Yesterday saw a plethora of headlines hit both the London papers and the web about the Jubilee Line, as it was revealed that closures would be required in order to allow work to address problems of acid damage to the tunnel wall segments along a 90m section of the line.

This is not a new issue, with the need for repair work having been identified for some time now. Indeed the “Baker Street to Bond Street Tunnel Reconstruction” project has been on both TfL and Tube Lines’ books since at least 2011, but the overrunning Jubilee Line signalling upgrades (with which relining could not be run concurrently) and the ultimate takeover and restructuring of Tube Lines meant that it is only recently that the project has begun to move forward in force.

The work will require a number of short closures on the line between Finchley Road and Waterloo over the remainder of 2013 and into 2014. The full list of closures can be found at the foot of this article, but they mainly follow the normal closure pattern used by the likes of TfL and Network Rail – total closure over the Christmas and Easter periods, coupled with late Sunday openings and isolated weekend closures.

Perhaps unsurprisingly, much of the press (and political) coverage has followed the now-traditional “transport chaos” pattern. The Evening Standard and Metro were arguably the biggest perpetrators of hyperbole, aided by a spectacularly misleading and uninformed quote from Manuel Cortes, head of the TSSA:

This is all we need. Now it’s the wrong sort of water. Jubilee line passengers and businesses served by the line have already suffered more than their fare [sic] share of disruption without more on the way.

Their fires suitably stoked, both papers led with “THE WRONG SORT OF WATER” with others, such as the Independent, following a similar theme (the Evening Standard also, rather oddly, seems to have opted with a photo which suggests the Jubilee Line has been unchanged since about 1979).

Coverage has also focused on the total cumulative closure time (approximately thirty days) rather the particular timing of them, something which again makes good copy but is something of a sleight of hand. Comments by a number of London Assembly members have also added to the confusion. Caroline Pidgeon’s question as to whether a block closure strategy had been considered was arguably a fair one, but veiled suggestions by herself and others in the Assembly that this work represents a failure to deliver on promises of an “end to Jubilee closures” was less fair – and, as with Manual Cortes’ comments – a case where those making such comments should really know better.

So with points political being scored, and hyperbolic headlines being written, it is perhaps worth us stepping back and taking a look at what the actual issue on the Jubilee is, and what will actually happen to fix it.

To do that we must at both the details that have already begun to surface about the project, and also take a brief trip into a rather fascinating (but largely forgotten) moment in the Northern Line’s recent past.

London: A City Built on Clay. Except When it Isn’t

It’s easy to think that London is a city, at least to the north of the Thames, built on very uniform ground. The key role that the rich deposits of clay to be found beneath our feet played in the construction of the Tube network is largely public knowledge. A relatively friendly (and non-fatal) material to tunnel through, particularly when you are just learning the art, its presence helped the Deep Tube take shape, and its absence limited progress south of the river Thames for some time.

As is the case with most things, however, the truth is more complex than it seems. General histories – and the beautifully coloured-in strata most LR readers will remember drawing in Geography classes – tend to imply a more strict demarcation between geological layers than actually exists in nature.

In reality, London is far more geologically diverse than one might initially think. Chalk and sand can all be found in layers beneath our feet and, as generations of Tube builders and workers have long discovered (sometimes at fatal cost), even the widest layers of clay can hold lenses of sand and imperfections.

A Certain kind of Chemistry

It is these discrepancies that make maintenance of the tunnels through which the Tube runs such an interesting exercise. Chemistry, like death and taxes, is something that cannot be avoided, and pushing a large iron tube filled with air through a diverse mix of subsurface elements and compounds can, over time, have interesting effects.

Although extensive details as to the cause of the acid problem on the Jubilee Line have yet to emerge, it seems likely that they are broadly similar to that discovered on the Northern Line at Old Street some years back.

In 1945, engineers noticed that a section of the Northern Line just south of Old Street station had begun to show signs of damage from sulphuric acid attack.

The cause of the acid attack, which affected both running tunnels wasn’t initially clear. The tunnel section continued to be monitored though, and when cracks began to appear in the tunnel lining in the 1960s London Underground began to further investigate.

What eventually became clear was that the geology of the Old Street area was far more complex than had previously been realised. Here, it emerged, a layer of London Clay met the Woolwich and Reading beds (composed of a mix of clay and sand). Between these two was a lens of sand, through which the Northern Line tunnels actually passed. Further analysis of this sand layer showed that it was full of iron pyrites.

For millions of years water, seeping down through the clay above, had come to rest in this sand and come into contact with these iron pyrites, with no effect. The arrival of the Tube, however, changed the chemical mix. Now, each time a train passed through the tunnel, minute quantities of air were forced out between the tunnel rings, this was something to which the wet pyrites had not previously been exposed, and they reacted with the air to produce, amongst other things, small quantities of sulphuric acid. Locked into the sand lens, like the water, over time this had built up and begun to attack the tunnel itself.

Although full details have yet to emerge as to the causes of the acid damage on the Jubilee, it seems likely that they are broadly similar to those that affected the Northern Line as well. As it was not until boreholes were drilled in the eighties that the problem at Old Street was fully understood, it is perhaps not entirely surprising that such issues have ultimately manifested elsewhere on the network.

Acid Damage on the JubileeAcid Damage on the Jubilee, as highlighted by Tube Lines safety notices for some time now.

To Block or Not To Block

Whatever the cause of the acid damage, the solution for the Jubilee will ultimately be the same as that taken for the Northern Line – where damaged, the tunnel will need to be relined.

It’s a simple answer, but one that requires a complex engineering solution. Although Caroline Pidgeon may have questioned why a block closure approach was not being sought, the fact is that on pure passenger numbers a process of short closures and work within engineering hours, if practical, will ultimately affect fewer passengers. For although much has been made of the disruption to businesses that might be caused by a loss of weekend and non-peak traffic, the reality is that the route of the closure is actually well served by alternatives where the key leisure destinations are involved, whilst preserving a more direct service for commuters is arguably more useful.

Indeed this was equally true for the problems at Old Street. By the late 1980s it had become clear that relining the Northern Line tunnels here was necessary and, even with lower passenger numbers on the network at the time, a similar decision was reached – short sharp closures would be less disruptive to traffic than one long closure.

Rethreading the needle

With the “what” and the “why” out of the way, we can thus finally turn to the “how” – how do you reline a whole section of running tunnel, in engineering hours, without disrupting or closing the whole of the line?

