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 underground cable line.
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 underground 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 geographical obstacles that have to be overcome with underground cables.
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 subsoil, high water permeability and the water pressure under the Elbe
The highly complex Mixshield is sealed against the water pressure 20 meters below the Elbe with a multiple sealing system. The TBM is not only digging 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 2025, the machine was dismantled, transported to Schleswig-Holstein, lifted into the shaft excavation pit in individual parts and assembled. The TBM will be operational in March-April 2025.
