Two teams dug under the sea from opposite shores and missed by only 30 centimetres.
Building the Channel Tunnel, British and French crews bored towards each other beneath the seabed. When the service tunnel broke through in 1990, the two halves were misaligned by just 30 centimetres sideways and 8 vertically. People had dreamed of the tunnel since 1802; it took until 1994 to open.
The idea is old. In 1802 the French engineer Albert Mathieu-Favier proposed a tunnel lit by oil lamps, with horse-drawn coaches and an artificial island mid-Channel for changing horses. In the early 1880s, boring machines actually dug nearly two kilometres from each side before the project was abandoned in 1883, after the British military warned that a tunnel might become an invasion route. Another attempt was cancelled by Britain in 1975.
The successful project began in 1988, led by Eurotunnel. Eleven tunnel boring machines cut three parallel tunnels: two for trains and a smaller service tunnel between them. The route followed a layer of chalk marl, a rock with enough clay to be watertight yet soft enough to cut easily; engineers tried to keep in its lower part, above a clay that swells when wet. The French side, with more difficult and faulted geology, used sealed machines that could withstand high water pressure.
On 1 December 1990 Graham Fagg from England and Philippe Cozette from France broke through the service tunnel in front of the cameras. A BBC commentator called Fagg the first man to cross the Channel by land for 8,000 years. The British boring machines were then steered downwards and buried beneath the tunnel, where they now serve as an electrical earth, while the French machines were dismantled.
The tunnel is 50.5 kilometres long, with 37.9 kilometres under the sea, the longest undersea section of any tunnel in the world. It came at a cost, human and financial: ten workers were killed during construction, and the final bill of £4.65 billion was an 80 per cent overrun. Traffic forecasts were too optimistic, and Eurotunnel needed a financial restructuring within a few years of opening.
Source: Wikipedia — Channel Tunnel · Text summarised from Wikipedia (CC BY-SA 4.0)
