Tunnels Under the Thames The Fifteen Billion Pound Railway

Underneath the streets of London...

LOUD TAPPING

..an army of more than 10,000 workers

is building a brand-new railway.

MAN: OK!

Crossrail.

Costing almost £15 billion,

it's the biggest construction project in Europe.

You need to get out of the way here,

because trains are going to start coming through!

One of the most complex challenges...

..building the train tunnels

that will pass underneath the River Thames.

This water is surrounding the whole tunnel all the way up and through.

It's tougher than anyone imagined.

This water's just coming through,

because our sealing isn't working the way it's designed to work.

This job, it's going to be a bucket of spiders!

This is the inside story

of the engineers building London's new Underground.

CHEERING

The Thames.

GULLS CALL

The original superhighway that allowed London to grow.

HORN BLASTS

Today, a crucial new artery is taking shape

that must pass right beneath this waterway.

Crossrail -

a 120-kilometre railway

connecting Reading and Heathrow Airport in the west...

..to London's major train stations...

shopping districts...

the square mile and the booming East End.

It's due to open in 2018.

The train tunnels for Crossrail

need to pass under water at two key points.

They must go under the Royal Docks at Custom House...

..and under the River Thames near Woolwich.

In their heyday,

the Royal Docks were the largest enclosed docks in the world.

Much of the old infrastructure remains in place today,

including an old Victorian passageway, the Connaught Tunnel.

The Connaught Tunnel runs underneath the water here.

Linda Miller heads a team

that is attempting to rebuild this old tunnel

to make it suitable for modern high-speed trains.

The mission for the Connaught Tunnel team is to turn

a 135-year-old beautiful piece of Victorian architecture

to a state-of-the-art, modern tunnel.

The tunnel as it stands

is too small for Crossrail's rolling stock to squeeze through.

Well, I've been on some very exciting jobs.

I've been lucky enough to build a new space launch complex

at Cape Canaveral, Florida, and do tunnels in other beautiful cities,

but I reckon this is my favourite job yet.

I love the idea that

we're bringing beautiful old... heritage railroad back to life.

The Connaught Tunnel was built in 1878.

Steam trains once ran through here, shuttling passengers and freight

to the ferry terminals at North Woolwich.

You may just see the old coke deposits

and memories of the steam trains left above there,

but actually what I see is a tunnel that's in cracking good condition.

Fantastically well built, you know, really built to last.

Dismantling and rebuilding this robust underwater tunnel

will be a complex job.

The Connaught Tunnel...

..is a single tunnel for most of its length,

except in the centre - under the docks - where it splits into two.

Linda's team must completely rebuild this section

creating a single taller, deeper and wider tunnel tube

big enough for two Crossrail trains.

The first job, then, was to start to deepen this tunnel

and you can see that's just what we've done, cutting away

and uncovering bricks that haven't seen the light in...in 130 years.

This is Alex, and this is her patch.

The work that needs going on here right in the heart of the job.

This is my first project that I'm working on,

so I'm really lucky to have such an interesting project as my first job.

We're currently right below the docks

and we're in one of the twin tunnels now. We need to turn it back into

one tunnel, cos our new Crossrail trains aren't going to fit in.

HOOTER BLOWS

By the 1930s,

the Royal Docks were some of the busiest docks in the world.

Ocean-going ships delivered grain, meat and sugar to the UK

from Australia and New Zealand.

The vessels were so large that their keels often scraped the roof

of the Connaught Tunnel that runs directly beneath the water.

Engineers at the time were concerned

that these boat strikes could cause disaster,

so they removed part of the tunnel roof to lower the dock floor

and sealed the tunnel from the waters above with steel rings.

Linda's team needs to remove these rings.

But a survey has revealed that there is a problem with the plan.

It was always assumed that we could cut these cast steel rings out

and replace them with rings that were slightly larger

and that that would all be fine, because we had a really good, er,

level of cover above the, above the crown of this old tunnel.

So it was shock and dismay after we had our first divers

clear away quite a lot of silt that was at the bottom of the docks

and do a proper survey and find that actually we have no cover at all.