Sadly although we know where the answer to this question can currently be found, much of the detail remain unclear. The where, it appears, is beneath Charing Cross.

Possessing now-disused tunnels built to the same pattern as the rest of the central section of the Jubilee Line, Charing Cross presented a perfect test bed for the engineering solution. It is thus here, over the last few months, that engineers have been working to put together a machine that can carry out the relining process.

New ring replacement machinery at Charing CrossNew ring replacement machinery at Charing Cross

A view which gives a wider view of the processA view which gives a wider view of the process

So far, the pictures above represent our only guide to the process that will be used. It does appear, however, to be similar to that taken on the Northern Line, so we can arguably head back to Old Street once again to get some idea as to what the process is likely to entail.

Returning to Old Street

From the 1960s onwards, London Underground put into place various measures at Old Street to try and correct or mitigate the continuing problem of acid damage. In 1963 almost 2500 gallons of sodium hydroxide was pumped into the ground around the affected area to try and neutralise the acid. The sheer levels of acid in the area, and the composition of the surrounding earthworks, prevented this from being effective though.

Vertical metal strapping was added to affected tunnel segments to give them more strength, and for a time this seemed to be effective. By the late eighties, however, it was clear that degradation was still continuing, and a more permanent solution was required. Investigations into what such a solution might be began, and its need was further reinforced when drillings carried out as part of the investigations themselves caused further cracking to appear in a number of tunnel segments.

Strapping on the Northern Line south of Old Street in the 1960sStrapping on the Northern Line south of Old Street in the 1960s, note the evidence of acid damage at the bottom of the tunnel

Soon it became clear that the only solution was effectively to start again. The existing lining over a 90m section of both running tunnels would need to be entirely removed and relined, this time with chromium duplex steel segments designed to resist the acid build up (indeed the resulting order for 750t of chromium duplex steel represented the largest in the world at that time).

Examples of the new tunnel segments, stacked before installationExamples of the new tunnel segments, stacked before installation

In order to lay those new tunnel segments Underground engineers faced the same problem as those on the Jubilee do today – they needed the ability to get into the running tunnels, get set up quickly, carry out the work required and then vacate before trains began to run again. Accepting that it was impossible within engineering hours to both remove and replace a tunnel segment, they also realised that their supporting machinery would need to remain in place during regular running, and then be returned to during the next engineering period or closure.

The result was the creation of a custom tunnelling shield. This could be manoeuvred into place around the section that needed to be replaced, and would support the surrounding tunnel wall while replacement took place. During operating hours, the shield would be left in place and trains would run through it.

Moving the Shield into placeMoving the Shield into place

It was a clever solution to the problem, and the photos of the work currently underway at Charing Cross, along with the limited information that has emerged so far from TfL, seem to suggest a broadly similar approach will be taken with the Jubilee.

Moving the Mess

One luxury that those working on the Jubilee line will not have, however, will be in the area of spoil removal and site access.

On the Northern Line it was identified at an early stage that site access – both for people and material – would prove problematic, especially given the limited period in which work could take place. Luckily, however, there was a solution. Running parallel to the tunnel sections in question was a disused siding tunnel. By sinking a shaft in the car park of a nearby school and building a connecting tunnel, the siding could be accessed and used as an entry and exit point.

Just what solution to this problem will be found for the Jubilee remains to be seen. Both men and material will still require access, and a new more creative solution to this problem will thus likely be required.

More than just a soundbite

Overall, as can be seen from the above, the acid issues facing the Jubilee Line represent far more than just a simple niggling engineering issue, or an excuse for another soundbite or emotive headline.

If the previous experience on the Northern Line is any guide, they represent an enormous test of planning and engineering skill. Keeping a running railway working underground whilst relining the very tunnels it passes through is an incredibly complex task, whatever the full extent of the work turns out to be, and it’ll be interesting to see how the challenge of doing so is addressed.

“The Wrong Kind of Water” may make a nice headline, but it’s about as far off the reality as it is possible to be.

The Announced Closures

The closures announced for 2013 are:

  • Sunday 16 June and Sunday 6 October
  • Bank holiday Monday 26 August
  • Weekend of 12 and 13 October
  • Entire Christmas period 25-30 December
  • Three further Sunday — dates to be announced — when service won’t start up to 11 am.

The closures announced for 2014 are:

  • Sundays of 12 January, 15 June, 17 August and 16 November
  • Weekends of 1 & 2 February and 8 & 9 March
  • Saturday 1 March
  • Four-day closure at Easter 18-21 April
  • Entire Christmas period 25-30 December
  • Further 17 late start to services on Sundays
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There are 66 comments on this article
  1. Walthamstow Writer says:

    In a past life I read some of the reports on this problem and sat in on some meetings. As you say the pathetic newspaper headlines do not do the problem justice. This is a serious issue that has required a lot of mitigation effort and monitoring to keep Jubilee Line services running. It has to be fixed and cannot be left. It also requires specialist knowledge and resources to fix it – there are not many people in the tunnel engineering business.

    I was never party to the proposed solutions but I am not surprised by a phased approach. If you think about it you can’t just rip the tunnel shielding down, stick new stuff up and walk away. No one really knows what is going on on the other side of the tunnel sections and nor what could happen when the existing shielding is removed for replacement. It is also likely that when new tunnel sections are installed that the behaviour of the water will change – you only need to see what happens with water ingress in stations to know that. You fix the problem in one place and within days the water appears somewhere else. Therefore a phased approach with time taken to evaluate what is going on and that the chosen methodology is correct is very sensible. I am sure Ms Pidgeon would be the first person calling for “heads on a platter” if the tunnel collapsed and services were suspended for months.

  2. Dubidub says:

    Is it possible to know in advance or at build time where sulphuric acid is present and may pose to be a problem later, so that more appropriate materials can be used?

    The Jubilee is the newest tube line in London and already sections of tunnel lining needs replacing. Is a lifespan of about 40 years short for such a structure built in modern times?

    Will this be a problem on Crossrail in the future?

  3. Pierre Ketteridge says:

    Tut, tut… you append [sic] to the misspelt comment “suffered more than their fare [sic] share”, but let “with no affect” through.

    Fascinating insights into London’s geology, though. It’s amazing what the engineers of the past were able to achieve, both in the tube lines and the sewer systems, without the benefits of our later technological, chemical and geological knowledge, and of course, hindsight.

