Single Shield TBM

Single Shield TBMs in operation

Single Shield TBMs are the ideal machine type for tunnelling in consolidated rock and other stable, non-water-bearing ground. Thanks to the typical tunnel lining method using segments or pipe jacking, high advance rates can also be achieved in rock formations with low rock strengths.

Advancing with power

In tunnelling with a Single Shield 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.

Precise control, easy tool replacement

The boring diameter of shielded hard rock TBMs is larger than the shield skin. In addition, the boring axis of the cutterhead is offset upward in relation to the machine axis. This overcut enables the machine to be steered and protects against jamming in the rock. Hydraulic stabilizers integrated into the shield reduce vibrations during the advance.

To steer the machine, either fixed drives with steering cylinders or displaceable drives with spherical plain bearings or torque box cylinders and additional longitudinal displacement cylinders are used. This enables very tight curve radii during tunnelling. In addition, the boring diameter can be increased by shifting the caliber rollers and optionally installing overcut housings. With all drive types, the cutterhead can be retracted for direct access to the tunnel face. Single Shield TBMs in pipe jacking have another special feature: their cutterhead can be rotated in both directions and counteracts the risk of the machine rolling. .

Fast and safe

Rock support for Single Shield TBMs is achieved using segments or pipe jacking. This minimizes the dependency between the tunnelling and tunnel lining operations in rock formations prone to collapse or consolidated rock with low rock strengths. The machine is protected at all times, additional rock support measures and the associated delays in the advance are generally not necessary. In accessible machines, it is possible to extend the geological area of application by means of prior soil conditioning. Water inflows can thus be reduced to a manageable level. For this purpose, a preceding injection body is created ahead of the tunnel face via injection drilling through the cutterhead and the shield. Dewatering systems pump out the water as it enters in a controlled manner.

Know-how for optimal tunnelling

The cutterhead design, the number of disc cutters and the cutterhead openings must be optimally matched to the expected ground conditions in terms of advance rate and wear. 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.