Railways floated across bogs - current engineering issues

[adamedwards]

I was just watching the new Man at Seat 61 video of the Fort William sleeper. At Rannoch Moor the line was constructed by floating it over the boggy land, as is also the case at Chat Moss on the Liverpool - Manchester line (and possibly other places I am not aware of). This prompted some questions I hope the expert engineers on the forum can answer:

• Over the years of adding more ballast on top, how deep does such a formation go, or is the ballast removed and replaced like track elsewhere?
• The original brushwood at the bottom of the formation is presumably now well into the boggy layer, but does it still survive, undecomposed, as the bog preserves organic material? Assuming yes, does it still retain the weight bearing qualities requried? (I am assuming yes as otherwise we'd have been hearing about track being dug out.)
• Have any of these locations reached the bottom of the bogland, due to added material pushing everything down to something more solid (rock?) underneath?
• Are current climate change issues like higher rainfall at some times of the year and drought (so drying out) at other times of the year causing issues (as we have dramatically seen with embankments collapsing)?

Many thanks in advance for the responses.

 

[Magdalia]

and possibly other places I am not aware of

A significant issue here in the Fens.

Are current climate change issues like higher rainfall at some times of the year and drought (so drying out) at other times of the year causing issues

Yes. Long speed restrictions between Waterbeach and Ely, and between Littleport and Downham Market were imposed in the drought last summer, necessitating imposition of an emergency timetable.

The same happened in the 1976 drought, notably between March and Whittlesea, when journey times were extended by 20-25 minutes. In those days the trains just ran late.

 

[fandroid]

Wasn't the Chat Moss line electrified relatively recently? That must have thrown up some engineering challenges with the foundations for the masts.

 

[Magdalia]

Wasn't the Chat Moss line electrified relatively recently? That must have thrown up some engineering challenges with the foundations for the masts.

This is also an issue in the Fens. There was a dewirement at Littleport on 5 January 2012 where one of the main causes was movement of OHL mast foundations combined with a high wind.

 

[306024]

A few years ago now, but one of the best presentations I ever saw was from a Network Rail engineer who was seeking additional possessions between Ely and Peterborough in order to maintain the track to standard, and prevent serious TSRs. The issues involved were fascinating.

This link, although not railway orientated and too long to quote, gives an insight.

https://www.greatfen.org.uk/about-great-fen/heritage/holme-fen-posts

 

[Magdalia]

A few years ago now, but one of the best presentations I ever saw was from a Network Rail engineer who was seeking additional possessions between Ely and Peterborough in order to maintain the track to standard, and prevent serious TSRs. The issues involved were fascinating.

This link, although not railway orientated and too long to quote, gives an insight.

https://www.greatfen.org.uk/about-great-fen/heritage/holme-fen-posts

It has railway relevance though. The Holme Fen Posts are less than a mile from the ECML, which crosses Holme Fen on the 2 track section just south of Peterborough. The challenges of maintaining the railway there are why that section has never been quadrupled.

 

[306024]

It has railway relevance though. The Holme Fen Posts are less than a mile from the ECML, which crosses Holme Fen on the 2 track section just south of Peterborough. The challenges of maintaining the railway there are why that section has never been quadrupled.

Indeed, it's fascinating (to me!) and why I always enjoy travelling towards Peterborough, however boring others think it is.

 

[GRALISTAIR]

Wasn't the Chat Moss line electrified relatively recently? That must have thrown up some engineering challenges with the foundations for the masts.

There are picture somewhere. Some of the concrete bases on Chat Moss were christened by some on this board as TGBUs - Thundering Great Big Uns

 

[LNW-GW Joint]

Wasn't the Chat Moss line electrified relatively recently? That must have thrown up some engineering challenges with the foundations for the masts.

If there was any special treatment it wasn't obvious.
Before electrification there was a long 60mph PSR over maybe 5 miles straddling Astley crossing, and 75mph elsewhere.
The new setup has a much shorter 60mph limit close to Astley, with the 60mph being raised to 75mph to the east of that and 90mph to the west.
The line was relaid at the time, but the only special measures I noticed were some enormous gravity pads (concrete blocks) for a number of mast foundations, and deep piles - most of the rest of the route had concrete foundations.
It's never been clear to me whether the present short 60mph PSR at Astley is because of ground conditions or for the crossing itself, which leads to farms in the moss south of the railway.
I can't recall any TSRs denoting issues over the moss, it seems a pretty reliable section these days.

HS2 was intended to cross Risley Moss (south of the CLC alignment) on the section towards Golborne, but that prospect has receded with its exclusion from the Crewe-Manchester Bill going through parliament.
That route will also cross peaty areas of Cheshire, not to mention brine salt workings.

 

[adamedwards]

A modern verstion of all this exists on the A414 at St Margarets in Hertfordshire where the road was built on polystyrene blocks to spread the weight on a spongy flood plain.

