Gripper TBM

Uncompromising in hard rock

In tunnelling with a Gripper TBM, a rotating cutterhead equipped with disc cutters is pressed against the tunnel face. High contact forces are required to work efficiently in hard rock with localized rock strengths of over 250 megapascals. Under this pressure, the disc cutters overcome the compressive and tensile strengths of the rock mass ahead and loosen so-called chips from the face. Water jets reduce the formation of dust and can cool the cutting tools. Buckets attached to the cutterhead collect the cuttings. As the cutterhead rotates, thanks to gravity they slide through integrated chutes to the center of the machine and fall through the funnel-shaped muck ring onto the machine belt. At the end of the machine belt, the rock chips are transferred to belt conveyors or transport vehicles and transported out of the tunnel.  

The disc cutters are mounted in the cutterhead in such a way that they can be changed from the rear under the protection of the structural steelwork of the cutterhead, without maintenance personnel having to enter the unprotected area in front of the cutterhead.

Bracing directly in the rock

Before each stroke, Gripper TBMs brace themselves firmly against the previously excavated tunnel wall using laterally extendable hydraulic cylinders. The gripper shoes on the outside are the core element of this machine type and give it its name. Thrust cylinders brace themselves against the braced gripper unit and press the rotating cutterhead against the tunnel face. Laterally extendable shields are pressed against the rock, stabilize the TBM during the boring process and reduce wear and tear. The invert shoe serves as a sliding shoe and as a pivot point when steering the TBM. Above this unit, a roof shield, often with a lamella roof extending to the rear, provides protection against falling rock. After a stroke has been completed, the advance is interrupted and the gripper unit is moved forward.

Flexible in squeezing rock too

Gripper TBMs from Herrenknecht offer a special advantage compared to closed shield types thanks to their partial shields. Depending on the machine, retracting all shields reduces the overall diameter by up to 150 millimeters during tunnelling. This enables a flexible response to swelling rock, even in squeezing rock, and prevents the machine from jamming. Depending on the diameter of the TBM, it is also possible to increase the excavation diameter. This is achieved via an extendable invert shoe in conjunction with shifting the caliber cutting tools and the optional installation of additional overcut housings.  

If necessary, the machine can even be completely retracted using the gripper unit. This allows direct access to the front of the cutterhead.

Know-how for optimal tunnelling

The cutterhead design, the number of disc cutters and thus the spacing must be optimally matched to the expected geology in terms of advance rate and wear and tear. This includes powerful cutterhead drives that provide sufficient torque even at high speeds. Thanks to numerous project references, Herrenknecht can draw on a unique wealth of experience and develop project-specific solutions.

Special solutions for smaller diameters

Gripper TBMs with diameters of less than 3.5 meters pose a design challenge. Extensive technology must be installed in a small space without restricting the required working area for the machine crew. For these small diameters, Herrenknecht opts for a shielded gripper TBM. With this special solution, the gripper shoes are arranged in an additional gripper shield. The front shield and the gripper shield are connected to the thrust cylinders, which apply the required contact pressure to the cutterhead and control the direction. Stabilizers are also integrated into the front shield, which reduce the vibrations that occur and transfer the necessary tensile forces to the surrounding rock when the gripper shield is repositioned.  

With these small machines, systematic rock support is only possible behind the gripper shield.

Anti-reverse lock for Gripper TBMs in inclined shafts

For use in inclined shafts, the Gripper TBM from Herrenknecht offers an innovative double anti-reverse lock for maximum safety. The system is based on a redundant design in which at least two of three independently operating bracing systems always securely fix the machine in the tunnel. The mechanical anti-reverse lock uses self-locking toggle levers that enable automatic wedging. As a result, even if the power supply and hydraulics fail, the TBM remains securely braced, reliably preventing it from slipping back. This advanced safety concept significantly increases operational safety and enables safe tunnelling even under extreme conditions.