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Dunsley Tunnel on Staffs and Worcs - shortest and oldest navigable tunnel?


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2 minutes ago, David Mack said:

When does a short tunnel become a mere bridge?

When it’s owner redefines it. There are undoubtedly longer bridges under CRTs jurisdiction than this tunnel but they are likely to be managed differently which is more important to the distinction between a bridge and a tunnel than any direct engineering criterion, for which there will always be an exception to the rule. This forum has been through that discussion to no avail previously.

 

JP

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10 hours ago, David Mack said:

When does a short tunnel become a mere bridge?

When is in neither? I'm struggling to define the Scraggy Rock Arch on the Boyne - it isn't a bridge as it doesn't carry anything, it isn't really a tunnel as it's too short, although if it were it would be the only one on the Irish Waterways and on a river navigation to boot.

 

I think it's like Winston Churchill's hippopotamus - difficult to define but easily recognisable. 

 

eta in reponse to the OP, I don't know that Dunsley is either the shortest or the oldest, but I can't name any other contenders at the moment

Edited by magpie patrick
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5 minutes ago, TheBiscuits said:

Do the mine tunnels at Worsley on the Bridgewater count as navigable?

 

You could use a boat in them if you were allowed in, and they are older.

It's the older I'd probably question - but I think not being allowed in makes them un-navigable! 

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8 minutes ago, magpie patrick said:

It's the older I'd probably question

 

Was the canal not built to service the mines, a decade or so before the S&W was built?  1761 was when they opened the four foot mine, the first of the Worsley Navigable Levels, and the Act for the S&W wasn't passed until 1766, opening in 1772.

 

10 minutes ago, magpie patrick said:

I think not being allowed in makes them un-navigable!

 

I think it's the Safety Elf that prevents it, well that and the width!  It's not navigable by the general public, but I'm sure I have seen videos of boats inside it doing inspections.

 

 

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2 minutes ago, TheBiscuits said:

 

Was the canal not built to service the mines, a decade or so before the S&W was built?  1761 was when they opened the four foot mine, the first of the Worsley Navigable Levels, and the Act for the S&W wasn't passed until 1766, opening in 1772.

 

I didn't word that well 

 

Of the claim that Dunsley is the oldest and the shortest navigable tunnel - it's the oldest part that I would question, I'm pretty sure there is nothing shorter, but there may well be something older

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6 minutes ago, magpie patrick said:

I didn't word that well 

 

Of the claim that Dunsley is the oldest and the shortest navigable tunnel - it's the oldest part that I would question, I'm pretty sure there is nothing shorter, but there may well be something older

Ah, I see!  I read it the other way round, obviously. :)

 

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29 minutes ago, magpie patrick said:

I didn't word that well 

 

Of the claim that Dunsley is the oldest and the shortest navigable tunnel - it's the oldest part that I would question, I'm pretty sure there is nothing shorter, but there may well be something older

I think the claim of ‘on the system’ means on CRTs infrastructure, in which case it’s probably true.

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1 hour ago, magpie patrick said:

When is in neither? I'm struggling to define the Scraggy Rock Arch on the Boyne - it isn't a bridge as it doesn't carry anything, it isn't really a tunnel as it's too short, although if it were it would be the only one on the Irish Waterways and on a river navigation to boot.

 

 

I can't find any reference to this.  I found a Scabby Arch on the Boyne.  It's an arch.  The clue is in the name.

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10 minutes ago, doratheexplorer said:

A bridge is built over something.  A tunnel cuts through something.  Length doesn't come into it.  A mile wide bridge is still a bridge.

That's what I thought but does Broad Street Tunnel in Birmingham cut through something...?

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4 minutes ago, doratheexplorer said:

I can't find any reference to this.  I found a Scabby Arch on the Boyne.  It's an arch.  The clue is in the name.

Don't trust Wikipedia - I'm working with Meath County Council and An Taisce - it's Scraggy Rock Arch.

