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تدريب الاستماع
تدريب الاستماع
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TED-Ed
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How the world's longest underwater tunnel was built - Alex Gendler
How the world's longest underwater tunnel was built - Alex Gendler
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ترجمة (77)
0:07
Flanked by two powerful European nations, the English Channel
0:12
has long been one of the world’s most important maritime passages.
0:16
Yet for most of its history,
0:17
the channel’s rocky shores and stormy weather
0:20
made crossing a dangerous prospect.
0:23
Engineers of the early 1800's proposed numerous plans
0:27
for spanning the 33 kilometer gap.
0:31
Their designs included artificial islands linked by bridges,
0:35
submerged tubes suspended from floating platforms,
0:39
and an underwater passage more than twice the length of any existing tunnel.
0:44
By the end of the century,
0:45
this last proposal had captured European imagination.
0:50
The invention of the tunnel boring machine
0:52
and the discovery of a stable layer of chalk marl below the seabed
0:57
made this fantastic tunnel more feasible.
1:00
But the project’s most urgent obstacles were ones no engineer could solve.
1:06
At the time,
1:07
Britons viewed their geographic isolation as a strategic advantage,
1:11
and fears about French invasion shut down plans for the tunnel.
1:16
The rise of aerial warfare rendered these worries obsolete,
1:20
but new economic concerns arose to replace them.
1:24
Finally, 100 years after the initial excavation,
1:27
the two countries reached an agreement—
1:29
the tunnel would proceed with private funding.
1:33
In 1985, a group of French and British companies
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invested the modern equivalent of 14 billion pounds,
1:40
making the tunnel the most expensive infrastructure project to date.
1:46
The design called for three separate tunnels—
1:49
one for trains to France, one for trains to England,
1:52
and one service tunnel between them.
1:55
Alongside crossover chambers, emergency passages, and air ducts,
1:59
this amounted to over 200 kilometers of tunnels.
2:04
In 1988, workers began excavating from both sides,
2:08
planning to meet in the middle.
2:10
Early surveys of the French coast revealed the site was full of fault lines.
2:15
These small cracks let water seep into the rock,
2:19
so engineers had to develop waterproof boring machines.
2:23
The British anticipated drier conditions, and forged ahead with regular borers.
2:28
But only months into the work, water flooded in through undetected fissures.
2:34
To drill in this wet chalk, the British had to use grout
2:37
to seal the cracks created in the borer’s wake,
2:40
and even work ahead of the main borer
2:43
to reinforce the chalk about to be drilled.
2:46
With these obstacles behind them, both teams began drilling at full speed.
2:52
Boring machines weighing up to 1,300 tons drilled at nearly 3.5 meters per hour.
3:00
As they dug, they installed lining rings to stabilize the tunnel behind them,
3:05
making way for support wagons following each machine.
3:09
Even at top speed, work had to proceed carefully.
3:13
The chalk layer followed a winding path between unstable rock and clay,
3:18
punctured by over 100 boring holes made by previous surveyors.
3:23
Furthermore, both teams had to constantly check their coordinates
3:27
to ensure they were on track to meet within 2 centimeters of each other.
3:32
To maintain this delicate trajectory,
3:34
the borers employed satellite positioning systems,
3:38
as well as paleontologists who used excavated fossils
3:42
to confirm they were at the right depth.
3:45
During construction, the project employed over 13,000 people
3:49
and cost the lives of ten workers.
3:52
But after two and a half years of tunneling,
3:55
the two sides finally made contact.
3:58
British worker Graham Fagg emerged on the French side,
4:02
becoming the first human to cross the channel by land since the Ice Age.
4:07
There was still work to be done—
4:09
from installing crossover chambers and pumping stations,
4:12
to laying over a hundred miles of tracks, cables, and sensors.
4:17
But on May 6, 1994, an opening ceremony marked the tunnel’s completion.
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Full public service began 16 months later,
4:26
with trains for passengers and rail shuttles for cars and trucks.
4:31
Today, the Channel Tunnel services over 20 million passengers a year,
4:36
transporting riders across the channel in just 35 minutes.
4:41
Unfortunately, not everyone has the privilege of making this trip legally.
4:46
Thousands of refugees have tried to enter Britain through the tunnel
4:50
in sometimes fatal attempts.
4:52
These tragedies have transformed the tunnel’s southern entrance
4:56
into an ongoing site of conflict.
4:59
Hopefully, the structure’s history can serve as a reminder
5:02
that humanity is at their best when breaking down barriers.
