IN the fields where Mr Anders Wede chased rabbits as a child, the Lolland Island native is now overseeing the biggest immersed tunnel project in the world, to provide a fixed link between Denmark and Germany, 18km to the south.
The Fehmarn Belt tunnel will create a 160km, high-speed low-carbon shortcut between Scandinavia and Central Europe, strengthening trade, cooperation, and growth opportunities in Northern Europe. The road and rail connection will save time, energy, and reduce transport CO₂ emissions, and free up capacity on the Danish rail network, shortening the journey time between Copenhagen and Hamburg from 4h 30min to 2h 30min.
The new fixed link is being built using the immersed tunnel method, where sections of tunnel are built on land before being floated out and sunk into place. This method was previously used for the 4km Øresund tunnel between Denmark and Sweden that opened in 2000. However, the Fehmarn Belt tunnel will stretch for 18km between Rødbyhavn, on the Danish island of Lolland, and Puttgarden, on the German island of Fehmarn. The tunnel will carry a four-lane motorway and two electrified rail tracks, taking 10 minutes to travel from Denmark to Germany by car and just seven minutes by train. Motorists will be able to drive at up to 110km/h in the tunnel, while trains will travel considerably faster at up to 200km/h.
The project is especially important for Wede, who was born and raised in the area before moving to Copenhagen to study. “It’s quite special to see the area changing in such a way,” he says. “I moved back with my wife, and we have lived here for the last seven years. A lot of my family still lives in the area.”
The tunnel consists of 79 individual elements, each 217m long and weighing 73,500 tonnes, and 10 special elements with a basement floor for equipment that will be used to operate and maintain the tunnel. Each standard element consists of nine segments manufactured on a production line before being joined together. The finished elements will then be floated and towed out to sea where they will be immersed in a 12m-deep trench in the sea floor.
When completed in 2029, the new tunnel will be able to withstand earthquakes, extreme weather conditions, and even collisions with passing ships.
The new fixed link will not come cheap, with a total construction budget of €7.4bn. To reduce the burden on taxpayers, the tunnel is user-financed with construction funded by means of state-guaranteed loans that will be repaid using revenue from tolls and user charges over 28 years from the opening of the tunnel. As a European priority project, the Fehmarn Belt tunnel has also been awarded DKr 8.4bn ($US 1.2bn) in support from the European Commission (EC).
Submersed facility
On-site work began in 2021, transforming the fields near the Danish portal into a 7km submersed tunnel element manufacturing facility, the largest in the world. An 11m-high dyke has been built around the site, replacing the old dyke that previously held the Baltic Sea back from flooding the hinterland that was removed to allow the tunnel elements to be towed out to sea. Femern, the company overseeing construction, has pledged to use 100% renewable energy to both build and operate the Fehmarn Belt tunnel.
Dredging of the tunnel trench was 95% complete as of October last year, though precision work to smooth out the trench will continue for another year. The 12m-deep trench is up to 42m below sea level at its lowest point. After the material has been removed, a robotic arm will place gravel in an S shape along the bottom of the trench, which the elements will then be placed on.
Two consortia, Fehmarn Belt Contractors (FBC) and Fehmarn Link Contractors (FLC), are responsible for construction of the tunnel. The contract with Dutch consortium FBC came into force in November 2019, and includes dredging, the construction of the two harbours and land reclamation for new nature areas. Femern then entered into the contract with FLC for the construction of the tunnel itself, its portals and access ramps in May 2020, with the contract effective from January 1 2021.
In May 2022 Femern signed a contract with Femern Systems Contractors (FSC) to equip the tunnel with electrical and mechanical systems including ventilation, lighting, and safety systems. The contract puts special emphasis on energy-efficient solutions and equipment adapted to future green technologies.
Femern signed a contract with Elecnor in December 2022 to build a large transformer station that will supply green power to tunnel installations and the railway between Denmark and Germany, as well as on Lolland.
During the short drive from the Femern office in Rødbyhavn to the construction site, Wede points out two companies that were moved from the site into newly-built premises. “We have built new facilities for them, so they are keeping work in the area,” he says.
“When we are up and running at full speed, we will be producing about 20% to 25% of the full amount of concrete used in Denmark on-site.”
Mr Anders Wede, Construction Area Manager at Femern
The rest of the area was previously dotted with wind turbines, which were removed ahead of the start of construction.
Manufacturing of the segments that will form the elements begins with the welding of steel rebar components that will then be assembled in the production halls “like a Lego set,” creating the frame around which the concrete is then poured. The rebar manufacturing hall is 210m long, 65m wide and 19m high.
Steel rebar arrives by ship in coil, mostly supplied from Germany and Spain, before being taken by road to the rebar factory. The full project will use 350,000 tonnes of rebar, with 70% handled inside the facility.
FLC decided to build the facility to reduce its reliance on external contractors. It has also decided to use innovative equipment to reduce the amount of material handled manually. This includes two robotic machines to manufacture the rebar panels, the first of their kind in the world, which can weld a full panel within four minutes. Each line will handle 400 tonnes of rebar a week.
The steel rebar elements are then transferred to the three production halls that house five production lines to manufacture the standard tunnel segments, while a sixth line to produce the 10 special elements is located outside the third hall as these are too large to be produced inside.
