Closer European integration inspired a series of civil engineering mega-projects in the late 1980s and early 1990s. While the Channel Tunnel grabbed many of the headlines in the UK, Denmark was getting on with a massive 18km road and rail, bridge and tunnel project across the Great Belt or Storebælt.
This crossing, completed physical transport links between the island of Zealand and mainland Europe.
The Storebælt crossing included a major suspension bridge and a rail tunnel at its eastern end. These converged on the island of SprogO before the road and railway ran alongside each other on multi-span viaduct.
Sprogø had to be artificially expanded with a huge land reclamation programme to accommodate approaches for the tunnel and bridges in a major land reclamation project.
The challenges were immense. The twin tunnel runs through unpredictable silts containing boulders. Initially, four tunnel boring machines, working from each end worked towards each other.
But at one point, one of the tunnel boring machines (TBMs) hit a void that unraveled to the surface, causing a flood, which backed up to the SprogO entrance before overflowing into the neighboring bore.
In 1994, a fire believed to have been caused by the ignition of leaking hydraulic fluid spray from one of the TBMs burnt out a large section of one of the bores at the eastern end of the tunnel, destroying its lining.
This led to a ground freezing operation to stabilise the surrounding ground before the machine making its way from SprogO could break through.
Floating plant played a key part in the construction of the western road and rail bridge. For this, Svanen, a purposebuilt floating crane, carried precast concrete caissons, piers and arch sections from a nearby casting yard.
The crane was a catamaran with electronically coordinated anchors, which helped pull it into exact placing positions.
Most of the eastern suspension bridge was built in or above the sea with huge precast elements for the piers transported by floating crane. Two huge 63m tall triangular concrete anchor blocks support the suspension cables for the 2.7km long suspended section, which included a 1.6km main span from the water.
Construction of the suspended section involved using a British made travelling gantry.
This straddled the suspension cables and was used to raise orthotropic steel box girder deck sections into position after they had been floated out to side by barge. It had to be capable of moving from the top of the 254m high pylons to the cables’ lowest point 65m above the sea.
The project took 10 years to complete, starting in 1988. Rail services starting in 1997 a year earlier than the road opened.