| Fact file |
When built: 1994
Height: 7.6m
Length: 50.45km
Depth: 40-75m below the sea bed
Workforce: 13,000
Timescale: Six years
Construction material: Concrete and steel
Capacity: 4 million cubic metres of chalk were excavated on the English side alone |
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A tunnel connecting Britain and France has been an engineering holy grail since the early 19th century. The first attempt at a tunnel excavation began in 1880, but the project was abandoned soon after and workings lay dormant for a hundred years.
In 1988, international treaties were signed and once more excavation work began in earnest.
At 50km from Kent to Normandy, with a full 39km passing 40m under the English Channel seabed, the Channel Tunnel is the world’s longest marine subway.
One of the most ambitious and costly engineering projects of its day, the Channel Tunnel cost £9 billion – enough to pay for the Golden Gate Bridge 700 times over.
Transmanche Link - the engineering firm behind the project – used seismic profiling technology, developed for deep-sea oil exploration, to check exactly what was under the seabed. This helped guide the excavations away from the soft clay beneath the Channel, giving the tunnel sturdy foundations in solid bedrock.
It took three years for the mammoth boring machines – which began simultaneously grinding away on either side - to meet under the middle of the Channel. The tunnel actually consists of three individual passages: 7.6m diameter tunnels carrying the trains, and a 5m diameter central tunnel for services and emergency access.
In its first six years of operation, 112 million passengers used the service.
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