  4. Greg Tingey says:

    Use concrete segments?

  5. Alan Griffiths says:

    Excellent proposal, Greg. Everybody knows that concrete is resistant to acid.

  6. swirlythingy says:

    I’m no expert, or even a convincing amateur, but I think the Crossrail tunnels (and also the ones on the Jubilee south of Charing Cross) are made entirely out of concrete, with the only iron being in the rails. This probably doesn’t render them immune to sulphuric acid, though.

    Pedant’s corner:

    “To do that we must at both the details…” I think you accidentally the verb.

    “…with no affect.” Tut!

  7. stimarco says:


    The section of the Jubilee Line under discussion wasn’t part of the later extension works. It dates back to the 1970s. The DLR’s extension to Bank came later, so that’s arguably the newest underground railway in London. A 40-year lifespan is quite short compared to some tunnels. The expected design life depends primarily on the total budget, the materials chosen to line the tunnels, and the geology the tunnels are built through. For some, 40 years may well be considered acceptable, but there are tunnels under London that are much, much older.

    The ground beneath London is mostly soft and wet and its tunnels are an ongoing maintenance project. Water seeps in all over the network and is pumped out in vast quantities. Infrastructure like this will cost more in maintenance than it ever did to build. Contrast with cities like Stockholm and New York, where the most common tunnelling method involves explosives. Those two sit mainly on hard rock. (That rock is how New York City could build a multi-level station like Grand Central Terminal so many years ago: the surrounding geology was a key enabler. If NYC’s Grand Central Terminal had been built on, and in, London Clay, such a station would probably have been beyond the abilities of the engineers of the time.)

    What John Bull is saying, however, is that the very act of building tunnels below ground can change the chemistry of that ground, particularly around the tunnel itself. Most of the time, the changes are minor, but not always: during the early days of the deep-level Tube lines, 4th rail electrification was ultimately adopted as the standard as the 3rd rail electrification used on the earliest lines was found to cause electrolytic corrosion to the metal tunnel linings. This is an electro-chemical reaction. The Tube has retained its 4th rail system ever since.

    Back to the Jubilee Line remedial works: the air that escaped from the tunnel linings whenever a train went by slowly and gradually caused the build-up of that sulphuric acid. It wasn’t there originally. At the time the line was built, such chemical repercussions were still poorly understood.

  8. [email protected] says:

    “will ultimately affect less passengers”

    so the bigger ones won’t be affected?

    “its presence helped the Deep Tube take shape, and its absence limited progress south of the river Thames for some time.”
    I’ve often wondered about how much of a factor this is, compared with the pre-existence of extensive suburban networks south of the river – the Southern companies not having much in the way of coal or long-distance passenger traffic to distract them. Remember that the first two Tube lines both crossed the river, and indeed until the Central Line opened in July 1900, 75% of Deep Tube stations, and all of them outside the Square Mile, were south of the river. (King William Street, City (W&C) and later Moorgate being the exceptions, the other nine being Borough to Stockwell inclusive, Waterloo, and later London Bridge, Clapham North and Clapham Common)

    I had read of the electrolytic problems before, but the exposure of the rock to air causing oxidation is a new one.

    @Alan Griffiths
    Have there been any problems noted on concrete-lined sections?

  9. Philip says:

    And there’s another breathtakingly irresponsible and ignorant story on the front of the Standard this evening, with totally uncritical coverage of a demand by “business” for the tube to run all night, with no reference whatsoever to the reasons why NEW YORK IS THE ONLY CITY WORLDWIDE THAT CAN DO IT.

  10. Malcolm says:

    “Business” can have its all night trains – if “business” pays for them. Just dig a third tunnel (on each line), then one of the three can be taken out of service each night (or even day) for maintenance. Simple!

  11. Anonymous says:

    24/7 coverage will clearly never happen, but there is no reason why post-upgrade the tube cannot run over Friday and possibly Saturday night. A number of other European metro systems that are single track have managed it (Barcelona and Copenhagen spring to mind. Or is it Stockholm). To begin though, just running until 2-3am will be enough. Would be an excuse for Tfl to cut back on night bus services to combat the inevitable shrinking in subsides for that network after 2015.

  12. marko says:

    Besides the predictable coverage in the press, there was also the BBC news article – complete with sound-bit from Fat Bob and the RMT that appears on almost any story about the Underground.

    In it, the RMT complain that this issue is the result of maintenance cut-backs – something that very evidently not the case.

  13. Anonymous says:

    Very good article. As an engineer it annoys me hugely that this has instantly generated nothing but uninformed negative press and stupid rhetoric. The engineering challenges are huge and have obviously been in preparation for a long time resulting in innovative construction methods and the absolute minimum in disruption considering the task at hand. This should have been the message conveyed to the public by the press, not the usual suggestion of incompetence.

  14. Walthamstow Writer says:

    On the subject of late night running it was interesting to note Sir Peter Hendy’s remark that LU is already considering this for upgraded lines for introduction in 2015. I assume this is because upgraded lines, once bedded in, should require less maintenance attention which can be achieved during reduced engineering hours. The other factor, which we cannot escape, is the ability for the Mayor to “trumpet” this initiative come May 2016 – cynical, moi? 🙂

    I would not count on late night tubes allowing much reduction in night bus coverage. In fact it might make matters worse because people will demand more connections from outlying stations. When there was an earlier plan to introduce late night tubes TfL identified a large number of bus routes which would gain later departures up to and after the arrival of the revised “last tube”. This will simply put costs up and I doubt many night routes could be reduced in scale given they serve many areas that will not have tube coverage – e.g. N26, N38 and N73 may well serve Walthamstow (which a night Vic Line could replace) but the tube doesn’t serve Essex Rd, Newington Green, Stoke Newington, Dalston or Hackney. Some reductions might be feasible but you can’t trim things back too far without causing problems for nights when no late tubes would work.

  15. Anonymous says:

    The problem though is that Tfl are going face huge pressure to reduce the several million pounds worth of annual subsides in order to keep a decent supply of funds for capital investment. The environment is very different to when Tfl talked about later finishes before. They no longer have 10-year funding agreements for one (and the amount is lower on an annual basis).

    Of course, they could just rack up fares to £2 for an oyster single plus a similar relative increase for weekly passes, not to mention remove universal free travel for u-18s, but I’d imagine they’d prefer a mixture of fare increases and cutbacks. Nightbuses seem like an ‘easier’ target to me if the tube starts to run later. Either way, I suspect the level of service provision will drop after the next funding agreement is done post-2015.

