Original subtitles

[narrator] Deep beneath the Alps, an elite team of engineers is

embarking on an extraordinary mission.

They are attempting to build the longest underground

railway tunnel ever constructed.

To succeed, they must drive giant tunnel drilling machines

through solid mountains.

Overcome unpredictable geology deep beneath the surface...

Attention!

...and crushing pressure...

...to build a revolutionary rail line that will transform

how Europe moves people and goods

for generations to come.

This incredible mega tunnel ranks in a league of ambitious

new engineering wonders that are bigger, faster,

taller, and more advanced

than anything ever constructed before.

This is the inside story of the extraordinary challenge of

building these giants.

♪♪

France and Italy are two of Europe's economic powerhouses.

Every year, over $100 billion worth of goods,

from food to fuel, moves between them.

But one of Europe's greatest natural barriers

separates these two nations --

the Alps.

For centuries, travelers and trade have had to

cross the mountains the hard way --

through deep valleys, narrow passes,

and winding routes.

But now, engineers are attempting

something extraordinary.

A joint French and Italian operation is building

a colossal 165-mile railway line to link Lyon in France

with Turin in Italy.

When complete, it could cut greenhouse gas emissions

by over one million tons,

and slash journey times across the mountains from almost

four hours to under two.

At the heart of the project

lies its most ambitious section.

Instead of going over the Alps,

the engineers are digging straight through them.

This is the Mont Cenis base tunnel,

a vast railway tunnel being carved deep beneath the Alps.

Stretching over 35 miles,

it will be the longest railway tunnel in the world.

And it must be ready by 2033.

It's the responsibility of CEO Maurizio Bufalini to keep

this vast international project on time and on budget.

[Maurizio] The cost of this project is 11 billion euros.

But it's not simply a cost, it's really an investment on

the future of Europe.

♪♪

Halfway between Lyon and Turin, the tunnel will link

Saint-Jean-de-Maurienne in France

to Susa in Italy, over 35 miles away.

Engineers are digging two enormous tubes,

each nearly 30 feet in diameter,

side by side, beneath the mountains.

One carries trains toward France, the other toward Italy.

Every 1,100 feet, passages connect the two

tunnels to create vital escape routes in an emergency.

Above the tunnel, engineers are also drilling four vertical

shafts, each hundreds of feet deep,

to help ventilate the tunnel.

When complete, trains will race beneath the Alps

at speeds around 125 miles per hour.

Work on this mega-project begins in 2001.

It takes 14 years to excavate almost 11 miles of preparatory

tunnels to study the rock, the water,

and the immense pressures deep beneath the Alps.

Now, engineers are preparing to

drive the two railway tunnels through the mountains.

Overseeing this vast operation is Constructions Director

Emmanuel Humbert.

In total, the railway project requires workers to excavate

37 million tons of rock across a 100 mile route,

enough to fill around 6,000 Olympic swimming pools.

This is how Emmanuel and his team will do it.

First, engineers dig an 11-mile network of four access points

and two tunnel portals at either end.

They divide the excavation into sections,

numbered from CO1 to CO9.

This allows engineers to work from several different

locations at once.

Underground, they assemble eight giant tunnel boring

machines, or TBMs.

These launch from different points within the Alps.

Attacking the mountain from multiple places

helps the engineers to reduce construction time.

Eventually, these sections will join to create

one continuous route.

♪♪

Engineers need a mega machine to dig

all the sections of this record-breaking tunnel.

Viviana is a tunnel boring machine, or TBM.

She's almost 600 feet long and weighs 2,500 tons.

The first challenge engineers face is to get the machine onto

the site and into the tunnel.

A manufacturer in Germany fabricates Viviana.

The engineers must transport the machine more than 300 miles

from the factory to the dig site

in Saint-Jean-de-Maurienne.

She's too big and heavy to transport in one piece,

so workers break her into sections.

A fleet of low loaders transports the parts

to the CO7 tunnel site.

Safety vehicles shepherd the truck for this hazardous

journey along narrow country roads.

And through small Alpine villages

with just inches to spare.

Now, the engineers need to assemble Viviana.

First, they lower each of her mega components through

an access point into the tunnel below.

Each one weighs an average of 66 tons.

Next comes the assembly stage.

At the front of the machine is the cutter head,

a wheel that weighs roughly 330 tons

and carries 61 disc cutters.

This is the part of Viviana that will grind the rock to

excavate the five and a half mile section

of the Mont Cenis base tunnel.

The engineers successfully assemble Viviana's critical

front section.

They turn the machine 90 degrees to access

the rock face.

It takes workers six months to

build the huge rear section of the tunneling machine.

