Marc Brunel built the first tunnel under a river in the history of the world. Let me repeat that.
Marc Brunel built the first tunnel under a river in the history of the world. Ever. Impressive, no? (Well I think so, and so should you!)
They say the Assyrians dug an underwater tunnel in Babylon, but the Assyrians moved the River Euphrates out of the way, dug their tunnel, and then returned the river to its original course so that the tunnel ran underneath it.
It's odd to say Marc Brunel 'built' the tunnel; maybe I should say he 'dug' the tunnel. But many men had tried to dig a tunnel under the River Thames, and exactly for that reason, they had failed.
You see, the soil underneath the River Thames (or any river) is very soft. When you dig a hole underneath a river, the water creeps in and collapses it. If you've ever dug a hole in the sand at a beach, you'll know what I mean. The waves come along, and it's 'good-bye' hole. Just a bunch of soggy sand where your hole once was.
But Marc Brunel decided to BUILD a tunnel. Here's the best part: his inspiration was a VERY HUNGRY WORM!
While working in the Chatham Dockyard, Marc had observed a wood worm (teredo navalis) tunneling into wood. When teredo navalis burrows into wood, it digs with its head. It chews up the wood, which goes through its body and passes out the back end. So there's no danger of collapse, because the worm's body supports the hole as he digs. Quite a genius, that worm!
Marc Brunel thought the same. So he designed a tunneling device which would act like a giant worm! He would build a shield to support the earth as men dug through it, and the dirt they excavated would be made into bricks. While workers dug at the front end, other workers would brick the freshly-dug tunnel passage behind them. The bricks would support the tunnel and keep it from collapsing.
The idea of a SHIELD, to support the tunnel as it was being excavated, is still used today. Next time you travel on the Jubilee Line to Canary Wharf, or through the Channel Tunnel, you may want to give a little thought to Marc Brunel and the very hungry worm.
I'll write more about Marc Brunel and the Thames Tunnel soon. But that's all for now!