The word we were worried about is, Oh, my gosh, as we try

and cut these rings off of the crown of this roof

and that much water is above us,

catastrophic inundation or the sluicing in,

the uncontrolled sluicing in of the Royal Docks into this tunnel

became quite the real...er, well, terror, really.

With little or no soil separating the tunnel from the water above...

..removing the steel rings could cause a catastrophic breach.

The only way to expand the tunnel safely is to seal off the passage

with giant steel barriers called cofferdams, drain the water,

and rebuild the tunnel, "top down", from inside this dry workspace.

Oh, my gosh! Well, when we started,

when this job was originally conceived five years ago,

we were never going to be in the water.

There was no cofferdam, there were no marine divers involved.

It was all going to be just safely and tidily done from within.

And, actually, the fundamental plan was broken.

And then, to go and visit with our neighbours and say,

"You know how for five years - eight years, really -

"Crossrail's been telling you we're not going to close this passage?

"We're going to close the passage."

Shutting off the waterway here could cause chaos.

It's the only way river traffic can pass to and from

the city's largest exhibition space, ExCel,

home to the annual London Boat Show.

Linda's team needs to wait until

the boats have left this year's show before closing the passage.

They have a narrow time window before it must be open again

for the next big maritime event - the Defence Show -

when naval ships will need to get through.

So we've only got six months to actually, um...build this.

Rebuilding this old tunnel won't be easy.

But south of the river at Woolwich...

..Crossrail engineers are gearing up for an even bigger challenge.

They're about to start building two brand-new sections of tunnel

from scratch passing underneath the River Thames.

In charge of the operation is Project Manager, Gus Scott.

Boring under the Thames is a huge undertaking.

Logistically, it's very challenging for us.

We've got a lot of work ahead of us,

but, er, looking forward to getting it finished.

The new train tunnels will connect North and South London together,

but digging them through the earth beneath the river won't be easy.

The ground is made up of sands and chalk, which hold water.

The tunnellers will face a constant battle

to keep the water at bay as they dig.

Excavating these tunnels carries the highest risk of flooding

of the entire Crossrail project.

So, to dig the tunnels, they need an extraordinary machine.

Wow. LOUD CRUNCHING

Take that!

It's been built at this factory in Germany.

It's probably the largest piece of rotating equipment

that I'll be involved in in my career!

Just the scale of it all, it just plays back to everything

I really was interested in in getting into this career -

playing with big boys toys. And it doesn't get any bigger than this.

This is Mary - a gigantic tunnel boring machine.

She cost £11 million

and is specially designed to dig under the River Thames.

Boring under the Thames, it really is high risk,

but it's all about really knowing the ground conditions

and making sure you select the best equipment on the market

and this, this is world-class.

It's like a thousand-tonne factory that will go under the Thames.

The tunnel boring machine, or TBM, has sharp cutters

in a huge rotating wheel that scrape at the earth like a drill.

Behind this cutterhead, an enclosed steel cage supports the earth

and creates a safe area for miners to build a concrete ring.

Seven pre-cast segments make up each ring.

A wedge-shaped keystone locks them in place.

Once a ring is complete,

hydraulic rams push the machine further forward into the ground.

Every metre and a half they advance, they can build another ring.

In perfect conditions, this digging demon can build up to 18 rings a day

leaving a water-tight, tube-shaped train tunnel in its wake.

This is designed really to do, at long average, 27 metres a day.

We hope, generally, on average allowing for maintenance,

we're doing 100 metres a week.

Mary's cutterhead is over seven metres across,

so that she can dig a tunnel wide enough for the new trains.

Her teeth are made of tungsten carbide -

tough enough to scrape away the chalks and flints.

Once underground, a crew of highly-skilled workers

will keep Mary running 24 hours a day.

You know, there's 60 men who'll work on these machines.

The crews that run these are a very close-knit group

who've all worked together before.

These tunnellers do it for their whole careers.

So it's still a very kinda like manual process, isn't it?