  16. Anonymous says:

    Despite all the political rhetoric over the years about introducing a 24 hour tube service do we know the operating hours of Crossrail? It beggars belief that politicians who canvas votes with empty promises would allow a brand new “tube” – as the core will be – to be built that won’t work around the clock. If Crossrail isn’t four-tracked through the centre why not?

  17. Walthamstow Writer says:

    @ Anon 2218 – yes I know all about the funding pressures. I wrote up the last proceedings of the Assembly Transport Committee which covered this point in excrutiating detail. I am at the point of exhaustion from hearing “no money, austerity, no money” chants from Government I am afraid I just don’t believe it any more. It’s utterly ludicrous – the UK is one of the largest economies in the world with massive wealth.

    The problem with venturing into the realms of cuts to services is that it will simply not wash when faced with continued population growth, continued economic expansion in London and the resultant massive pressure on the transport network. Why would TfL cut any part of the transport network in any substantive way when the same TfL has stated that spare or new capacity is used up within weeks and Crossrail will be full upon opening? Politically it would be disastrous and we would we be back where we were years back when business moaned every month about how utterly horrendous the transport network was. We seem to have escaped those moans in more recent times as improvement has been delivered and reliability has largely stablilised. Does the Government and the Mayor really want us back in that era given the damage that would be done to our international reputation and our ability to attract inward investment?

  18. Anonymous says:

    On the subject of a 24-h tube – if Barcelona can do this, then why not London?

    I heard sometime ago that the tube ran for 24h there and only just checked it out – prompted by the article.

    Here are some of the details:

    Hours of operation of metro and tram
    Sun-Thu: 5am-0pm
    Fri: 5am-2am
    Sat: 24h
    24 hours also on January 1, June 24th, August 15th and September 24th. On December 24th, trains stop running at 11pm.


    So how is this possible? What are they able to do in Barcelona that we can’t seem to do here in London?

    I know nothing of how the tube runs there, and how this compares to London. But it begs the question of just how they can run the tube EVERY Friday until 2am, and then have a 24-h operation of the tube EVERY Saturday. Do they have three tunnels?

    I suspect the answer lies in knowing how local government works, how the local tax system operates, the local political parties committment to public transport etc.

    It seems that progressive political parties should be sending someone to Barcelona to find out how this is all funded and then coming back here and saying “This is how we do it”.

  19. The other Paul says:

    @Anonymous 10:31PM, 30th April 2013
    If Crossrail isn’t four-tracked through the centre why not?


    I kind of agree, 4 tracks would be nice and potentially give us both a metro and a regional/inter-city service through the core, with all night operation in the metro area. But doubling the amount of tunnelling and station platforms wouldn’t be cheap.

  20. Taz says:

    Back in the 1960s the Northern Line problem was put down to an ancient printery cess pit!

  21. DW down under says:

    @ ToP – agreed. Cost a lot more now, than if it had been approved during the early planning stages.

    Maybe XR2 should be designed around 3 running tunnels and 4 platform stations?

  22. stimarco says:

    @Anonymous (10:31 PM, 30th April 2013) & The other Paul:

    It’s _already_ four-tracked through most of the centre of London. Crossrail provides “express” services that complement the existing Central Line. It’s not following the Central Line route all the way, but the core is where there is most need for relief lines.

    Quadrupling the existing Tube lines would end up continuing the stupidity of retaining the custom-built toy trains currently in operation on the deep-level lines. It’s much better (and cheaper long-term) to build to industry main-line standards and avoid having to buy those expensive custom trains and equipment in the first place. Being able to get all your kit off the shelf from multiple suppliers brings both the one-off up-front capital costs and the ongoing, never-ending maintenance costs down. (Oh, and you get to fit air conditioning too.)

    Even CR2 will, to all intents and purposes, provide a similar pair of ‘relief’ lines for the Victoria and Piccadilly through central London. Most of the debates over it have been about where the ends of the tunnelled section should be, but that it’ll be a roughly SW-NE alignment has never been in dispute.

    The multiple lines to Dartford are an echo of a similar approach to adding capacity to an existing route, as are the Catford Loop and, to a lesser extent, the “cut-off” line from Brixton to Beckenham via Penge East. Each was originally intended to provide an ‘express’ line for long-distance services, while the stoppers trundled over the older lines.

  23. MikeP says:

    Were cuts to services to be brought in and have a serious impact on travelling in London, businesses wouldn’t just be furious about the effect on their operations. They’d be asking very loudly exactly what they were getting for the £4.1bn they ‘re putting directly into Crossrail ( ). Because Crossrail isn’t, as we all know, some sort of stand-alone railway. It has to work with the rest of the system. If that gets broken, Crossrail’s useless too.

  24. Anonymous says:

    I understand Crossrail “shadows” the Central through the core but will that mean Crossrail will run 24 hours most days and on those nights it’s closed for engineering works the Central will suddenly have a 24 hour service stopping at the interchange stations to compensate? I doubt it. My point is politicians always pledge a 24 hour tube yet it seems they’ve allowed Crossrail to be built without provision for 24 hourrunning. I understand the difficulty of not being able to increase services through 100 year old + tunnels but on a service due to open in 2018? Not exactly the envy of the world!

  25. ASLEF shrugged says:

    The politicians can pledge and business can demands whatever they like, the simple fact is that the Tube needs “engineering hours” between switching the “juice” off and switching it back on again to carry out inspections and maintenance. From 2015 LUL intends to run an hour later and then open an hour later the next morning at weekends on all lines apart from the Piccadilly where Heathrow want the early trains.

    We only ever run all night on New Year’s Eve but that is only possible because we run a severely reduced service the next day as staff are restricted by law as to how many hours we can work and breaks in between shifts. If we were to run all night on Saturday it would mean drastically cutting back on Sunday services and maybe closing come stations. If we were to run on both Friday and Saturday nights you’d need a lot more staff, not only on trains but also on stations where “Section 12s” have minimum staffing levels. With engineering hours reduced you’d also need more staff to cope with the workload.

    With LUL currently facing at a £12bn funding shortfall I don’t think anyone is going to be prepared to hire the extra staff.

