By Paul Gorman
People and substances are rarely content staying in one place. It’s always a matter of wanting to go from A to B. That’s the same whether it’s the flow of money or jobs, or the force of gravity.
But geography often gets in the way. In difficult terrain or where there is high population density, the dream A to B route may be impossible. Rushing to the rescue are engineering and technology. How about tunnelling straight through the middle of that mountain or under the ground?
Tunnelling projects can be lengthy and cost billions of dollars. The final price tag will depend on how tricky the construction is, based on the depth and length of the tunnel, the rock and soil conditions around it, the need to use heavy tunnelling equipment such as boring machines, and the development’s complexity in terms of secondary tunnels, stations and storage areas.
Tunnels are not just conduits for people and freight travelling along roads and railways. They can be used by ships, in mining operations, as sewers, and for freshwater supply.
Here, then, are a handful of tunnels, chosen by Seequent Segment Director Civil Pat McLarin, which are changing the way people live:
The seabed stretch of the Channel Tunnel is 37.9km long, making it the longest underwater tunnel in the world.
The Channel Tunnel
The only fixed-link between Great Britain and mainland Europe since way before Brexit. The £4.65 billion (1994 figures), 50km-long tunnel connects Folkestone with Coquelles near Calais and was opened in 1994 after six years of tunnelling, using up to 11 boring machines cutting through sedimentary rocks from both ends. The section below the seabed of the English Channel is 37.9km long, making it the longest underwater tunnel in the world. Its three tunnels have carried nearly 500 million passengers since it was opened .
The Gotthard Base Tunnel is notable for being the first flat route through a mountain range.
Showdown in The Alps: The Gotthard Base Tunnel vs the (under construction) Brenner Base Tunnel
The former, between Switzerland and Italy, is currently the world’s longest and deepest railway tunnel, 2300m down and 57.1km in length. Opened in 2016, it is especially notable for being the first flat route through any mountain range. However, the new Brenner Base Tunnel, between Austria and Italy, promises to take top honours and will be 64km long, using part of the 12.7km Inn Valley Tunnel too. The estimated cost is currently €10.5 billion, with completion scheduled for 2032.
Connecting fjords – the Stad Skipstunnel
In The Hitchhiker’s Guide to the Galaxy, planet designer Slartibartfast says he won an award for the coast of Norway. He may have mixed views about this construction project, a now 5.1 billion Norwegian kroner tunnel for ships, expected to begin this year, which will allow vessels of up to 16,000 tonnes to travel through mountains between two fjords and avoid the storm-wracked Stadhavet, the most dangerous stretch of Norwegian coast.
The Mponeng Gold Mine in South Africa is a mind-boggling 3891m below ground, making it the world’s deepest tunnel.
Photo: Stock image
World’s deepest tunnel – the Mponeng Gold Mine in South Africa
The depth of Mponeng, about 90km from Johannesburg, is mind-bending, plummeting to 3891m below ground level, or 2062m below sea level. The most economic gold reefs are being mined between 3160m and 3740m under the surface. The mine, opened in 1986, is Harmony’s largest gold producer, with about 18% of its total yield. Production in the last financial year was 17% higher at 281,350 ounces compared with 239,490oz the previous year.
Environmental concerns – the Parallel Thimble Shoal Tunnel Project
There is already one two-lane tunnel between artificial islands crossing the state of Virginia’s environmentally sensitive lower Chesapeake Bay. The new $US1.074 billion project will add a second tunnel to the 28km-long bridge and trestle scheme, allowing two lanes of traffic southbound as well as northbound. It is expected to open early in 2028.
The Thames River is cleaner thanks to the Thames Tideway which has kept an estimated 6.2 million cubic metres of sewage from the river since becoming operational in August 2024.
Super sewer – the Thames Tideway
London’s River Thames is now a lot cleaner, thanks to the commissioning of the about £5 billion 25km-long sewer which diverts raw sewage for processing at the Beckton treatment works in east London. For many years the city’s existing infrastructure has been operating at capacity, handling sewage and rain runoff, and even light showers could trigger overflows into the river. The 7.2m-wide tunnel starts in west London, runs close to the path of the river and into the Lee Tunnel. Since August last year, it has kept an estimated 6.2 million cubic metres of sewage from the river.
London was the first city to have a mass-transport underground rail network, transforming the way people live in big cities.
The Tube – the London Underground
London isn’t the only large city to have a mass-transport underground rail network but it was the first, with the opening of the London Metropolitan Railway, using shallow cut-and-cover tunnels, in January 1863. The electrified grid has grown to 11 main lines with more than 270 stations.
On any average day, there are around four million passenger journeys, with close to 1.2 billion each year. It’s now difficult to imagine any city of this size or larger being able to work efficiently without tunnels below speeding people to their destinations.