Viviana is now ready to punch her way beneath the Alps.

Engineers in France and Italy are digging the world's longest

railway tunnel beneath the Alps.

Their next challenge is to complete the first section of

the over 35-mile route

from Saint-Martin-la-Porte to La Praz.

The nearly 600-foot-long tunnel boring machine,

Viviana, is vital.

The tool engineers will use to excavate the rock face is

the 34-foot-wide cutter head at the front of the machine.

It consists of 61 cutters made of tungsten.

The head completes up to three rotations a minute to excavate

2,200 tons of rock in a day.

At its fastest, the machine can excavate nearly 50 feet of

mountain every 24 hours.

But as the machine drives deeper beneath the Alps,

the team faces a dangerous challenge.

Every foot it cuts leaves

a stretch of excavated tunnel behind it.

The weight of the mountains can cause the newly opened ground

to close up.

This movement is called convergence.

[Emmanuel speaks]

If the team fails to support the excavation fast enough,

the mountain can distort the tunnel,

drop unstable rock onto the machinery,

or even trap the machine underground.

This is the team's solution to

prevent a catastrophic tunnel collapse.

A mechanical erector arm lifts the precast concrete segments

into place.

Each curved segment weighs 11 tons.

Together, the segments form a complete ring

that supports the tunnel.

Once the ring is complete, hydraulic rams push against it

and drive the machine forward.

The machine then excavates the next section of tunnel.

Behind the shield, engineers inject grout into

the gap between the lining and the rock.

The grout fills the void, stabilizes the ground,

and seals the tunnel.

It's Guillaume Lefrere's responsibility to make sure

the tunnel remains stable for that long.

The machine's robotic arm delivers

the first concrete segment.

It must place it with millimeter accuracy.

Small errors that accumulate over the length of the tunnel

could create a dangerous misalignment.

[Guillaume speaks]

The machine's workers slot the segment into position.

One by one, the arm lifts and places

the remaining segments

to create a complete ring

around the inside of the tunnel.

This rigid collar is strong enough to resist the weight of

the mountain above it.

The next challenge for the engineers is to ensure that

Viviana is heading in the right direction.

It's critical that she follows

a precise route to dig her section.

Any deviation will mean that her tunnel will not line up

with the other tunnel sections.

Correcting the misalignment will put the engineers

behind schedule.

Engineers in France and Italy are digging the world's longest

railway tunnel beneath the Alps.

The nearly 600-foot-long tunnel

boring machine, Viviana, is vital.

To keep Viviana on track, her driver, Christelle Desmons,

relies on a special digital guidance system.

[Christelle speaks]

Engineers above ground use GPS to plot

the tunnel's exact path.

Underground, Christelle tracks Viviana's course relative to

the planned route.

The guidance system warns

Christelle when Viviana drifts offline.

Christelle then adjusts the angle of the machine to

correct the deviation and keep the tunnel on course.

♪♪

For now, Viviana is right on track, and she continues

tunneling towards the team digging in La Praz,

five and a half miles away.

To stay on schedule, the machines digging

the 35-mile-long Mont Cenis base tunnel

need a steady supply of concrete segments.

The tunnel's location creates a big problem

for the engineers.

The nine sites above ground are isolated

and sit in narrow alpine valleys.

The CO7 site that supports

the tunneling machine Viviana is no exception.

Trucking in concrete segments will clog up the narrow

mountain roads with traffic for a decade.

The engineers' solution is to make what they need

from the tunnel itself.

Viviana excavates 2,200 tons of material a day.

It's critical that the supply of concrete components keeps

pace with the demand from the tunneling team.

So the engineers build this --

the Illaz Transformation Plant.

It's a huge concrete factory near the tunnel entrance that

turns the rock that Viviana

excavates into building materials.

Project Director, Sébastien Paulet,

oversees the operation.

Once the rock arrives at the plant,

the recycling process begins with quality control.

The plant feeds material into powerful industrial crushers.

These break the rock down into smaller and smaller pieces.

These pieces then pass over a vibrating screening system

that separate them into different grain sizes

for different purposes.

At every stage, machines monitor the material

for impurities.

An industrial washer then removes dust, clay,

and other unwanted material from the crushed stone.

The final product is then dried and emerges as aggregate.

The material this factory makes is turned into concrete

segments for Viviana to line the walls of the tunnel.

Workers will also use it as backfill for stations

and viaducts along the route between Turin and Lyon.

♪♪

The Mont Cenis base tunnel project aims to process over

25 million tons of rock, and to reuse at least half of

the excavated material.

The project underground could slow to a crawl

if Sébastien's plant fails to keep up with demand.

