More and new high voltage power cables are being added to existing electricity networks to strengthen and expand the grids. Many projects are underway, at strategic sections of the grids in numerous countries, including Germany, Sweden and UK, and more.
While the choice of using surface or elevated (pylon) grid links over underground placement continues on, in varying settings with different economics, a number of those capital investment projects already involve construction of carrier tunnels, such as in the countries mentioned.
GERMANY – SUEDLINK
Tunnel boring at the River Elbe for Germany’s SuedLink grid project involves a 4.9m-diameter Herrenknecht Mixshield constructing a 5.2km-long power cable carrier tunnel.
The Factory Acceptance Test (FAT) of the TBM was in mid-2024 for site assembly to be underway later in the year, at the launch site in in Schleswig-Holstein.
The diameter of the TBM gave the advantage of the cutterhead being able to be transported, delivered to site and assembled as a complete component. The TBM was launched in March 2025.
The TBM’s long launch pit near the River Elbe called for diaphragm wall construction and then excavation through the previous autumn, winter and spring. The D-Walls are up to 50m-60m deep, the launch pit 25m deep. Severe weather presented challenges for construction, including high wind limiting crane operation, and sodden ground making spoil removal, transport and site logsitcs more difficult.
Geology along the alignment comprises of clay, peat, sand, and gravel as well as stones and boulders. It runs below the river from Wewelsfleth, in Schleswig- Holstein, to Wischhafen, in Lower Saxony.
Construction is by ARGE Tunnel Elbx, a JV of Porr and Wayss & Freytag.
The Suedlink project will enable the electricity generated by wind farms in northern Germany to reach the south of the country, some 700km away. The river crossing is a key part of the Suedlink grid expansion project, which stretches from Brunsbüttel, in Schleswig- Holstein, in northern Germany to Großgartach in Baden- Württemberg.
The operators of the transmission system are TeneeT and TransnetBW
SWEDEN – ANNEBERG-SKANSTULL
Main excavation was recently completed for Stockholm’s key new power tunnel, on the Anneberg-Skanstull section of the electricity grid that is being upgraded and expanded.
The Anneberg-Skanstull power cable tunnel project is being undertaken by the Swedish National Grid (Svenska Kraftnät, SVK) as part of its wider City Link electricity network improvement project.
For the Anneberg-Skanstull project, Hochtief-Implenia joint venture used a Herrenknecht open gripper machine to bore the 5m-diameter through hard rock at depths of 50m-100m. TBM ‘Elektra’ broke through in early May 2025 to finish main tunnelling for the link under the Swedish capital. While the rock was hard, much injected grout was needed for the ground conditions at various points along the project.
The project also includes six ventilation shafts, elevator systems, the construction of technical buildings for electrical equipment at Anneberg and the shafts across the city.
The carrier tunnel will connect with substations at Anneberg and Skanstull parts of the city, respectively. The project is the second of four phases in City Link.
While working with the challenges of a major underground project in the capital, the tunnelling activity also had handle excavations needed close to the Strömmen passage (part of the Baltic Sea) as well as several historic and sensitive buildings, such as the University of Stockholm, museums and galleries.
UK – THAMES CABLE TUNNEL
London has seen extensive power cable tunnelling work over recent years, calling for major shaft construction in numerous locations and long TBM drives between those points.
One of the next grid tunnel projects near the capital is the Thames Cable Tunnel, which received planning approval earlier this year.
The Thames Cable Tunnel is being built by National Grid to run below the River Thames, on the estuary side to the east of London, and replace an existing link.
The project calls for construction of shafts and then a 2.3km-long tunnel to run below a wide stretch of the river.
National Grid is undertaking the capital investment to replace the existing Thames Cable Tunnel, in Kent. Originally installed in the 1960s, the current tunnel and cables have reached the end of their operational life.
Thames Cable Tunnel is part of the company’s Great Grid Upgrade to strengthen the UK’s energy network. The new project to replace the old link has received full planning approval.
The alignment of the new power tunnel runs from Grain to Tilbury. In addition to the main carrier tunnel, the project involves construction of new headhouses to access each end of the tunnel, and installation of new cabling.
Early construction is underway. Ferrovial is working in partnership with Bemo (Ferrovial Bemo JV) on the project, which is expected to be completed in 2029.
