The "Chunnel"

Great Britain and France are separated by the English Channel, a body of water that connects the Atlantic Ocean to the North Sea. The Channel ranges in width from 240 kilometers to a mere 34 kilometers between Dover and Cap Gris-Nez. This natural barrier between the British Isles and continental Europe isolated the British from the rest of Europe. Around the early 1800s, some enterprising people began to think about the idea of building a tunnel under the English Channel linking Britain with Europe. During the 19th century, several attempts were made to start digging, but the task was too great and these early efforts came to nothing.

In 1986, the governments of France and Britain decided to cooperate in building a channel tunnel. They signed "The Channel Tunnel Treaty" in which each country agreed to finance half of the project. The tunnel, which became known as the "Chunnel", would include a 50 km rail connection running under the English Channel at an average depth of 45 m between Folkstone, England, and Calais, France.

The engineers assigned to do the work were faced with a huge challenge. Not only would they have to build one of the longest tunnels in the world; they would also have to convince the public that passengers would be safe in a tunnel this size. How did the engineers resolve this problem? They built an escape route.

The Chunnel actually consists of three tunnels. There are two rail tunnels, each 7.6 m in diameter, and a central tunnel, 4.8 m in diameter, that is used for maintenance, ventilation and as the emergency escape route. There are also several "cross-over" passages that allow trains to switch from one track to another The depth of the tunnels below the seabed averages about 45 m.

Just one year after the Chunnel opened, this engineering design was put to the test. Thirty-one people were trapped in a fire that broke out in a train coming from France. The design worked. Everyone was able to escape through the service tunnel.

Construction began in 1987. The Chunnel would be built from two sides, the French and British engineering teams each digging independently from their respective starting points (Calais and Folkstone). The two countries differed in their techniques and equipment. Both sides used huge tunnel-boring machines to dig parts of the tunnel but the French were still more advanced in other machinery. They used machine-built cages to reinforce the tunnel while the English used hand-made, steel tunnel-liners and concrete segments.

British and French tunnel workers raced to reach the middle of the tunnel first. The British won. In 1990 the two sections of the tunnel met up. Today, trains roar through the tunnel at speeds up to 160 km per hour and it's possible to get from one end to the other in only 20 minutes!