en.Wedoany.com Reported - SuedLink is one of Germany's planned ultra-high voltage direct current transmission lines and a key project for the country's energy infrastructure expansion. Its core component—the Elbe crossing tunnel—has been completed, with the tunnel boring machine (TBM) "Elsa" breaking through into the target shaft after excavating approximately 5.2 kilometers. This tunnel, connecting Wewelsfleth in Schleswig-Holstein with Wischhafen in Lower Saxony, is a vital part of the roughly 700-kilometer-long "electricity highway" known as SuedLink.
Operated by transmission system operators TenneT Germany and TransnetBW, the SuedLink route is designed to transport offshore and onshore wind power from northern Germany to industrial regions in the south, such as Bavaria and Baden-Württemberg. With a transmission capacity of 4 gigawatts, this 525 kV direct current line must cross the Elbe River. PORR is building the cable tunnel on behalf of TenneT and has commissioned the joint venture ARGE Tunnel ElbX, formed with Wayss & Freytag Ingenieurbau AG, to carry out the construction. In addition to laying six underground cables, the tunnel will be equipped with safety, control, and monitoring systems, as well as maintenance tracks.
To address the complex geology beneath the Elbe, the ARGE Tunnel ElbX consortium ordered a specially customized Mixshield tunnel boring machine from Herrenknecht AG. The machine has a diameter of 4,900 millimeters, a total length of 190 meters, and weighs 700 metric tons. Since its launch in February 2025, the TBM has advanced at an average rate of 303 meters per month, installing an average of 233 concrete segment rings per month. Key challenges of the project included highly variable geology, high ground permeability, significant water pressure beneath the Elbe, and the relatively compact machine diameter.
Herrenknecht Project Manager Johannes Faißt stated that the geological conditions along the tunneling route include clay, silt, peat, sand, gravel, and boulders. To handle the highly adhesive Lauenburg clay, the TBM is equipped with a powerful central flushing system, with a flow rate of 500 cubic meters per hour at the cutterhead and 1,200 cubic meters per hour for the entire bentonite slurry circulation system, preventing cutterhead clogging. The Mixshield can withstand water pressures of up to 3.8 bar through a multi-layer sealing system. The tunnel has an inner diameter of 4 meters and an outer diameter of 4.6 meters, lined with precast concrete segments. Herrenknecht subsidiary VMT provided the navigation system to precisely control the tunneling route.
For auxiliary systems, Herrenknecht Separations provided a customized separation system equipped with chamber filter presses for dewatering fine solid particles, along with two water treatment plants at the launch and reception shafts. Gino Vogt, Head of Herrenknecht Separations, noted that the filter presses ensure effective dewatering of extremely fine particles, reducing disposal costs, while the water treatment plants guarantee resource-efficient supply of process water and safe discharge. Additionally, Herrenknecht Formwork supplied precision formwork and handling equipment for producing approximately 4,000 rings (totaling 24,000 segments) of tunnel lining, ensuring high dimensional accuracy of the segments and tunnel structural quality.
Herrenknecht stated that the ElbX project is a typical example of mechanical tunnel boring technology supporting grid expansion. In Germany, numerous grid expansion projects such as SuedLink are expected to involve approximately 4,500 underground crossings.