  26. ngh says:

    Soon it became clear that the only solution was effectively to start again. The existing lining over a 90m section of both running tunnels would need to be entirely removed and relined, this time with chromium duplex steel segments designed to resist the acid build up (indeed the resulting order for 750t of chromium duplex steel represented the largest in the world at that time).

    For the non specialist engineers out there Chromium duplex steel = high strength stainless with good resistance to acidic corrosion mechanisms (but not high temperature oxidation or chloride corrosion mechanisms etc.)

  27. aussie sheila says:

    @Anon 11:03, Barcelona doesn’t have 3-track tunnels. Saturday night 24 hour operations were introduced at the behest of politicians, and as their TfL equivalent is a public company their costs are presumably included in the subsidy. I’m amazed that given the extensive service cuts in Spain the Saturday night running is still in place. They also have more automation than we do in London (line 11 is driverless and lines 9 and 10 are unattended).

    Regarding night running on post-upgrade lines, a key requirement for being able to operate shuttles on one track whilst maintaining the other is whether the signalling system is set up for bi-directional working. I believe that the new CBTC systems procured under the PPP are not, whereas those procured directly by TfL are (although I would happily be told I’m wrong about that).

  28. Anonymous says:

    Aslef: I take on board and agree with all your points about the current tube network but my point is regarding Crossrail which is a brand new operation. If New York 100 years ago could build a subway system that works 24 hours a day surely Crossrail in 2018 should do the same? I’m not suggesting drivers or platform staff work longer hours, I’m suggesting you build this into the system: enough staff, enough trains and enough room to perform engineering works safely while services continue. I know it all comes down to money but I think it’s amazing that newspapers quote politicians and business organisations who call for 24 hour tube running but don’t ask those same public figures why they happily signed off a brand new modern subway system that will probably run to the same operational hours as its 150 year old cousin.

  29. marek says:

    @ Anonymous, 12:59

    Perhaps because operating hours are not a free good, and each successive hour is more expensive than the one before. So the questions are:

    a. what are the initial investment costs which would produce a railway capable of operating without regular breaks in service, over and above what is currently planned?

    b. what are the recurrent costs of maintaining a railway without requiring breaks in service, again, over and above the costs for what is current planned?

    c. what benefits accrue to whom as a result of extended service hours?

    d. what additional revenue would result from extended service hours?

    If c > a + b the case for doing it would be strong. But is, as seems more likely, c is relatively small and a and b are relatively large it would be odd to do it at all.

    And even if c were large, that still leaves the revenue problem. Unless d > a + b, which seems vanishingly unlikely, whatever wider social benefits which might have been captured by c will need to be turned into hard cash somehow. I somehow don’t see the casino owners quoted in the Standard article queuing up to recognise this as a cost of their business model, and I certainly don’t see it as the highest priority for additional subsidy funding (even if there were any to be had).

  30. JM says:

    Great article.

    Firstly this quote in the Standard did and still is bugging me

    ‘Simon Thomas, owner of the Hippodrome Casino in Leicester Square and a member of the West End Commission said: “It would be great if Transport for London got themselves organised so they can run through the night on Friday and Saturday — the maintenance could be condensed on the other nights. We need transport infrastructure that does what the city needs not just what is practical for Transport for London.” ‘

    Applying the same kind of logic, I’m sure plenty of uninformed people not involved in the night time entertainment business could come out with the same rhetoric about getting yourself organised so revellers don’t engage in anti-social behaviour at chucking out time.

    Given some of the quotes attributed to people, is there any scale of stakeholder consultation so that members of the LA, unions, West End Comm, London First etc may not rush to go public with these qoutes and stigmatise the whole project?

    The NL must be due more disruption than this in the next 6 months alone, this is a complete non story in terms of disruption to the public.

    That said, I do think caroline Pidgeon has a point. As someone hugely affected by the Central Line closure in 2003, I do think some bulk closures can be justified with good planning where there is good local access to other lines, temporary bus routes and anything that can help mitigate. I know the numbers are vastly inferior to most London routes but interested how in the Oldham/NE Manchester effect of Metrolink (line closed for slower yet more intensive service) taking over the rail service worked.

    Re 24 hour operation.

    Given how busy some night bus routes are at very short frequencies (25 prime example), I always think there will be too much demand to have bi-directional working, if not straight away, then within a few years.

    Surely a useful short term measure could be the introduction of limited stop night bus routes stopping at tube line stations alone akin to Rail Replacement buses. Not practical for all part of all lines but would be an improvement on the N5/N20/western end of N98/N11 now which can leave quite tedious journeys using lots of bus stops that probably don’t justify a 24 hour service.


    Agree quadrupling tube tunnels is hard to justify if you start having various Crossrails to deal with day demand and doing it purely for 24 hour service that could realistically only be justified 3 nights a week max doesn’t seem like vfm. Agree more useful might be larger tunnels/longer trains/linear motor tubes in the much longer term.

    This is probably an over simplified question but could doubling the maintainance personnel on the tube have a like for like effect on the required time to maintain it?

  31. Simon says:

    Did you actually read the Independent article? It was an entirely drama-free, objective report of what the union guy and a politician said.

  32. John Bull says:

    Did you actually read the Independent article? It was an entirely drama-free, objective report of what the union guy and a politician said.

    ..with a big whopping headline about the “wrong kind of water” which was my point.

    That aside, if you’re going to copy and paste press releases, at least pick accurate ones to work off of, or do some background research.

  33. Anonymous says:

    “The NL must be due more disruption than this in the next 6 months alone, this is a complete non story in terms of disruption to the public.”

    I think the issue is the Jubilee has had several years of closures which dwarf what’s happened on the NL since last year. That being said it’s being blown out of portion hugely because a) the number of total weekend closures is not that many; b) it’s a much smaller section of the line than previous closures, a section which is broadly paralleled by the Met and Bakerloo.

    On block closures, Tfl have done them before on the w&c line, part of the h&c line and part of Wimbleware no? Maybe the jubilee simply has too many passengers, the Met wouldn’t cope from Finchley Road.

  34. Greg Tingey says:

    Alan Griffiths
    SNARL – Concrete is LESS vulnerable to acid attack than steel, shall we say?
    Or had you not considered that simple possibility?

    Yes, cynical – you’ve moved to Walthamstow & it goes with the territory, actually (especially if you have anything to do with LBWF ….. )
    “Cuts” the real problems are the internal inefficiencies in both public & private “enterprises”. IF you could bear down on those … like all the “middle management” most of whom should have been sacked yesterday at the latest ….

