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Today on "Impossible engineering"...

The Gotthard base tunnel...

the longest tunnel in the world.

A staggering 35 miles through the heart of the Swiss Alps...

Firing!

...it took revolutionary engineering.

...to make the impossible, possible.

Captions by vitac www.Vitac.Com

captions paid for by Discovery communications

The Alps, the tallest mountain range in Europe.

At its heart is the Gotthard pass,

a crucial route linking the north and south.

Traffic has increased tenfold in recent decades.

The mountain passes are at a standstill.

The solution?

Bore a tunnel directly through the mountain range.

The Gotthard base tunnel will be 35 miles long

and a mile and a half underground.

Constructing a tunnel this long is dangerous business.

Before any digging can begin,

engineers need to be sure

that the earth deep beneath the Swiss Alps

is safe for boring.

Geophysicist dirk krueger's job

is to reduce risk as much as possible.

Rock conditions under the Alps can change from foot to foot.

The location of the proposed tunnel

is too deep to sample from above-ground.

There's no way to predict

what dangers lie ahead for the digging team.

Drilling blindly into the earth could be deadly.

Dirk needs a solution before the team can dig.

It's a challenge that would have been impossible

without an invention from the 19th century.

Japan is the most seismically active country on earth.

Around 1,500 quakes occur each year.

For centuries,

no one knew where or why they struck.

That was until 1880,

when British engineer John Milne

experienced an earthquake while surveying in Japan

and began recording what he felt.

What I've created here

is a simple demonstration of a seismograph.

I've got a pen attached to a pendulum.

When I shake the table and pull the paper through,

you will start to see the pen record

the number of shakes on the paper,

and that represents the frequency and the amplitude,

or the number of times per second of the shakes

and the size of those shakes.

So let g'sive it a try.

My assistant Kirk here

is going to come and shake the table

and as I pull the paper through...

...you can start to see the trace on the paper

and then if Kirk gives it a really big shake.

You can see the increase in amplitude,

and then as it calms down, it gets less again.

And we can see here where the really big shake was

compared to the rest of the time.

It's really simple,

but quite effective demonstration

of how a seismograph works.

John Milne devised

the first continuously running seismographs,

helping detect the epicenter of quakes in Japan.

His design is still used all over the world.

Engineers at the Gotthard base tunnel

are using Milne's seismographs in an innovative way

to help them paint a picture of what's in store.

They are testing their new system today

at the V.S.H. Hagerbach tunnel research facility.

Explosive charges are placed within the rock face.

Each detonation sends out shock waves

which are measured by the engineering team.

Changes in the rock show up as a shift in the wave pattern

providing a clue to what dangers lie ahead for the drilling team.

Construction begins on

history's most ambitious subterranean project in 1996.

The route consists of two tunnels.

Teams drill from opposite sides of the mountain

with the ultimate goal of joining up in the middle,

deep underneath the Swiss Alps.

But to pull off the seemingly impossible,

the team is going to have to break out the big guns.

These machines are really very amazing.

You have to imagine it's 400-meter long,

the whole machine.

In the mountains of Switzerland,

engineers are undertaking

one of history's most audacious construction projects...

...a 35-mile tunnel driven straight through the Alps.

It is the longest and deepest ever built.

Renzo Simoni is on the team

charged with achieving the impossible.

So how do you dig 35 miles through a mountain range?

It's a challenge that would've been impossible

without an invention from the 19th century.

London, England.

Every day, four million people

descend into a complex network of tunnels,

more than 20 of which crisscross beneath the river thames.

But it wasn't always this way.

By the early 19th century, Londoners had given up all hope

of having a tunnel beneath the river.

Several previous attempts

to tunnel under the thames had failed

and the problem was

the soft and malleable London clay and sand.

Hard rock miners had come from Cornwall,

but the techniques they used on hard rock had failed,

leading to collapse and flooding.

Eventually it was decided that the project was impossie, bl

and it was written off.

Engineer Marc Brunel had a radical idea.

Brunel observed the perfect tunnel-like structures

left by shipworms as they burrow through timber.

As it digs, this marine mollusk

shoves pulpwood into its mouth and digests it,

and its bivalved head and hard shell

help support the creature as it moves through the wood.

The pulp is then excreted as a hard brittle residue

that lines the rear space,

creating a tunnel-like structure.

The key is to not actually suck all the sand out of the tube.

The mollusk then uses its back legs

to grip itself to the side of the tunnel

and push itself forward

into the space that it has created...

...repeating the process

until it finds light at the end of the tunnel.

And this is exactly the process that Brunel sought to emulate.

Brunel's idea started an underground revolution,

some of which can still be found.

Now this place is really incredible,

really amazing.