Even though it's all automated,

-you're still relying on the skill of the operator.

-Absolutely.

The responsibility of the operator is... It's on a high level.

Mary's cutterhead will dig through several areas

of high water pressure under the Thames.

If any of her tungsten carbide teeth break,

workers will have to pass through an airlocked chamber to repair them.

-So it's like a submarine that goes underground.

-Yeah.

-It's this type of a thing.

-Should paint it...should paint it yellow!

-Yeah!

-Yeah!

-GUS LAUGHS

Very good, yeah!

Mary is one of eight tunnel digging machines

being built at this factory for the Crossrail project.

Each one is shipped to London, like a giant jigsaw puzzle,

in more than 50 pieces.

Workers must re-assemble these kits before digging can begin.

At this worksite just east of Canary Wharf, a team is preparing

to put the most critical piece of this tunnelling machine in place.

They must lift the enormous cutting wheel

and connect it to the rest of the machine.

Lift manager, Lee Bartley, is on site

-to make sure nothing goes wrong.

-SHOUTING

The TBM itself is made up of many, many, er, different bits and we've,

we've, er...had to sort of put together about,

something in the region of, er, 70, 80 pieces to get to that stage now.

This is the essential part of the tunnel boring machine.

This is the face, what does the actual tunnelling process.

Without this, it's nothing. It is vital that this is right.

The cutterhead weighs 62 tonnes

and needs two cranes to raise it up into place.

It's critical their movements are in sync

or the heavy load could swing out of control.

-WOMAN: OK, he's coming down a touch.

-Stop!

-Stop!

-Stop!

Commanding the operators is banksman Clare Hallewell.

'I was in the armed forces for 7½ years, so, erm,'

this is pretty much similar to what I used to do.

We used to build bridges

'and go in the back of tanks. We're used to dealing with big lifts.'

OK, ready.

Just take it up that angle and then....

-Paul can track back, he can jib back and take the weight as well.

-OK.

Look, they're just doing their own thing here.

Stop 'em both and then, go and talk to 'em both

and so they're clear with what you want to do.

MAN: Stop!

Stop.

TIMBER CRACKS LOUDLY

TIMBER CRUNCHES

OK, stop there.

-MEN SHOUT:

-OK!

-OK.

SHOUTING CONTINUES, INAUDIBLE SPEECH

-LEE:

-Finally in now, and they're all bolted up,

so, very pleased to say yes, another one in and successful.

Woo-hoo!

Crossrail have christened all eight of their tunnel boring machines

with women's names, like ships.

This one is called Elizabeth, after the Queen.

The team "launches" Elizabeth by lowering her down a 35-metre hole.

From here, she will begin an epic underground voyage to Farringdon.

Her first port of call

will be the newly-constructed station at Canary Wharf.

One stop east back at the Royal Docks...

-Thank you very much.

-..Linda and structural engineer David Wilde

are doing further research on the new plan

to seal off the waterway above the Connaught Tunnel

so they can rebuild it from the top down.

The original engineers' drawings of the tunnel

are held in the archives at the Museum of London Docklands.

So there it is, there's the Victoria Dock.

This is going to be the Albert Dock when it's done, isn't it?

But at this time, it's actually called "proposed extension",

cos they haven't actually decided on a name for it.

I have to say, I've never started a job

-where I've had to go back and look at, er...

-The drawings.

-..the original drawings.

-DAVID LAUGHS

-135-year-old drawings there.

-Yeah.

We've been presented with the same problems

as the original construction.

Basically, a lot of it's to do with water,

and how you actually build something with all the water around it.

Linda and David are encouraged to see that

their new plan for rebuilding the tunnel mirrors the techniques

used by the engineers who originally built it.

"Existing dam" - see that's history repeating itself there.

This one is good in so far as I believe it shows the open cut.

-Mmm.

-The way it was excavated and installed in the first instance.

What they would have done is,

instead of tunnelling underneath the ground,

they've actually excavated around the profile,

and then installed the tunnel in there.

