Tunnel Boring Machine: Definition & Working Principle

A tunnel boring machine (TBM), also known as a mole or worm, is a specialized piece of tunnel boring equipment designed to excavate round tunnels through soil and rock. I rely on tunnel boring machines for tunnel projects because they feature a spinning cutterhead, a protective shield, and systems that ensure tunnel stability. These machines use hydraulic jacks, conveyor belts, and install tunnel lining as they advance, making the tunneling process safer and more efficient. According to civil engineering resources, the tunnel boring machine is essential for tunnel construction and can operate in various ground conditions. For challenging projects, I often choose a slurry balance tunnel boring machine or a double shield tunnel boring machine. NHI offers a range of advanced tunnel boring equipment, and you can explore their options at www.nhiglobalequip.com. Overall, tunnel boring machines significantly improve the speed, safety, and precision of tunnel excavation.

• Other names for tunnel boring machines include:
  • Mole
  • Worm

TBM Components

Cutterhead & Rotary System

The cutterhead and rotary system help the machine break soil and rock. The cutterhead spins at the front and uses tools to cut material. Hydraulic jacks push against the tunnel walls so the cutterhead can move forward. In hard rock, disc cutters work better. The rotary system controls pressure at the tunnel face. This stops the tunnel from collapsing and keeps workers safe. I check torque and thrust to make sure tunneling goes smoothly.

Tip: The cutterhead’s shape changes for different ground. This helps tunneling stay safe and work well.

Shield & Support

The shield protects the TBM as it moves. A steel frame holds back the ground while the machine goes forward. Hydraulic jacks push the shield ahead to give strength. Right behind the shield, concrete rings support the tunnel walls. This step-by-step support keeps the tunnel strong and stops collapse. The shield’s design changes for different soils. This is important for safe tunneling in soft ground.

Conveyor & Muck Removal

Getting rid of muck is important for nonstop tunneling. Belt conveyors move the dug-up material from the TBM to the surface. These belts work all the time and carry lots of soil or rock. Loaders help move muck to crushers or trucks. Sometimes, safe agents are added to make slurry solid. This makes disposal easier and safer. Machines do most of the work, so fewer workers are needed. This lowers accident risks and makes tunneling safer.

Guidance & Control

Guidance is very important for tunneling machines. Laser tools and robots help track where the TBM is underground. Data shows up on a tablet and tells where the cutterhead is. Sensors watch speed, torque, and pressure. Computers use this information to help steer the TBM exactly. This keeps the tunnel on the right path and meets safety rules.

How Tunnel Boring Machines Work

Tunnelling Process

When I start a tunnel project, I follow clear steps. This helps keep everyone safe and makes work faster. Here is how a tunnel boring machine works from start to finish:

1. First, I plan the project. I study the ground and the environment. This helps me pick the right tunnel boring machine.
2. Next, I choose workers and get all the needed tools. This makes sure we have good support and supplies.
3. My team puts the tunnel boring machine together at the site. We check every part before we start digging.
4. The rotary cutting head starts to dig into the ground. As it moves forward, it takes out soil and rock. We call this muck. Conveyor belts carry the muck out of the tunnel.
5. At the same time, I put in concrete lining pieces behind the machine. These pieces hold up the tunnel walls and keep them strong.
6. I set up drains and supports to control water and keep the tunnel safe while digging.
7. After digging is done, I add things like air flow, lights, and phones. This makes the tunnel safe for people to use.
8. Last, I test everything and make sure the tunnel is safe before people or trains use it.

Note: Using earth pressure balance technology helps keep the tunnel face safe. This is very important when digging in soft ground in cities.

Tunnel Lining

While digging, I must put in tunnel lining to keep the tunnel safe. Here is how I do this part of the job:

1. As the tunnel boring machine moves, I use a segment erector to place concrete lining pieces inside the tunnel.
2. These pieces fit together to make a strong ring. Each ring has four to ten pieces. Each piece is shaped to fit just right.
3. I use special lifts to move and place the pieces quickly and safely.
4. When a ring is done, the tunnel boring machine pushes off the last ring to move forward.
5. After putting in the pieces, I fill the space between the lining and the ground with grout. This keeps water out and makes the tunnel strong.

The concrete pieces are made to be very strong and last a long time. I sometimes add special things to the concrete to help it flow and dry faster. For tunnels with tough water, I use extra coatings to protect the lining.

Tip: Putting in tunnel lining while digging makes work faster and safer. It also lowers the chance of the ground falling in, which is a big worry in city tunnels.

Curved Tunnelling

Sometimes, I need to build tunnels that curve to go around things or follow a path. Making curved tunnels with a tunnel boring machine needs careful planning and control. Here is how I do it:

• I use a tunnel boring machine that can bend and follow a curve.
• I change the cutter discs to cut a little more, so the machine can turn.
• For sharp turns, I use smaller tunnel lining rings to fit the curve.
• I watch the machine’s position all the time with sensors and lasers. This helps me keep the tunnel on the right path, even in tight spots.
• I also use special conveyor belts and carts that can work in the small space of a curved tunnel.

This way, I can build tunnels under busy cities without making extra holes or causing big problems above ground. It also keeps the tunnel safe and strong, even if the ground changes.

TBM Advantages

I use tunnel boring machines for many projects because they have many good points:

• Efficiency: Tunnel boring machines let me dig and put in lining at the same time. This makes the work go faster and saves time.
• Safety: The tunnel boring machine protects my team from falling rocks and dirt. Machines and real-time checks lower the chance of accidents. I also use good air flow and fire safety systems to keep workers safe.
• Precision: With lasers and computers, I can guide the tunnel boring machine very accurately. This is important in cities, where I must avoid buildings and pipes.
• Environmental Impact: Tunnel boring machines make less noise, dust, and shaking than old ways of digging. This is better for cities and places that need to stay quiet.
• Adaptability: I can use different tunnel boring machines for different ground, from soft dirt to hard rock. Some machines can even change how they work for mixed ground.
• Cost-Effectiveness for Long Tunnels: Tunnel boring machines cost a lot at first, but they save money on long tunnels. They work faster and need less extra support.

Callout: New ideas, like variable density tunnel boring machines and self-driving features, make tunneling even safer and faster. I now use smart sensors and artificial intelligence to watch the machine and plan repairs.