  35. JM says:

    @Anonymous @4.42

    Would argue the significant stretch of traffic is that south of the river round to the wharf from experience and might well remain unaffected. Commuters to the west End from Kent/Sussex who may change at London Bridge still have Charing Cross/Bakerloo/Northern as access to the west end.

    Commuters to and from west London can use the DLR at Bank/Monument.

    Not altogether certain from memory how far west and east (or north and south) from Bond Street you can turn trains around though.

  36. Anonymous says:

    “Not altogether certain from memory how far west and east (or north and south) from Bond Street you can turn trains around though”

    presumably Waterloo and Finchley Road, since those are the stations between which the line will be closed (trains from the north can be reversed at Charing Cross, if the obstruction is between Green park and Waterloo)

  37. Anonymous says:

    Just to clarify – if the acid is being produced due to contact with air – can the joins between metal segments be welded after assembly to stop air getting through the gaps – or is it a case that it’s too late and the surrounding ground is now full of acid and it will all need replacing again at some point in the future?, or is it the case that small air gaps between the outside of the tunnel and ground it is being driven through start the chemical process anyway? and where the Austrian tunnelling method is used does that eliminate the problem?

  38. JamesC says:

    This is an ongoing issue that not only affects tube lines. The transport infrastructure of the entiree uk is ageing and going tonneed serious investment to keep running over the next 30-40 years. Examples of this are the many concrete bridges that were built in the 60’s that are showing signs of internal corrosion of the reinforcing rods (A4, and A40 for example)

    This sort of womrk is something we are all going to need tonget used to over the coming decades, and its going a cost a lot as well.

    As for relining the tunnels in this case the decision between fererous based linings and concrete is a dificult one with numerous factors to figure in which indoubt anybody here has access to, and will include factors like the soil content of trace elements, alkalinity of surounding soils, the actuall strength of the acid seeping in and how thisnwill react with other chemicals in the soil, and most importantly the load it needs to take as if the concrete needs reinforcing this will involve introducing ferous metals into the mix again which cound infact make the situation.

    Looking around the network itts easier to see other areas where corrosion is occuring due to seepage, London Bridge Jubilee station is a prime example, with lime deposits and rust clearly visible on the inside of the steel lined tunnels. I doubt anybody really wants to know whats going on on the other side!

  39. Anonymous says:

    I agree with your evaluation. However, it looks like your keyboard is suffering from corrosion.

  40. peezedtee says:

    This article needs the following corrections:

    “with no affect” should be “with no effect”

    “will ultimately affect less passengers” should be “will ultimately affect fewer passengers”

    “much of the details remain” should be “most of the details remain” (or alternatively “much of the detail remains”)

  41. Fandroid says:

    Concrete tunnel segments can be made to resist many of the environmental chemicals out there. Even in the old days there was sulphate-resistant cement. However, I think it is almost certain that any concrete segment used in a rail tunnel is going to have some form of reinforcement. There is now the option of fibre-reinforcement. Steel fibres have been used, but I understand that the HS1 tunnel linings were reinforced with polypropylene fibres. I have had a quick look at Crossrail items on the web, but haven’t found anything that reveals the reinforcement used.

    Any steel reinforcement used can be of an appropriate specification to resist corrosion.

  42. answer=42 says:

    … alkalinity of surounding soils,…
    surely, in this situation, simply deploy Greg?
    But then I’m no engineer.

  43. John Bull says:

    Thanks Peezedtee – corrected.

  44. Mike Horne says:

    Returning to the original subject of Jubilee Line acid erosion, I gather from a former LU engineer on another group I’m a member of (Geoff Virrells) that the section of tunnel affected by acid comprises unbolted cast concrete segments held in position entirely by the compressive force of the clay. This being the case, the job of replacing segments by bolted stainless steel segments is a very different proposition to anything that happened on the Northern Line and requires all kinds of special equipment to expand the rings to allow segments to be removed. Bear in mind such segments are keyed into the adjacent rings, an obvious thing to do during construction, but not a method conducive to removing segments later on. How joints are made between the new segments progressively going in, and the old ones about to come out, should be quite interesting.

    Perhaps someone familiar with this section of line could confirm segment type. I believe them to be 600mm wide with an internal ring diameter of 3810mm.

    I suppose it is worthy of note that, as far as we know, the northbound tunnel, in similar ground, is unaffected.

  45. Greg Tingey says:

    Yes, the closeness of separation yet a difference ….
    Tunnellers always have to watch for this, there’s a classic historical example: Kilsby tunnel L&B Rly.
    There, it was known, from the previous canal tunnel, that there might be a problem with water/quicksands inside the hill, so they carefully drilled quite a lot of trial bores from the surface.
    And missed the water-bearing volume by approximately a metre on each side!

  46. Graham Feakins says:

    @ Mike Horne – You make an interesting comment. My guess is that the concrete lining segments on the original stretch of the Jubilee Line were designed and supplied by C. V. Buchan Limited.

    At the time of construction, the segments had mating profiles which were indeed keyed in such a way that, once joined together along the length of the tunnel and around the tunnel ring, it was impossible for them to be disconnected without structural destruction. One version (from 1992) is here, as illustrated in a patent application:

    If you explore look too far, you’ll discover that I was the author of that patent specification!

    Some versions incorporated seals to ensure prevention of ingress of fluids from outside the tunnel. As you say, the concrete segments were cast, with no internal metal reinforcement and the technique was first used on the Victoria Line.

    In fact, having visited one of Buchan’s manufacturing site’s in the 1980’s and inspected a stand-alone prototype tunnel lining set up with several segments, it is apparent that the connections between segments do not rely on the compressive force of the surrounding clay as such. Once joined together, they hold together. Remember that the tunnel bore was not entirely compressive when constructed and grouting had to be used to fill gaps behind the segments. Of course, the segments were thrust out onto the clay during actual construction of the tunnel.

  47. Anonymous says:

    Mainly aimed at Mr Anonymous 24 hours.
    ” If New York 100 years ago could build a subway system that works 24 hours a day surely Crossrail in 2018 should do the same?”
    As stated above, the geology of New York made excavation easier, back in the 19th century when navies were cheap and expendable it was easy for them to build four lines for not much more than the price of two.