Through a tiny door up at the street,

down a rickety old scaffolding,

and we find ourselves here in this cathedral-keli space.

Brunel dug the first-ever tunnel under the river thames

using his engineering equivalent of a shipworm.

A mobile steel framework called a tunneling shield

acts like the worm's hard head,

supporting the earth and preventing collapse.

Working in individual compartments,

miners excavate just four inches

before the whole tunneling shield

is pushed forward using screw jacks.

A second group of men working behind them

line the tunnel with bricks to prevent its collapse.

Finished in 1843,

Brunel's thames tunnel

was hailed as the eighth wonder of the world

with almost 50,000 visitors on opening day.

Today it forms part of the London rail network,

and it all began in this hidden chamber.

Most people would have no idea that it's here.

But of course, it's importance to engineering

and to tunnel engineering in particular,

really can't be overstated.

The Gotthard base tunnel

is 140 times longer than Brunel's thames tunnel.

To dig 35 miles through the Alps,

Renzo and his team are using a supersized version

of Brunel's 19th-century excavator.

At over 1,300 feet long,

tunnel boring machines, or T.B.M.S,

are almost the same length as the thames tunnel.

They weigh 300 tons,

making them the biggest vehicles on earth.

They are so huge

they need to be shipped in sections

and assembled on site.

As the T.B.M. Head turns, it exerts 35 tons of force,

chipping away the rock.

Excavated rock passes through the machine

and onto a conveyor.

The T.B.M pushes into the void using hydraulic legs.

These mechanical mollusks

munch through 130 feet of rock a day.

In the wake of the T.B.M.,

the walls are sprayed with shotcrete,

a form of liquid concrete.

But how will two teams

digging on opposite sides of the Swiss Alps

meet in the middle?

Calculating a straight route

is difficult enough above ground.

There are trees, hills, and buildings in the way.

Using landmarks to navigate

or relying on towers to get direct sightlines helps.

When plotting a course underground,

even the slightest miscalculation

could yield disastrous results.

In Switzerland, engineers are undertaking

one of history's most audacious construction projects.

To reduce gridlock and pollution,

they're attempting to build

the longest and deepest tunnel in the world.

The Gotthard base tunnel will slice a 35-mile route

straight through the Swiss Alps.

But with two teams digging on opposite sides

of the mountain range,

engineers face the challenge of meeting in the middle.

Getting the T.B.M.'S meeting in the middle

is a very, very big challenge

because we have so long distances.

The solution comes from one of the greatest innovations

of the 20th century.

In 1960, Theodore Maiman built the world's first laser.

He bought his materials out of catalogs.

Maiman placed a small ruby

inside a photographer's flash bulb.

His invention changed the world,

allowing highly-accurate measurements to be taken

over great distances.

Less than a decade after Maiman's prototype,

lasers were bounced off reflectors

on the surface of the moon,

so the Apollo 11 crew

could accurately calculate their distance from earth.

At the Gotthard base tunnel in Switzerland,

lasers guide huge tunnel boring machines.

G.P.S. maps the entire route.

But witho nsatellite signal below ground,

each T.B.M. relies on a geodetic guidance system

to stay on course.

A laser theodolite is attached to the tunnel wall.

It fires a beam at a target on the front of the T.B.M.

As the T.B.M.S chew through the mountain side,

they hit unstable earth deep under the Swiss Alps

as the T.B.M.S chew through the mountain side,

bringing the whole operation to a grinding halt.

Squeezing occurs when the pressure of the mountain

pushes against weaker rock.

In extreme cases,

it results in the tunnel closing up again

after it's been bored.

If the team uses a tunnel boring machine

in a squeezing rock zone,

the consequences could be disastrous.

So the dig team must go back to basics,

using techniques championed

in the days long before tunnel boring machines.

Engineer Luke Bisby is in Cornwall

on the southwest tip of britain.

He is exploring an area once dependent on tunneling.

So it is hard to believe that 200 years ago

underneath the sea

was the largest concentration

of submarine tin and copper mines

anywhere in the world.

This region was

the world's largest producer of copper and tin

in the 19th century.

There are an estimated 30 to 40 miles of mine shafts

beneath the waves.

More than 2,000 mines like this one

would have dotted the county.

Cornish miners were considered the best in the business.

Their expertise was sought after

for tunneling projects all over the world.

By today's standards,

their methods were incredibly inefficient and dangerous.

So this is black powder.

This is the world's first chemical explosive.

It's better known as gunpowder.

Early miners bored hos leby hand,

then laid the explosives.

I'm going to light the fuses

and then we should have more than a minute

to head down the tunnel.

Oh!

All right, okay, so let's see what's happened here.

