“An underwater tunnel is impracticable,” declared engineers in 1809. A team of miners had been working to bore a tunnel under the River Thames in London to connect the north and south banks. Unfortunately, the attempt was hampered by the soft clay and quicksand – and the pilot tunnel flooded twice. After four years, the project was abandoned as impossible.
Engineering pioneer Marc Kingdom Brunel and his son, however, were determined to build the Thames Tunnel. It took cutting edge technology, near misses with fires and floodwater and almost twenty years, but eventually the world’s first underwater tunnel was completed in 1843.
Today, engineers in Norway are considering another world first: a floating underwater tunnel to traverse the deep, wide fjords between Kristiansand and Trondheim. The floating tunnel will push the boundaries of modern engineering – and throw up many challenges that might be difficult to anticipate. But what are the parallels between these tunnels separated by two hundred years – and how has technology moved on in that time?
The twenty-year tunnel
At the start of the nineteenth century, London was an extremely busy shipping port. Docks had been constructed on both sides of the Thames at Wapping and Rotherhithe, once the river became too busy for the floating wharfs originally used to offload goods. It became clear that a tunnel connecting the northern and southern docks would make it much easier and quicker to transport incoming goods further on their journeys.
However, an underwater tunnel had never been constructed before – and brand-new engineering technology would be needed. Fortunately, just a few years earlier Marc Kingdom Brunel had invented a tunnelling shield, that split construction into “cells” where workers could safely excavate sections of earth. With this innovation in place, work on the Thames Tunnel could begin in 1826, on the south bank of the river at Rotherhithe.
Construction, however, was difficult and dangerous. Workers faced fires, leaks of toxic gases and repeatedly flooding. But with an improved tunnelling shield, Marc Kingdom Brunel and his son persevered. Nearly twenty years after work started, the Thames Tunnel finally opened to the public in March 1843. Brunel proved that underwater tunnels were possible – and the tunnel is still in use today, as part of the (ironically named) London Overground.
A new world first
Almost two centuries on, engineers in Norway are looking to push the boundaries of construction further, with the world’s first floating underwater tunnel. The 680-mile journey from Kristiansand to Trondheim traverses deep, wide fjords surrounded by steep mountains. That means travellers at present take seven ferry trips – and can expect to spend around 21 hours on the road.
The nature of the terrain makes it difficult to build bridges or drill tunnels. So, an engineering team is considering a 4,000-foot-long floating tunnel – around three times the length of the Thames Tunnel. The structure would consist of two concrete tubes suspended by cables 100 feet below pontoons on the surface.
The design borrows existing ideas from off-shore oil ridges, suspension bridges and of course tunnels. However, the combination of features is entirely new – so the project is likely to throw up many challenges. Planners will need to anticipate factors like the impact of strong currents in the fjord, the possibility of a ferry or submarine striking the bridge and the level of load the structure could hold safely.
But there are significant gains to be had from pushing these boundaries. A floating tunnel would have a significantly lower environmental impact than traditional bridges and tunnels. Travel by water on the fjord could continue overhead, thanks to the wide gaps between pontoons. And critically, it’s estimated that the structure could cut journey times from 21 hours to 10.5. Alternatives are still being considered. But if work goes ahead, the world may have a new engineering first in the next couple of decades.
Technology for today’s tunnels
Like the Thames Tunnel, there’s no doubt that the world’s first floating underwater tunnel would be an incredible feat of engineering. However, the project can benefit from a number of technologies that weren’t available in the early nineteenth century, that might have significantly helped Brunel and the Thames Tunnel team:
- 3D modelling: Brunel’s design team had to make do with paper plans, drawn painstakingly by hand and passed between workers on the site. But today, engineers can used advanced 3D modelling to design and simulate new structures. With tools like virtual reality, stakeholders – including members of the public – can see the designs ahead of time
- Advanced scheduling: Sophisticated engineering projects take intricate planning, to ensure that schedules are followed and materials are available as needed. Digital planning tools can help project teams work out precisely when different labourers and materials will be needed, to avoid the kind of delays seen on the Thames Tunnel
- On-site (and off-site) collaboration tools: Ensuring that everyone is working from the same plans becomes even more important on advanced engineering projects, to avoid mistakes and miscalculations. The floating tunnel project is likely to involve multiple teams working away from the site. Digital collaboration platforms can ensure that every collaborator has the latest information to hand, to keep projects on track
Two hundred years separate the Thames Tunnel and the floating tunnel proposed today. But each case involves pioneers using innovative engineering concepts and cutting-edge technology to push the boundaries of construction.
The work of the Brunels has stood the test of time. The tunnelling shield innovations informed the technology that’s still used today and the Thames Tunnel itself is still used by Londoners to cross the water – even if it’s not on the gas-lit horse-drawn carriages originally planned. The Norwegian floating tunnel could represent another incredible world first – and let’s hope it can enjoy similar longevity.