    In London, with its difficult soil conditions, in 2013 with expensive labour, each additional tunnel is a lot more difficult to dig. 24hr running on Crossrail isn’t happening because it would have involved at least three tunnels, which means 50% more tunnelling and bigger stations. Given that we only just got funding for two tunnels, after 18 years of funding squabbles, perhaps you can see why it won’t be 24 hours.

    It wasn’t a choice between 2 tunnels and 3 tunnels. It was a choice between 2 tunnels and 0 tunnels.

  48. Sleep Deprived says:

    @ Graham Feakins
    The design was not by C. V. Buchan Limited. I’m afraid to say that they also do not resemble that shown in the link you provided.

    On the Crossrail front, I remember listening to a talk in the past that stated Crossrail being mentioned in the national transport plan as far back as 1946! As much as we may gripe about some limitations with the existing scheme, I am glad we are getting a scheme which will achieve so much!

  49. Graham Feakins says:

    Sleep Deprived – You are right but I thought it might have been Buchan’s predecessors, Leonard Fairclough. Others in the field were Halcrow’s and Charles Haswell. Charcon and Edmund Nuttall were also in the field. Now you’ve got me looking!

    I only used the Buchan patent to show an example of how the segments could be held together but a good, illustrated description is to be found here from page 17 describing the tunnel linings for the Victoria Line:

    It is likely that same or very similar was used on the Jubilee (Fleet) Line.

  50. Sleep Deprived says:

    @ Graham Feakins
    To save you looking, they were designed by Halcrow and I believe that they were not too dissimilar to the Victoria line linings shown in the attachment you link to.

  51. Fandroid says:

    For those unbolted tunnel segments which interlock with each other, there is normally a narrow wedge-shaped segment rammed in from the direction of the TBM. Pushing this wedge into place then effectively expands the whole ring onto the surface of the clay. Grout is pumped in behind the rings to take up any unevenness in the cut surface and to reduce later ingress of water. The next ring to be assembled then pushes up against the broad end of the wedge so fixing it in place.

    Dismantling those rings can be achieved by cutting up a wedge. Once one ring is dismantled, the wedges in each subsequent ring are more easily got at and removed.

  52. DW down under says:

    @ Sleep Deprived. The plan was the result of work that was commissioned during WW2, looking at what would be needed when “peace broke out.” So it has its origins as far back as 1944. (Source: Rails through the Clay)

  53. Tom Burnham says:

    It’s a while since I was involved in the cement industry, but I believe sulphate-resisting cement is no longer made in this country – nowadays ground blastfurnace slag or power station coal ash are added instead. These react with surplus lime released when the cement sets and make the concrete less alkaline than it would otherwise be, and so not so prone to acid attack. Having said that, it’s difficult to make concrete that can withstand sulphuric acid for decades. Also, the concrete is always at least slightly permeable, so acid can gradually soak through and attack the steel reinforcement. When this corrodes, it expands and cracks the surrounding concrete, allowing more fluid to enter, and so on…

  54. Anonymous says:

    From (subscription required), citing LU’s Head of Tunnel Engineering:

    “The focus of the work is on replacing a 200m section of concrete lining between Baker Street and Bond Street stations dating from the 1970s.”

    “The primary cause of the damage was clay shrinkage in the ground around the tunnel.”

    “While work to replace the concrete linings is underway, London Underground will also carry out repairs to cast iron linings in an adjacent section of the same tunnel to the south. ‘We will be using a gel grout to create an airtight seal between the flanges of the cast iron lining to prevent air leaking from the tunnel and reacting with the naturally occurring groundwater and pyrite in the surrounding ground.'”

  55. DW down under says:

    Anonymous @ 05:45PM, 23rd May 2013: Thank you for that info. Answers my question on what steps were being taken to hermetically seal the new lining to limit the extent to which the problem is perpetuated.

  56. Graham Feakins says:

    @ Anonymous 05.45PM, 23rd May 2013 and ALL – Here is the full article from “New Civil Engineer” as publicly available online by using a mild ‘trick’, simply via a well-known search engine:

    “Engineers ramp up Jubilee Line tunnel repair effort

    23 May, 2013 | By Claire Symes

    Engineers were this week ramping up efforts to head off a worsening structural problem on a section of London Underground’s Jubilee Line, NCE can exclusively reveal.

    Engineers ramp up Jubilee Line tunnel repair effort

    Final testing is underway to prove the concrete lining replacement that London Underground (LU) is to use to repair a damaged section of the southbound tunnel.

    The focus of the work is on replacing a 200m section of concrete lining between Baker Street and Bond Street stations dating from the 1970s.

    LU has built a specially designed train to carry out the replacement work and the overrun tunnel at Charing Cross has been used for testing and training before the main work starts.

    The repairs will be undertaken during engineering hours and 31 day closures of the line over the next 18 months, Transport for London announced at the end of April.

    The primary cause of the damage was clay shrinkage in the ground around the tunnel, LU principal tunnel engineer Keith Bowers told NCE. Other factors, including probable issues with the quality of design and construction, are thought to have worsened the problem.

    Bowers said that there was evidence that during construction of this section there was a failure to properly align joints between the 22-segment expanded concrete rings. This meant they were stepped in places.

    “About 10 years ago we started to notice concrete spalling and a few years later tension cracks was recorded,” he said.

    Inspection routines were stepped up, monitoring was installed and remedial repairs involving the use of steel straps and the removal of loose concrete was undertaken to allow the section to remain in use.

    “The cause is complicated,” he added. “For three decades there were no problems, but the damage has increased in the last 10 years.

    “The depth of the tunnel is a contributing factor and means that the ground loads are high – up to 220t/m – which is one a half times the load of other zone 1 tunnels.

    “The design of the segments with a curved edge means that the joints are vulnerable unless they are perfectly aligned. The [mass concrete] segments were made as small as possible to avoid the need for using reinforcement. If not well aligned, the stress concentration moves to the edge, which has caused the spalling.”

    The affected section of tunnel was built in the 1970s, using a mix of cast iron and concrete segments. According to Bowers, the decision to use concrete on this section was driven by the need to avoid the use of more costly and time consuming cast iron bolted segments. Variable ground conditions were another influencing factor.

    “The alignment of the southbound tunnel was driven by the need to pass under the Bakerloo Line and as result this section of tunnel on the Jubilee Line is one of the deepest in zone 1, reaching depths of up to 36m,” said Bowers.

    “This depth takes the tunnel out of the London Clay and into the Lambeth Group, which is highly variable with sand beds within the clay. It is also faulted.”

