Black Bridge, Nuneham: southern abutment failure

[whole diary]

[Mark A]

An informative short discussion and a couple of images from 11 months back here on Linkedin (which will try and persuade the visitor to create an account/log in etc...) & kindly flagged by Hamish Harvey on Twitter.

Some evidence that the bridge deck is/was managing to push the tops of the wing walls out - and then also the wing walls showing signs that the pier was sinking/moving.

Mark

https://www.linkedin.com/posts/simon-deakin-woods-718aa2107_xeiad-networkrail-isar3-activity-6934582807071506432-dl3M/

[TaplowGreen]

An informative short discussion and a couple of images from 11 months back here on Linkedin (which will try and persuade the visitor to create an account/log in etc...) & kindly flagged by Hamish Harvey on Twitter.

Some evidence that the bridge deck is/was managing to push the tops of the wing walls out - and then also the wing walls showing signs that the pier was sinking/moving.

Mark

https://www.linkedin.com/posts/simon-deakin-woods-718aa2107_xeiad-networkrail-isar3-activity-6934582807071506432-dl3M/

Does rather beg the question - how on Earth did Network Rail allow it to get into this state before action was taken given that the damage had already been noted and these pictures are almost a year old and even then showed some pretty dramatic issues?

I also saw Paul Clifton's pictures on Twitter - most alarming.

[Oxonhutch]

In short without borehole data I would not like to make a judgement about what is going on in the superficial layers (which might go quite deep). 

I am a geologist, and I agree with you.

I too suspect the failure of wooden piles to account for the recent rapid movement.

[Electric train]

An informative short discussion and a couple of images from 11 months back here on Linkedin (which will try and persuade the visitor to create an account/log in etc...) & kindly flagged by Hamish Harvey on Twitter.

Some evidence that the bridge deck is/was managing to push the tops of the wing walls out - and then also the wing walls showing signs that the pier was sinking/moving.

Mark

https://www.linkedin.com/posts/simon-deakin-woods-718aa2107_xeiad-networkrail-isar3-activity-6934582807071506432-dl3M/

Does rather beg the question - how on Earth did Network Rail allow it to get into this state before action was taken given that the damage had already been noted and these pictures are almost a year old and even then showed some pretty dramatic issues?

I also saw Paul Clifton's pictures on Twitter - most alarming.

I am absolutely certain Network Rail Wales and Western Region Structures Asset Management team had a plan.  It is entirely plausible the subsidence has accelerated faster than they anticipated, yes the state of this abutment has been known about, there are quite a number of things that perhaps needed to be resoulved, like Environment Agency approvals for river access, land owner access (for site access) railway possessions / blockades; not to mention the design of the solution.  

NR^» (Network Rail - home page) Assets teams are not large in numbers of people, they are reliant on contractors who are managed by the Capital or Works Delivery organisations.  It could be argued why NR does not have own in-house expertise to do all this, its down to how the railways were privatised and the governance placed on it by the DfT^» (Department for Transport - about) and ORR^» (Office of Rail and Road formerly Office of Rail Regulation - about)
    

[Red Squirrel]

As discussed elsewhere there are other (probably many other) structures that appear long overdue for maintenance. I wouldn’t want the job of trying to guess which one was going to cause problems next…

[TaplowGreen]

As discussed elsewhere there are other (probably many other) structures that appear long overdue for maintenance. I wouldn’t want the job of trying to guess which one was going to cause problems next…

Quote from a driver (with respect to Paul Clifton's pictures) "it’s looked pretty much like that for the last few months, with a steadily reducing speed restriction (90-50-20-5)"

Here's the view from space............

[IndustryInsider]

Here's the view from space............

I think somebody has attached a comedy ‘hall of mirrors’ lens to that camera.

This is what it looked like three weeks ago without distortion from above or foreshortening from a telephoto lens.  Rather less dramatic.

[grahame]

For the record, JourneyCheck has added a week since I last looked ...

Due to urgent repairs to a bridge between Didcot Parkway and Oxford the line is closed. Disruption is expected until the end of the day on 30/04/23.

but still misses the extra text on the end "and probably for some time beyond".