So they've built it from the top downwards, effectively.

The plan was that we were going

to enlarge the Connaught Tunnel from within. And we were never

going to need to put cofferdams down and block off the passageway.

But now, on reflection and looking back at these drawings,

and looking at the two twin-walled cofferdams standing there

with 1872, 1874 written in the corner of the drawings, I...

I think it was meant to be!

The London Boat Show is now over.

As the last luxury yachts cruise out of the docks,

the narrow window of opportunity opens for Linda's team.

They can now close the passage directly above the tunnel.

They must reopen it again in time for navy ships

to get to the Defence Show in just seven months' time.

Working with ExCel to try and fit this in between

their London Boat Show and the Defence Show coming in September,

we'll try and quickly get in here, do open heart surgery on this tunnel

from the top, rebuild it into a larger tunnel

and get out of here by the time the Defence Show comes.

It's hard work.

With the clock ticking, Linda's team wastes no time draining the water.

As they pump the last drops out, a specialist team moves in.

Well, we're here today really, er,

just as part of the welfare.

Obviously, there could be some fish trapped in between the cofferdams

and there's an opportunity arised whereby

the water's at a level where we can sweep round with a seine net

and basically see if there's anything in there that needs rescuing.

Years ago, this river used to have salmon, sea trout,

sturgeon running through it.

There is always a possibility, with the water getting cleaner,

that those fish could have come back.

You might pick something up strange like that in here,

so, er, you never say never.

That's is as low as it's going to go, I think.

I'm going to go down in the cage with it,

cos I think it'll be easier to get out.

-I'll meet you at the bottom of the steps.

-OK.

It opens inwards!

-Ready?

-Yup.

-Are you going to get in?

-I will do once you're in.

Whoa, whoa, whoa!

-That's a baby mullet, innit?

-Yeah.

Ooh...

Unfortunately, we've got lots of muck and debris.

Well, there's a handful of small...small fish.

HE GRUNTS

We haven't got many there,

cos a lot of them were these real small fellas here,

which went through the net, and they're a type of scad.

Then we've got...a sprat.

I think that's juvenile bass,

which will grow up to the sea bass that you find in the restaurants.

And then, somewhere in here, we've got a young...

a baby young bronze bream, which is called a skimmer.

They release the rescued fish into the open dock.

They should be happy in their new home now.

So away they go.

South of the river near Woolwich...

HORN BLASTS

..Gus's team is putting together the giant jigsaw puzzle

that has arrived from Germany.

Mary, the £11 million tunnelling machine

that will dig Crossrail's new Thames tunnel.

The big thing is how huge these bits are, you know, the...

40 tonnes, 35 tonnes here, 10-tonne, 15-tonne bits

all bolt together to make this 1,000-tonne factory.

The team will guide Mary north under the river from here.

CHEERING

Everyone's chomping at the bit to get her going

and she is a beautiful machine, she is.

On the team is Peter Bermingham.

He's been tunnelling for 50 years and turns 70 today.

APPLAUSE

Thank you very much. That's it. Help yourselves, please.

Digging Crossrail's Thames tunnel

will be Peter's final project before retiring.

Peter's two sons, Dan and Robert,

are working shoulder to shoulder with their dad

building the Crossrail tunnels.

I've spent three minutes of my life making him,

and I've spent three minutes of my life making him.

SOME LAUGHTER Yeah, Mum doesn't...

Mum doesn't reckon it wasn't that long, really!

LAUGHTER

There's been three really significant tunnelling projects.

There's been the Channel Tunnel, the Jubilee Line extension,

and now Crossrail and he's been sort of, like, intricately involved

in all three of those, you know, that's a hell of a thing to leave.

When these new tunnels are finished,

Peter will have tunnelled under the Thames ten times.

I don't think anybody in history's done that and

it'll be a long time before anybody else does.

The son of Irish immigrants, you know, you were a "navvie"

and, er, this is a "navvie" becoming a highly-respected professional.

What have we got here?

Tunnelling was very different when Peter first started out.

