(soft music) ♪ (bright music) (narrator) The Channel Tunnel, a 50-kilometer railway that connects Britain with France.

This incredible feat of engineering carries passengers and freight 50 meters below the seabed.

♪ It's the longest undersea tunnel in the world.

It was a phenomenal achievement.

♪ (narrator) More than 13,000 workers from Britain and France tunneled out from the shore, racing to be the first to reach the breakthrough point under the English Channel.

♪ (man) I was the first one to actually cross that line into France.

It can only be done the once.

Vive la France!

(narrator) Building a tunnel on this scale was an epic engineering endeavor.

The tunnelers had to battle with the elements.

(man) It was like being in a war with the earth or the rock or the machinery you were using or the air you were breathing.

(narrator) Catastrophic floods... (man) We thought that could be the end of the Channel Tunnel.

(narrator) ...and an arsenal of dangerous machines packed into a confined space.

(man) It's not a place where somebody who doesn't know what they're doing should be anywhere near.

(narrator) This is the inside story of the race to build the Channel Tunnel, one of the engineering wonders of the modern world.

♪ (engine whirring) (soft music) This train is on a remarkable journey.

It's traveling under the sea through one of the biggest engineering projects ever undertaken.

The Channel Tunnel is a vast railway network that carries both freight and foot passengers between Britain and France.

The public can even drive their cars onto specially constructed railway wagons to travel between the two countries.

♪ (dramatic music) Building it required an ambitious plan.

Engineers from Britain and France would dig out from either side of the English Channel, racing to be the first to reach the breakthrough point under the sea.

Today, at the British entrance to the tunnel, supervisor Colin Saxby oversees this extraordinary subsea railway.

(Colin) On our busy days, which are midweek, Tuesday, Wednesday, Thursday, we get about 3,000 lorries going one way.

That's just to France.

For passenger vehicles, on busy days, we increase up to about 10,000 vehicles a day.

(narrator) When it opened in 1994, the public were wary of traveling so far under the sea.

Today, up to 400 trains pass through the tunnel each day carrying an average of 57,000 passengers, 6,000 cars, and 54,000 tons of freight.

(Colin) People have definitely embraced using the tunnel now as opposed to when it first started.

I mean, when it first started, we heard stories that they'd be able to see fishes there driving through the tunnel and everything like that.

But they've definitely embraced it more, especially the value that you can-- the speed and also that you can stay with your vehicle.

(narrator) In the control center, a 24-meter-long display panel tracks the position and speed of every train.

♪ The train driver doesn't need to look out of the window to see the signals.

This information is sent through track circuits directly to a display panel in the driver's cab.

♪ It all adds up to a huge amount of infrastructure that needs to be looked after.

The drainage stations, the firefighting, the cooling, and the ventilation, it's not just a concrete tube.

(soft music) (narrator) On the British side, the Channel Tunnel connects to a high-speed railway that runs straight into the heart of London.

♪ We zip through it now and we forget, probably, about the massive, massive number of people involved in this project who have toiled under the sea for years to get this thing working.

♪ (narrator) The project cost the equivalent of over $21 billion today.

♪ When the Channel Tunnel was first conceived back in 1986, engineers planned to build three tunnels: two carrying trains running in either direction with a smaller service tunnel in the middle.

Giant tunnel digging machines would excavate over 10 million cubic meters of earth.

They would then line the tunnels with the world's strongest concrete.

All three would be linked by cross passages to provide access.

Trains speeding through the tunnel build up huge air pressure in front of them, so these overarching ducts would divert that air into the neighboring train tunnel, reducing buffeting and providing a smoother ride.

♪ Giant crossover caverns would allow trains to switch from one tunnel to another for maintenance or in an emergency.

♪ It would take more than five years and over a million tons of concrete to build the Channel Tunnel.

It was an extraordinary engineering feat.

(man) It was a phenomenal achievement in terms of scale, in terms of how it transformed the industry, in terms of how it changed working practices.

So yes, it was genuinely a phenomenal achievement.

(narrator) To dig out the tunnels, engineers would use 11 of these subterranean digging demons called tunnel boring machines, or TBMs.

(man) It's an orange spiral, it's like a monster.

That's just--you can't stop it.

