Milepost 31 kids

Milepost 31 for kids: How to make a tunnel turn

Crews aboard a massive tunneling machine named Bertha are building a two-mile-long bored tunnel beneath Seattle. They do this by installing one large concrete ring at a time. When the project is complete, the 9,270-foot tunnel will be made up of about 1,426 individual tunnel rings. Not only do these rings become the outer wall of the tunnel, but the way they are placed helps “steer” the tunnel.
 
How? We’ve created a video for kids that explains with a hands-on activity.