In Tokyo and other big cities, underground space is used for all kinds of things, from subways and shops to the gas, water, and power lines that bring us the basic things we need for daily life.
A shield tunneling machine seen from the side. (C)Taisei Corporation
In the past, tunnels had to be hollowed out from ground level, and this cost a lot of time and money. Today, however, tunnels can be dug much more efficiently thanks to cutting-edge machines made in Japan. These "shield tunneling machines" dig an underground route by pushing against the soil, boring a hole through the soil, and strengthening the tunnel walls as they move forward. Much less time and money are needed to build a tunnel this way, and the work is safer, too. Japan’s shield tunneling technology is the most advanced in the world. Japanese machines are so precise that they can build two tunnels for different subway lines separated by a wall just 1 meter thick.
The shield tunneling machine has blades at the front and builds a wall as it turns and digs out the earth. It also hardens the wall with concrete as it goes.