[paul7575]

There’s an Environment Agency closure notice for the southern span, lasts for a month, it mentions a pontoon will be present under the bridge, navigation limited to the northern span:

This restriction is for initial works to be taken under the south railway arch prior to further bridge repairs, during the overall repair of the bridge abutment.

During this time there will be a restricted river under the southern arch of the railway bridge. Caution is to be taken by boat masters when travelling via northern arch route, as this will be two-way traffic, and masters must take note of any instructions given by staff as to navigation past this point.

A pontoon will be moved into position to enable works to be taken from beneath the railway bridge in the channel. This will completely obstruct the southern arch during works. Subsequently the pontoon will be removed to a safe mooring when work is finished.

https://www.gov.uk/government/publications/nuneham-railway-viaduct-repairs-2023-river-restriction-notice/nuneham-railway-viaduct-repairs-2023-river-restriction-notice

[stuving]

This is what it looked like three weeks ago without distortion from above or foreshortening from a telephoto lens.  Rather less dramatic.

That depends what you were looking for. In terms of estimating the vertical movement since (1) the bridge was built and (2) whenever the track was last levelled, there is not so much difference. I make the first answer about half a metre, and the second at least 10 cm (but neither is meant to be closer than +/- 30% at best).

Presumably Simon Deakin-Woods' picture, of 10 months ago, was before that last visit from a stone-blower, and I'll be returning to what that shows shortly.

[stuving]

This picture was in the Oxford Mail, but credited to Network Rail.


It shows two "long-range stone-suckers", and the pipes lead to one of those vacuum excavation trucks. Deballasting isn't really evidence of what the planned work is, as it's the first step in most possible plans.

There's another picture of just to the right of that, in railforums, that can be compared with the one we had from Linked-In.

You can't see much of the wing wall (shown by the BBC^» (British Broadcasting Corporation - home page) or in post #63), but you can see a steep slope down in the top of the embankment. The abutment's movement has led to shear strain in the soil over about three metres.

One the right, the "bearing" block sits on the abutment wall, while at the other side there is a column of brickwork so the bearing sits forward of the wall. That must be to do with the skew of the bridge; my guess is that the abutment wall turned out to be not parallel to the mid-river pier, and this gets over that problem. The size of that column does suggest that supporting the weight of the bridge was not a big deal, for the 1906 designers.

The left wing wall has failed in shear, but the vertical movement across it is less than two courses (20 cm) so well short of the full distance. But a lot of the outer half has been patched or even rebuilt. So I wonder if that got so bad that major reconstruction was needed, and more than once. When the brickwork is intact, with good strong mortar and engineering bricks, it can provide significant support to the abutment. Once it fails it can't, so that may be one reason for the "sudden" burst of subsidence recently.

If flooding is relevant, then like ellendune I don't see how that can have much impact under the abutment (and below the water table). Surely it is the embankment that is likely to be destabilised most by a thorough soaking. And it does take significant shear stress to produce the observed shear strain in settled soil, which is another upward supporting force for the abutment. Soggy soil is more mobile, so a lot of the supporting force disappears. In combination, the total reduction in upward force could explain the extra and rapid subsidence recently.

Incidentally, what looks like horizontal shear between the brick courses isn't due to any extra cause, it's just how shear works. The internal bricks feel much the same forces whether the shear is applied to the sides or the top and bottom. There's a more complicated, and rigorous, explanation of all this but it means resorting to tensors ...

[Oxonhutch]

At least with bricks, it is simple shear 

[grahame]

The Independent

Engineers have spent the weekend examining the structure and, on Easter Monday morning, Network Rail announced: “Disruption between Reading and Oxford is expected until at least the end of the day on Wednesday 31 May.”

[stuving]

The Independent

Engineers have spent the weekend examining the structure and, on Easter Monday morning, Network Rail announced: “Disruption between Reading and Oxford is expected until at least the end of the day on Wednesday 31 May.”

The Independent seems to have misunderstood what "a lot of movement" in the bridge means:

Main rail line to close until June due to a wobbly bridge

Passengers between the north of England and the South Coast are being advised to travel via Bristol or London instead

[TonyN]

National Rail Enquires now saying 9th June.

Disruption between Reading and Oxford is expected until at least the end of the day on Friday 9 June.