Crossing the Fehmarnbelt strait
Oct 7, 2021
The Denmark-Germany Fehmarnbelt tunnel will improve rail connections between Scandinavia and mainland Europe when it opens by the end of the decade. With initial construction now underway, David Burroughs explains how the project is being implemented with insight from Femern contract director, Kirsten Margrethe Christensen.
FOLLOWING years of planning, approvals and tendering, work has begun on the 18km Fehmarnbelt road and rail tunnel between the islands of Lolland in Denmark and Fehmarn in Germany, which when completed in 2029 will be the longest immersed tunnel in the world. The tunnel will provide a more direct route between Copenhagen and Hamburg, and from Scandinavia to mainland Europe, by removing the need to travel west via the island of Funen to Fredericia on Jutland and then south to Padborg on the German border.
The tunnel will be constructed by digging a trench along the sea floor, before large prefabricated concrete sections are floated out and lowered into place. Cut and cover tunnels will be built at both ends to connect the tunnel to the portals. The tunnel will have capacity for up to 70 freight and 38 passenger trains a day.
Construction of the tunnel was authorised by the signing of a state treaty between Denmark and Germany as long ago as December 2008. Under this agreement, Denmark is the sole owner and will bear the full risk of financing the construction of the tunnel, as well as for upgrading the Danish hinterland road and rail connections. The link was approved in Denmark through the Danish Parliament’s adoption of the Construction Act in 2015, while final approvals in Germany were granted in January 2019. Two public undertakings have been entrusted with the planning, construction and operation of the project in Denmark: Femern Landanlæg for the Danish hinterland connections and Femern for the coast-to-coast infrastructure.
The overall cost of the project is budgeted at DKr 55.1bn ($US 8.6bn) at 2015 prices. This will be funded through state-backed sovereign loans, which will be repaid through tunnel access charges over 28 years. The same type of financing model will also fund the DKr 9.5bn project to rebuild the 115km Ringsted – Holeby line as part of the Danish hinterland upgrade.
Contracts awarded
Femern awarded four major construction contracts worth almost DKr 30bn to two consortia in March 2016. Femern Link Contractors (FLC) was awarded three of the contracts for the north and south tunnel portals and ramps sections of the link. FLC comprises Vinci Construction Grands Projects, and Soletanche Bachy International, France, Per Aarsleff Holding, Denmark, Wayss & Freytag Ingenieurbau and Max Bögl Stiftung, Germany, CFE and Netherlands Dredging International, Belgium, and BAM Infra and BAM International, Netherlands.
The dredging and land reclamation contract was awarded to Fehmarn Belt Contractors (FBC) comprising Boskalis International and Van Oord Dredging and Marine Contractors, Netherlands.
In February 2020, Femern appointed SNC Lavalin subsidiary Atkins to provide railway technical consultancy services for the project. Atkins will deliver multidisciplinary railway consultancy services throughout the project, which will include the track, overhead catenary, power supply, signalling, train control system and telecommunications. Atkins will also collaborate with German engineering firm Gauff, which will focus on the German elements of the new railway.
The tunnel and hinterland connection will have a major effect on long-distance trains travelling from Scandinavia to Germany and central Europe, reducing Copenhagen – Hamburg travel times from 4h 30min down to around 2h 30min.
Femern contract director, Ms Kirsten Margrethe Christensen, says awarding these contracts while the approvals process was ongoing meant work could begin as soon as they were obtained. The first step in the implementation phase was the construction of the large harbour to take delivery of the huge quantities of sand, cement, steel and gravel required to cast the tunnel sections. The tunnel factory built behind the harbour will manufacture the 79 217m-long standard concrete sections that will be used to construct the tunnel, and 10 special sections with a lower floor to hold the tunnel operation and maintenance equipment.
The sections weigh 73,000 tonnes and contain two tubes for the motorway, two for the railway and one for the central service passage. The sections will be immersed in a 12m-deep trench dredged on the seabed at a depth of up to 30m. Dredging the trench will produce 19 million m³ of soil, sand and stone which will be used for land reclamation to create new beaches and recreational areas adjacent to the project.
The tunnel sections are being cast incrementally in segments over a skeleton of reinforcing steel in large casting moulds, with each section taking nine weeks to manufacture. Once the concrete is set, the mould will be removed, and the section will be pushed into a dry dock. Both ends will then be sealed with a bulkhead and the dry dock will be filled with water, before the section is towed out into the deep end of the dock, after which the water level is lowered to sea level. The tunnel section will then be towed out into the Fehmarnbelt, where the ballast tanks will be filled to lower the section onto the seabed with millimetre precision. The sections will then be pulled together and the water pumped out, creating a partial vacuum to ensure a watertight connection. A protective layer of stone will be laid on top of the tunnel, with the current gradually covering the tunnel with sand.