I first started tunnelling in 1964, on the Victoria Line.

A hand-driven tunnel, bored by hand.

We wore cloth caps, no helmets or protective clothing at that time.

The machinery wasn't that powerful. Most of it was hand tools.

I cannot believe it was in my time. It looked like

walking back on Victorian times, you know. We've come so far.

With the equipment we've got down there now, absolutely fantastic.

There is a special breed of tunnel guys.

You can't be normal if you go underground, can you?

I mean, you're living in the bowels of the Earth,

but, er, it's a proud industry to be in.

And the technology's come along so much and so fast, you know, to be

able to go through ground we never thought possible, it's incredible.

With the cutterhead in place, she's set for launch.

MEN SHOUTING

It takes three days to push the 150-metre-long machine

into the earth on the South Bank of the Thames.

20 workers, in two shifts, will keep her drilling 24 hours a day

through one and a half kilometres of boggy ground beneath the river.

It will take eight months

for the machine to resurface on the other side.

One stop west at the Royal Docks...

..Linda's team has no time to lose.

They have drained the dock,

exposing the roof of the old Connaught Tunnel.

They now have just six months left to completely rebuild this tunnel,

re-flood the dock and reopen this passageway for ships.

We've got, um, we've got lots of work fronts going on,

so we're working in the tunnel, working in the dock.

We're all a team, basically, working together trying to achieve one goal.

The team must complete a laundry list of challenges

in a very short time.

First task - remove the steel rings lining the twin tunnel section.

Then knock down the connecting wall to create

a single, bigger passageway for Crossrail trains to run through.

What you can see quite clearly here, now that the docks are empty,

you can see the cast steel barrel.

The Crossrail tunnel is going to be wider and rectangular

and fit its haunches within the old tunnel.

The team makes good progress removing the rings.

But as they cut the steel away in this corner,

they reveal a completely unexpected brick arch behind.

That's the problem.

The new tunnel is supposed to fit inside this arch.

But it hangs too low for the new tunnel to fit in.

That's got to be removed.

Linda and the team can't just remove the arch,

because it could be supporting the docks above.

You're not going to be able to take a section out of this

and still be able to hold onto your arching effect.

-Very unlikely.

-Unlikely.

-Is it the same on the other side?

-Yeah, but we don't know how far.

All the rings they've taken out so far, we've got the reduced dimension.

All right. Yeah.

So, this is yet another time when this tunnel shows us new mysteries.

This job actually started construction

a year ahead of when everyone said that it needed to.

And it was because a predecessor of mine said,

"It's going to be a bucket of spiders."

And, oh, my goodness! Have we used every bit of that?

And now we're staring at the end date

that we never thought that we would need to be worried about.

Linda and the team are already facing a very tight deadline.

They can't afford this new delay.

They need to find out as quickly as possible if the arch is

holding the docks above or if it's safe for them to remove it.

Somebody's going to get Central Engineering to start having a look,

the Chief Geotech, and I want them to hear about it now

so when they show up at the meeting on Friday they will already have had

a chance to think it through, maybe look up some information on it

to either say it's going to work or it's not going to work.

One stop east at Woolwich...

..the Thames tunnelling machine

has started burrowing her way underneath the river.

MEN SHOUT

Engineers have locked the first few hundred concrete panels

that form the walls of the tunnel in place.

They have over a thousand more to go.

It is hard to get lost down here, cos there's only one way in and out,

but I tell you something, if the lights went off

and it was pitch black, you'd have a hard time finding your way about.

At key points, Dan's team needs to drill through the panels

to create cross passages,

connecting the east- and west-bound train tunnels together.

We're literally going to break these out.

We'll, obviously, stitch drill around the area where it needs to,

then break it out and have a back hoe digging out

and sprayed concrete lining inside.

The panels hold back huge amounts of ground water.

The team must battle this water before they drill through them.

We've got 2½ bar water pressure behind us at this point,

so we need to grout the ground behind

to seal off any water before we open up.

These things here are valves and, obviously, we'll pump grout through

these valves behind the back of the ring and into the open ground.

