HS2 Colne Valley Viaduct construction updates

[Fazaar1889]

lovely view of the viaduct. looks like one of those maglev bridges you find in futuristic sci-fi films. Looks really good

View of the Colne Valley Viaduct from Denham Water Sky Club .

HS2 (High Speed Two) Ltd on Instagram: "This week we'd like to share these fantastic moments : 1) Cutterhead at our Victoria Rd Crossover Box site . 2) Highfurlong Brook beams in position from above . 3) View of the Colne Valley Viaduct from D

27 likes, 0 comments - hs2ltd on December 13, 2023: "This week we'd like to share these fantastic moments : 1) Cutterhead at our Victoria R..."

www.instagram.com

 

[Nicholas Lewis]

lovely view of the viaduct. looks like one of those maglev bridges you find in futuristic sci-fi films. Looks really good

It will be well weathered by the time any of the Sci-Fi trains run over it

 

[Fazaar1889]

https://x.com/HS2ltd/status/1740674148546871736?s=20

Construction of our #ColneValleyViaduct passed the halfway mark earlier this year. 500 out of 1,000 segments have been installed, meaning 1.1 miles of Britain's longest railway bridge is now assembled. #HS2in2023

I just noticed that there are now sound barriers atop the bridge, a bit sad that we won't be able to see outside once the train goes over. The view will be blocked!

 

[swt_passenger]

I just noticed that there are now sound barriers atop the bridge, a bit sad that we won't be able to see outside once the train goes over. The view will be blocked!

The slab track finished level will be a bit higher than the current deck. I suspect the sound barriers will be only marginally above bogie height, the train windows will still be significantly higher then the barrier. But the existence of the sound barriers has been mentioned on and off in this thread for a few months, eg post 119 in July, they’re not actually a new arrival on the scene…

 

[Fazaar1889]

The slab track finished level will be a bit higher than the current deck. I suspect the sound barriers will be only marginally above bogie height, the train windows will still be significantly higher then the barrier. But the existence of the sound barriers has been mentioned on and off in this thread for a few months, eg post 119 in July, they’re not actually a new arrival on the scene…

Ah, I completely forgot about that post, I have too many watched threads. Regardless, thanks for the info, glad I'll still be able to see the trees!

 

[Snow1964]

New drone views have appeared of Colne Valley viaduct on You Tube

 

[gravitystorm]

The PWI have released a presentation from two members of the engineering team, looking at some of the different aspects of design and construction techniques:

 

[Nicholas Lewis]

New drone views have appeared of Colne Valley viaduct on You Tube

Hopefully passengers will be able to see that view from the train windows and not just a sound barrier although if its like European high speed lines im not holding my breath

 

[Bald Rick]

Hopefully passengers will be able to see that view from the train windows and not just a sound barrier although if its like European high speed lines im not holding my breath

The design has a transparent sound barrier, as per this photo on the HS2 website.

 

[stuu]

Hopefully passengers will be able to see that view from the train windows and not just a sound barrier although if its like European high speed lines im not holding my breath

It literally says transparent sound barrier on the image

 

[DelW]

The design has a transparent sound barrier, as per this photo on the HS2 website.

It literally says transparent sound barrier on the image

Which is good, but it does require some maintenance effort to keep it that way. I can think of examples at stations where once-transparent panels are now opaque with decades of dirt, algae and moss that have never been cleaned off. Will 'elf-n-safety ever allow these to be cleaned?

 

[Bald Rick]

Which is good, but it does require some maintenance effort to keep it that way. I can think of examples at stations where once-transparent panels are now opaque with decades of dirt, algae and moss that have never been cleaned off. Will 'elf-n-safety ever allow these to be cleaned?

I should imagine that with trains whipping past at 300kph dirt, algae and moss will never have a chancce to settle . (But one hopes cleanign will be in the maitenance schedule)

 

[Nicholas Lewis]

I should imagine that with trains whipping past at 300kph dirt, algae and moss will never have a chancce to settle . (But one hopes cleanign will be in the maitenance schedule)

That will be expensive working at height, possessions and isolations!!

 

[jfowkes]

That will be expensive working at height, possessions and isolations!!

We have ballast cleaning trains right? A bridge cleaning train can't be beyond the wit of man.

 

[zwk500]

That will be expensive working at height, possessions and isolations!!