 

[Ploughman]

On the NYMR you have Fen Bog at the line summit.
That is built on sheep fleeces and sticks reportedly, undertaken by someone called Stephenson..
Plus many years of top up ballasting, with the latest fix trying Geocell and other membranes.

 

[WesternBiker]

The embankments of the Bristol-Taunton line across the Somerset levels seem to have been relatively stable over the years, despite being over marshy ground and being formed simply of the material excavated from the side ditches. The same cannot be said of the many over bridges on this section, 22 of which settled/subsided (and 4 even collapsed) soon after construction: the original brick arches were replaced in many cases by timber (later replaced by iron/steel spans) to allow for a degree of movement. There's a fascinating research paper on the subject here.

I'm less familiar with the construction techniques of the later GWR cut-offs between Castle Cary and Taunton which do see a lot more flooding on the adjacent levels.

The minor roads adjacent across the levels do seem to suffer badly during dry weather.

 

[Annetts key]

Speaking of which, in the very late 1980s/very early 1990s, BR apparently used polystyrene blocks and lightweight concrete blocks when building some of the new station platforms to spread the weight on poor ground. For example Worle (Wikipedia mentions just lightweight construction- see here).

The station at Worle was developed as a joint initiative between British Rail and Avon County Council. It cost £700,000 and was built using lightweight construction materials due to being sited on marshy ground.

 

[InOban]

From what I've seen on this forum, polystyrene blocks seem to standard practice on new platforms.

 

[Ploughman]

Also to be found in Embankments running up to Bridges.
Recall Irlam as one example.

 

[MisterSheeps]

Not exactly related to decay of submerged wood or sheep fleeces, but relevant to crossing bogs, I did read that the OLE masts on Chat Moss had to be linked to the track, not sure how, because as an electric train moves there is a standing wave ahead of it, and not doing so would cause the pantograph to lose contact with the contact wire

 

[D365]

It has railway relevance though. The Holme Fen Posts are less than a mile from the ECML, which crosses Holme Fen on the 2 track section just south of Peterborough. The challenges of maintaining the railway there are why that section has never been quadrupled.

Is this not still an eventual aspiration? Proposal for full four-tracking north of Huntingdon seem to come and go every five years.

 

[Magdalia]

Is this not still an eventual aspiration? Proposal for full four-tracking north of Huntingdon seem to come and go every five years.

I think it is only an aspiration for people who haven't thought about how they might actually do it.

 

[matchmaker]

A modern verstion of all this exists on the A414 at St Margarets in Hertfordshire where the road was built on polystyrene blocks to spread the weight on a spongy flood plain.

Also on the M80 at Auchenkilns - the road is on piled foundations.

 

[zwk500]

I think it is only an aspiration for people who haven't thought about how they might actually do it.

ISTR it's been mentioned before that it got very close at previous modernisations. Presumably if it was possible to do it for one pair of 125mph tracks, it's possible to do it for another pair of 100mph tracks. The cost/benefit is always going to be a problem though.

 

[Mcr Warrior]

To what extent are railways through locations such as Chat Moss and Rannoch Moor built on top of seemingly "bottomless bogs"?

Presume there must be some point at which firmer ground is reached? How far down are we talking? Thirty foot depth? Fifty foot? More?

 

[zwk500]

To what extent are railways through locations such as Chat Moss and Rannoch Moor built on top of seemingly "bottomless bogs"?

Presume there must be some point at which firmer ground is reached? How far down are we talking? Thirty foot depth? Fifty foot? More?

Chat moss is quoted as 25- to 30-foot depth on Wikipedia.

 

[Mcr Warrior]

Chat moss is quoted as 25- to 30-foot depth on Wikipedia.

Thanks. Deep enough but not bottomless?!

Presume partly floating the line across the bog at Chat Moss was a cheaper and more practical solution than bringing in and tipping in wagon loads of suitable material from somewhere else, although one source has a Chat Moss contractor as doing exactly this, and reputedly still not finding the bottom after three months.

 

[zwk500]

Thanks. Deep enough but not bottomless?!

Presume partly floating the line across the bog at Chat Moss was a cheaper and more practical solution than bringing in and tipping in wagon loads of suitable material from somewhere else, although one source has a Chat Moss contractor as doing exactly this, and reputedly still not finding the bottom after three months.

Not bottomless but when a horse is the most powerful machine you have to use it's still a blooming big problem. A railway is approximately 8m wide across a 2-track formation, or 24ft. so 30x24foot = 720 cubic feet of material required for every foot of linear line length. c.4.75miles of line crosses the Chat Moss, or c.25,000 feet.