This water is surrounding the whole tunnel all the way up and through.

You can try and de-water it, but there's so much, it'll take forever.

So what we do is just seal up the fissures in the ground,

and push it away from the area that we're going to tunnel through.

It's a great challenge.

Tunnelling under the Thames

has been a Great British obsession for hundreds of years.

The first tunnel ever built beneath a river anywhere in the world

was the Thames Tunnel built by Marc Brunel

and his son Isambard Kingdom Brunel.

This tunnel was a twin-track passage,

designed for horse-drawn vehicles.

It still exists today and carries rail traffic.

To build it, Marc Brunel designed a revolutionary invention.

Called a tunnel shield, it was an iron cage protecting 36 miners

excavating clay by hand at the digging face.

DIGGING AND SCRAPING

As the men dug further, enormous screws inched the structure forward.

STRAINING AND SQUEAKING

Behind, bricklayers shored up the exposed tunnel walls.

SCRAPING AND TAPPING

Two shifts of men drove the tunnel forward 16 hours a day.

SCRAPING AND STRAINING CONTINUES

It took them 16 years to dig from one bank to the other -

a distance of just a quarter of a mile.

Brunel's Thames Tunnel opened in 1843,

initially as a pedestrian walkway.

BUZZ OF CONVERSATION

More than one million people, half the population of London,

visited this subterranean wonder

within the first three months of its opening.

A modified version of Brunel's shield

was later used to excavate the London Underground.

Today, the machines digging Crossrail's Thames tunnels

are souped up versions of his design.

TBMs have been around...

Well, Isambard Kingdom Brunel's dad invented them didn't he, really?

The first shields, the hand shields, and it's just advanced from there.

It's very difficult to tunnel through here.

Every time you go under, technology makes it

just that bit easier, it always moves on.

-Go?

-That's it, go.

But you do have a lot of heavy kit in close quarters.

MACHINERY WHIRRS

There's no such thing as a small hurt. If you make a mistake on here,

there's no such thing as a small error.

The impact is quite severe, so you've got to get it right, yeah.

It takes the driver and miner less than an hour

to install each of the concrete rings that keep the water at bay.

Pipes and pumps suck the clay slurry

away from the digging face as they advance.

DRILLING, MEN SHOUT

We mark every ring, and number it based on...

The first ring of the tunnel is ring number one.

This is actually 1,232, but on that ring, I managed to drop the number,

so it's under the segment feeder somewhere.

It'll come out the back, it's no problem,

but I don't know whether I should improvise a number one or...

That's a convincing number 1, I think. That'll do me.

Maybe this is just pride of project or whatever,

but out of all the projects, this is one I prefer to be on.

You know, it's the most unique.

And, er, we're going under the river,

so there's a bit of a pride about it, so there is.

A rubber seal surrounds each concrete panel.

The crew must check the seals for punctures, and grease them,

before bolting the panels together

to make sure the tunnel walls are watertight.

Basically, this whole tunnel, we were mining under the water table.

We never mine above water and we're in water-bearing strata as well,

so it's all around us right now. But the sealing systems of the ring

and the design of the ring means that we keep it out.

The final layer of protection - a foam band

that will expand on contact with water to block any leaks.

Even with all this technology, no tunnel is ever 100% watertight.

We've got a little bit of water coming through there.

If there's nothing there to stop that coming through,

obviously, we would have a very wet tunnel.

Yeah, we'll need to keep an eye on it, because, if it gets any worse,

we'll make sure we can come back and repair it,

we know exactly where it's at

and do any remedial works that are necessary.

Millions of people will be doing this in a couple of years' time.

I just hope it's a bit less noisy and a bit less bumpy.

That's our work done for the day. I've been in to see the lads.

These guys are going to carry on a few hours.

It's my last shift here, so...

I'm on my way home now up to sunny North Wales.

North of the river at the Connaught Tunnel...

..Linda's team is back on track.

Their survey revealed that the passageway's brickwork

is strong enough for them to remove this low arch

without risk of the whole tunnel caving in.