Isn't the line going to shut every night like HS1 and every LGV for routine maintenance and inspection tasks?

 

[Bald Rick]

That will be expensive working at height, possessions and isolations!!

cleaners will be on the inside, surely.

 

[stuving]

There was a report in the local paper, the Bucks Free Press, saying:

A section of concrete in a new viaduct set to carry the HS2 railway between London and Buckinghamshire is being removed, a contractor has admitted.

This is misleading, as the fuller report in New Civil Engineer shows:

HS2 Ltd has confirmed that the works will involve repeating cable tensioning on the section of the viaduct most recently completed. This will involve drilling out the span’s concrete join.

I'm a bit surprised that there is no designed access to the post-tensioning points. Is there really no need to check this and if need be adjust it during the service life?

 

[swt_passenger]

There was a report in the local paper, the Bucks Free Press, saying:

This is misleading, as the fuller report in new Civil Engineer shows:

I'm a bit surprised that there is no designed access to the post-tensioning points. Is there really no need to check this and if need be adjust it during the service life?

Isn’t this referring to the cast in-situ closing section, midway between two piers? If they’re expecting to change the tension of the viaduct section on one or both sides of the join, the join has to be free to split?

 

[Fazaar1889]

There was a report in the local paper, the Bucks Free Press, saying:

A section of concrete in a new viaduct set to carry the HS2 railway between London and Buckinghamshire is being removed, a contractor has admitted.

It's funny the way they worded that. "Oh no! A contractor is doing proper safety and quality control! How awful!" They phrased it as "admitted" as if the contractor has committed a sin... Spotting bias in media has become remarkably easy these days, the anti-HS2 rhetoric is rampant!

 

[Grimsby town]

It's funny the way they worded that. "Oh no! A contractor is doing proper safety and quality control! How awful!" They phrased it as "admitted" as if the contractor has committed a sin... Spotting bias in media has become remarkably easy these days, the anti-HS2 rhetoric is rampant!

The Bucks Free Press don't even tried to hide the bias. They run anti-HS2 social media accounts and campaigns.

 

[InOban]

The story is now in New Civil Engineer. They're having to break out the concrete joining the last two sections.

 

[swt_passenger]

The story is now in New Civil Engineer. They're having to break out the concrete joining the last two sections.

The NCE article was linked in the post by @stuving yesterday, it is what I based my question in reply on.

 

[DelW]

I'm a bit surprised that there is no designed access to the post-tensioning points. Is there really no need to check this and if need be adjust it during the service life?

It used to be normal to have no access for retensioning the deck; there was none on the only post-tensioned bridge I worked on. The strands were stressed and locked-off, the ducts grouted, the jacks removed and an in-situ concrete diaphragm poured across the back of the anchorages.

That was nearly 50 years ago though, and I think that specifications may have changed since. There have been a number of cases where post-tensioned road bridges have had to have major repair work because of loss of prestress or of tendon corrosion. AIUI tendons are now normally not grouted, and designs are more likely to consider how to access the tendons to carry out remedial work if and when necessary.

 

[snowball]

There was a lot of worrying about post-tensioned bridges, maybe about 20 years ago? A number of road bridges from the 1960s or so were having failures in their tensioning cables but they were inaccessible within the concrete. An example was Mossband Viaduct carrying the A74 at high skew over the WCML between Carlisle and Gretna. If it had not got upgraded to M6 when it did, with a new box-type viaduct, the old structure would have had to be replaced anyway. From then on I think a number of bridges were built with external cables, but I can't remember any locations and don't know what the long-term consequences are.

 

[swt_passenger]

It used to be normal to have no access for retensioning the deck; there was none on the only post-tensioned bridge I worked on. The strands were stressed and locked-off, the ducts grouted, the jacks removed and an in-situ concrete diaphragm poured across the back of the anchorages.

That was nearly 50 years ago though, and I think that specifications may have changed since. There have been a number of cases where post-tensioned road bridges have had to have major repair work because of loss of prestress or of tendon corrosion. AIUI tendons are now normally not grouted, and designs are more likely to consider how to access the tendons to carry out remedial work if and when necessary.

Your post #94, where you were referring to a photo in post #84, had proposed that the cables would be accessible from within the precast segments. They certainly seem big enough for normal maintenance access.

