Black Bridge, Nuneham: southern abutment failure

[whole diary]

[ellendune]

https://www.networkrailmediacentre.co.uk/news/network-rail-engineers-work-around-the-clock-to-repair-nuneham-viaduct-with-the-line-expected-to-be-closed-until-early-june

Sounds like they are going to do it once and have done with it, as opposed to a temporary fix. Although I might have misunderstood it.

That's my reading too. After a lot about how they knew what was going on all the time, honest squire, and tried squirting some kind of glue (polymers, I gather) under the abutment but it still suddenly dropped a whole load more, this is the plan:

Engineers have been working around the clock since the line was closed and are now working to replace the southern support structure with a new one, which will provide a long-term fix and allow for both passenger and freight trains to run again between Didcot Parkway and Oxford by Saturday 10 June. The work to replace the support structure will be complex and challenging owing to ground conditions at the site, including the proximity to the River Thames and the heavy clay soil in which the new support will need to be secured.

I feared this might be the case at least it will get the job done once for all.

Does anyone know what is happening to the BMW traffic to Swindon?

[Mark A]

It may be that the intervention precipitated the accellerated subsidence. (Empathy rather than finger-pointing if it did, plenty of quick fixes *do* work...)

Mark

[eightonedee]

There's just been more about this on BBC^» (British Broadcasting Corporation - home page) local TV news, presented by Paul Clifton, including a description of the temporary structure they are construction to hold up this end of the bridge while permanent works to restore the abutment are undertaken.

[CyclingSid]

Some of Paul Clifton's reports
https://www.bbc.co.uk/news/uk-england-oxfordshire-65249735
which also highlights the possible bus availability problems from next week
https://twitter.com/PaulCliftonBBC

[Surrey 455]

Some of Paul Clifton's reports
https://www.bbc.co.uk/news/uk-england-oxfordshire-65249735

From that article

Mr Hopwood said GWR^▸ (Great Western Railway) was also "looking at whether we can run some more trains from Oxford into London with Great Western using the Chiltern Railway route".

So would that be Paddington - West Ealing - Greenford - Chiltern line to Oxford?

[IndustryInsider]

Yes, that’s the only way to do it now the Wycombe Line connection at Old Oak isn’t available.

[Oxonhutch]

Yes, that’s the only way to do it now the Wycombe Line connection at Old Oak isn’t available.

It would liven up the Greenford signaller's day.

[paul7575]

Hasn’t the Network Rail view for some while been that the full Crossrail timetable prevents regular use of the flat junction at West Ealing?  Is that not why the Greenford shuttle was removed from Paddington?

Paul

[grahame]

Hasn’t the Network Rail view for some while been that the full Crossrail timetable prevents regular use of the flat junction at West Ealing?  Is that not why the Greenford shuttle was removed from Paddington?

Paul

Maybe - but then the bridge failure is hardly "regular", is it?

[Electric train]

Hasn’t the Network Rail view for some while been that the full Crossrail timetable prevents regular use of the flat junction at West Ealing?  Is that not why the Greenford shuttle was removed from Paddington?

Paul

Maybe - but then the bridge failure is hardly "regular", is it?

There will freight paths to / from Acton which could be made use of, although freight will have been diverted this routes already.  One or both of the Padd - Didcot could be changed to a Reading start / terminate this would free up that path between West Ealing and Padd.

The other consideration is GWR^▸ (Great Western Railway) train crew route knowledge vis the Chiltern line

Edit: fright -> freight (Red Squirrel)

[Gordon the Blue Engine]

Paul Clifton’s assertion that NR^» (Network Rail - home page) “..have no idea what the foundations are like.” doesn’t quite square with Electric Train’s comment (post 78) that he is absolutely certain that NR had a plan [for the bridge]

I assume that NR carried out site investigations as soon as the southern abutment began causing concern back in 2018 or before, so they would have known (I hope!) about the ground conditions and the below-ground condition of the abutment well before its recent failure.  Presumably these investigations must have shown that a new abutment would be required at some point as the current one isn’t sitting on something solid.  Even if design work had not already started on a new abutment before its recent failure, I would have thought that, assuming all the site investigations have already been done, design and construction is achievable within 8 weeks.

Piles will be required of course, though the number, diameter and depth will depend on the ground conditions.  Fairly standard civil engineering work.

If there is to be a “temporary” support for the deck in the short term it’ll be interesting to see what form it takes, but I would have thought that would need piles too.

[IndustryInsider]

Yes, that’s the only way to do it now the Wycombe Line connection at Old Oak isn’t available.

It would liven up the Greenford signaller's day.

Into Marylebone would be another option of course (but with 5-car max if it was an IET^▸ (Intercity Express Train)).

[stuving]

Piles will be required of course, though the number, diameter and depth will depend on the ground conditions.  Fairly standard civil engineering work.

If there is to be a “temporary” support for the deck in the short term it’ll be interesting to see what form it takes, but I would have thought that would need piles too.

I had assumed that, but I'm not 100% sure now. Yesterday's BBC^» (British Broadcasting Corporation - home page) piece showed showed some aggregate corraled in sheet piles as where the temporary support would go. So maybe piles are not involved there, unless it's just something for the piling engine to stand on. Remember that this temporary prop has to go some way away from the bearings, to allow space for the work on the abutment, which is why this support base is partly in the river. Even then, without moving the span, piling under it may not be feasible.

I was also puzzled by the comment about "heavy clay" making the work difficult. I'd have though that was the best sort of clay! Clay rather than gravels might be a bad thing, of course. So maybe they do intend to did a big trench and have a look at exactly what is there, and if it's not what they like replace it.

Alternatively, and assuming the abutment+wings has to end up looking like before (to please the planners), I guess you pile under the current wing walls. The transverse beam has to go near ground level, to stay within the profile of the embankment and wing walls. The bridge bearings are raised on struts above this, and the whole faced in brick.

Or, alternatively, they have a different plan!

[CyclingSid]

Clay rather than gravels might be a bad thing

You tend to get both together in the Thames Valley

[Gordon the Blue Engine]

So maybe they do intend to did a big trench and have a look at exactly what is there, and if it's not what they like replace it.

Site investigations into ground conditions involve a specialist geotechnical company drilling down and collecting core samples.  Trench digging is not required, which is just as well because you could be going down 25 metres or more.  The cores are laid out and the materials are identified and logged to record the depths at which they occur.  The strength and other attributes of the materials found are analysed and noted. 

This information, along with the load to be supported, is used to design the piles.  It is not especially complicated and the conditions at Nuneham are unlikely to be abnormal for the Thames Valley.