PORR has announced the breakthrough of the ElbX electricity tunnel beneath the River Elbe, a central construction element for the SuedLink power transmission project.
Achieved on 22 June, the breakthrough follows months of work connecting Schleswig-Holstein and Lower Saxony with a tunnel measuring approximately 5.2km in length.
The project, carried out on behalf of Germany’s largest transmission system operator, TenneT Germany, is regarded as an important section in the ongoing effort to transport renewable energy from northern to southern Germany.
The construction of the ElbX tunnel is designed to provide a route for high-capacity, high-voltage direct current (HVDC) cables. These cables are expected to support the delivery of wind-generated power across regional boundaries, contributing to Germany’s plan to reduce reliance on fossil fuels and shift the national energy mix.
The ElbX tunnel, constructed at a depth of about 40m, uses mechanical tunnelling combined with segmental lining to navigate the technical challenges posed by the Elbe’s subsurface conditions.
Construction on the ElbX crossing officially began in September 2023 with a symbolic groundbreaking event in Wewelsfleth, Schleswig-Holstein, after which preparatory work commenced. This included the establishment of access roads to the construction site, and the excavation of the starting pit on the Schleswig-Holstein side.
Simultaneously, in Lower Saxony, teams began work on the receiving shaft at Wischhafen. The main phase of mechanical tunnel boring started in February 2025, using a tunnel boring machine (TBM) named Elsa.
During operations, Elsa advanced at roughly 10m per day under typical conditions. The tunnelling team faced significant technical challenges, particularly while crossing beneath the riverbed and the main Elbe shipping channel.
This section required the TBM to cut through the dense Lauenburg clay and work under compressed air conditions reaching up to 4.8 bar, limiting the amount of time workers could spend at the cutterhead to around 50 minutes per shift. These factors contributed to increased staffing requirements.
PORR reported that, in the final 400m of tunnelling, favourable ground conditions allowed for new performance milestones. The team achieved a maximum daily advance of 32.6m, or 25 segment rings, and set a weekly record of 158.7m.
Across the entire construction period, progress was influenced by variable and challenging conditions in the Elbe’s groundwater, but the breakthrough still occurred ahead of schedule.
PORR CEO Karl-Heinz Strauss said: “The tunnel construction under the Elbe is a significant and complex project that has repeatedly presented us with engineering challenges. Despite this, we’ve managed to achieve this milestone ahead of schedule.”
As the TBM approached the “halfway point” in December 2025, having completed 50% of the tunnel route, construction also continued on the associated shaft structures. By this point, teams in Schleswig-Holstein had begun work on the second basement level, while progress reached the fifth basement level in Lower Saxony.
The completion of the receiving pit in 2025 enabled Elsa to break through at the target shaft in mid-2026.
The next phase of the project will involve internal works and the technical fit-out of the tunnel, preparing it to accommodate HVDC cables. These are scheduled to begin operation in 2028, transporting wind power from northern Germany to the country’s southern regions.
PORR’s scope on the project extends beyond tunnelling and civil engineering, encompassing specialised underground construction and BIM coordination by pde Integrale Planung.
The ElbX tunnel is seen as a pivotal component of the SuedLink corridor and an essential element in Germany’s future power transmission infrastructure as the country pursues its energy transition objectives.
