Tunnel boring machines (TBMs) work by excavating tunnels through various geological formations in a controlled and efficient manner. Here’s an overview of how a TBM operates:
Setting Up the TBM: The TBM is assembled at the launch site, usually at the entrance of the tunnel. The machine is positioned on the rails or tracks that guide its movement through the tunnel alignment.
Rotating Cutting Head: At the front of the TBM is a rotating cutting head equipped with cutting tools. The type of cutting tools and their arrangement depends on the geological conditions the TBM will encounter.
Shield and Tunnel Lining: The TBM typically has a shield or front-end structure that surrounds the cutting head. Behind the shield, precast concrete tunnel lining segments are placed. These segments will be installed as the TBM progresses to create the tunnel’s final lining.
Excavation Process: As the TBM advances, the cutting head rotates and excavates the material in front of it. The cutting tools break up the rock or soil, which is then loosened and transported to the rear of the TBM.
Spoil Removal: There are various methods for removing the excavated material, depending on the TBM type and the ground conditions:
Conveyor Belt: In some TBMs, a conveyor belt system transports the spoil to the rear of the machine, where it is then transported out of the tunnel.
Slurry Transport: In soft ground conditions, a slurry TBM can be used. It mixes the excavated material with a slurry (a water and bentonite mixture) to create a slurry flow that carries the spoil to the surface through pipes.
Earth Pressure Balance: Earth Pressure Balance TBMs use the excavated material to create a paste-like mixture, which is then removed and transported away.
Tunnel Lining Installation: After a section of tunnel is excavated, the precast concrete tunnel lining segments are installed. These segments fit together to form the tunnel’s inner lining, providing structural support and preventing collapses.
Advancing the TBM: The TBM advances continuously or in increments, depending on the project requirements and geological conditions. The process is repeated as the TBM bores deeper into the ground.
Monitoring and Control: TBMs are equipped with various sensors and monitoring systems to ensure safe and precise tunneling. These systems track the TBM’s position, monitor ground conditions, and manage parameters like pressure and speed.
Maintenance: Regular maintenance and inspections are crucial to keep the TBM operating efficiently. This may involve changing cutting tools, lubricating components, and checking for wear and tear.
Tunnel boring machines are versatile and can work in various geological conditions, from soft soils to hard rock.
They offer advantages in terms of safety, speed, and environmental impact compared to traditional tunneling methods, making them a preferred choice for many tunnel construction projects around the world.
