator ?
The collapse did happen whilst there was a track renewal going on, and there were excavators and dozers on the viaduct at the time. From the internal briefings it's definately part of the investigation trying to establish whether that happened or not, although no firm conclusion either way has been reached yet.
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.
Yes and no. As others have said, the side walls are structural in that they retain the ballast etc, and thus you couldn't put a railway track there without them. However, the fact that they have detached doesn't mean the rest of the viaduct structure underneath is unsafe - it's not.
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>
Having gone across that viaduct on a narrowboat myself, I can very much attest it was a bit scary but also pretty cool. We did get several people who were walking ask to step onto the boat and lok over the other side, and they all found it awesome but scary at the same time. It's a long drop!!
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"
A back cab view cab over the viaduct during these works
Brilliant videos both - thank you.
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