Really, obviously, you can, but it's just like a monster just eating earth and just spewing it out the other end.

(narrator) Work began on building the Channel Tunnel in January 1987.

Workers and machines assembled at the White Cliffs of Dover to start digging.

(dramatic music) ♪ Two dedicated teams of men and women worked day and night to keep the monster digging machines on track, to ensure the tunnel's success.

♪ (woman) I look back at it and think it was an incredible project to be part of.

(Kevin) I just think construction workers in general don't get enough recognition for their efforts to keep the country going, to build it, to extend it, to modernize it.

(man) A brilliant achievement.

In fact, in my opinion, we should build another one.

♪ (narrator) Before the Channel Tunnel was built, the only cost-effective way to get to France was by ferry.

(horn blowing) Sailing across the English Channel could be unpredictable.

Bad weather and delays plagued ferry crossings.

A faster, more efficient way to cross the English Channel was needed.

In 1984, the most unlikely of allies came together to turn that dream into a reality.

Britain's conservative prime minister, Margaret Thatcher, and socialist French president, François Mitterrand, announced they'd agreed to build a physical link between their two countries.

(birds squawking) (man) There were all sorts of ideas about how to get across the channel underneath it.

(orchestral music) (narrator) Many schemes proposed a way for people to drive their cars through a tunnel to get to France.

♪ (solemn music) A group called EuroBridge proposed a double-decker drive-through motorway housed inside a tube suspended from a bridge, then a train tunnel running beneath the seabed.

(Graham) EuroBridge, uncosted, pushing the limits of technology, nobody really thought that they would be able to finance it.

♪ (narrator) The Channel Expressway's bid was for a mix of road and rail.

(man) We thought the ideal tunnel would be a drive-through.

You know, 20 minutes, and you drive your car or your lorry through to the other side.

(Christian) To get rid of the exhaust fumes, you would've had to build ventilation shafts.

In one of the busiest waterways in the world where also there's a lot of fog and an awful lot of shipping, it becomes a huge risk.

(narrator) The third proposal called EuroRoute featured a tunnel between artificial islands approached by bridges.

It boasted that you could drive all the way to the continent.

(Tim) Of course, this was actually a terrible idea!

I mean, think of all those ships sailing past that could easily hit those islands.

It looks like something out of a sci-fi novel even now.

♪ (narrator) One scheme stood out.

The Channel Tunnel Group's bid was the only one not to feature a road.

Cars and lorries would drive onto specially constructed railway wagons to pass through the tunnel while foot passengers could climb aboard a high-speed train.

With the entire project privately funded, the banks were keen to bag the most reassuringly straightforward plan.

♪ (Graham) The Channel Tunnel Group won, I think, because if the banks were going to put a lot of money, the initial loan was five billion pounds, they wanted reasonable assurance that this was gonna be built on time and to budget or somewhere near it.

(narrator) December 1986, the first challenge was to work out where exactly to dig this tunnel.

(mellow music) Geologists had identified a layer of rock they thought would be ideal.

It was called chalk marl and appeared to stretch from one side of the channel to the other.

(man) Chalk marl is almost impervious to water, so it makes excellent material for the tunnel boring machine to tunnel through.

(narrator) Impermeable chalk marl is a soft rock perfect for underwater tunneling.

But there was a drawback.

Its path beneath the English Channel was narrow and undulating, making it difficult to follow.

♪ As a result, a straight, level tunnel underneath the channel wouldn't be possible.

Instead, the three tunnels would have to rise and fall following the route of the chalk marl seam.

This didn't deter the British tunnelers.

They were full of confidence and soon bonded, coming up with a name for themselves, the Tunnel Tigers.

(Kevin) People make their mark on history, but I think the project put its mark on people as well.

And that's what I did.

I'm proud of meself.

♪ So I got this design of a tiger, a Tunnel Tiger, and that's it there.

(narrator) February 1988.

The tunnel boring machines were hard at work, slicing through the rock face.

(man) To drive one of these things, it's big, heavy, long, and dangerous.

(narrator) The tunnel boring machines weighed in at around 760 tons and were 250 meters in length, the size of two football pitches.

They were designed specifically for digging the Channel Tunnel and were crucial to the operation.

At the front of the machine was a seven-and-a-half meter wide cutting blade.

