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Bridges and tunnels


Peter-Bullfinch

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Whilst it is reasonably easy to find the length of tunnels around the system it's not to easy to find the length of tunnels created by wide bridges.

Why does this matter?  They are often wide and easy to see through. Well..it doesn't really, its just that we were both discussing this as we went along.

On the Bridgewater at Stretford there is the huge bridge where the M60 crosses.

In Stoke the Trent and Mersey is crossed by the A50 and this creates a tunnel over 70 yards long and this one is lit. We wondered where there were longer ones?

We do recall a very short tunnel on the Regents Canal but we are unsure if this is the shortest.

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Finding the length of wide bridges should in some cases be worked out from the road width. Motorways do have a standard width. But, with road widening that is different. And there is also the railway crossings which can be variable. On the BCN Digbeth Branch the canal passes under the railway bridges. These are a composite group of bridges that start by the Proof House and end up near the bottom lock. It is a curving waterway at this spot so the end cannot be seen. The Bridges overhead are:

Midland Railway widening (2 tracks)

Original LNWR extension into New Street (2 tracks)

London & Birmingham/ Grand Junction tracks into Curzon Street ( originally passenger & goods, later goods, later still parcels and now to be HS2). There is also the rising viaduct that takes the Aston line over one of the Coventry Lines

It is a lengthy "tunnel"

 

 

Edited by Heartland
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1 hour ago, Heartland said:

Finding the length of wide bridges should in some cases be worked out from the road width. Motorways do have a standard width. But, with road widening that is different.

 

 

You are ignoring the affect of skew angle which would make pretty much every motorway bridge different in length.

12 minutes ago, David Mack said:

So what is the distinction between a wide bridge and a tunnel?

There is no absolute distinction. It's however the infrastructure owner decides to define it. The key factor is generally the inspection regime. For instance railway bridges are inspected as one entity with one set of condition statements. A tunnel is inspected in 10 metre lengths and each has its own condition statements. Theoretically a bridge is less than 50 metres long and a tunnel is 50 metres or more long but there are long road bridges of over 50 metres in length that are not managed as tunnels and equally there is no reason why a bore of less than 50 metres can't be managed as a tunnel.

JP

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27 minutes ago, Nightwatch said:

Isn't a 'tunnel' cut through the earth. A long bridge isn't.

There is no single definition. Cut and cover and immersed tubes are both common tunneling methods that don't cut through the earth. A standard method of constructing culverts (small bridges?) is to bore them.

JP

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2 hours ago, Captain Pegg said:

There is no single definition. Cut and cover and immersed tubes are both common tunneling methods that don't cut through the earth. A standard method of constructing culverts (small bridges?) is to bore them.

JP

My point exactly! Galton and Summit 'tunnels' on the BCN were created by infilling cuttings originally built 150-200 years earlier. So are they bridges or tunnels?

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38 minutes ago, Peter-Bullfinch said:

Is there any Dept of Transport guidance to say when a bridge over a canal should have towpath illumination I wonder? Maybe that is down to the bridge architect?

More likely it's whoever the bridge design team* ends up dealing with at the relevant navigation authority.

* probably not the architect - more likely a grunt in the contracts office

You could have a look through the DoT DMRB (Design Manual for Roads and Bridges) but I doubt you'll find anything helpful.

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4 hours ago, Peter-Bullfinch said:

Is there any Dept of Transport guidance to say when a bridge over a canal should have towpath illumination I wonder? Maybe that is down to the bridge architect?

Anyone building a bridge over CRT's canal has to meet CRT's reasonable requirements. So it is up to CRT to specify this sort of thing, although the local authorities will usually have some requirements as well.

On the other hand there is no point in specifying lighting or similar things if there is no budget (or willingness) to maintain it.

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16 hours ago, Derek R. said:

As stated, I don't think there is any definitive criteria, though if one thinks of bridges as being built over something, and tunnels as being bored through something, then there does appear to be a distinction.

As David M has said, some now classed as "tunnels" have been built by creating a tube, then covering over it.  The pair on the New and Old BCN main lines at Galton being an  obvious example.

I suppose strictly they are "cut and cover" tunnels, as the covering that has gone over the tubes in the 1970s has replaced soil that was removed to create the two massive cutting involved when those two canals were first built.  Possibly two "cut and cover" tunnels with some of the longestr time between "cut" and "cover"!

Don't forget that many things on the canals are badged "tunnel" that many would consider a bridge - - another obvious example on the BCN being Broad Street.

Also that there are several "tunnels" than are these days neither a tunnel or a bridge, such as Armitage or Fenny Compton.

As an aside, I have never understood why Dudley tunnel is recorded as one of the longest, with a single length quoted.  As it has stretches that are completely in the open, surely it is multiple shorter tunnels?
 

