The Channel Tunnel Has the World's Longest Undersea Stretch
Of its 50 kilometres, nearly 38 run beneath the English Channel — the longest undersea section of any tunnel on Earth.
The Channel Tunnel between England and France, officially opened on 6 May 1994, runs 50 kilometres (31 miles) from coast to coast. What sets it apart is the middle: 37.9 km of it lie beneath the seabed, the longest undersea section of any tunnel in the world.
It is really three parallel bores — two single-track rail tunnels carrying trains in each direction, plus a smaller central service tunnel that handles ventilation, maintenance and emergency escape.
Tunnelling crews dug from both the English and French sides, boring through a band of soft, waterproof chalk marl chosen precisely because it kept the seawater out. At its deepest the route passes about 75 metres below sea level.
The two ends had to meet in the middle with extraordinary precision after years of digging from opposite shores — a feat of surveying as much as of excavation.
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