It looks complicated, but the way it worked was remarkably simple.

As the machine's driver, Graham Fagg, explains.

(rumbling) (Graham Fagg) We take the plastic tube as a TBM, and the TBM advances into the material, and as it goes forward, we remove the cut material in the back of the machine.

Advance and remove more material, and that is the basic tunneling technique, and it doesn't change, it is always the same.

(solemn music) (narrator) As the machine advanced, it exposed fresh segments of chalk.

Robotic arms lined the chalk with concrete panels and fixed them in place with cement to form a watertight ring of concrete.

A conveyor belt carried the debris away from the cutting head.

Hydraulic jacks could then push the cutting head forward at around five meters an hour.

The most important job was to make sure these goliaths didn't stray off course.

(machinery clunking) Driving the machine, steering it, it could be, actually, quite stressful when it was going off line and it wouldn't come back.

(dramatic music) (Alan) They don't forgive you.

You do something wrong on a TBM, you will suffer.

(narrator) It was the job of geologists to plot a safe route for the tunneling machines.

They predicted a water-free digging route, so engineers decided the British would tunnel a bit further.

♪ The midpoint, known as Point M, would see the British digging about 22 kilometers and the French just over 15 kilometers.

(Christian) Point M was a point that actually wasn't quite in the middle, but almost in the middle, a bit on the French side, that was the one they were both aiming at to bring the two tunnels together.

(engine whirring) (narrator) The British expected a dry route, so they used tunnel boring machines that weren't waterproof.

(soft music) The French knew they'd meet wet ground, so they used tunnel boring machines that were completely waterproof.

(narrator) The French waterproof machines were 25% slower than their simpler British rivals.

But if they hit water, they could keep digging.

♪ As the tunnel progressed, just getting people to and from work every day was a major challenge.

(Graham Fagg) Here we have an old TML man rider.

And these were going in and out on a regular basis carrying personnel.

They would finish their shift and personnel who were starting their shift.

This material was added for very good reason.

It's a safety measure.

I've spent many an hour dozing as we went in and out.

We weren't supposed to, but if you're tired and it's a long journey, you're bound to get-- just nod off a little bit and you could go arm out, leg out, and before you know it, you've got an injury, a serious injury.

That's why these were added.

Good little machines, we used to look forward to seeing them come in and we used to look forward to seeing them go out, but it's good to see one again after all these years.

(dramatic music) ♪ (narrator) There were 183 locomotives running on over 240 kilometers of track, making this the biggest construction railway in the world.

(soft music) It was also a railway that never slept.

These locomotives traveled 130,000 kilometers in one month, equivalent to over three times around the equator.

♪ For the workers riding them, it could take hours to get to and from this underwater construction site.

This was when boredom could set in.

Alcohol and cigarettes were banned underground, but some tunnelers found ingenious ways to get around the security checks.

(Kevin) I saw him go in his locker and he got a big, juicy grapefruit out, put it on the bench next to him.

Thought, "That's what he's having for his lunch."

No sandwiches.

And then I saw him look around like that, like a secret agent, looking over his shoulder, and then he went in his locker and he got a syringe out, and I thought, "Oh, my God, he's gonna jack up with some sort of drugs, heroin or something."

And then the next minute, he gets a little half bottle of vodka and he sucks the vodka up in the syringe and he injects it into his grapefruit.

So he had a--obviously had a lovely tea break four hours later with a nice vodka grapefruit cocktail.

(man) Guys did smoke.

They used to hide their cigarettes in spirit levels and stuff like that to get them past the security.

Rules were broken all the time, but I--I didn't break any.

(mellow music) (narrator) This workplace was hot, noisy, and dangerous.

On the British side, there were 1,100 workers underground, and the vast majority were men.

(man) Are there one or two of the tunnelers who actually don't like women down here?

Yeah, but we win 'em over.

We show we muck in with the guys, we get covered in mud, that sort of thing, they accept us.

(narrator) A chance phone call from a colleague attracted engineer Sarah Chapman to the project.

(Sarah) "We need some more engineers on the Channel Tunnel.

It is a temporary job, but it might lead to a permanent job.

Are you interested?"

(narrator) Before long, Sarah was underground with a crucial role to play.