 

[stuving]

It used to be normal to have no access for retensioning the deck; there was none on the only post-tensioned bridge I worked on. The strands were stressed and locked-off, the ducts grouted, the jacks removed and an in-situ concrete diaphragm poured across the back of the anchorages.

That was nearly 50 years ago though, and I think that specifications may have changed since. There have been a number of cases where post-tensioned road bridges have had to have major repair work because of loss of prestress or of tendon corrosion. AIUI tendons are now normally not grouted, and designs are more likely to consider how to access the tendons to carry out remedial work if and when necessary.

There is a lot of detail about the three kinds of post-tensioning in the PWI presentation linked from post #157 (from 20 minutes). That makes the point that for structures made of precast segments, internal (i.e. in holes through the solid part of segments) PT was banned over 30 years ago. For this one, they have put in extra features to overcome that - notably lining those channels with insulating waterproof pipes.

It also shows (but with words and pictures not always matching each other) that these three PT systems are:
1. cantilever PT, with tendons from the face of each added segment on one side to its opposite number
2. continuity PT, through the midspan join between matching segments on each side of it, stopping short of the piers
3. external PT, which is in the main void within the segments, tensioned above the piers, and always accessible during service.

Only 1 has to be put in during erection, and it does not go through the midspan.

I always wondered whether they really, as most of the videos seemed to show, built the cantilevers using just glue to hold them in place - it sounds so unlikely. Now I know they don't do that. I was also puzzled by their describing the angled walls on the sides, under the walkways, as "non-structural". It turns out they do hold up the edges of the deck, but are not part of the main bridge structure - not connected between segments.

That's what I made of the presentation, but I'm not a structures engineer - so please do correct anything that's wrong.

 

[DelW]

Your post #94, where you were referring to a photo in post #84, had proposed that the cables would be accessible from within the precast segments. They certainly seem big enough for normal maintenance access.

Gosh, well spotted, I'd completely forgotten that I'd chipped in on the subject before

At least I seem to have said something similar both times.

 

[swt_passenger]

Gosh, well spotted, I'd completely forgotten that I'd chipped in on the subject before

At least I seem to have said something similar both times.

I had to do a quick rewrite - I didn’t realise I was quoting your own post the first time…

 

[DelW]

There is a lot of detail about the three kinds of post-tensioning in the PWI presentation linked from post #157 (from 20 minutes). That makes the point that for structures made of precast segments, internal (i.e. in holes through the solid part of segments) PT was banned over 30 years ago. For this one, they have put in extra features to overcome that - notably lining those channels with insulating waterproof pipes.

It also shows (but with words and pictures not always matching each other) that these three PT systems are:
1. cantilever PT, with tendons from the face of each added segment on one side to its opposite number
2. continuity PT, through the midspan join between matching segments on each side of it, stopping short of the piers
3. external PT, which is in the main void within the segments, tensioned above the piers, and always accessible during service.

Only 1 has to be put in during erection, and it does not go through the midspan.

I always wondered whether they really, as most of the videos seemed to show, built the cantilevers using just glue to hold them in place - it sounds so unlikely. Now I know they don't do that. I was also puzzled by their describing the angled walls on the sides, under the walkways, as "non-structural". It turns out they do hold up the edges of the deck, but are not part of the main bridge structure - not connected between segments.

That's what I made of the presentation, but I'm not a structures engineer - so please do correct anything that's wrong.

One of the issues with this type of construction (cantilevering out from each pier) is that bending moments during construction are significantly different from those in service. Failure to allow for this adequately contributed to several major failures of box girder bridges during their construction in the early 1970s. So I think that separating the tensioning systems numbered 1 and 2 simplifies the analysis, as each can be designed for the relevant condition.

Anything like that is and was well beyond my design skills though!

 

[BRX]

One of the issues with this type of construction (cantilevering out from each pier) is that bending moments during construction are significantly different from those in service. Failure to allow for this adequately contributed to several major failures of box girder bridges during their construction in the early 1970s. So I think that separating the tensioning systems numbered 1 and 2 simplifies the analysis, as each can be designed for the relevant condition.

Anything like that is and was well beyond my design skills though!

In the PWI video above they explain that there are temporary extra steel props each side of the piers, while the segments are being put into place, to deal with this problem.