How are tunnels dug?
Worm Through Stone
How are tunnels dug?
You've probably walked through a tunnel — maybe under a busy street or through a mountain. But how do you even start digging a hole that big? Someone has to go first, chewing through all that rock and dirt. Let's follow the machines that do the job.
For a long tunnel, engineers bring in a tunnel boring machine — a TBM. Picture a enormous steel cylinder as wide as a house, lying on its side. The front end is a giant rotating disc covered in teeth. Those teeth are the hardest cutting tools humans make, tougher than the rock they're about to eat.