It was really making sure that the tunnel went in the right direction, that it was big enough, that it wasn't tilting forward, left, right, top, bottom sort of thing.

(narrator) Sarah was one of only a handful of women working underground.

(Sarah) There were no toilet facilities down the tunnels.

You've gotta allow what often was about an hour to get in, an hour to get out, so there were sort of 10 hours where you actually don't have access to a toilet.

That was fairly difficult, and I do remember actually raising that issue and was pretty much laughed at and told, "Well, you want to work here, you want to be one of the men, just deal with it, get on with it."

(soft music) As a female, there were times when it was quite difficult, and I'm sure the other females on the job felt the same, and that we've made huge leaps forward.

(drilling) (narrator) Sarah would spend over a year working underground, ensuring the path of the tunnel remained on course.

♪ (calm music) The dangers of digging underwater have long been known to British and French tunnelers.

♪ The first person to successfully tunnel under a river was a Frenchman.

His name was Marc Brunel, and he did it here in London on the banks of the River Thames.

♪ (man) Marc Brunel, father of our most famous engineer, Isambard Kingdom Brunel, actually built this huge chamber above the ground and sunk it.

So this is 50 feet in diameter, it's about 1,000 tons in weight.

It was built on an iron ring, and it is, in effect, a massive pastry cutter.

(narrator) The whole shaft gradually sank under its own weight, slicing through the soft ground.

Workers dug a tunnel extending out from this shaft underneath the Thames beginning in 1825.

Marc Brunel designed a revolutionary system called a tunneling shield to help excavate the tunnel.

This shield was made up of individual cages.

Inside each one, a man would dig out the wall directly in front of him.

It was a primitive version of the tunnel boring machine.

In each cage, each man or tunneler has a wall of planks, and they're held in place by metal poles, and each man in each cage takes out the top two poles, takes out the plank, digs to four inches, which is about the size of a brick, replaces the plank, replaces the poles, takes out the one below, digs to four inches, replaces the plank, replaces the poles.

So it's incredibly laborious.

(narrator) It was also dangerous.

The tunnel flooded many times, but eventually, the Thames Tunnel was completed in 1843, 18 years after work began.

(Robert) This is not just the first tunnel under a river anywhere in the world, this is the birthplace of the Underground railway.

This is the tunnel that changed the shape of our cities and changed the shape of our lives.

(solemn music) (train whooshing) (narrator) 150 years later and the Channel Tunnel would once again revolutionize how we travel.

As work progressed, excavating the tunnels for the railway, another set of engineers were busy designing a groundbreaking fleet of high-speed trains to shuttle freight and passengers under the sea.

This proved to be another unique engineering challenge.

(soft music) The project needed shuttle wagons capable of loading and unloading large lorries.

Two different types of wagon were also required for passenger vehicles, single-deckers for coaches, and double-deckers for cars.

♪ For foot passengers, France had been operating high-speed TGV services since 1981, and so this type of train was the clear favorite to operate in the tunnel.

The TGV, which actually means the Trains à Grande Vitesse, the high-speed train, is a record breaker.

It held the world record for the fastest train in the world for many, many years.

Even Britain's fastest train, called the InterCity 125, was no match for this new breed of high-speed locomotive.

The sleek new Channel Tunnel trains were called Eurostar.

They took their name from the company set up to run passenger services through the Channel Tunnel.

(man) The Eurostar trains looked futuristic in a way that British Railways, most of British Railway's stock didn't.

You still, at that time, had your flat-fronted, yellow-painted, slam-door passenger stock.

These looked like something out of the 21st century.

♪ (dramatic music) (narrator) What made these Eurostar trains stand out was their speed.

They would travel at 160 kilometers per hour in the Channel Tunnel and over 290 kilometers per hour through the open French countryside.

But running the high-speed Eurostar trains would prove to be a problem in Britain.

The network was largely made up of twisting railway lines designed back in the days of steam.

These high-speed trains would need to slow down when they reached Britain.

(Ed) The U.K.'s railway system is so old, it was the first in the world.

Many of the lines were actually built to accommodate much smaller locomotives and carriages.

So this high-speed train had to be narrower so that it would fit within the British Railways' Southern system.

♪ (narrator) The task of designing this new generation of trains was considerable.