    According to Bowers, the same design has been used elsewhere on the Tube network but both tunnels – one in an overrun tunnel at Charing Cross and another at Heathrow airport – are in London Clay and at shallower depths.

    “It is the lining design in combination with the depth and construction issues that have contributed to the problems on the Jubilee section,” he said.

    “The real trigger for the problems has been the shrinkage of the clay surrounding the tunnel. The lining is permeable and the process of driving trains through the tunnel over the last 40 years has warmed the ground.

    Cores taken show that the first 500mm beyond the tunnel is quite desiccated.

    “This is a problem that is only going to get worse, which is why we are taking action to replace the concrete with new cast iron segments.

    “We started testing the solution by hand in 2010 and built the train wagon to speed up the work and reduce the manual handling.”

    The selection of cast iron to replace the damaged sections has been driven by the need for a modular solution with plenty of redundant capacity to cope if the ground conditions continue to deteriorate with further clay shrinkage.

    Training in the repair method is continuing but enabling work on the section between Baker Street and Bond Street section has started. The first lining is expected to be replaced in late June.

    While work to replace the concrete linings is underway, London Underground will also carry out repairs to cast iron linings in an adjacent section of the same tunnel to the south.

    “We will be using a gel grout to create an airtight seal between the flanges of the cast iron lining to prevent air leaking from the tunnel and reacting with the naturally occurring groundwater and pyrite in the surrounding ground,” said Bower.

    “The reaction has resulted in the formation of sulphuric acid that has caused damage to the linings and the gel grout will prevent the need for the linings to be replaced.” “

  57. DW down under says:

    Thanks indeed, Graham F. So now we see, there are two separate problems on that stretch of track.

    1) The unreinforced concrete linings where they have become misaligned, are starting to crumble; and

    2) Further along, acid has been corroding cast iron segments due to the action of passing trains aerating groundwater and triggering a reaction with endemic iron pyrites.

    Both are to be resolved by rebuilding the lining in cast iron with a gel grout to hermetically seal the lining and hence reduce if not eliminate the air-water-iron pyrites-acid-corrosion sequence problem.

  58. Greg Tingey says:

    Tom Burnham 14th May
    I thought you could mix additives in to concrete at the mixing stage to render it waterproof?
    Or does that simply lower the permeability by a large amount?

    The copy of the article is fascinating stuff.
    And yet again shows up the difference between the engineering & management sectors of LUL in terms of competence ….
    I wonder how much gel grout they are going to inject, & how deep (far from the tunnel walls) they expect to push it.
    Is the intention to, effectivel;y, encase the tunnel in an impermeable gel layer? I’m assuming that the gel will set over time, creating a thin shell – rathe like a rubber glove, or (ahem) a “protective”.

  59. stimarco says:

    @Greg T.

    The problem is, making cement water-resistant (known as “hydraulic cement”) doesn’t automatically make it acid-resistant too. It’s possible to create some forms of cement that can resist certain damaging fluids, but concrete linings alone aren’t enough to stop the problem here. They don’t provide an airtight seal.

    From an engineering standpoint, the problem here isn’t the acid, it’s the creation of that acid. Every time a train passes through the tunnel, it’s blasting air from inside the tunnel out into the groundwater and pyrites. The resulting chemical reaction is where the sulphuric acid is coming from. That acid wasn’t there before the tunnels were built.

    The correct engineering solution is to fix the cause of a problem, not its symptom. The sulphuric acid is a symptom.

    The cast iron rings will replace the old concrete segments, but that’s not the solution to the underlying cause. The solution is that gel: Its purpose isn’t to stop the acid getting in, but to stop the air inside the tunnel getting out and creating that acid in the first place. So, yes, it’s basically a giant ‘rubber’, but not a rubber glove—the latter is used to keep undesirable substances out, not in!

  60. DW down under says:

    @ Greg T. The article did mention fracturing of the surrounding material up to 500mm from the lining. One presumes that this would represent the maximum, and actual would vary from ring to ring.

  61. Walthamstow Writer says:

    Rail and Tube Panel paper and presentation of the Jubilee Line tunnel relining works.

  62. Greg Tingey says:

    How do you FIND these things on TfL site?
    Their search engine is useless – & when I look for the other useful section ( “corporate” ) that can’t be found, either?
    Tips would be appreciated

  63. Greg,

    Go to TfL Website. Go to bottom and the left column. Select Publications and Reports.

    When in there it is often useful to filter by Category “Committee and Planning Meetings”.

    The ones you should be really interested in are:

    Board Meetings
    Rail & Underground Panel
    Finance & Policy Committee
    Surface Transport Panel

    As stated in an article, Finance & Policy Committee is much more interesting than it sounds. Documents for the meeting are published a few days beforehand. Make a note in your diary for around 7 days before the next one is due and be first with the news.

    Also on the last page of Publications and Reports is the link to the Working Timetables. There are other ways of getting to these but this is the quickest as you can go straight to the last page where they are.

    Note: Might not work too well on an ancient web browser.

  64. Walthamstow Writer says:

    @ Greg – PoP has very kindly saved me a lot of typing having provided clear instructions. I don’t diarise when the meetings are but I check back every so often and this week just happens to have two sets of Panel papers being uploaded. TfL’s commitment is to put the papers up 7 days before the meeting. Things like revised TfL Budgets, Business Plans, Annual Reports all tend to have fixed times in the year when they’re dealt with but external events like elections or Autumn Statements can also trigger changes.

    I maintain a series of spreadsheets on things like the Budget numbers and forecasts, actual modal usage per period, bus network costs and bus network patronage so I have numbers and changes in numbers to hand or available quickly. I find discussions work better when you can present facts or calculations rather than “wavy hand” guesstimates.

    While I agree TfL’s search facility is hopeless the website isn’t that horrible to work your way round but I confess I’ve used it a lot so have learnt where things are. One issue I have is that previously valuable info and documents tends to get booted off the website when a project has finished. That can be incredibly irritating if you want to research something or simply double check your understanding. A project archive with the supporting papers and presentations that were previously published should not be beyond the wit of TfL IM although I recognise there will be a file storage and administration overhead. Just seems a shame that so much good stuff just gets binned and probably breaks links on other blogs and websites as a result. Losing history of events will not do the future any favours.

  65. Greg Tingey says:

    Many thanks
    Both of you

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