 

Also, on the 1900 25inch map it's referred to as a tunnel

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13 minutes ago, doratheexplorer said:

A bridge is built over something.  A tunnel cuts through something.  Length doesn't come into it.  A mile wide bridge is still a bridge.

I think it's more subtle than that - especially for the historian

 

questions

 

was it tunnelled under a natural feature  -if so it's a tunnel

 

Is it a LOT longer than it's width and height? - if so it may be a tunnel (or possibly a culvert)

 

Is there much fill between the roof of the "tunnel" and the surface above - if the roof and the surface above are the same structure then it's not a tunnel

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26 minutes ago, doratheexplorer said:

A bridge is built over something.  A tunnel cuts through something.  Length doesn't come into it.  A mile wide bridge is still a bridge.

Firstly a tunnel is simply a subset of the wider group called bridges, as is a viaduct. In infrastructure management it’s generally the opposite. The purpose or construction is irrelevant and length is key as that’s the principle factor that defines the risk involved. On the UK’s railways a tunnel is nominally an overbridge of over 50 metres in length and a viaduct is an underbridge (and occasionally an overbridge) with more than 3 arches.

 

The purpose of the distinction is to define the inspection and maintenance regimes. A bridge is inspected and condition scored as a single entity whereas a tunnel is divided into 10 metre lengths for that purpose and a viaduct into individual arches.

 

The accountable engineer can ultimately decide which assets to classify as which according to their assessment of the risk (many motorway bridges are over 50 metres in length but managed as bridges not tunnels) which leaves the only givens as a tunnel ultimately has to be more than 10 metres long and a viaduct has to have more than one arch or span.

 

I suspect CRT have a similar system. With Dunsley the risk is it being partially unlined rather than its length. If it were fully lined CRT may consider it a bridge.

 

JP

Edited by Captain Pegg
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14 minutes ago, Rob-M said:

That's what I thought but does Broad Street Tunnel in Birmingham cut through something...?

Who knows.  Put simply, if what's above you is all man made, it's a bridge.  If what's above you includes solid rock, it's a tunnel.  I suspect Broad Street is a tunnel.

7 minutes ago, Captain Pegg said:

Firstly a tunnel is simply a subset of the wider group called bridges, as is a viaduct. In infrastructure management it’s generally the opposite. The purpose or construction is irrelevant and length is key as that’s the principle factor that defines the risk involved. On the UK’s railways a tunnel is nominally an overbridge of over 50 metres in length and a viaduct is a underbridge (and occasionally an overbridge) with more than 3 arches.

 

The purpose of the distinction is to define the inspection and maintenance regimes. A bridge is inspected and condition scored as a single entity whereas a tunnel is divided into 10 metre lengths for that purpose and a viaduct into individual arches.

 

The accountable engineer can ultimately decide which assets to classify as which according to their assessment of the risk (many motorway bridges are over 50 metres in length but managed as bridges not tunnels) which leaves the only givens as a tunnel ultimately has to be more than 10 metres long and a viaduct has to have more than one arch or span.

 

I suspect CRT have a similar system. With Dunsley the risk is it being partially unlined rather than its length. If it were fully lined CRT may consider it a bridge.

 

JP

You're defining it in narrow engineering terms.

15 minutes ago, magpie patrick said:

Don't trust Wikipedia - I'm working with Meath County Council and An Taisce - it's Scraggy Rock Arch.

 

Also, on the 1900 25inch map it's referred to as a tunnel

I haven't been on wikipedia.  I've been on fishing sites.  (not phishing sites!)

 

Do you have a link or a picture.

 

Google comes up with nothing for Scraggy Rock Arch.

13 minutes ago, magpie patrick said:

I think it's more subtle than that - especially for the historian

 

questions

 

was it tunnelled under a natural feature  -if so it's a tunnel

 

Is it a LOT longer than it's width and height? - if so it may be a tunnel (or possibly a culvert)

 

Is there much fill between the roof of the "tunnel" and the surface above - if the roof and the surface above are the same structure then it's not a tunnel

Yes it is.

