Close menu Close

Main Beam TBM

Tunnel Boring Machines

Tunnel Boring Machines

In hard rock nothing bores tunnel faster than a Main Beam TBM.

If you want to bore a tunnel through hard rock in the shortest time possible, then the Robbins Main Beam TBM is the right solution. Get the best machine for the job and the most experienced team working with you. The results will be greater reliability, higher advance rates, and record-breaking performance.

What is a Main Beam TBM?

A Robbins Main Beam TBM is complex in its design, yet relatively simple in concept. The front of the TBM is a rotating cutterhead that matches the diameter of the tunnel. The cutterhead holds disc cutters (ranging from 14″ to 20″ in diameter) which are positioned for optimal boring of the given rock type. As the cutterhead turns, hydraulic propel cylinders push the cutters into the rock. The transfer of this high thrust through the rolling disc cutters creates fractures in the rock, causing chips to break away from the tunnel face. A unique floating gripper system pushes on the sidewalls and is locked in place while the propel cylinders extend, allowing the main beam to advance the TBM.

The machine can be continuously steered while gripper shoes push on the sidewalls to react the machine’s forward thrust. Buckets in the rotating cutterhead scoop up and deposit the muck onto a belt conveyor inside the main beam. The muck is then transferred to the rear of the machine for removal from the tunnel. At the end of a stroke the rear legs of the machine are lowered, and the grippers and propel cylinders are retracted. The retraction of the propel cylinders re-positions the gripper assembly for the next boring cycle. The grippers are extended, the rear legs lifted, and boring begins again.

A Main Beam TBM’s open design allows quick access directly behind the cutterhead for the installation of rock support (rock bolts, steel mesh, ring beams, and shotcrete), making it an ideal solution for unlined tunnels. The reliable Main Beam design reduces maintenance and maximizes boring time. This reliability explains why Robbins Main Beam TBMs set so many tunneling records and why so many others attempt to copy its design.

“The 3.25 m (10.7 ft) Main Beam machine performed well and the availability was excellent. The layout made it feel like a much bigger machine.”

-John Arciszewski, Project Manager, Southland Contracting

Robbins Main Beam TBMs are suitable for competent to slightly fractured rock. We design the machine to your tunnel specifications in diameters from 3 to 15 m (10 to 50 ft). This range is constantly being extended for new applications.

All Robbins Main Beam Machines are Equipped With:

  • A custom-designed rotating cutterhead matched to the geologic conditions to ensure smooth, efficient boring
  • Large-diameter high-load capacity disc cutters to penetrate the rock efficiently
  • A large-diameter main bearing and bull gear assembly specially designed for high-thrust applications in underground conditions
  • Robbins’ unique floating gripper system for continuous steering capability
  • Hydraulically actuated side and roof supports to stabilize the cutterhead by minimizing cutter wear
  • Laser target steering for tunnel accuracy
  • Steel dust shield to maintain a seal between the tunnel and the cutterhead, trapping dust in the cutterhead for removal by scrubber through the main beam
  • Efficient belt conveyor inside the main beam transfers muck from the cutterhead to the rear of the TBM

Depending on Project Geology, TBMs Can be Equipped With:

  • Roof drills to stabilize weak rock
  • Ring beam erectors for quick installation of tunnel support
  • Back-loading cutters for faster and safer cutter changing in unstable ground
  • Probe drills for pre-excavation investigation and ground consolidation
  • Variable cutterhead speed
  • Methane and other gas detectors
  • Data acquisition system: Automatic acquisition, monitoring and storage of real-time data from the machine functions including penetration rate, thrust pressure, cutterhead speed, gripper pressure and many more machine parameters
  • Automated, precision guidance system
  • Closed circuit television system
  • Automatic fire suppression system
  • Closed loop cooling system for conservation of water

Robbins designs TBMs to meet the criteria of each specific project, including the geologic conditions, tunnel design, construction plan, project schedule, site logistics and many other factors. When you contact Robbins, we review your project specifications in order to determine the best tunneling system for your project. In some cases, an entirely new tunnel boring machine will be the answer and on other projects, the best decision may be to refurbish an existing TBM, to save you time and cost.

To learn more about Robbins’ past projects, search our Project Solutions section. This section will give you an idea of what history-making successes we have accomplished in the past and how our innovative solutions can make your next project a success.

Whether you are in the planning phase of tunnel construction or about to bid on a project, our engineers can help you identify the best solution to achieve your objectives. For more information, complete our on-line inquiry form or contact Robbins at your nearest location.

A Machine for Every Geology

See which machine is right for your project

Main Beam TBM

Competent Hard Rock


Soft Ground


Variable Geology

Double Shield TBM

Fractured Hard Rock

Single Shield TBM

Fractured Rock With Water Inflows

Mine Development Machine