I am sure you are familiar with my fascination with underground tunnels etc – and you probably know that in addition to the obvious tube network and municipal services, that there are a fair number of other tunnels under the city.
Some are tiny lines built just below the surface and of no real interest – but there are some whoppers down there and obvious when you think about it, they are rarely named if you ask people to name the tunnels they think are under their streets.
BT have a large network of deep level tunnels which are human sized for their telecoms network – much of it built very deep during the cold war when BT was state owned as a protection against a nuclear strike on the city. The military have a few very old tunnels under Whitehall, and Thames Water famously built their huge ring mains around London in the 1990s.
What about electricity though?
Well, naturally there are cables running under the streets – but high voltage cables cannot be simply buried in a sub-surface structure, but have to be buried deep underground – and in large tunnels with the cables kept separate from each other to prevent overheating. The work on the Stratford site for the Olympics included one such sizeable tunnel to remove all the above ground electricity pylons. The pylons are being removed now that the tunnel is complete – although one will remain, as a visual marker for people to navigate by.
Anyhow – I was researching the recent deep tunnel construction behind Harrods department store recently (I bet that interested you!), and by accident came across reference to the Wimbledon-Pimlico tunnels dug by London Electricity in the early 1990s and been researching that. Some sort of write up might be forthcoming shortly.
I thought I would offer a teaser though – and here is a map from one report published by the Proceedings of ICE I have which shows the layout of some tunnels under the center of London built recently to carry electricity mains. These tunnels are nearly tube sized in width, so they are quite impressive in scale. Its a bit of a pity that they are so little known as they are a very significant engineering exercise.