Latest video explaining progress on site:
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Nuneham Viaduct shut - Didcot- Oxford
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mr_moo
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Kudos to Stuart - refreshing honesty and frankness. Looks like great progress.
swt_passenger
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I wonder if there’ll be a longer version in news programmes later today, that seemed a bit short…
WesternBiker
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Absolutely - it's much better PR in my view (especially in these days of hyperactive speculation on social media) to be clear and transparent.
Mikey C
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Looked fine to me. Short and snappy, and nice to see the rowers going under the bridge too!
GRALISTAIR
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Absolutely- perfect length for 99.5% of the population.
Yes, OK, but we technocrats would like more details. For example, why so many temporary piles? How big are they, and how long? Were they driven or bored? How far down do they go before ground of an adequate bearing strength was found? Will they be filled? - and if so what with? What will the supporting beam be like? and - and - and . . .
jfowkes
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Given the time constraints, I'd rather they get on with doing it. Maybe we'll get a nice long technical video with a very exhausted Stuart Calvert after June 10th.
Well from the video, it looks like 12 round driven piles on each side. Given the number I’d hope they wouldn’t need to fill them as well.
I’m guessing the large number is to reduce the anticipated load so the weak bearing capacity of the ground can cope and they don’t have to be stupidly deep (unlike the anticipated 25m permanent piles).
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https://www.bbc.co.uk/iplayer/episode/m001lf5y/south-today-evening-news-26042023 is yesterday evening's South Today, the report on the viaduct starts at 4:18. There's not a huge amount more than in the version on Twitter.
Nicholas43
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Many thanks for posting the link.
mr_moo
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I stress that I'm not involved in this project at all, and thus my answers here are pure educated guesses, but I am a railway engineer and a chartered member of ICE, so here's my thoughts...
Given the timescales that this job was done in, the calculations to work out how many piles would be genuinely needed would take too long, and would involve some pretty big assumptions about the ground type anyway. If this were a project on a normal timescale you'd do some robust ground investigation, but there's no time for that here, plus the ground is known to be settling/moving/substandard because, well...
Accordingly, the design methodology is likely to look more like 'take whatever information we can glean from similar situations and any records we have available. Make some pretty generous assumptions about the loadings and the ground stiffness and stability. Work out the resultant number of piles required. Double or even triple it if the assumptions were big. Go for installation.
Almost certainly 660mm diameter as this was one of the most common pile types used on the electrification project, and thus is probably what was in a store somewhere. The piles look very much like leftover electrification foundation piles - look at the tops - those are screw fixings for OLE mast brackets.
How long - piles were frequently up to 5m long, sometimes longer, so probably about this.
Length was probably also 'driven to refusal', or driven until they were presenting a certain resistance force. By doiing this you can install to a reasonable level of confidnce that the piles can bear a certain amount of weight, and thus would be suitable for the temporary scenario.
This is also supported by the pile tops all being slightly different heights - being driven to a force rather than a depth would mean they all reach that force at slightly different points.
Almost certainly vibrated or hammered (or a bit of both) down. You're putting these into a river bed so you really don't want to be boring or augering if you don't have to.
The designers probably only had a very rough idea of what they could expect for that, hence my above assumption of driving to a force rather than a depth.
Unlikely. If they were filled they would be filled with concrete, which would make removal much harder. Given these are temporary, almost certainly with the river authority demanding a removable solution, you want them to be able to be removed fairly easily, or, if they refuse to come back out again, able to be cut off at the river bed.
My best guess would be something like the 'superprop' from mabey: https://www.mabeyhire.co.uk/MabeyHi...ropping-and-Jacking-Brochure-web.pdf?ext=.pdf
Probably a plan to cut the tops of the piles off at the same level and place some props across the top.
However, there's a plethora of options for this one.
