Thirty years ago, the Channel Tunnel—the tunnel connecting England and France—began operations.

The Idea

Wanting to build a tunnel under the English Channel goes back centuries. French mining engineer, Albert Mathieu-Favier, pitched it to Napoleon Bonaparte in 1802. Napoleon liked the idea, but the British didn’t. They worried Napoleon would use the tunnel to invade England.

On and off over the next two centuries, various plans to connect the two countries were proposed but none succeeded. Each time the tunnel idea popped up, something shot it down. Political discord, financial problems, and fear of invasion all kept the idea from becoming a reality.

Did You Know…

• In 1839, a French engineer performed the first geological and hydrographical surveys of the English Channel between Calais, France, and Dover, England.
• In 1866, an English civil engineer surveyed the floor of the Strait of Dover. Finding it composed of chalk like the adjoining cliffs, he proved a tunnel was feasible.
• In the early 1880s, one plan got off the ground, but after digging a mile of tunnel, the project was abandoned.
• Because of invasion fears, early designs included the ability to flood or blow up the tunnel.
• Winston Churchill advocated for a channel tunnel in the 1920s and 1930s.
• By 1955, planes made the fear of invasion through a tunnel irrelevant.
• In 1964, the U.K. and France officially agreed to build a channel tunnel, but construction didn’t begin until 1974. Then, a year later, amid the growing economic crisis, Britain pulled out.
• Illegal immigrants using the tunnel wasn’t an initial worry, but the spread of rabies through it was. Britain has been rabies-free since 1902, so officials worried infected animals might come into the country through the tunnel.

The Tunnel

In 1978, national railways in England and France once again raised the idea of a tunnel. But it wasn’t until 1984, British Prime Minister Margaret Thatcher and French President Francois Mitterrand agreed a physical link between their countries would be mutually beneficial. Since neither country’s government could fund such a massive project, they decided to hold a contest. Contestants would submit plans for a link and a way to raise the funds needed to build it.

So, before the winner could begin digging, money had to be raised. Experienced engineers and 13,000 other skilled and unskilled workers had to be hired. Special tunnel boring machines had to be designed and built. And the exact location of the tunnel had to be determined.

Did You Know…

• Only ten proposals were submitted to the contest.
• Part of the contest’s directive was that the project must survive for at least 120 years.
• A consortium of British and French corporations and banks privately financed the tunnel build. (Over fifty large banks provided loans to the project.)

Tunnel Construction

The tunnel is under the English Channel, but it’s not in the water. It’s in the seabed under it, in a seam of marine sediment called Chalk Marl. Chalk Marl’s high clay content makes it impervious to water and perfect for a tunnel.

Tunnel excavations began in 1987-88. The English side used six tunnel boring machines (TBMs). The French side used five. Finally, on October 30, 1990, the French’s TBM met the British probe for the first time. Believe it or not, the difference in alignment was just 14.09449 inches horizontally and 2.283465 inches vertically!

Did You Know…

• Each TBM was 750 feet long, weighed over 15,000 tons, and cut through the chalk at fifteen feet per hour.
• English TBMs had technical names. French TBMs had women’s names.
• The U.K. increased its size by 90 acres with the “spoil” (chalk) removed from its side of the tunnel.
• As the TBMs cut through the chalk, the newly dug tunnel’s sides were lined with some of the strongest concrete in the world. This aided in waterproofing while helping the tunnel withstand the intense pressure from above.
• The Channel Tunnel was designed to leak. A mixture of groundwater and seawater naturally permeates from the material above. It’s collected at six drainage stations along the tunnel and is pumped away by five pumping stations.
• At the peak of construction, 15,000 people were employed on the tunnel build.
• During construction ten people were killed.

Tunnel Stats

The Channel “Tunnel” is actually three separate tunnels running parallel to each other: two rail tunnels for freight and passenger trains, and one service tunnel in between them for emergencies and maintenance. A year after the service tunnel was dug, digging was completed on the two rail tunnels. After that, crossover tunnels between the three tunnels and the land tunnels from the coast to the terminals had to be dug. Electrical and ventilation systems, train tracks, pumping stations, etc., had to be added. And the large train terminals on both sides of the channel had to be built. The full project was finally finished in late 1993.

Did You Know…

• The two train tunnels are 24 feet in diameter. One carries passengers from France to England, while the other carries passengers from England to France.
• Trains can change tunnels, if needed, in the tunnel’s “English and French Crossover.”
• Smoke doesn’t enter the service tunnel from the rail tunnels because the ventilation system keeps greater air pressure in the service tunnel.
• The Channel Tunnel is 31.35 miles long, the third-longest rail tunnel in the world. At its deepest point, it is 246 feet below the seabed and 377 feet below sea level. (On average, it’s about 148 feet below the seabed.)
• The Channel Tunnel’s underwater section is 23.5 miles long, making it the longest underwater tunnel in the world.
• Counting the smaller tunnels that connect to the rail and service tunnels, the Channel Tunnel contains roughly 95 total miles of tunnels.
• The Channel Tunnel is believed to be one of the most amazing engineering feats of the modern world. It’s the first fixed land link between the island of Great Britain and the European mainland since the Ice Age, about 8,000 years ago.