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Cut and cover was the first method by which London gained its Underground railway. The cost was kept to a minimum by cutting beneath existing roads (causing chaos), as to do so beneath buildings would bring down claims of compensation for damage to foundations and the property at large, something to be avoided at all costs as said railways were built using shareholders money, and they wanted dividends paid! But the covered sections were still known as tunnels, definitely not bridges. Later, the Greathead shield was developed and deep tube lines were created going well beneath foundations, sewers and service mains. So a tunnel can be either - bored, or cut and cover.

So, when does a bridge become a tunnel? I would suggest it might be when the width of the bridge overall is greater than the overall width of the 'tunnel' beneath it. And when they are both equal? Toss a coin.

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3 hours ago, Derek R. said:

Cut and cover was the first method by which London gained its Underground railway. The cost was kept to a minimum by cutting beneath existing roads (causing chaos), as to do so beneath buildings would bring down claims of compensation for damage to foundations and the property at large, something to be avoided at all costs as said railways were built using shareholders money, and they wanted dividends paid! But the covered sections were still known as tunnels, definitely not bridges. Later, the Greathead shield was developed and deep tube lines were created going well beneath foundations, sewers and service mains. So a tunnel can be either - bored, or cut and cover.

So, when does a bridge become a tunnel? I would suggest it might be when the width of the bridge overall is greater than the overall width of the 'tunnel' beneath it. And when they are both equal? Toss a coin.

And by that definition a great many canal bridges are tunnels.

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Another variation is the Asda  store built over the start of the Huddersfield canal in Ashton Under Lyne. This created a 'tunnel' 166yds long. If I recall it is illuminated but has no towpath. I may be wrong because it was last summer we were  last there.

No one has suggested the longest tunnel formed by a bridge yet. I would imagine Birmingham must have a number.

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15 minutes ago, Peter-Bullfinch said:

 

No one has suggested the longest tunnel formed by a bridge yet. I would imagine Birmingham must have a number.

Galton Tunnel or the extended railway bridge over the Digbeth Branch must be good candidates.

And what about Preston Brook Tunnel? Originally a bored tunnel the middle section was rebuilt as cut and cover in the 80s. So is it now 2 tunnels and a bridge without any gap between them?

And the longest tunnel of all, Standedge, was extended at the west end when the railway was built. So is that another combined tunnel/bridge?

Edited by David Mack
  • Greenie 1
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Tunnels are a subset of bridges. They are long bridges. There is therefore no absolute definition that will distinguish one from the other. The idea of the longest tunnel formed from a bridge is nonsensical. As I stated earlier C&RT will designate which structures are managed as tunnels primarily according to a length criteria with local variations according to specific risk.

JP

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I would have thought that a bridge is built when something needs to go over a canal, (or railway, or road, or whatever). Whereas a tunnel is created when the canal needs to go through something, usually a hill or land of some other kind.

Bridges go over something, tunnels go through something?

 

I dont know the definitive answer - Just my take on things.

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32 minutes ago, Richard10002 said:

I would have thought that a bridge is built when something needs to go over a canal, (or railway, or road, or whatever). Whereas a tunnel is created when the canal needs to go through something, usually a hill or land of some other kind.

Bridges go over something, tunnels go through something?

 

I dont know the definitive answer - Just my take on things.

So what are Galton and Summit tunnels on that basis? Both were built to carry a road over the canal. But the canals had originally been built in deep cuttings to go through high ground.

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On 24/08/2017 at 20:32, BEngo said:

Not just lighting under bridges-the ones in Newbold tunnel are now terminally poorly because noone seems to have maintained them.

N

They only worked during the day when they were installed, then they weren't to see with but look pretty 

On 24/08/2017 at 08:34, Peter-Bullfinch said:

Whilst it is reasonably easy to find the length of tunnels around the system it's not to easy to find the length of tunnels created by wide bridges.

Why does this matter?  They are often wide and easy to see through. Well..it doesn't really, its just that we were both discussing this as we went along.

On the Bridgewater at Stretford there is the huge bridge where the M60 crosses.

In Stoke the Trent and Mersey is crossed by the A50 and this creates a tunnel over 70 yards long and this one is lit. We wondered where there were longer ones?

We do recall a very short tunnel on the Regents Canal but we are unsure if this is the shortest.

Just wait for HS2 on the Middlewich Arm

 

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Perhaps CRT should record the wide bridges, in fact perhaps all bridge widths need to be recorded for historical purposes. And it would be useful to mention construction material and rough guide to age. But then this would take a lot of time and so is perhaps something for a society dedicated to it to do-  such a mythical assembly might be given the abbreviation BAOCRAKE?

British Association of Canal Bridges Recording and Knowledge Enhancement (BAOCRAKE)

And thinking about it more, it does fall within the remit of one group- The Transport Trust

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