Original subtitles

Do you know where the longest tunnel in

the world is?The 5000 meter high Alps is

a natural barrier for Italy to the Nordic

region since 1980.

The traffic volume here has grown rapidly

and the existing roads and railways have

reached their limits and are often closed

due to bad weather.

In order to strengthen the connection

between the Nordic countries, engineers

decided to build a new tunnel across the

Alps. This is the St. Gothard Base Tunnel

in Switzerland, which cost nearly 70

billion and took 17 years to build.

It is 57 kilometers long, and its deepest

point is more than 2,440 meters

from the ground. It consists of two huge

tunnels with a diameter of 8 meters,

allowing trains to travel at a speed of

250 km/h for 100 years.

To understand the rock conditions around

the tunnel, they first dug a smaller

exploratory tunnel and then used a 20

million euro rock shield machine to

complete the tunnel excavation. At the

same time, another group of workers will

use explosives to blast and dig cross

tunnels and emergency shelters.

Although this segmented excavation method

can shorten the construction time by

half, engineers must ensure that the

tunnels can be accurately connected.

When building a straight Rd. on the

ground, there will be obstacles such as

trees, hills and buildings, which can be

easily solved by relying on navigation or

high towers.

But underground, even the slightest

misjudgment can have catastrophic

consequences, so engineers can only use

GPS to mark the entire tunnel line first.

But since there is no satellite signal

underground, each shield machine will

rely on a laser guidance system to

maintain its course.

Engineers will install a laser theodolite

on the tunnel wall and use the principle

of rectilinear propagation of light to

guide the shield machine to dig in a

straight line to ensure that the tunnel

direction does not deviate.

Because the shield machine is too large,

in order to facilitate transportation

from Germany to the construction site,

engineers disassembled it into sections

and transported it to the dock. Then

hundreds of heavy trucks were used to

cross mountains and narrow roads to

deliver hundreds of thousands of parts to

the entrance of the tunnel.

In the next four months, the shield

machine will be reassembled here.

Although this tunnel is only 57

kilometers long, it took 17 years to

build.

Every day, this shield machine can dig

forward 20 meters, but when it encounters

squeezing rock layers, it must stop.

It took a total of 17 years to build this

tunnel.

When many workers first built the tunnel,

their children were still in elementary

school.

After the construction was completed,

their grandchildren were born. In order

to build this tunnel, the engineering

team used 4 million tons of concrete,

which is equivalent to 40 times the

world's tallest building, the Burj

Khalifa. They excavate about 2,000 tons

of rubble every day, and then transport

it to the outside of the tunnel through a

conveyor belt. The factory here will

recycle the rubble and process it into

concrete ring segments. Not keeping up

with the progress of the shield machine,

The segments will be transported to the

depths of the tunnel 24 hours a day.

Workers use mechanical arms to install

the 4-ton concrete segments to the

appropriate position. These segments are

of different sizes and different

interfaces. Each piece contains two

layers of thick waterproof membranes.

Workers must assemble them carefully to

ensure the integrity of the tunnel. As

the shield machine moves forward, workers

pour concrete on the outer layer of the

segments to enhance the tunnel strength.

The inner wall of the tunnel was also

formed synchronously and the workers

behind installed the track and signal

system at the same time.

But when the shield machine encountered

softer squeezed rock, the workers had to

use the initial drilling and blasting

method.

In order to speed up the progress of the

project, they used an advanced 3D rock

drilling trolley, which sprayed water

while the drill bit rotated to cool the

constantly heated drill bit and improve

the working environment of the workers.

In order to break the rock into small

pieces that can be cleaned, each

explosive will explode with the next

explosive for a millisecond of rock.

After the blasting is completed, the

surface of the rock wall is uneven and

the workers will spray a layer of

concrete on the surface and support it

with concentric ring brackets.

This bracket is different from the

traditional rigid arch frame. It can move

within a certain range and resist the

pressure of mountain squeezing.

Although building this tunnel was a very

challenging project, the workers

persisted and finally successfully

completed the task. So, what kind of

tunnel is safe?The train is running in

the tunnel and the view is not wide.

In order to ensure the safety of

passengers, the engineers of the Saint

Gotthard Base Tunnel designed 2 one way

tracks which completely prevented the

collision of two trains, but they still

faced the threat of fire.

In 1999, a serious fire accident

occurred in the 11 kilometer Mont Blanc

Road Tunnel.

A truck suddenly caught fire in the

center of the tunnel. The fire quickly

engulfed more than 30 cars around it. The

tunnel was filled with a lot of smoke,

and the surrounding temperature instantly

soared to more than 1000 degrees.

It took more than 50 firefighters 3 days

to put it out, and the fire killed 39

people, most of whom died from inhaling

toxic fumes. The Gotthard Base Tunnel is

57 kilometers long, and the consequences

would be disastrous if a fire broke out.

Therefore, engineers built three

emergency shelters inside the tunnel.

Passengers can enter the 470 meter long

central shelter through fire doors, where

they can wait for rescuers, who will use

another tunnel to get there.

To prevent toxic gases from entering the

shelter, the ventilation system will be

remotely activated and powerful fans

above the track will suck in toxic fumes

and exhaust them from the exhaust vents

above.

At the same time, imported fans will

replenish clean air in the tunnel.

This ingenious safety system adds

38.5 million francs to each shelter.

The total cost reached 95.6 billion

Swiss francs, which is equivalent to

about 68.1 billion yuan.

According to official data, the tunnel

only reduced the travel time between

Milan and Zurich by 50 minutes, which is

not much more efficient, but it can

better withstand the changing climate and

traffic of the mountains, making trade

between European countries closer.

In short, the Gotthard Base Tunnel is a

testament to the ingenuity and skill of

modern engineering. It is an incredible

achievement that connects countries and

enables faster and more efficient

transportation. Who knows?Maybe one

day you will have the opportunity to

experience this impressive tunnel in

person.

Thanks for joining me on this tour of

Gothard Base Tunnel.

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