Engineers needed to build 40 electric locomotives with 252 carriages for passengers and the same number for goods vehicles.

♪ March 1988.

Three months into digging out the Channel Tunnel, and British engineers hit a big problem.

It was the one thing they feared most.

(water spraying) (Mark) We got down there, and it was literally like Niagara Falls.

It was coming in round about 300 to 400 liters per minute.

(narrator) The British had gambled on a dry run, but it hadn't paid off.

Thousands of liters of water were flooding the tunnel.

This was a huge setback.

(Mark) It was just an ongoing battle trying to pump the water out as it was coming in.

(man) It was very wet and, uh... -It was horrendous!

-Terrible, yeah.

The water was coming in quite badly.

It was like a car wash in places.

(narrator) Then, their worst nightmare: a crack started to appear in the tunnel roof.

You'd have bits falling out of the ceiling with guys trying to work underneath, trying to put in these concrete segments, waist-high in water and mud and slurry, and so, yeah, that was pretty dangerous.

(narrator) If the leak couldn't be stopped, the tunnel could cave in on their heads.

The British engineers needed a solution, and they needed it fast.

(Alan) It's every miner's nightmare, to hit water.

(woman) We were scratching our heads, why should it be like that?

(Kevin) But you think, "No, this won't collapse."

(Mark) If this is not sorted, this could be the end of the Channel Tunnel.

(narrator) There were only two places it could be coming from.

(Helen) I used my initiative and actually tasted it, and it wasn't salty.

So we knew it wasn't coming from the English Channel.

(narrator) The geologists had to find out what was causing the leak.

(Mark) It was rain water that had filtered through and it was trapped within the middle chalk, and that was filtered in through the fault lines into the tunnel.

(narrator) The problem lay in an aspect of the chalk marl that the surveys could never have predicted.

Up close, it was clear that this stretch of chalk was full of fissures.

These tiny cracks contained water trapped in the rock from when it first formed.

It was this water, not water from the sea itself, that was streaming into the tunnel.

Engineers were relieved that the leak wasn't coming from the seabed, but they had to devise an innovative solution to stop the flooding.

(Kevin) We would eject these chemicals, like a resin, from the service tunnel ahead of where the running tunnels were gonna follow, the tunnel boring machines.

(narrator) Engineers injected resin into the fissured chalk marl.

The resin solidified and froze the rock.

This made the rock easier to drill through.

(Mark) We were pumping hundreds and hundreds of cubic meters of grout to try and solidify the ground and seal up the ground in advance for the TBM to try and improve conditions.

(narrator) It took three months before the tunnels hit drier ground again.

(Kevin) So that was panic over for everybody, we were saying, "Ooh, thank God for that.

We can carry on," you know?

(narrator) With the leak fixed, the pressure was on for the British to make up for lost time.

(Kevin) There's a magazine called The Link, and on the back of it showed you the progress from the French side and the British side.

Little red blocks.

Obviously, as the job progressed, the little blocks got closer and closer, and you could see how ours was going further towards France than they were towards us.

(narrator) To keep up the momentum, substantial bonuses were on offer to whichever team could work the fastest.

(reporter) Is there a rivalry between the different shifts?

-Different gangs?

-Oh, yeah!

I mean, you're all trying to do more rings than the last one.

That's the whole part of the game.

-It spurs you on?

-Well, the more you do, the more you get paid.

(Alan) There was a huge carrot dangled in front of you called "Bonus."

And if you had a bad day and you didn't earn bonus, there were some long faces.

(narrator) In just one week, workers dug 428 meters in one tunnel alone.

That's the length of 35 double-decker buses.

(piano music) Building the Channel Tunnel was a 24/7 operation.

Workers were housed in temporary accommodation close to the tunnel entrance.

♪ These prefabricated huts housed over 1,000 workers.

There's not much to see today, but for tunneler Kevin Milne, the memories are still vivid.

(Kevin) My home for three and a half years in the '80s and '90s.

A lot of memories already along with the place.

I look around, my block was just here on the right, D3.

I think I was the second tier up, that direction a bit, and I look at it now 30 years later, and it just--it's a weird feeling, obviously.

I look at this and it's a monument to the guys who worked on the Tunnel and who lived here.

Sorry.

