German rail tunnel expansion commences

Over the next few months, the Arge consortium of Porr GmbH, Feldhaus Bergbau GmbH and Heinz Schnorpfeil Bau GmbH will operate two Herrenknecht Tunnel Enlargement Systems (TES) – Nora and Tilly von Cramberg – to dismantle the existing structures and install a temporary support using shotcrete.

The work is being carried out on behalf of Deutsche Bahn, which is renovating and modernising six tunnels along the Lahntal line, and the tunnels will remain open to rail traffic during the works.

The 426m-long Fachinger Tunnel lies between Diez and Fachingen; the Cramberger Tunnel between Balduinstein and Laurenburg is 732m long.

The tunnelling portal at the Cramberg Tunnel Credit: Arge Porr/Feldhaus Bergbau/Heinz Schnorpfeil

Preparatory work, including creating the construction site facilities, dismantling the tunnel portals, installing the slope stabilisation, constructing the stop walls and installing the tunnel widening systems, started in January last year and was completed in October.

The construction site at the western portal of the Fachinger Tunnel got under way in October with the naming ceremony and the symbolic tapping of the tunnel. The tunnel will be driven from there in the direction of Diez.

The 46m-long, rail-bound TES weight around 270 tonnes and incorporates all equipment required for the refurbishment or enlargement, including a protective canopy that separates the working area from rail traffic. Rail traffic continues to run safely on a newly laid track in the centre of the existing tube under the protection of the canopy.

During construction work, rail traffic will continue to run on a newly laid track in the centre of the tube under the protection of canopy Credit: Arge Porr/Feldhaus Bergbau/Heinz Schnorpfeil

The tunnelling cycle begins with the demolition of the existing shell, consisting of masonry and back packing. The face is then opened and the rock material is broken off. Chisels are predominantly used for this, with controlled blasting in isolated cases. Once the face has been sealed and the tunnel reveal has been secured for the first time, the outer reinforcement mesh is installed and injected together with a steel support arch. If necessary, anchors are drilled to secure the rock in the tunnel.

Finally, an inner reinforcement layer is installed and the shotcrete layer is completed to the required thickness. After filling the side track with excavated material, the cycle starts again.

In an interview with T&TI last year, Herrenknecht project manager Volker Breuning said enlarging and relining a tunnel with the TES resulted in a cross-section and durability similar to a new tunnel.

Herrenknecht supplied its first TES to a rail tunnel upgrade in Spain in 2017.