Tunnel Boring Machines (TBMs) are engineering marvels designed to excavate tunnels with a minimum of disruption. These machines are capable of cutting through rock, soil, and other materials to create tunnels for subways, roads, water supply lines, and other infrastructure.
How does a tunnel-boring machine work?
The huge cutting head on front of the TBM rotates, with hydraulic cylinders pushing it forward from behind. Hardened cutter discs mounted on the cutting head do the actual work of breaking away the soil and rock.
Conveyer belts and pipes inside the TBM take the rock and soil to the end of the machine and then to the surface.
The TBM places curved pieces of concrete to make the newly dug tunnel watertight.
Here’s a general overview of how a TBM works:
1. Cutting Wheel
At the front of the TBM is the cutting wheel, also known as the cutterhead. This large, rotating disc is studded with cutting tools, often made of tungsten carbide or diamond, which are designed to break up the material in front of the TBM. The cutting wheel rotates and pushes against the ground, breaking the material into smaller pieces.
2. Conveyor System
Behind the cutting wheel is a conveyor system that transports the excavated material away from the cutting face. This system consists of a series of conveyors that move the debris to the rear of the TBM where it can be removed from the tunnel. The efficiency of the conveyor system is crucial for maintaining the TBM’s operational speed.
3. Support and Lining
As the TBM excavates the tunnel, it simultaneously supports the tunnel walls to prevent collapse. This is typically done using precast concrete segments or steel rings that are placed around the perimeter of the tunnel immediately behind the cutting wheel. These segments are joined together to form a continuous lining, providing structural integrity to the tunnel.
4. Hydraulic and Electrical Systems
The TBM is powered by a combination of hydraulic and electrical systems. Hydraulic systems control the movement and operation of the cutting wheel, while electrical systems provide power to the conveyors and other machinery. These systems are complex and require regular maintenance to ensure the TBM operates smoothly.
5. Navigation and Control
Modern TBMs are equipped with advanced navigation systems that allow for precise control over the direction and depth of the tunnel. These systems use lasers, GPS, and other sensors to guide the TBM along the desired path. Operators in the control room monitor the TBM’s progress and adjust the machine’s movements as needed.
6. Environmental Control
Excavating tunnels can generate a significant amount of dust and heat. TBMs are equipped with ventilation systems to ensure that air quality is maintained within safe levels for the crew working inside. Additionally, these systems help to cool the machine and maintain optimal operating temperatures.
Types of TBMs
- Earth Pressure Balance (EPB) TBM: Used in soft ground, the EPB TBM balances the pressure at the tunnel face by controlling the removal of excavated material.
- Slurry TBM: Also used in soft ground, the slurry TBM uses a slurry mixture to balance pressure and transport muck.
- Hard Rock TBM: Designed for excavating through solid rock, these machines are equipped with disc cutters that crush the rock into smaller fragments.
Applications
TBMs are essential in constructing tunnels for various infrastructure projects, including subways, highways, railways, and utility tunnels. Their ability to work in a variety of ground conditions with minimal disruption to the surrounding environment makes them a preferred choice for modern tunnel construction.
