Part of the Jubilee Line is to be closed between Finchley Road and Waterloo for repairs over the next two years due to acid eating into the tunnel linings.

Predictably, lots of wailing about woes and doom from rent-a-quote politicians who, had the last  election taken a different turn, would now be explaining how these are necessary and unavoidable.

Also a snarky headline from the Evening Standard about the wrong sort of water. In fact acid erosion is a common problem in London.

However, those with longer memories (or a penchant for tube history), will know that acid erosion of tube tunnels is not an unusual thing, and neither is the replacement of tunnel linings.

In fact, its a well tried method.

You may recall that in 1991, a section of the Northern Line needed repairs for exactly the same problem. Around 90 meters of tunnel lining had to be replaced just south of Old Street station as it had suffered from attack by sulphuric acid — or Oil of vitriol as I still prefer to call it.

It was in fact the tunnel itself that caused the introduction of oxygen into the soil, and started the chemical process of converting soil based pyrites and water into an acid.

The solution then was to replace the grey cast-iron linings with larger diameter acid resistant linings made from cast duplex stainless steel. The works were carried out at night using a special shield, through which the trains passed during the day.

That project took six years from initial concept to completion, including more than four years of research and design, a precasting contract for the linings and finally nine months of installation works.

They were however exceptionally lucky to have an abandoned tunnel right next to the works site, which helped immensely with storage of materials and equipment, and may go someway towards explaining why the work was able to be compressed into 9 months, when the Jubilee Line works will take longer.

So, despite the inconvenience, the replacement of rusted tunnel lining rings is itself not an unusual or unexpected thing to happen in London’s water logged soils.

Off on a totally different, but vaguely related issue…

The original “northern line” was much smaller than the current tunnels, and was widened in the 1920s. When the Old Street tunnel linings were replaced, they were also slightly, wider as well, mainly as it was easier to work that way.

When pondering the issue of overly hot tube tunnels, one of the biggest problems is that heat has built up in the clay surrounding the tunnels and cannot absorb any more surplus heat.

It struck me some time ago, that using long-proven tunnel widening techniques, and an unlikely to arrive pot of cash — a tunnel such as the Bakerloo Line could have its 100 year old tunnel linings replaced and at the same time, significantly widened.

The multiple benefits being new tunnel linings of course, but also you cut out a metre or so of surrounding soil and effectively cart away several decades of heat in the skips overnight. An inner lining is added to preserve the “air-piston” effect of the trains passing through, but over the years/decades, the linings are all slowly replaced with wider ones.

In the long term, you widen the tube tunnels to mainline train sizes, so that over a fairly long time frame, there comes a point where the Bakerloo Line can have a massive capacity upgrade in the form of larger trains.

Pie in the sky I know — but not technically impossible.


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One comment
  1. N Ridge says:

    1) I think you will find that “oil of vitriol” refers only to concentrated sulphuric acid – the stuff with a red label that is kept well locked up. The naturally generated stuff will be much weaker, but still pretty good at eroding cast iron.

    2) To enable “full size” trains to operate means opening out the nominally 12′ diameter tunnel to 16′ – this means removing as much spoil again as was taken out for the original construction. I would suggest that a more efficient ploy would be to extend the station tunnels to accommodate longer trains.

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