SuedLink Elb crossing ElbX, Wewelsfleth / Wischhafen

On behalf of the leading European transmission grid operator TenneT TSO GmbH, PORR and its tunnelling, special civil engineering and civil engineering divisions are realising the ElbX Elbe crossing with an underground tunnel in the course of the SuedLink expansion. The tunnel construction is one of the most challenging project sections for the construction of the power line, which is to transport wind power from the north to the south.

Hand in hand: tunnelling, special civil engineering, structural engineering and cable construction

A 5.2 km long tunnel with an inner diameter of 4 m is being built from Wewelsfleth to the target shaft in Lower Saxony near Wischhafen. As the start and target shafts are located in groundwater, the construction pits for the shafts have to be made watertight and stable before excavation. Afterwards, the construction pits, which are around 25 m deep, are excavated under water. This is followed by buoyancy control and the casting of the underwater concrete base. To construct the shaft building, the construction pits are first drained and secured with steel girders. These will be dismantled as construction progresses. Then the preparations for the tunnel drive and the assembly of the tunnel boring machine, which is specially manufactured for the subway, begin. It is designed for the changeable ground conditions under the Elbe.

For tunnelling, the segmental construction method is used. Around 20 m below the Elbe, the tunnel boring machine will work its way through the soil. Six 525 kV direct current cables will be pulled into the finished tunnel and connected to the SuedLink underground cables on both sides of the Elbe. Rails in the tunnel allow tunnel vehicles to drive through, so that the tunnel can be accessed quickly and safely for maintenance and repair work even after the construction phase has been completed.

SuedLink as a decisive milestone for the energy transition

To enable energy from wind power to be transmitted from north to south, a so-called HVDC link is being built with SuedLink. Two underground cables are to transport four gigawatts through the country via "high-voltage direct current transmission". However, renewable energies are not only produced decentrally everywhere in Germany - they also fluctuate greatly in their feed-in. The direct current technology with which SuedLink is being realised makes it possible to react more flexibly to the fluctuations and to better control load flows in the grid. The transmission capacity is roughly equivalent to that of four nuclear power plants. In mathematical terms, around ten million households can be supplied with electricity.