Tunnel boring machine types

Types of tunnel boring machines

A tunnel boring machine (TBM) refers to a huge digger used to excavate tunnels through various soil and rock mixtures. Many TBM designs exist to achieve different tunneling goals more efficiently.

• Earth Pressure Balanced TBM

  The EPB TBM suits tunnels dug through soft or cohesive soil. An EPB TBM has a front shield that creates working pressures to prevent soil saturation or cave-ins. The TBM's cutting wheel turns the soil into excavated material. Then, an auger or conveyor belt removes the material from the tunnel.

• Hard Rock TBM

  A hard rock TBM produces tunnels in solid rock formations. Instead of using a circular cutter head to excavate soil, this type of TBM uses discoid or diametric cutters to break Hard Rock. After excavation, other machines in the TBM's train support tunnel lining.

  Like other types of TBMs, hard rock TBMs use a thrust system to push themselves forward as they dig tunnels.

• Open Face TBM

  The open-face tunnel boring machine digs tunnels through soil or rock with adequate external support. An open-face TBM has an unclosed front section that exposes the cutting head. It supports the front section with pre-injected concrete, steel frames, or wooden supports. This tunneling machine works in places like the ground level and doesn't suit regions with unstable soil or rock. Compared to TBMs with closed faces, the open-face offers a cheaper tunneling solution. However, it lacks pressure control and excavation protection.

Specifications & Maintenance of Tunnel Boring Machine Types

Different types of tunnel boring machines feature distinct specifications depending on what they are designed to do. While the following specifications are common, they may vary with each tunnel-boring machine.

• Diameter: Tunnel-boring machines come in various sizes, but their diameters typically range from 3.5 to 17 meters. Larger machines are specially made to suit unique projects.
• Length: The length of a tunnel boring machine is dictated by the type of machine it is, the specification of the project, and how it will be assembled. Generally, a typical length of a TBM is about 6 to 12 meters. Larger machines can be up to 20 meters or more in length.
• Weight: The weight of a tunnel boring machine can range anywhere from 300 tons to over 1,000 tons, depending on its size, type, and the construction materials used to make it.
• Thrust and Control System: The thrust of a tunnel boring machine refers to the force generated by the machine to push itself forward into the tunnel it is excavating. The thrust used in tunneling varies by the type of machine being used. Tunnel boring machines also have various control systems that allow the operator to maneuver and steer the machine as per the tunneling project's requirements.

Maintaining a tunnel boring machine is as important as its specifications. How the machine is handled determines its longevity. Here are a few important tunnel boring machine maintenance tips to consider:

• Regular Inspection: Conduct routine inspections to identify potential damages and issues. This can help in discovering any underlying minor problems before they turn into major costly ones that can affect the entire tunneling project.
• Lubrication: Regularly and promptly lubricate the moving parts of the TBM. This lessens friction and keeps wearing out to a minimal level, ultimately prolonging the service life of the machine.
• Cleaning: Because tunnel boring machines excavate diverse types of soil and rock formations, they are prone to build-up and clogs. Make sure to carry out thorough cleaning to avoid clogs and keep the machine in optimal working condition.

Application scenarios of tunnel boring machine types

The creation of tunnels is increasingly becoming a core focus area worldwide as countries look at sophisticated systems to decongest traffic. There are many applications for tunneling machines in creating tunnels without disrupting the landscape.

• Transportation Tunnels: These are the most common applications for tunneling machines. Road and railway tunnels help decongest traffic in urban areas, providing alternative routes for travelers. Huge tunnels with multiple lanes are created using the shielded and the mixed machines, which are suitable for building massive, complex tunnels.
• Utility Tunnels: Utility tunnels help protect overhead electricity, water, and gas lines. They also ensure easy maintenance of these lines. Utility tunnels are often built using the earth-pressure balance and the shielded tunnel boring machines. Single or multiple utility lines can be laid out in these tunnels.
• Metro and Subway Tunnels: The urban population is increasingly taking the train and subway systems to move from one point to another. In such cases, tunnel boring machines create metro and subway lines beneath the city. Tunnel boring machines help create subways and underground train systems, so people don't have to move around in traffic.
• Hydraulic Tunnels: These tunnels help in the movement of water, like in the case of reservoirs, dams, or drainage. Tunnel boring machines create precise and efficient waterways, reducing the risk of leaks and improving the flow control.
• Cross-Sectional Tunnels: These are tunnels created for pipelines and cables. The diameter of the tunnel is usually small. Tunnel boring machines with a precise cutter head are used to create these tunnels horizontally under the ground.

How to choose tunnel boring machine types

Considering the following factors, investing in the right tunnel boring machine will be more accessible.

• Project requirements analysis

  First, determine the features and specifications of the machine required for the job. The project's diameter, length, soil composition, geological structure, and pressure from overlying ground or surrounding water must be considered when selecting the right boring machine.

• TBM types

  Buyers should understand the features of each TBM type so they can make an informed decision. The Earth Pressure Balanced Machine and Shielded Machines are ideal for cohesive and non-cohesive soil; the Mixshield works well when interacting with water and soil. The Slurry TBM is a solid option in difficult geological conditions. The Single Shield TBM is a cost-effective option when moving sand, gravel, cobbles, or boulders. In places where the tunnel must curve or where space is limited, the Random Cutting Head TBM is a good option. In areas where it isn't possible to use excavated material as a single shield, Replacement Heads PB machines work well.

• Machine size

  The size of the tunnel needed and the diameter of the tunnel boring machine impact will be more than project costs and deadlines.

  The TBM will need to be disassembled into manageable parts and transported to the launch site. Once it arrives on-site, it will need to be assembled and launched.

• Budget and supplier selection

  These factors will impact budget constraints, such as assembly and transportation costs, rental or purchase, and any long-term guarantees and support services for the machine. Choosing a manufacturer with a solid reputation and extensive experience in the industry is essential. The international standards certification and track record for supplying durable, reliable, and high-quality tunneling equipment with excellent after-sales support should be considered.

Q&A

Q1: How does a tunnel boring machine work?

A1: TBMs excavate tunnels by using a circular cutterhead that rotates and moves through the ground. As the cutterhead advances, it cuts the earth into smaller pieces. The fragmented material, or muck, is then conveyed out of the tunnel through systems such as belts or pipes. Once the tunnel is excavated, support and lining materials are installed simultaneously to stabilize the tunnel.

Q2: What are the benefits of using a tunnel boring machine?

A2: Using a TBM offers several advantages. TBMs can excavate large and consistent tunnel diameters faster than other methods. TBMs can also bore tunnels at great lengths without needing intermediate shafts. In addition, TBMs can efficiently bore through different types of soil and rock. Other benefits of using a TBM include better tunnel support, lower project costs, and reduced impact on the surrounding environment.

Q3: What are the limitations of a tunnel boring machine?

A3: The main limitation of a TBM is its high construction and maintenance costs. The initial cost to manufacture and set up a TBM for a project can be prohibitively expensive. Other limitations include lengthy preparations for tunneling and constraints when boring through certain geological conditions.