Keeping in mind that it would have taken a couple of hours

to drill each of these holes by hand,

to then put the black powder in

and only move that amount of rock

despite a pretty big bang,

is a bit disappointing frankly.

The miners would come back

inking that the charge hadn't gone off.

The charge would then detonate quite late,

and the miners could be maimed or even killed,

and in many cases, they were.

The invention of a new, more powerful explosive

proved even more dangerous.

So what I have here is a jar of nitroglycerine,

and it was first synthesized in 1847.

And you can see just how volatile it is.

If I take a small drop and place it on the steel plate

and then I hit it with a hammer.

So where black powder needs a heated charge

in order to coax an explosion,

nitroglycerine just needs a small tap,

and of course down a mine, that could spell disaster.

Swedish explosives expert Alfred Nobel's brother

died in a nitroglycerine accident

in the 1800s.

After the incident,

he was determined to create a safer alternative.

He realized that if he took nitroglycerine

and mixed it with kieselguhr

which is a naturally occurring clay-like material,

he would end up with dynamite.

And you can see that it's quite loose

but quite malleable

and it could be rolled

to eventually form dynamite sticks.

To make his dynamite, Nobel had to figure out a way

to safely handle vast amounts of nitroglycerine.

He found his solution in Scotland.

Nobel really favored this area because of its remoteness,

and the Sandy soil allowed him

to shape the landscape around his factory

to protect production workers from potential explosions.

It also allowed him to build mounds,

such as thesare ound us.

And on top of these,

he could place his nitroglycerine production huts.

In each nitroglycerine hut,

one man was in charge of monitoring the temperature

and another mixed,

sitting on a one-legged stool to ensure he kept his focus.

But sensitivity to temperature and friction

meant that nitroglycerine couldn't be safely pumped,

and so it was set to trickle down

from the huts to the factory,

letting gravity do the work.

Once it reached the factory, it was mixed with clay

before being rolled into stickofs dynamite.

Nobel had created a product that was now so stable

that it could be dropped on the ground

or even thrown into fires without exploding.

The new dynamite,

along with the invention of pneumatic powered rock drills,

gave birth to a quicker anmod re efficient

form of tunneling called "drill and blast"...

All right, that's it.

Let's get out of here.

...Ushering in a new age of mining.

3, 2, 1, firing.

Wow, so that was quite something.

Lot of power in that one.

So we can really see here

the power of the dynamite as compared to the black powder.

The dynamite has tenak that entire mass of rock

and thrown it sideways.

You can see what a game changer this would have been

for the miners working down here.

Whenever engineers at the Gotthard base tunnel

encounter rock too soft

for the massive tunnel boring machines,

they revert to the drill and blast method...

...but with a 21st-century twist.

Known as jumbos, these 60-ton drilling rigs

make drilling and blasting easier than ever before.

Each 10-foot arm has a powerful electrohydraulic drill

to bore holes for the explosives.

As one arm drills, thope erator lines up another.

Modern emulsion explosives are only active

when mixed together at the rock face,

much safer than drilling

and blasting using traditional dynamite.

Each detonation takes eight hours to prep

making drilling and blasting much slower than the T.B.M.S.

But without it,

finishing the tunnel would be impossible.

But as the team drills further into the Alps,

it's becoming difficult to hold back

the enormous pressure of the mountain above.

They need a solution fast.

The Gotthard base tunnel is an epic engineering project.

Massive 1,300-foot tunnel boring machines

are grinding away 130 feet of rock each day

with the goal of completing a 35-mile long tunnel

directly through the Swiss Alps...

the longest tunnel in the world.

The team is nearing the finish line,

but the immense pressure of the mountains above

is slowly closing the tunnel back in on itself,

not long after a stretch has been bored.

The steel arches used to hold back the mountain

are failing.

The success of the whole project is in jeopardy.

Engineers need an answer fast.

In 1932,

engineers Heinrich Toussaint and Egmont Heintzmann

revolutionized the German coal mining industry

when they invented

the t.H. Yielding steel arch support.

Capable of withstanding huge pressure without collapsing,

they made it possible

to excavate deeper than ever before.

Unlike a conventional rigid steel arch,

the jointed concentric rings of their design

change shape to accommodate the pressure of the rock,

rather than totally resist it.

The solution is to bore a tunnel

with a wider circumference than is needed.

The yielding rings allow just enough movement

to prevent the supports from collapsing,

resisting the pressure of the squeezing rock enough

to keep it from closing the tunnel completely.

On October 15, 2010,

after 14 years of digging, boring, and blasting,

e thdream becomes a reality.

A T.B.M. Crashes through the final few feet of rock.

The two halves of the tunnel join for the first time.

Bravo!

Thanks to a cutting-edge laser-guidance system,

the T.B.M.S complete their monumental job

with incredible accuracy,

excavating more than 70 miles of rock.