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1 minute ago, doratheexplorer said:

Who knows.  Put simply, if what's above you is all man made, it's a bridge.  If what's above you includes solid rock, it's a tunnel.  I suspect Broad Street is a tunnel.

That theory doesn't work though where tunnels were constructed by cut and fill as it wouldn't be solid rock above.

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7 minutes ago, doratheexplorer said:

You're defining it in narrow engineering terms.

You won’t do it consistently in any other way and ultimately does it matter to anyone else other than the engineer responsible for its safety?

 

The overall point is that a tunnel on the canal network is ultimately defined as such for no other reason than CRT say so.

 

There’s no harm in a user defining it their way for their own satisfaction since it’s of no consequence, just be aware there will always be an exception to your rule. As I forewarned and is being demonstrated.

 

And anyway it’s not an engineering definition, it’s an asset management definition.

 

JP

Edited by Captain Pegg
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3 minutes ago, Captain Pegg said:

You won’t do it any other way and ultimately does it matter to anyone else other than the engineer responsible for its safety?

 

The overall point is that a tunnel on the canal network is ultimately defined as such for no other reason than CRT say so.

 

There’s no harm in a user defining it their way for their own satisfaction since it’s of no consequence, just be aware there will always be an exception to your rule. As I forewarned and is being demonstrated.

 

JP

It's of interest to all sorts of people other than engineers, including me.

 

Give me an example of an exception to my rule?

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16 minutes ago, doratheexplorer said:

It's of interest to all sorts of people other than engineers, including me.

 

Give me an example of an exception to my rule?

Gerrard’s Cross railway tunnel. 300 odd metres long of arched construction and earth fill above. Notorious for having collapsed during construction. Built over a pre-existing railway.

 

I know of loads of examples from experience which is why I know you will not succeed in defining it by construction or function. Been there, tried it and failed in possibly the only environment where it matters.

 

A better example may be the Metropolitan and District railways in central London. Excavated from the top down and built over. I think you’d be in a massive minority of engineers or normal folk who don’t consider them as tunnels.

 

I’ll add another that defies conventional definition, the immersed tunnel under the River Conwy on the A55. A tube laid on the river bed and covered with a protective earth bund. That’s a standard tunnelling method in the modern world.

 

JP

Edited by Captain Pegg
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Is this a tunnel or a bridge? It is on the Rouge Canal, just to the west of Nanjing, and was built circa 1390AD. There were originally two 'bridges' of sandstone left when excavating the cutting, though one collapsed later.

Rouge Canal.jpg

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24 minutes ago, doratheexplorer said:

 

I haven't been on wikipedia.  I've been on fishing sites.  (not phishing sites!)

 

Do you have a link or a picture?

See the caption - Holten has written the definitive work of the 21st century on the Boyne - I am not fit to lace his boots. I also have the O'Neil report of 1970 - arguably the definitive work of the 20th century on the Boyne Navigation. He also refers to Scraggy Rock Arch. Often it's just known as Rock Arch or Scraggy Arch. By your definition it's a  5 metre long tunnel 

20200709_095852.jpg

20200709_095858.jpg

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38 minutes ago, Captain Pegg said:

Gerrard’s Cross railway tunnel. 300 odd metres long of arched construction and earth fill above. Notorious for having collapsed during construction. Built over a pre-existing railway.

 

I know of loads of examples from experience which is why I know you will not succeed in defining it by construction or function. Been there, tried it and failed in possibly the only environment where it matters.

 

A better example may be the Metropolitan and District railways in central London. Excavated from the top down and built over. I think you’d be in a massive minority of engineers or normal folk who don’t consider them as tunnels.

 

I’ll add another that defies conventional definition, the immersed tunnel under the River Conwy on the A55. A tube laid on the river bed and covered with a protective earth bund. That’s a standard tunnelling method in the modern world.

 

JP

 

Galton Tunnels on the Old/New Main lines in Smethwick were built similarly to the Gerards Cross one

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