The grid expansion project SuedLink of the two transmission system operators TenneT and TransnetBW will transport electricity over 700 kilometers from Brunsbüttel in Schleswig-Holstein, northern Germany, to Großgartach in Baden-Württemberg, southern Germany, once completed. This section is considered a key project for the large-scale Sued-Link project.
SuedLink is one of several extra-high-voltage direct current (HVDC) transmission lines planned in Germany. The “electricity highway” is intended to connect the wind power regions of northern Germany with the industrial locations of Bavaria and Baden-Württemberg in southern Germany.
A consortium, ARGE Tunnel ElbX, is building an approximately 5.2 kilometers long tunnel from Wewelsfleth (Schleswig-Holstein) to Wischhafen (Lower Saxony) on behalf of the transmission system operator TenneT. The tunnel will accommodate six 525 kV cables and the associated building, safety, control and monitoring technology as well as rails for the tunnel vehicles required for maintenance and repairs.
ElbX is an outstanding example for the 4,500 crossings involved in the numerous grid expansion projects in Germany alone. Here, the new lines such as SuedLink encounter existing infrastructure and topographical obstacles that have to be crossed underground.
Herrenknecht delivered a tunnel boring machine (TBM) specially designed to meet the project requirements. On its way under the Elbe River, it will encounter varied geology consisting of clay, peat, sand, gravel as well as stones and boulders. The TBM of the Mixshield type has a diameter of 4,900 millimeters, is 190 meters long and weighs a total of 700 tons. Challenges are the heterogeneous ground, high water permeability and the water pressure under the Elbe.
The Mixshield is sealed against the water pressure 20 meters below the Elbe with a multiple sealing system. The TBM is not only excavating the tunnel but is also lining it at the same time with prefabricated concrete segments. The tunnel will have an inner diameter of 4 meters and an outer diameter of 4.60 meters.
After factory acceptance in July 2024, the machine was dismantled and transported to Schleswig-Holstein. The TBM started tunnelling in March 2025.
