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Single Shield

Tunnel Boring Machines

Tunnel Boring Machines

Contractors rely on Robbins Single Shield TBMs in massively fractured rock.

When you have large sections of broken ground to bore through, your project risk can be significant. The Robbins Single Shield TBM provides the rock boring capability of a Robbins Main Beam TBM and protects against rock collapse like a Double Shield TBM, but with minimum shield length.

What is a Single Shield TBM?

Robbins Single Shield TBMs protect workers from broken rock until the tunnel lining can be safely installed. The body of the machine is enclosed in a shield that is marginally smaller than the diameter of the tunnel. The flat, low-profile cutterhead minimizes disturbance of the face as it bores, and prevents large blocks from collapsing and causing excessive boring stresses. The front of the TBM is a rotating cutterhead that matches the diameter of the tunnel. As the cutterhead turns, a ring of hydraulic cylinders provides forward thrust through shoes that push against the tunnel lining. The cutterhead holds disc cutters (ranging from 11″ to 20″ in diameter) positioned for optimal boring. The transfer of high thrust through the rolling disc cutters creates fractures in the rock, causing chips to break away from the face. Boring and lining installation are performed sequentially. To steer, cylinders orient the articulated cutterhead in the required direction.

Robbins Single Shield TBMs are available in diameters from 1.6 to 15 m (5 to 50 ft). All Single Shields are equipped with high-speed segment erectors for rapid tunnel lining installation. To steer the machine, the cutterhead is articulated. The short shield length enables a small turning radius and minimizes exposure to squeezing ground forces that could potentially trap the machine. Robbins Single Shield TBMs are designed with maximum equipment life in mind. Every machine is rated for 10,000 hours of excavation.


  • Probe drilling equipment for determining rock conditions ahead of the TBM.
  • Automatic monitoring and data acquisition to store the real-time data from the machine functions, including penetration rate, thrust pressure, and drive motor current.
  • Closeable muck bucket doors to control muck inflow.
  • Tail seals with grease system to prevent muck from entering between the shield and the lining.
  • Ultra-high emergency thrust system to prevent entrapment in squeezing ground.


  • Flat, low profile cutterhead to enhance face support in broken rock.
  • Back-loading cutters for safer cutter changing in unstable rock conditions.
  • Recessed muck buckets with grill bars to prevent ingestion of large rock blocks.
  • Fast resetting propel cylinders.
  • Skew ring to react cutterhead torque.
  • Articulated cutterhead for steering.
  • High-speed segment erector (single- or dual-arm depending on machine diameter) to install pre-cast concrete segments with precision.
  • Short shield for a small turning radius and minimum exposure to trapping friction.
  • Digital guidance system for continuous information on alignment.

Robbins designs Single Shield 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 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 rebuild 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.

Main Beam TBM

Competent Hard Rock


Soft Ground


Variable Geology

Double Shield TBM

Fractured Hard Rock

Single Shield TBM

Fractured Rock With Water Inflows