80 The Mole Machine-Low

The MOLE MACHINE FOCUS Question How do machines make tunnels?

The Mole: A Natural Digger What are the best tools for digging a tunnel? Moles are animals that have strong paws for digging tunnels. Their paws are like shovels. They push dirt out of the way. A molehill tells you that mole tunnels are under your feet. You do not see moles above ground very often. They live underground in the tunnels they dig.

Tunnel Time People make tunnels, too. Tunnels help people get from place to place. Earth has many mountains and many bodies of water. How can we move past these things to get where we need to go? One way is to dig a tunnel. We build tunnels under the water, through mountains, and even under cities! Train tunnels and sewer tunnels might run underneath your street. Wowser! Switzerland has the longest railway tunnel in the world. It is 57 kilometers (35 mi.) long.

Pick Your Place Some tunnels go through hard, dry rock. Others go through sandy or muddy places. Engineers study where a tunnel should be built. They study the ground and make a plan for digging into it. Making a tunnel is not like building things in other places. If there is a problem, the digging must stop. The workers must be kept safe.

Dig This! It is important to have the right machines when digging a tunnel. The first step is to dig a deep hole. Special machines carry the dirt out of the hole. A crane is used to move heavy things. A crane has pulleys to make the work easier. It has wheels and axles, too. The crane has a heavy bottom so that it will not tip over. The crane's long arm places the tunnel-boring machine into the hole. (The word bore means to make a hole.) The tunnel- boring machine is also called a mole machine.

Mole Machine A mole machine is much stronger than a real mole. The mole machine can cut through rock! The front part is the cutter head. Have you ever seen a cheese grater cut cheese? The cutter head cuts through rock as if it were cheese. Behind the cutter head is the shield. It protects the workers from flying rocks. The rocks are moved out of the tunnel after they are cut. As the mole machine digs, workers put up strong rings in the tunnel. The rings keep the walls of the tunnel from falling in.