It was built below the seabed, underground, and not in the water, as many people think. Inaugurated in May 1994, the Channel Tunnel connects France and England and is 51 kilometers long. After consuming six billion dollars, it became the most expensive work in the world paid entirely with private money. Raising all that money and coordinating a consortium of dozens of contractors, banks, investors and shareholders was as or more difficult than digging the tunnel – and all of this dealing with the culture and laws of two different countries. “While the engineering challenges were the most hyped, they were actually the easiest to overcome. Of course, we shouldn’t underestimate them, but the problems of financing, logistics, environment and politics to carry out a gigantic project like this were very complicated obstacles”, says engineer John Neerhout Jr., executive director of the project for the company in charge tunnel concession.
The achievement is even greater if we consider that there were more than 200 years that tried to make this idea viable. At the beginning of the 19th century, the project of a tunnel excited Napoleon, the French emperor at the time, but the British, fearing that the passage would facilitate an invasion of Great Britain, did not let the thing go ahead. Incidentally, this fear of the British military was the biggest obstacle to the construction of the tunnel until the end of World War II (1939-45). In 1984, finally, the two countries signed a treaty authorizing the work and, in 1987, it began. Four years later, in record time, French and British workers met deep underground and opened champagne to celebrate the feat. The tunnels, which were being dug on both sides of the channel, were only a few centimeters misaligned. A true precision marvel.
Work passes 50 meters below the seabed
1 – The tunnel was excavated in a layer of calcareous clay – a kind of chalk. On average, it lies 50 meters below the North Sea bed. Geological studies, with sonar, radar, drilling and dynamite explosions, looked for the safest path for the tunnel. Between 1958 and 1987, 94 geological drillings were made in the region
2 – The excavation was carried out with equipment called TBM, which stands for “Tunnel Drilling Machines”. Monstrous robotic moles measuring 8 meters in diameter, the TBMs were telescopic, meaning they could shrink and extend. Fully extended, they reached 200 meters in length, or two football fields.
3 – Three tunnels were drilled. By the two outer ones, trains pass, one in each direction. The middle one serves for maintenance operations and as an emergency exit. Every 375 meters, passages connect the three tunnels. At two points along the route, there are huge caverns that allow trains to change from one tunnel to another, if necessary.
4 – Every 1.5 meters of excavation, the tunnels were lined with a precast concrete ring, divided into segments and assembled on the spot. In some parts, the gaps between the rings and the walls of the excavated tunnels were filled with liquid cement. Assembly of a single ring took 50 minutes
5 – Every 250 meters, small ducts were built connecting the upper part of the two main tunnels. Such ducts are important to relieve the air pressure produced by the rapid movement of trains.
6 – After the tunnels were excavated and lined, all the electrical and safety systems were assembled. Several pumps remove water that comes from infiltrations and cold water pipes control the heat caused by the friction of the trains, creating a comfortable temperature inside the tunnels
7 – The two main tunnels are covered by the Eurostar – a bullet train for cargo and passengers – and by the Euro Tunnel – a special train capable of transporting drivers with their cars. The crossing takes 35 minutes and is the fastest way to travel between the two countries, because by plane you lose a lot of time at the airports
England “grew” almost 370 thousand m²
The limestone earth that was excavated for the construction of the three tunnels was brought to the surface by a combination of pumps, wagons, tracks and tractors. But what happened to her? The land served to cover certain coastal areas. With the remains of construction, England alone gained almost 370,000 square meters in its territory, the equivalent of 53 football fields. Today, this landfill is a recreational area, used for walks, picnics and fishing.