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Tunnels are never boring….

by AprilSix Proof

Picture the scene. Midday on Thursday 11th December. I’m in a mostly-empty building on Dean Street, awaiting the start of a safety briefing. I’ve just been handed a bag of high-vis clothing, a pair of steel-toe boots and a hardhat. This was no ordinary Thursday. This was the day I’d get to visit the Crossrail tunnels at Tottenham Court Road station.

When not at Proof, I can be found working on my first popular science book, called “Science and the City”, due for publication by Bloomsbury Sigma in 2016. This book will be an introduction to some of the science, engineering and technologies (SET) that keep our cities moving, and, looking at current research, will suggest how tomorrow’s skylines will look. It’s basically my scientific love letter to the great cities of the world!

Anyway, part of the writing process involves conducting lots of interviews with experts from across a range of sectors – I’ve been lucky enough to speak to the Bill Baker (Chief Engineer of the Burj Khalifa) and Ron Slade (Lead Engineer on The Shard). A few weeks back, I spent several hours with the Chief Engineer of the Crossrail project, Chris Dulake, talking about all things tunnel-related. At the end of our meeting, Chris invited me to visit the tunnels myself. And this is where I found myself last Thursday.

Crossrail is Europe’s largest construction project, which aims to deliver a high frequency, high capacity train service from Reading in the west, to Abbey Wood in the east. To do this, two 21 km long tunnels have been dug under central London, threading their way through a packed subterranean world. Currently, over 10,000 people are working on the project, across over 40 construction sites. This truly is mega engineering.

Key to Crossrail’s success has been their eight tunnel boring machines (TBMs) each weighing in at 1000 tonnes. Churning though London clay at the rather impressive rate of 100m a week, they have now almost completed their task. To give you some perspective on that rate; it took Brunel 16 years to dig the original Thames Tunnel whereas Crossrail’s new ‘Thames’ Tunnel took just 8 months.

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Figure 1: Red circle shows the tunnel excavated by the TBM (diameter: 6.2 m). Blue circle shows the approximate diameter of a platform tunnel, with sprayed concrete lining (diameter: 9.5 m)

Bored tunnels are one thing, but to build the much larger platform tunnels, you need more than just a TBM. You need concrete, and lots of it!

Crossrail use their fibre-reinforced concrete in a rather interesting way – they spray it! The process involves rapidly spraying newly-excavated ground with concrete to stabilise it. Then a layer of waterproofing material is sprayed on, followed by a second, thicker layer of concrete, reinforced with glass fibres. A final layer of glass-reinforced concrete is added to act as fireproofing, and the permanent tunnel lining is complete. All of this is laser-scanned continuously throughout the process, to ensure the layers are evenly applied.

Needless to say, I had an incredible time wandering around under London with engineer Andy Alder. I learned a lot about the materials and the structural engineering that goes into a tunnelling project. It will help me hugely as I move through the writing process – sometimes it’s nice NOT to be the expert!


While writing the book, I’ll be writing regular blog posts to give you a sneak preview, so keep an eye on @ScienceAndCity for updates.

If you have any questions please email me at or tweet me at @laurie_winkless.