They would also almost certainly have lots of monitoring sensors on the piles and props to ensure he piles don't shift too much when they are loaded.
edwin_m
Veteran Member
With this lack of certainty I wonder if they need to take precautions in case the span starts settling back during the abutment work. For example they could leave the middle or the sides of the existing one in place while they build the first part of the new one, so there is always something to catch the span if it drops.
Nicholas43
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There was a lot of hammering, audible for miles around.
The span will be being held up by the temporary structure in the river, won't it?
What I've seen in the background of those videos, mounted on a big digger, is a Movax side-grip vibratory pile driver (SG series). And TMS list one as part of their equipment for piling contracts, though call it SPH-75 (and they have hired in excavators). I think that's an outdated model name for the same thing, Movax having decided to make a clearer distinction between their side-grip vibrators and their pile hammers.
A Movax piling hammer would be a tall orange thing (man-size at least) that sits on top of a pile, and they are sometimes used to take over once a pile being vibrated in has reached "refusal". But I've seen so sign of one of those.
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DidcotDennis
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More news on Twitter: https://twitter.com/networkrailwest/status/1651886169997692929?ref_src=twsrc^tfw
Piles are down 15 metres I think he said.
Piles are down 15 metres I think he said.
DelW
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That's a good update, succinct and informative. Good to see it coming from an engineer (I think) rather than PR people.
They've made impressive progress considering the mobilisation was almost from scratch when the previous grouting scheme failed to prevent the subsidence increasing. Having spent quite a few years planning and designing temporary works schemes (including emergency response work on occasion), I can see how much effort must have been put into this!
edwin_m
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In view of the preceding post mentioning uncertainty about the ground conditions under the temporary structure, I wondered if there was a risk of it starting to sink under the weight of the span.
Oxfordblues
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Impressive indeed. I especially like the deployment of a Network Rail river-boat to ferry staff around. Do they have a small fleet of these or was it perhaps hired-in from a local boatyard?
I would have thought the numerous piles under the temporary structure provide much better support than anything under the original abutment. However, there will be jacks between the pile-capping platform and the bridge span, so these can be extended or supplemented by chocks if there's settlement and if it isn't too disastrous.
Snow1964
Established Member
There is also lot less load, basically got deadweight of a static steel bridge deck.
Completely different to also having the dynamic load of moving train added to the weight, plus any slight wheel flat on a train, creates a like hammering in like vibration into the foundations.
So temporary piles carry much lower load than the permanent ones.
From 2nd May GWR will start running shuttles between Oxford and Radley, and between Didcot and Culham. It will be pilotman working at both ends, using the down line to and from Radley, and the up line to and from Culham. Trains will not be able to call at Appleford in the Culham direction, due to the platform being on the offside and no DOO equipment fitted, but will be able to call in the Didcot direction.
They have gone to the trouble of providing a service, and yet only calling at Appleford in one direction. That's bad, isn't it? Why can't they provide a proper service? Is it because they are going to use one track to give rail access to the works, do you think? There will be a lot of spoil coming out when the abutment is demolished, and it could go by rail. But where to?
No crossover, I would imagine, and I don’t think the “Kletterweiche” would go down very well with the safety authorities!
DelW
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The shuttles have to go out and back on the same track, so whichever one they use one of the Appleford calls will be stopping in the "wrong" direction for that platform.
The only crossovers are at Kennington Junction (between Oxford and Radley) and between Appleford and Didcot.
I think the implication from at least one of the videos with NR was that spoil was going to be removed by road.
edwin_m
Veteran Member
Digging back the embankment a few metres from the abutment, the spoil would only fill a handful of wagons. And it would have to be got along and up the embankment and into the train somehow. Far easier just to bring a truck up near the site, drop the spoil straight from the digger, and swap trucks when full.
nickswift99
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Could they not find some process involving a competent person on the platform to allow the train to safely arrive/depart?
For a station which sees, at the very most about 25 passengers a day?
For a station with such low use I wouldn't be surprised to see it permanently lose all of its train services in the next few years...
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