Text version of the Specialised TBM diagram

A specialist TBM

The specialised TBM will combine two types of TBM technology into one machine, allowing tunnel builders the flexibility to adapt to different ground conditions as the machine progresses.

Both these two technologies keep the pressure inside the chamber the same as the pressure in the ground outside to control the excavation process:

• Earth pressure balance mode
  Uses a screw to conveyor and valve to control the pressure by reulating the amount of spoil in the machine. Used for rock conditions.
• Slurry mode
  Uses pipes and fluid to control the pressure in the machine by turning the excavated material into a slurry and pumping it out. Used for sediment materials

Numbers outlining diagram:

1. Material excavated into pressurised chamber
2. Slurry mode: Fluid pumped into chamber to mix with spoil to form a slurry. Screw conveyor sealed off in slurry mode
   Earth pressure balance mode: Spoil picked up by screw conveyor then transported onto conveyor belt
3. Slurry pumped out to surface to remove spoil from fluid
4. Conveyor moves rock through the machine and out of the tunnel behind it
   Concrete ring segments delivered to the ring building area
5. Concrete ring is built by putting together the segments using a special vacuum lifting device
6. The gap between the concrete ring and the rock is filled with grout - this helps keep water out of the tunnel
7. When complete, the ring is connected to the previous ring
8. The machine moves forward about 1.7 metres then the process starts again