(soft music) (narrator) The drive to get the job done took its toll on this workforce as the number of accidents increased.

(Alan) Quite a few incidents occurred with the trains, collisions, derailments, all dangerous.

(Kevin) People broke their arms, their legs, some guys got their fingers chopped off.

If you got injured down in the tunnel, there was no morphine like in the coal mines.

You would just suffer the agony of whatever happened to you until the nurse or the doctor come in.

(narrator) The first fatal accident happened on the 23rd of January, 1989.

(Graham Anderson) A young 19-year-old surveyor's assistant missed the train that was meant to be taking him, and he started walking along the track.

♪ He then got caught as two trains reached his position simultaneously.

♪ It was an extremely nasty, extremely unpleasant tragedy.

(narrator) It wouldn't be the last.

Alan Cottiss witnessed firsthand just how dangerous this workplace could be.

(Alan) Worked with a lad who was only about 12 feet away from me when he was crushed.

And poor lad didn't survive it.

(narrator) A piece of equipment failed while a crane was lifting a concrete ring into position.

(Alan) The lad was working at the ground level, and there was electrical fault, and it felt wrong.

It didn't feel safe, and it retracted and crushed his chest.

♪ (narrator) Eleven men lost their lives building the Channel Tunnel.

This plaque near the old work's entrance is a stark reminder of the human cost involved.

(Alan) I think it's an accepted thing in tunneling that people will get hurt or will even be killed.

♪ (narrator) At one point, the medical center was treating over 1,500 cases a month.

The company responded by introducing a much more rigorous health and safety training program to cut the number of accidents.

Despite concerns over safety, there was no let up in the pace.

(dramatic music) September 1989.

Twenty-one months after tunneling first began, the British have dug nearly 12,000 meters out from their own coastline.

While work progressed on the tunnels, another team were gearing up to undertake one of the project's most difficult engineering challenges... ♪ ...constructing the vast crossover caverns that connected the two rail tunnels together.

These were gigantic cathedral-like spaces.

(Sarah) Building the crossover was not a straightforward project, partly because nothing like that had been done before.

It was the biggest subsea excavation that had ever been built.

(narrator) In the event of an accident in one tunnel, these crossover caverns would allow trains to swap over to the other tunnel.

These were the largest undersea spaces built anywhere in the world.

Constructing them would be a risky endeavor.

At over 15 meters high, the top of the crossover cavern was closer than ever to the seabed.

With 1,000 billion tons of water right above the tunnelers' heads, the pressure here on the seafloor was enough to crush a car.

(soft music) The caverns were too big to line with concrete rings.

The engineers had to find another way to make them watertight and safe.

(Sarah) The crossover construction, we were just digging into bare rock, and then we'd make certain parts safe by actually spraying concrete onto the surface of the rock, which we called shotcrete.

(narrator) To begin with, the spray-on concrete appeared to hold, but soon, signs of strain began to show.

A torrent of water was causing a crack to form in the cavern roof.

(man) The crack was several meters across, it wasn't just a little crack like you have in your wall, in your wallpaper at home, it was quite a big, gaping hole.

(narrator) If this hole got any bigger, the consequences could be disastrous.

(John) If it burst and therefore filled up with water, the momentum of water then coming up the tunnel would be catastrophic, really.

(Kevin) It was a big setback, because there was rumors that the job wouldn't go ahead.

It was that bad at times.

(narrator) Once again, the engineers were faced with a serious leak, and they needed to come up with a solution fast.

(Kevin) They injected it with like some sort of special chemical.

Engineers used these chemicals to fill in the leaking fissures and solidify the rock.

♪ (Kevin) It was a hold-your-breath moment for everybody.

(narrator) Although there has never been a serious flood in the tunnel, radical plans were put in place to make sure it doesn't happen.

(machine whirring) It was a system of sealed doors, so if you went in there and the leak was bad, it was gonna shut the doors.

(narrator) With a serious flood, it's important to contain the water.

Anyone unable to escape before the doors of the crossover cavern was shut tight would be trapped inside.

(John) Anybody who was in there, well, you have to take one for the country, I'm afraid.

(intense music) (narrator) It's a stark reminder of just how dangerous a place this can be.

(dramatic music) Despite the hazards, the project was making good progress.

But the scale of this excavation created another challenge for engineers: where to put the 4.9 million cubic meters of rock and earth that was being dug out.

This waste material is called "spoil."

♪ Space wasn't an issue on the flat French shoreline, but 50-meter cliffs on the Kent coast meant land was at a premium.

♪ (man) There was lots of ideas about where to put the spoil from the Channel Tunnel.

In fact, there's about 70 different options given.

(narrator) There were concerns that giant piles of waste material would look unsightly if dumped across the picturesque Kent countryside.

(man) I can remember getting into an argument with the man who was in charge of the tunnel, 'cause they were taking all the waste out and dumping it.

One of my arguments at the time, where are you dumping all your rubbish?

(soft music) (man) There was a big question of the spoil disposal where all the material would go and lots of studies were done with environmental groups to make sure that it had as limited environmental impact as possible.

(narrator) Engineers devised a simple but ingenious solution.

(Paul) It was decided the best option was to put it at the bottom of the White Cliffs of Dover here, and the advantage of it was, there was no lorry movements of chalk marl anywhere around Kent.

You can imagine that 4.9 million cubic meters shifted by a lorry, it would've been a huge disturbance to the local communities.

(narrator) To avoid this problem, engineers designed a huge artificial lagoon.

Workers constructed 1.7 kilometers of steel wall built in two rows on the seabed.

They filled the gap between the walls with concrete.

This unique method of construction was the largest sheet steel structure ever built at the time.

Engineers then erected temporary steel walls to split the lagoon into smaller pools.

They filled the gaps between the walls with gravel.

Trucks carried everything that had been dug from the tunnel the short distance to the lagoons and tipped it inside.

The gravel-filled walls of the temporary partitions allowed the water to drain away to the neighboring lagoon.

Slowly but surely, the sea gave way to the land.

(mellow music) ♪ Once all the spoil had settled and dried, Britain had grown by 86 acres.

The new land provided much needed additional space for storing the thousands of concrete rings needed to line the tunnel.

Today, this area is a country park called Samphire Hoe, a new part of Britain where you'd never guess the ground beneath your feet came from deep under the sea.

(Paul) Even I find it difficult to believe, really, that it was a massive industrial work site, but you look at it now and you think, "Wow, that's a huge, a huge change."

The vegetation's grown so much that we can have sheep and cows grazing it and the number of plants has increased enormously.

It's an amazing story.

(bright music) ♪ (narrator) September 1990.

The British had completed over 90% of their stretch of one of the three tunnels.

They were just under four kilometers from the French team, but one critical question remained: Would they join up?

(Helen) To keep the tunnels on line and to make sure they met up was a huge challenge for the survey teams.

The difficulty of getting the two tunnels to meet up was you're basically driving blind.

(solemn music) (narrator) Building a straight and level railway is relatively easy.

Surveyors can see in front of them and calculate their direction from landmarks in the countryside.

Underground, the only thing they could see was rock.

♪ (Helen) The potential for errors and sort of creeping up errors, accumulating errors on the survey is very, very big.

(narrator) When multiplied over the entire length of the tunnel, small deviations from the correct route could have disastrous consequences.

Ultimately, the two sides could miss each other by as much as 200 meters.

Engineers had to devise ingenious technology to keep the digging machines on track.

♪ (Mark) The tunnel boring machine was guided by a laser beam.

It was linked back to the surface contrail, so we knew exactly where it was at any point in time relative to the designed tunnel alignment, to make sure that we were going in the right place.

(narrator) Lasers at fixed points near the start of the tunnel were fired through a series of targets.

When the beam reached a sensor on the tunnel boring machine, it allowed the driver to continuously correct the course of the machine.

(Mark) What the driver is trying to do is to steer to zero, so if he drives to the left, it'll tell him he's going to the left.

If he drives down, it'll tell him he's going down.

(narrator) Checks showed their laser system was keeping the digging machines on target, but until the two tunnels met up, no one could know for sure.

(Richard) I think in the buildup to the breakthrough, there was quite a bit of concern that they would be successful and the tunnels would meet, and it was the culmination of the whole of the project.

If the tunnels had missed, it would've been rather embarrassing.

♪ (narrator) The first of December, 1990.

The moment of truth had arrived.

The first of the three tunnels to meet up was the smallest service tunnel.

Workers demolished the last remnants of rock live on television.

Drilling on the British side was Graham Fagg.

Everybody was looking forward to it, you know, looking forward to the fact that we'd achieved the object that we set out to do.

(narrator) Tunneling on the French side was Philippe Cozette.

(narrator) Finally, at 12 minutes past 12 French time, an historic moment.

Not since the Ice Age had Britain been joined to France.

(applause) (Graham Fagg) And the television crew behind us are saying, "Oh, we can't see Philippe, we can't see-- can we see Philippe?"

So I waved him forward, and he came halfway through.

So I had to sort of say, "Go back, go back," you know, "you're coming the wrong way!

Go back, Philippe."

And when he went back, we then started again, and we made it big enough so that we could go through.

So I was the first one to actually cross that line into France.

(cheering) (narrator) To celebrate, the French laid on some sophisticated refreshments.

On the British side, when they broke through, the French welcomed them with champagne, canapés, and the like, whereas on the other side, when the French broke through to the British, you know, they were lucky to get a cup of warm water, nothing else.

(narrator) There may have been no champagne on the British side, but there was still lots to celebrate.

After a combined drilling distance of 50 kilometers, the two tunnels were off by just 35 centimeters.

(Mark) It was absolute elation.

We all went to the pub and got drunk.

(cheering) (narrator) April 1994.

(dramatic music) The Channel Tunnel was finally completed.

At a grand event, the construction authority TML handed over control of the tunnel to its operator, Eurotunnel.

For everyone who'd contributed to this project, it was a cause for both celebration and relief.

♪ Sixth of May, 1994.

With the tunnel completed and the trains delivered, it was time for the Channel Tunnel to formally open for passenger service.

So the grand open day arrived and the plan was the Queen was going to travel from Waterloo Station aboard the first official train.

(narrator) The Queen arrived at Calais where she met President Mitterrand and officially opened the French terminal.

(applause) ♪ Despite competition from the ferries and the airlines, the sheer convenience of the Channel Tunnel won people over.

(whistle blowing) Since it opened in May 1994, almost 430 million passengers and 86 million vehicles have traveled through the Channel Tunnel.

Keeping this volume of traffic flowing freely takes a lot of work.

Technician Mark Empson oversees many of the tunnel's most important control systems.

(Mark Empson) We look after all the pipework, the drainage stations, the firefighting, the cooling, and the ventilation.

It's 58 kilometers, and as you can see, there's a service tunnel light every five meters.

We've got quite a bit of gear down here.

(soft music) (narrator) On tonight's to-do list, the maintenance team is examining the tunnel's cooling system.

(Mark Empson) Trains make the air warm in the tunnel.

Once the air temperature gets above 30 degrees, it affects the efficiency of the trains, which means they cost more money to run.

(narrator) If the outside air temperature in the tunnel gets above 30 degrees, the temperature inside the trains would also rise.

This would become uncomfortably hot -for passengers.

-So, if we can cool the tunnel and keep it below 30 degrees, it makes the whole system more efficient.

(narrator) Large pipes run the length of the tunnel.

Cold water is piped in from one end.

The water absorbs the heat in the Channel Tunnel and is sent back to the cooling plant where it is recycled.

(birds squawking) The plant itself is the largest cooling system in Europe.

(bright music) Building the Channel Tunnel was a monumental engineering endeavor.

♪ (Tim) It's actually almost inconceivable that 35, 40 years ago they actually could've done this, you know, gone from city center to city center in just one vehicle.

♪ (train engine roaring) (narrator) Today, this marvel of engineering stands as a testament to a colossal collaboration, a new fixed link between an island and a continent.

(Sarah) I say to people, "I worked on the Channel Tunnel," and you feel like you've built it.

(Alan) It was an amazing engineering feat to be involved in.

(Graham Fagg) I look back on our time with pride.

You know, we've done a good job, we've done it in fair time as well.

(Alan) I'd love to do it again.

Definitely, love to do it again.

Absolutely amazing.

(upbeat music) (narrator) From a Victorian pipe dream to the enormous challenge of its construction and its final triumph as the world's longest undersea railway, the Channel Tunnel has rightly earned its place as one of the engineering wonders of the modern world.

♪