Chunnel… Get it? It’s Channel + Tunnel

So this was originally supposed to be one of our podcast topics (haven’t listened to us yet? Click here!) but good ol’ technology let us down and the recording cut out about 4 minutes into the show. Don’t worry, you’ll be able to learn everything about the Chunnel that you ever wanted to know in much less time by reading this.

I’m sure we all know what the Chunnel is to some extent, but let’s start from the top. It is one of the biggest engineering projects ever undertaken in the UK, and I suppose France as well. It took over 5 years of construction time and more than 13,000 workers to make it happen and has been named one of the 7 modern wonders of the world. Pretty impressive!

Although only opened on May 6 or 1994, the idea for the Chunnel dates back to 1802 when Albert Mathieu of France proposed the concept, but for horse drawn carriages, with an island in the middle where you could swap out horses for the rest of your voyage. Not until the 1980’s did a useful plan start to form, where a number of ideas were kicked around like a 4.5km suspension bridge, a road enclosed in a tube, a drive-through tunnel, and today’s high-speed rail link. Obviously, the rail won out (seems like a solid choice) and for just $14.7 billion of today dollars or so (up for debate), the project was complete.

As amazing as it sounds, surveying for this project started in the early 1800’s, establishing the seabed depth at a maximum of about 55 meters (180 feet for those of you like me). Additional surveying continued through the years, helping to understand the terrain, in particular finding the best rock strata through which to dig. At about 25-30 meters deep (90’ish feet) a layer of chalk marl was found, ideal for tunneling since it has a clay content of 30-40%, making it impermeable to water! What luck!

A total of 11 boring machines were used to create the Chunnel (5 on the French side, 6 on the English). These machines could be a post on their own, so how about just some fun facts about them?

  • Weight – 12,000 tonnes (more than the Eiffel Tower)

  • Length – Longer than 2 football fields

  • Cost – One sold for 40,000,000 pounds in 2004

  • One of these machines got stuck and left under ground

  • The soil deposited on the English side created an extra 90 acres of land

Something I didn’t realize, which I probably should have, is that the Chunnel is actually 3 tunnels, not 1. This means there are 2 tunnels for trains to pass through, and a third that acts as the service tunnel. The service tunnel was always being created ahead of the other tunnels, acting as a pilot / exploratory effort. It is now also doubles as an emergency escape tunnel, being kept at a higher pressure in case of a fire (which there have been 3 of, but none serious enough to close things down).

With the tunnels created, all that is left is laying down the track and providing power. A Low Vibration Track (LVT) was chosen for this project as it is a cost effect option, reduces wear and therefore part replacement. It is held in place by gravity and friction, as well as being reinforced with 100kg concrete blocks every 60mm. The power is delivered by an overhead line at 25kV, keeping things going and helping provide you with wifi on your trip!

Now that the Chunnel is finished, up to 400 trains pass through each day, carrying an average of 50,000 passengers, 6,000 cars and 54,000 tonnes of freight per day! Want some more fun facts?

  • Shuttle trains are 775 meters long

  • It takes 35 minutes to pass through the Chunnel

  • In 2009, 4 trains broke down stranding 2,000 people for 16 hours

  • When digging finished, the tunnels coming from both sides were only 300 millimeters off course

So that is everything you need to know about the Chunnel to have an intelligent conversation with your friends. Well, maybe not intelligent, but a conversation none the less. If you have any questions, want to point out something we missed, or just want to say hi, make sure to reach out to us at UnprofessionalEngineering@gmail.com.


Originally published on Unprofessional Engineering. You can view the original here.



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