Grades 3–5 · Machines
How does a huge machine leave a finished tunnel behind it?
A tunnel boring machine does much more than make a hole. The shield machine shown here works through suitable soil while helping support the space it opens. A large cutting head at the front rotates and loosens material.
In the diagramA moving construction site undergroundSchematic earth-pressure-balance shieldLining ringsCutting headConveyorScrewSupported faceSoil travels outSupport, removal and lining are coordinated
Behind the cutter is a chamber containing excavated soil. Carefully controlled pressure in this chamber helps hold up the ground at the tunnel face. The strong outer shield surrounds the working area immediately behind it.
The loosened material, called spoil, must leave the tunnel. A screw carries it out of the chamber, and a conveyor transports it toward the surface. Removing material and advancing the machine are coordinated so that support at the face is maintained.
Behind the shield, an erector places curved concrete pieces into complete lining rings. The rings form the tunnel wall left behind as the machine advances. Other tunnel boring machines use different arrangements for different ground. Cutting, support, spoil removal and lining must work together for this remarkable moving construction site to make progress.
About this explanation
Starting knowledge: Understand a rotating cutter, a conveyor and a protective wall.
Sources
- Herrenknecht — Vienna Extension Metro Line 2
- Herrenknecht — Lyon Metro Line B