 

[Taunton]

The embankments of the Bristol-Taunton line across the Somerset levels seem to have been relatively stable over the years, despite being over marshy ground and being formed simply of the material excavated from the side ditches. The same cannot be said of the many over bridges on this section, 22 of which settled/subsided (and 4 even collapsed) soon after construction: the original brick arches were replaced in many cases by timber (later replaced by iron/steel spans) to allow for a degree of movement. There's a fascinating research paper on the subject here.

I'm less familiar with the construction techniques of the later GWR cut-offs between Castle Cary and Taunton which do see a lot more flooding on the adjacent levels.

I have commented here before about how the original Bristol to Taunton line (engineered by Isambard) has stood up well for about 180 years, whereas across the fields the Castle Cary line, with all the advances of being built in the 20th century, has been nothing but trouble ever since. It was an unending source of weekend overtime for the Taunton pw team, and countless wagonloads (that should probably be quarryloads) of ballast went in for decades. About once in a generation some civils leader from HQ gets a budget to provide a "once and for all" solution there (same as at Dawlish). Those seem not to work either.

 

[The Planner]

It's never been clear to me whether the present short 60mph PSR at Astley is because of ground conditions or for the crossing itself, which leads to farms in the moss south of the railway.

Its the crossing.

 

[Ploughman]

Not bottomless but when a horse is the most powerful machine you have to use it's still a blooming big problem. A railway is approximately 8m wide across a 2-track formation, or 24ft. so 30x24foot = 720 cubic feet of material required for every foot of linear line length. c.4.75miles of line crosses the Chat Moss, or c.25,000 feet.

Don't forget that while it may be 8m wide at the surface, it will be a lot wider at the base.
Spreading out in a rough ratio of 45 degrees varying with depth.

 

[WesternBiker]

I have commented here before about how the original Bristol to Taunton line (engineered by Isambard) has stood up well for about 180 years, whereas across the fields the Castle Cary line, with all the advances of being built in the 20th century, has been nothing but trouble ever since. It was an unending source of weekend overtime for the Taunton pw team, and countless wagonloads (that should probably be quarryloads) of ballast went in for decades. About once in a generation some civils leader from HQ gets a budget to provide a "once and for all" solution there (same as at Dawlish). Those seem not to work either.

Fascinating: the 1906 GWr cut-off line was partly built on the original Taunton-Yeovil branch line (around 4-5 miles I think), which was both doubled and raised (to reduce flooding). I wonder if this section gave greater or less trouble than that entirely constructed from new? (One could conjecture that adding to an original single-track branch line might produce more problems if that original wasn't built to main-line standards.)

There's also not much depth of peat closer to the coast (if any - it's alluvial clay, albeit still close to or below sea level), whereas I'd expect the area further inland to have more depth of peat, which is always likely to be troublesome.

 

[Old Yard Dog]

Sad to see the final demise this year of the extensive network of Bord Na Móna peat harvesting trains from Ireland's bogs. I believe some of the locos have gone elsewhere for preservation - but are there plans to preserve any of these lines in situ as heritage railways?

 

[Taunton]

Fascinating: the 1906 GWR cut-off line was partly built on the original Taunton-Yeovil branch line (around 4-5 miles I think), which was both doubled and raised (to reduce flooding). I wonder if this section gave greater or less trouble than that entirely constructed from new? (One could conjecture that adding to an original single-track branch line might produce more problems if that original wasn't built to main-line standards.)

There's also not much depth of peat closer to the coast (if any - it's alluvial clay, albeit still close to or below sea level), whereas I'd expect the area further inland to have more depth of peat, which is always likely to be troublesome.

The section which incorporated the Yeovil branch is the part adjacent to the River Parrett, which was grossly prone to flooding at Langport West station, down the branch and thus not rebuilt. The thoughts of the gangers at Taunton was the whole 1900 main line over The Levels had indeed still been built about 5 feet too low, not only for physical flooding but also to install effective drainage under the tracks and over the winter water table (it's quite variable here between winter and summer). The news pictures from some years ago of an HST amid extensive floodwaters was on exactly this stretch, it is actually the worst bit. Train timer Cecil J Allen once commented, on reviewing his various speed logs over time, how often there was a permanent way check on this section. You can see what was raised at, for example, Athelney level crossing, which is a substantial hump in the road.

Up and over at Athelney ...

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There's nothing to prevent a major railway being built across such wetlands, as practice elsewhere clearly shows - otherwise there would be no railways in much of Florida.

In passing the M5 motorway, which closely parallels Brunel's original line from Weston to Taunton over this ground, built in the 1970s, also had major subsequent problems with subsidence, and had to be substantially rebuilt after about 10 years. Its substructure was originally done with a large number of trainloads of fly ash from power stations, Aberthaw in South Wales and others, which were hauled in by double-headed Class 37 for a considerable period during construction, to special sidings near Highbridge. I think they used different material in the rebuilding. I wonder if Mr Brunel was laughing ...