Giant Subway Tunnel Boring Machine [VIDEO]

If you've traveled anywhere in Europe, you've probably been exposed to the vast network of underground subway tunnels. But how are new subway tunnels built in highly populated and established metro areas?

That's where giant tunnelling machines by companies like Herrenknecht come in. These tunnel boring machines (TBM) are some of the largest earth moving equipment, built to handle the earth's pressure, and able to dig through the hardest stone underground to create new utility and transportation tunnels. While they're excavating, they also are laying the new segments necessary to create the tunnel.

Most of these underground tunnels are being built in Europe and Asia for increased mobility in large cities like Guangzhou and Rome. In Guanzhou, China, 76 Herrenknecht tunnel boring machines excavated more than 230km of tunnel through various layers of granite, sandstone, claystone, siltstone limestone, clay, sand, gravel, and marl to build new metro networks. At their peak performance, the boring machines were able to tunnel 48m per day and 691m in a month.

Here's another video from Herrenknecht with more details on exactly how these large tunnel boring machines excavate and lay new tunnel walls: