INTERVIEW | KEITH BOWERS
machine can last the distance then there are actually very substantial advantages in just running a single system. It is less intensity of work, less capital cost. Very importantly there is substantially less carbon as well. So there are a lot of boxes that you can tick. “And ultimately you focus your team
on running one machine, not two, which has to be a less stressed task at the end of the day.” Slightly related to that, one of the early
discussions he was involved with in the Silvertown tunnel was deciding whether to construct it as a bored tunnel or an immersed tube. “That was interesting. I had two periods
Above Graphic of SCL tunnels at Bond St station, London (LU new tunnels in yellow, Crossrail new tunnel in blue)
want to get on your brand-new sensitive electronics. So you have a clean, dry, sealed-off space underneath the road deck where you can start fitting out the power supplies and the transformers and the cabling for lighting and control systems and ventilation fans. “So that’s a really good example of how
we can actually get really tangible benefits from the very large size of the bore. “The diameter also means that the
user experience will be quite different to those in old and generally rather cramped tunnels. The intent is to create an environment where there is free- flowing 70 mile an hour traffic in three lanes; it would be much closer to what you would experience on the open road, which is very different to what we have at the current crossings. There are safety considerations as well:
if
there’s an accident in one lane, it is more manageable when you still have two lanes working and more space for emergency services to get there. “We shall be using a single TBM which will drive both bores. Two TBMs in parallel was an option we discussed for a while; it is the safer, more conservative assumption for planning but when we brought the contractor on board they were always clear that they saw advantage in doing this with one machine. Distance is key here: our distances are sitting in the middle, close to the tipping point. Each bore is four kilometres so the
38 | February 2026
...THE LARGE DIAMETER DOES START TO GIVE US SOME REAL OPPORTUNITIES TO DO THINGS A LITTLE BIT DIFFERENTLY.
total drive is 8 kilometres, and in principle 8 kilometres is perfectly doable with a modern machine. And obviously for us it briefly pops out into daylight halfway through when it finishes the first bore and is turned round for the return, so you get a good chance to look at it and maintain it at half time. “On balance we concluded that a single
machine offered a number of advantages. Clearly it will take slightly longer to drive one machine there and back than it would take to drive two side by side but that’s not the only consideration. The intensity of the work, the service these machines demand because of their size, the rate of spoil production, the demand for electricity consumption - all those sort of things are very, very large here. And obviously if you do two machines side by side you have to do twice as much as of all of that. You need a slurry treatment plant that is twice the size just for starters. “So when you when you work it through, if you are confident that one
of close involvement with Silvertown and that was the earlier one, around 2014. Transport for London’s planning service had been developing the project but it had effectively become stalled because of that issue. At the time my role strictly was with London Underground rather than with TfL” [The former deals with the metro, the latter with buses, trams and the entire transport network] “and so in a sense I was outside the camp that was developing the scheme directly so they asked me for an outside view. “The way we did it was by establishing
an industry panel of suitably skilled people. We had a little group of eminent names, both from contractors and consultants, plus me from a client, and we did a review of the whole thing. It wasn’t a totally straightforward decision but in the end it was a clear recommendation that we gave. “If you look around the world, a lot of
estuary and river crossings are done in immersed tubes. One of the fundamental reasons is because an immersed tube is inevitably shallower which means that your portal ramps at either end can be shorter. So they take up less land and you can start them much closer to the riverbank or even build them out into the estuary and thus reduce the length of your tunnel. Therefore they cost less. “But with Silvertown a couple of big
factors negated that. One was that the route on the Greenwich side was always going to go underground across the peninsula to have its portal over near the Blackwall approach road. It was never going to be close to the riverbank, so you couldn’t get the advantage of a shorter tunnel. “The other factor was essentially environmental. The riverside obviously
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