Inside the mammoth halls, production of the segment starts from the northern side, furthest away from the coast. The floor panels are laid and welded to form the base, before this is then dragged forward on steel sleds into a stiffening frame, around which the rebar for the walls and then the roof is installed. Placing and welding the rebar for each segment takes around a week.
Basement level
The full frame, which weighs around 430 tonnes, is then pulled further down the production line into the casting pits, where large steel frames are placed to form the mould for the concrete to be poured around. Pouring the concrete for each segment takes 30 to 36 hours, and this must be carried out without interruption to avoid the creation of cold joints within the concrete.
The 10 special elements include a basement beneath the tunnel that will house equipment such as pumps and electrical equipment, as well as an extra lane for maintenance vehicles to park without interrupting traffic. As these are being cast outdoors, production can be restricted by the weather. However, Wede explains that it was estimated that there would be enough clear days to manufacture the 10 elements required.
Beside the three halls sit two concrete batching plants, each capable of producing up to 300m3 of concrete an hour. This rate of production is required to keep up with the number of segments being manufactured at a time. Producing the bottom slab, for instance, requires 200m3 of concrete per hour.
“When we are up and running at full speed, we will be producing about 20% to 25% of the full amount of concrete used in Denmark on-site,” Wede says. “This is all handled automatically. All the materials are being brought in by ship and transported by conveyor belts or pipelines into the batching plants to be mixed. We have different mixtures for the different parts of our segments, for instance it is a bit stiffer going up through the walls than on the bottom slab.”
New harbour
Following casting, the now 8100-tonne segment is moved out of the hall on six concrete “skidding beams” covered with an epoxy layer. Hydraulic arms are placed behind the segment, pushing it forward 2m at a time before the “body” of the arm is dragged behind it, akin to how a caterpillar moves.
Once the nine segments are completed, they are then assembled to create the full element weighing 73,000 tonnes.
Each of the five production lines should produce one element per week. To allow this rate of production, around 800-900 staff will be working in the halls when at full capacity. This includes two shifts to install and weld the rebar, and either two or three shifts to pour the concrete.
The segment is then sealed and pushed into one of three basins that open out into a newly built harbour carved out from the sea bed. Beside it now lies a new plain of reclaimed land made from material excavated from the trench, the newest part of Denmark. “In total we are enhancing the state of Denmark with 300ha,” says Femern communications manager, Mr Morten Nielsen.
The project will employ up to 3000 people, with around 2000 workers already employed at the end of October 2023
The connection between the middle basin and harbour is sealed by a large floating gate, before four pump add 820,000m3 of water into the basin. This raises the water level by 10m, allowing the segment to float and to be towed to the front of the basin. The water is then pumped out, the gate opened and the segment is towed out by tugboat. Flotation pontoons are attached to the side of the segment, before 4000m3 of concrete is added for additional weight, removing the segment’s natural buoyancy.
“That makes it a lot easier when we have to immerse it in the tunnel trench,” Wede says.
The segment is lowered onto the seabed using steel cables, with a tolerance of only 15mm, before additional material is placed on top to secure it to the sea floor.
The first element is due to be immersed this summer, and each element will take four to six days to be assembled, towed out to sea and placed into position.
As this can only take place during good weather, an area has been created to store up to 12 elements at a time in order to allow manufacturing to continue during bad weather.
To the west, work is well underway on the northern tunnel portal and ramp (TPR) site, which includes the construction of a cut-and-cover tunnel connecting with the first tunnel element, the tunnel portal, and toll booths for the road. A similar facility is under construction in Germany near the rail and road connections to the tunnel.
To allow FLC to build the cut-and-cover tunnel below sea level, a dyke has been built around the site by FPC. Construction of the tunnel is underway, including a section similar to the 10 special elements with a basement to house equipment. The cut-and-cover tunnel is being cast in three parts, with a membrane placed between each section. Once the tunnel portal is built, the dyke will be removed to allow it to be flooded over, before the first element is floated into place.
The project will employ up to 3000 people, with around 2000 workers already employed at the end of October 2023 at construction sites in Denmark and Germany, and even more at the 700 subcontractors throughout Denmark. As the tunnel workforce is nearly twice the size of the population of the nearby village of Rødbyhavn, the construction site includes a temporary village housing 1200 staff.
This is equipped with an on-site hospital, staffed by a doctor and two nurses. The site also features a cinema, games room, fitness centre, hairdresser, kitchen, and laundry rooms. Each staff member has their own room and bathroom, due to regulations introduced after the Covid-19 pandemic.
“Having that many people living in such a compact area in two to three shifts, not waking each other up as they are coming back and going to work, is quite difficult,” Wede says. “[The site manager] is serving a lot of meals two times per day, so compared with a normal hotel that’s quite an achievement.”
The government included the staff village as a requirement in the construction contracts, as previous major projects in Denmark which also relied on large numbers of overseas workers did not provide adequate living conditions for staff.
Wede says having most staff living in a single location helps to ensure they are living in suitable conditions, are being paid appropriately, and treated fairly by the contractor.
Attracting the right people has been a challenge, and a large educational programme is underway to train and upskill staff.
It is combined with financial incentives for staff who stay with the project to prevent experience being lost. Social clauses in all major contracts mean that contractors must create apprenticeships equivalent to at least 500 full-time jobs.
This will ensure the project has a lasting impact on the construction sector in Denmark, as well as the surrounding region, for generations to come.