But for now, the entire operation is on track.

Today, the team has produced 880 tons of aggregate.

[Sébastien speaks]

Engineers in Italy and France are building the world's

longest railway tunnel under the Alps.

Punching a hole this long beneath a mountain range

presents them with a big challenge.

The Alps are made from 15 different types of rock,

from hard, gneiss, and metasandstone

to flaky layered rock called schist

and fractured limestone that holds vast amounts of water.

The hole a tunnel boring machine makes through gneiss

holds its shape because of the strength of the rock.

This makes it easy for the crew

to reinforce the tunnel with concrete.

But a tunnel through the wetter, less stable rock

is more likely to contract

as the huge weight of the mountains above

pushes down on it.

This creates a big problem for the engineers, as they discover

close to the Saint-Jean-de-Maurienne

section of the tunnel.

[Maurizio] We have found the ground very full of water.

And when you do the excavation, you excavate ten meters.

In a few days, it was closing of two meters.

It was incredible.

If you have a situation like this with a tunnel boring

machine, the tunnel boring machine has not the time to

create the ring, and so it will be blocked in the mountain

and then will die inside.

A tunneling machine works best

when the geology is predictable.

When it's not, the engineers turn to

explosives to smash big holes in the rock.

This method is called drill and blast.

It gives engineers more control because they can excavate

the tunnel in short sections and inspect the ground

after every blast.

Drilling rigs bore dozens of holes into the rock face in

a precise pattern.

Engineers position each hole to control

how the rock will fracture.

Next, crews load the holes with measured explosive charges.

Electronic detonators link the charges and fire them in

a timed sequence.

The blast then ripples through the rock

in fractions of a second.

The force drives forward, breaks the rock face,

and protects the tunnel walls.

Crews clear the rubble.

Then, they spray shotcrete onto the walls.

This quick-drying concrete firms the tunnel

and stops it from contracting.

By using this method, the team can carve out up to

13 feet of tunnel and 880 tons of rock every day.

Constructions Director Emmanuel Humbert oversees

this delicate process.

Emmanuel's team builds a digital 3D profile of

the rock face using data from surveys and laser scanning.

This shows precisely where the explosive charges need to

go to ensure the rock fractures cleanly.

A huge machine called a jumbo drills the holes in the rock.

At the ends of the jumbo's three hydraulic arms are

powerful drills that punch into the rock simultaneously.

The jumbo uses the digital pattern to drill the holes to

a precise position, angle, and depth.

Each hole must follow the drill pattern precisely.

Just one misaligned hole,

and the explosion could fail to break the rock cleanly.

[Emmanuel speaks]

Next, workers load each hole with an explosive charge.

Blasting the rock is a delicate

and perilous balancing act.

Too little power and the blast will fail to break

the rock cleanly.

Too much and the tunnel itself could be put at risk.

With the charges set, the crew

retreats to a safe distance

and prepares for the detonation.

Attention!

Nelson Gomes Pina and a small team of miners assess

the results of the blast.

[speaks French]

[in English] An excavator shovels the hundreds of tons of blasted

rock into waiting dump trucks.

These take it to the Illaz processing plant,

where the rock is turned into aggregate to make concrete

segments that line the tunnel.

It takes the team two hours to clear the debris and prepare

the face for the next cycle.

♪♪

Engineers building the world's longest railway tunnel are

blasting their way through the rock beneath the Alps.

Attention!

They're constructing the over 35-mile long tunnel in separate

sections that will join into one length.

A team clears away the rubble

from a controlled blast in tunnel section CO8.

The next challenge is to make the freshly blasted tunnel safe

for the crews that will install its concrete lining.

The team uses a mechanical breaker to smash any dangerous

overhanging rock left after the blast.

[machinery beeps]

The next task is to line the tunnel

with a material that will stabilize it.

The team uses a substance called shotcrete,

a fast-setting concrete that workers fire from special hoses

at high speeds.

It sticks to the rock and dries quickly to form a hard

protective shell that helps to hold the tunnel shape.

♪♪

[music ends]

With the shotcrete dry, the tunnel is ready for

the next stage of construction.

It is the responsibility of Georgiana Noreanu Bocur

to oversee the installation of

the tunnel's permanent concrete lining.

The shotcrete is only designed to ensure

the short-term durability and safety whilst the works of

excavations are carried out.

If we don't install the permanent lining all

around, the tunnel, yeah, might cave in at long-term.

Georgiana's team faces a big problem.

The extreme pressure nearly 1,500 feet beneath the Alps

forces groundwater into the tunnel.

The team must stop this water and make sure the tunnel is dry

before they line the wall with concrete.