With the digging done,

the engineering team turns to their biggest challenge yet,

making sure the 35-mile-long tunnel is safe

for the thousands of people that will pass through.

The Gotthard base tunnel in Switzerland

is a true feat of underground engineering.

With passengers and freight traveling at high speeds

through 35 miles of confined space

under a mile and a half of solid rock,

an accident would be catastrophic.

For Renzo and his team,

memories of onofe Europe's worst traffic accidents

in another alpine tunnel are on their minds.

In 1999, a truck caught fire

in the middle of the 6-mile-long mont blanc tunnel

linking France and Italy.

The tunnel quickly filled with smoke,

as the Blaze engulfed over 30 vehicles.

The inferno raged for over two days.

39 people lost their lives,

most due to smoke inhalation.

To ensure the Gotthard base tunnel

is the safest ever built,

its engineers are taking inspiration

from the innovations of the past.

In the U.K.,

a groundbreaking engineering project

below Liverpool's river Mersey

changed tunnel safety forever.

So this is the Queensway tunnel.

And when it opened,

it was the biggest and longest underwater road tunnel

in the world.

Opened in 1934,

it took 1,700 men over 8 years to construct.

But it is not the digging of this tunnel

that makes it revolutionary.

About 30,000 cars travel through this tunnel every day,

and even with modern exhaust systems,

that's a lot of fumes.

And the engineering innovation in this tunnel

is what solved that.

By the early-20th century,

tunnel engineers had to contend with toxic fumes

from the cars using them.

To keep poisonous fumes at bay,

the builders of the Mersey tunnel

turned to physiologist, John Scott Haldane.

And this is what they came up with.

It is the world's largest ventilation system,

and incredibly, this system is still in use today.

In each of the six huge ventilation towers,

fresh air drawn in at roof level

is pumped underneath the roadway

before being blown into the tunnel

through ducts along its sides.

At the same time, exhaust fans draw toxic fumes

out through holes in the roof.

The George's dock ventilation tower

is home to six massive fans

circulating air through the Mersey tunnel system.

Incredibly these are the original fans

that were first installed down here almost 100 years ago.

Each fan can move

83,000 cubic feet of air a minute

safely pumping exhaust fumes

from the top of the 200-foot high tower above.

Now this is a place

that very few people get a chance to see.

I'm standing right at the bottom

of one of the ventilation shafts.

The huge height of the tower

ensures the air supply isn't contaminated

by vehicle exhaust fumes from the street.

It's said that the air down here

is even cleaner than the air

for the people walking around in the streets of Liverpool.

Once the largest tunnel ever drilled,

the road only uses the top half of the original tunnel.

Most people when they drive through the tunnel,

they think they're at the bottom,

but they're not.

Actually below them is this two-story high space

called Central Avenue.

The lower level was designed to house a tram line,

but it was never built.

Now it serves as the main air supply duct

where air from the tower is blown into the road deck above.

It's pretty amazing to think

that there's this space like this

down beneath the road deck

and I have to say,

it's pretty cool to be down here.

With its revolutionary ventilation system,

the Queensway tunnel provided the blueprint

for all tunnel designs that followed.

The designers of

the 35-mile-long Gotthard base tunnel

are taking the systems pioneered at the Mersey tunnel

to new heights of sophistication.

Electric trains will run through the tunnels,

so they won't have to contend with exhaust gases.

But the ever present risk of fire in the tunnel

requires a cutting-edge solution.

In the event of a fire,

trains will either be diverted out of the affected tunnel

at two crossover points

or directed to one of two emergency stations.

As a train that's on fire approaches,

the station's ventilation system will activate remotely

via the tunnel control center.

Powerful 2-1/2 megawatt extractors above the track

will suck toxic smoke fumes out of the tunnel,

releasing it at the surface

through an exhaust shaft 2,600 feet above.

Inlet fans will replenish the tunnel with clean air.

Each of the tunnel's six jet fans

will raise the air pressure in the unaffected tunnel,

keeping it free of smoke during evacuation.

This system is safer

than the rest of the railway network in Switzerland.

If you are here as a passenger using the tunnel,

you're safer tn haoutside.

Once complete,

the Gotthard base tunnel

will not only redefine the map of Europe,

it will rewrite the rules of tunnel construction.

It stands as a testament to the people,

past and present,

who helped design and build it.

By drawing on the innovations of the past...

Oh!

...Adapting, improving,

and making groundbreaking innovations of their own,

the engineers and designers of this incredible tunnel

have succeeded in making the impossible possible.

Generations of engineers

wouldn't have been able to do this.

I'm very lucky to have spent 20 years of my professional life

together with this project.

It's like a part of me.

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