How the world's longest underwater tunnel was built - English Channel

 

     The Underwater construction was started on 1960 many construction was built underwater in 1960 but no one was aware of it. But today everyone is aware about underwater construction techniques. English Channel Tunnel or Chunnel is one of them and one of the longest tunnel in the world its length is around 50 Km.       

     Flanked by two powerful European nations, the English Channel has long been one of the world's
most important maritime passages. Yet for most of its history, the Channel's rocky shores and and
stormy weather made crossing a dangerous prospect. Engineers of the early 1018 hundreds
proposed numerous plans for spanning the around 33 kilometer gap. Their designs included artificial islands
linked by bridges, submerged tubes suspended from floating platforms, and an underwater passage
more than twice the length of any existing tunnel. By the end of the century, this last proposal had
captured European imagination. 

     The invention of the tunnel boring machine and the discovery of a stable layer of chalk marl below the
seabed made this fantastic tunnel more feasible. But the project's most urgent obstacles were ones
no engineer could solve. At the time. Britain's viewed their geographic isolation as a strategic
advantage, and fears about French invasion shut down plans for the tunnel. The rise of aerial warfare
rendered these worries obsolete, but new economic concerns arose to replace them. 

     Finally, 100 years after the initial excavation, the two countries reached an agreement the tunnel
would proceed with private funding. In 1985, a group of French and British companies invested the
modern equivalent of £14 billion, making the tunnel the most expensive infrastructure project to date.
The design called for three separate tunnels one for trains to France, one for trains to England and
one service tunnel between them alongside crossover chambers, emergency passages and air ducts.
This amounted to over 200 tunnels. In 1988, workers began excavating from both sides, planning to
meet in the middle. 

     Early surveys of the French coast revealed the site was full of fault lines. These small cracks let water
seep into the rock, so engineers had to develop waterproof boring machines. The British anticipated
drier conditions and forged ahead with regular borrowers. But only months into the work, water
flooded in through undetected fissures. To drill in this wet chalk, the British had to use grout to seal
the cracks created in the borer's wake and even work ahead of the main border to reinforce the chalk
about to be drilled. 

     With these obstacles behind them, both teams began drilling at full speed. Boring machines weighing
up to 1300 tons drilled at nearly three 5 meters/hour. As they dug, they installed lining rings to
stabilize the tunnel behind them, making way for support wagons following each machine. Even at top
speed, work had to proceed carefully. The chalk layer followed a winding path between unstable rock
and clay, punctured by over 100 boring holes made by previous surveyors. 

     Furthermore, both teams had to constantly check their coordinates to ensure they were on track to
meet within 2 each other. To maintain this delicate trajectory, the borrowers employed satellite
positioning systems, as well as paleontologists who used excavated fossils to confirm they were at
the right depth. During construction, the project employed over 130 people and cost the lives of ten
workers. But after two and a half years of tunneling, the two sides finally made contact. British worker
Graham Fag emerged on the French side, becoming the first human to cross the Channel by land
since the Ice Age. 

     There was still work to be done, from installing crossover chambers and pumping stations to laying
over 100 miles of tracks, cables and sensors. But on May 6, 1994, an opening ceremony marked the
tunnel's completion. Full public service began 16 months later with trains for passengers and rail
shuttles for cars and trucks. Today, the Channel tunnel services over 20 million passengers a year,
transporting riders across the Channel in just 35 minutes. Unfortunately, not everyone has the
privilege of making this trip legally. 

     Thousands of refugees have tried to enter Britain through the tunnel in sometimes fatal attempts.
These tragedies have transformed the tunnel's southern entrance into an ongoing site of conflict.
Hopefully, the structure's history can serve as a reminder that humanity is at their best when breaking
down barriers. Fissures, leaks and cracks were a major obstacle in the construction of the English
Channel tunnel. But what if there was a type of concrete that could heal itself?
It's not science fiction. It's a modern, mind boggling material that could change the future of
engineering. Learn more with this article, or stay on track and explore the London Underground.

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