Over the next few years, Deutsche Bahn will be renovating six tunnels on the Lahntal railway between Wetzlar and Koblenz. PORR was awarded the contract for the first two lots, Fachinger Tunnel and Cramberger Tunnel, in a consortium. The cross-sections of the structures have to be widened in order to comply with current regulations. The tunnel widening is being carried out using the tunnel-in-tunnel method under rolling wheels.
Tunnel structures from pre-imperial times
Between Diez and Nassau, the Lahn winds its way through the landscape in narrow loops. For the most part, the double-track Lahntal railway follows the course of the river, only in some places does the line branch off through tunnels, most of which were cut into the rocks of the Rhenish Slate Mountains in the 19th century. Both the 426 m long Fachinger Tunnel between Diez and Fachingen and the 732 m long Cramberger Tunnel between Balduinstein and Laurenburg were put into operation in 1862. As they show considerable signs of damage, they need to be renewed structurally after 160 years of operation. PORR's Düsseldorf tunnel construction specialists are working in a consortium with FELDHAUS Bergbau GmbH & Co. KG and Heinz Schnorpfeil Bau GmbH for the tunnel renewal.
Tunnel renewal under rolling wheels
The existing tunnel cross-section must be widened in order to guarantee the prescribed loading gauge. In addition, space must be created in the Cramberg tunnel for lateral escape routes. Furthermore, the track spacing must be increased to 4 m. The listed portal structures of the Cramberg Tunnel will be demolished and replaced by portal structures that will follow the historical models as far as possible in their appearance. Parts of the old tunnel portal, which is worth seeing, are to be secured and, if necessary, placed with the surrounding communities. Since a years-long shutdown of the railway line, which is very important for rail commuters and tourists, is out of the question, the work will be carried out under rolling wheels, while railway operations are restricted to one track. For this purpose, the existing tracks will be dismantled and a new track will be built in the middle of the tunnel.
Construction using the "tunnel-in-tunnel method" (TiT method)
The work is carried out from a tunnel driving portal, which is driven in the longitudinal direction of the tunnel. At the portals, cuts are made with soil nailing and partial net securing. After the complete demolition of the masonry existing vaults, a horseshoe-shaped inner shell made of water-impermeable concrete C35/45 with high sulphate resistance will be constructed. It consists of foundations and an attached inner shell. The expansion is carried out by chiseling and blasting the rock. Anchors and a reinforced shotcrete shell, also with grade C35/45, are used as securing means.