Water is a really big problem in the tunnel because when it

gets in contact with the concrete, it may infiltrate

and may create, like, micro cracks, which may develop

in time and actually damage the lifespan of the concrete.

This is why we are installing all of

the waterproofing layers.

The waterproofing consists of three special sheets --

a membrane that repels water,

a super strong textile that prevents punctures,

and an inner layer that

protects the waterproofing from jagged edges.

Now it's time to line the tunnel with concrete.

First, the team cuts and welds nearly 4,500 tons of steel

rebar to make the bottom curve of the tunnel section.

They then pour 2,825 cubic feet of concrete

at a time into this frame.

The steel strengthens the concrete

and extends its lifespan.

We need to ensure a permanent concrete lining at least

50 centimeters thick.

We have to build the tunnel

basically for a lifespan of 120 years.

So this is to ensure the long-term durability

of the tunnel.

It takes the workers two hours to finish the first stage.

They then raise the height of the next concrete pours

until the whole tunnel is lined.

By the end of the day, Georgiana's team completes

32 feet of tunnel.

[Georgiana] Wonderful teamwork again today!

We've got a big job ahead.

So this is one concrete pour down and still a couple of more

kilometers to go.

But smashing through the rock creates huge clouds of dust

and sometimes releases pockets of toxic gases.

Prolonged exposure to these could damage the health

of the team underground.

The engineers' solution is to dig four ventilation shafts at

the halfway point in the tunnel.

Technical manager Helene Roulet

oversees this part of the construction.

[Helene speaks]

Helene's team must dig two pairs of vertical shafts from

the surface down to the tunnel below.

[Helene speaking]

Digging shafts this deep is a huge engineering challenge.

This is how Helene's team will do it --

engineers drill a pilot hole from the surface to the tunnel,

about 1,600 feet below.

The hole is just 15 inches wide,

the size of a dinner plate.

If the drill drifts by more than nine inches,

it could miss the tunnel.

At the bottom, crews attach a giant cutting head

called a reamer.

This steel disk spans 17 feet

and carries dozens of hardened cutters.

A winch pulls the reamer up through the mountain.

As it turns, the reamer chews through the rock and opens

a 17-foot ventilation shaft.

♪♪

The team positions the drill,

and it begins boring the pilot hole.

Its target is the tunnel about 1,600 feet below.

After six weeks, the drill bit breaks through

the tunnel's roof.

Next, a team inside the tunnel constructs the reamer

from 32 special discs.

The team above ground spins these cutters and pulls them up

to bore out a huge 17 foot diameter shaft.

Helene's team constantly monitors the reamer

to make sure it cuts the rock cleanly and efficiently.

It takes the team two and a half months to excavate

the over 1,600 feet to the surface.

The engineers' next challenge

is to secure the walls of the shaft.

Loose rock could fall and injure the workers below,

so they must find a solution.

Engineers in France and Italy are digging the world's longest

railway tunnel beneath the Alps.

Their next challenge is to secure the walls to the shaft.

Loose rock could fall and injure the workers below.

Their solution is to spray shotcrete onto the surface of

the shaft to firm it up.

Dangling a human on a rope with a shotcrete hose is

unsafe and impractical,

so Helene's team uses this special robot.

Today, the engineers are firing it up for the first time.

Workers connect the shotcrete pipe to the robot

and lower it into the hole.

The robot's pilot deploys its four legs to brace it

against the wall of the shaft.

[worker] OK. Down.

[machinery honks]

The robot gets to work.

The robot's nozzle sprays an even coat of shotcrete onto

the rock as it descends.

When the robot completes 490 feet of shaft, workers install

super strong metal ribs to reinforce the shotcreted walls.

The ribs form a shell that strengthens the unstable

sections of the shaft.

It allows crews to stabilize the wall

before they install the permanent lining.

It takes Helene's team and the robot six months to

shotcrete and reinforce the first shaft.

Once all four shafts are complete, they will supply

fresh air for the crews working deep beneath the Alps.

And when the tunnel is finished, they will become

vital access points to rescue passengers

in the event of an emergency.

The Mont Cenis base tunnel is one of the most ambitious

engineering projects ever attempted.

Foot by foot, the teams building it are

getting closer to completing the longest

railway tunnel in the world.

You can see the tunnel and the permanent works growing

under your eyes.

To see the results of your own work every day, it's amazing.

From the 2030s, high speed trains will use it to race

between Lyon and Turin in a fraction

of the time it takes today.

But this is not only for people today.

This is really an opportunity, a big opportunity for our sons

and daughters in the future.

These huge peaks divided Italy and France for centuries.

Now, engineers are punching a new path under them that

brings Europe closer together.