What are the 'beams' on the Northampton Loop?

[Aviator88]

Pretty much as per the title - I'm curious what the horizontal beams are that run for about 500 metres at the Northern end of Roade cutting, where the Northampton Loop meets the WCML.

I'm assuming they act as braces/further reinforcement for the retaining walls either side of the line, but I've not seen this used anywhere else, so any further history on the construction and/or complications that led to this would be really interesting!

Cheers

 

[snowball]

You've deduced their purpose correctly. The flying arches over the Manchester-Preston line near Chorley had a similar purpose (steel support arches were added to the original stone structures a few years ago).

Here on Google Streetview are some props for the retaining walls of a modern road cutting near Poynton.

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[plugwash]

I'm fairly sure there are some beams like this on HS1 too.

 

[John Webb]

Both approaches to the Silvertown tunnel under the link between the Royal Victoria and Royal Albert Docks in East London had similar 'flying arches' when used by the North Woolwich-Stratford line. I assume these have been retained when the tunnel was altered to accommodate the Elizabeth line.

 

[DelW]

There are modern (railway) examples either side of the Shortlands dive-under near Bromley, and original stone arches near Llansamlet in northern Swansea.

Propping a high retaining wall is structurally much more efficient than cantilevering up from the base.

 

[Taunton]

Both approaches to the Silvertown tunnel under the link between the Royal Victoria and Royal Albert Docks in East London had similar 'flying arches' when used by the North Woolwich-Stratford line. I assume these have been retained when the tunnel was altered to accommodate the Elizabeth line.

Still there. Also nearby to there, they were installed on the DLR west of West Ferry station, which reused a long-abandoned Victorian viaduct, although slightly different in approach, as the Silvertown ones, concrete, support cutting walls, whereas the DLR ones, steel, reinforce a brick viaduct. Pictured here:

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[snowball]

Some modern urban road cuttings have had temporary props while under construction, removed on completion. I thought the ones on the A555 (see link in #2) were going to be like that, but they turned out to be part of the permanent design.

 

[Taunton]

A further variant are the multiple internal props inside the open escalator etc area at Westminster Underground station, rebuilt for the Jubilee Line Extension. Pictured here:

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[DelW]

Some modern urban road cuttings have had temporary props while under construction, removed on completion. I thought the ones on the A555 (see link in #2) were going to be like that, but they turned out to be part of the permanent design.

There are some unusual props over the A34 at its junction with the M4. I think they may have been principally needed during the construction stage but retained as beneficial to the final situation as well.

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[swt_passenger]

There are some unusual props over the A34 at its junction with the M4. I think they may have been principally needed during the construction stage but retained as beneficial to the final situation as well.

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That’s the one I immediately thought of. I think it’s possibly needed because the overall cutting and bridge structure has a more significant height/depth in combination?

 

[DelW]

That’s the one I immediately thought of. I think it’s possibly needed because the overall cutting and bridge structure has a more significant height/depth in combination?

My thought is that they were probably needed to prop the secant pile walls during the excavation of the trench for the low-level A34 carriageway. But they would also be useful in propping the double-height abutments of the M4 bridge. There may or may not be a structural slab below the A34 carriageway, but even if there is, the props would reduce the loading on it.

 

[snowball]

When junction 5 of the M74 was converted to 3 levels by digging a new one at the bottom, early drawings showed props for the cutting, but as finally built it doesn't have them, though the bridge structures over it may help.

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[30907]

Pretty much as per the title - I'm curious what the horizontal beams are that run for about 500 metres at the Northern end of Roade cutting, where the Northampton Loop meets the WCML.

Just to add: presumably the LNWR (not known for its extravagance) wished/needed to reduce its land take at that point - in other circumstances, the Loop might have been built slightly further East to allow a conventional earth slope.

 

[Peter Mugridge]

This would probably be the single worst place on the network to have a fast up train derail wouldn't it...?

 

[Aviator88]

Cheers for all the replies, very interesting!

This would probably be the single worst place on the network to have a fast up train derail wouldn't it...?

Due to it being on a right hand elevated section, likely sending the derailed train crashing down onto the aforementioned piece of infrastructure?

 

[swt_passenger]

A comparatively recent installation of horizontal beams can be found in the new Acton diveunder, installed a few years ago as part of the Crossrail on-network changes.

 

[Class93]

Video of the Chorley ones being replaced

 

[Lucan]

I would say they are quite common in steep sided masonery wall cuttings. Outside the north tunnel portal just south of West Brompton on the LU District line for example.

 

[Peter Mugridge]

Due to it being on a right hand elevated section, likely sending the derailed train crashing down onto the aforementioned piece of infrastructure?

Yes - with all those rather sharp corners of the beams in the last place you'd want them in such circumstances!

 

[Aviator88]

Yes - with all those rather sharp corners of the beams in the last place you'd want them in such circumstances!

Thanks - I'd not given it a second thought until now. Now I'll think of it every time I head past!