In fact, Linda has discovered that the brickwork is unusually strong.

The mortar between them is 100% full. There's no gaps here at all.

It's a fantastic, fantastic job.

And then, the 135 years of earth pressure and water against it

has sealed it up to where it's behaving more like stainless steel

than it is brick and mortar.

The strong mortar is now causing the latest problem for the team...

DRILLING

..they can't get the bricks out quickly enough.

So just over a third of the way to go, but, er...

it's quite slow going, this brickwork.

You know, I've seen brickwork like this taken down

and all you normally need to do is have a couple of stabs at the mortar

and that whole brick layer goes off.

-A couple more stabs at the mortar, the next layer goes off.

-Yeah.

I know the men are taking a short break here now,

but hand breaking out this 130-year-old brick

-is just, well, it's just hard work.

-Yeah, it's going to take a while.

I know they're working it night and day,

-I know they've got extra crews in, but there's not much time.

-Yeah.

Linda's crew has just two weeks left before they must reflood the dock.

They are behind schedule.

Here we are in the last throes of the last couple of weeks

before we put the water back in.

We couldn't be throwing more into it than this.

We're all doing shifts, covering each other, and just doing

everything we can to get it all done by our deadline date next weekend.

September 2nd is not that far away.

And we're going to see military ships

that are going to be looking at us over our cofferdams

unless we get out of the water.

Underneath the river at Woolwich, the Thames tunnel boring machine

is nearly halfway through her long drive to the northern bank.

DRILLING AND RATTLING

Each six metres the tunnel advances,

the crew must extend the rails for locomotives,

and the pipes that carry the waste away from the digging face.

A team of nine, working seven days on and four days off,

keep the machine moving.

It's hard work, but it's an entry into a tunnelling career.

No matter how hard they work, the team and tunnelling machine

can only advance as fast as the chalk and flint

is removed from the tunnel face.

A 3km long network of pipes, snaking under London,

transports the clay and slurry to this plant in Plumstead.

If this facility goes down, tunnelling grinds to a halt.

This humble-looking shed houses the pinch point of the entire operation.

Whatever we excavate, the chalk, sands and gravels

all get pumped back in slurry through this pipe.

We take out all the larger particles through the trommel,

through the de-sanding unit, through the de-silting unit,

and then the waste slurry.

Everything that hasn't got anything over about half a millimetre

gets stored in a huge tank outside, and then we pump it over into

this room, the filter press room,

where we've got six of these presses.

The principle behind it is very simple.

Basically, to hold the slurry so you can squeeze the moisture out,

recycle the water and be left with the cakes.

I guess in a way the simple things are the best ideas.

We can do 40, 50 tonnes an hour here.

Gus' team ships the cakes to Essex

where they are used to nourish grassland conservation areas.

And this really controls the advance rate of the TBM.

If we can't get the materials out quick enough then we can't advance.

Two stops west, the tunnel-boring machine called Elizabeth

is homing in on Canary Wharf.

Elizabeth has tunnelled nearly 2km through solid ground

and must now hit a target, the newly-built station box,

with millimetre precision.

We're at the minus six level of the Canary Wharf box

and we're just waiting on our first TBM to pop its head through

for our first breakthrough.

This is our first breakthrough on an existing structure, so for us

this is all about making sure that the machine is where it should be.

Canary Wharf station is a giant six-level box,

with a garden, shops and restaurants on the upper floors...

and the platforms deep below ground.

Peter Main's team must drive their tunnel-boring machine through

the station's concrete walls, hitting a specially-designed target.

You do a lot of hard work on it and one little hiccup,

it's only one decimal point you need to be out,

and it could be metres off.

On the other side of the station wall,

the tunnelling crew put the final rings in place.

In charge is Scott Moss - one of almost 200 young graduate engineers

hoping to follow in Brunel's footsteps,

and join in the Great British burrowing obsession.

I have to check the rings.

Make sure all the rings are intact, no damages to them.

If it wasn't for the segments, there wouldn't be a tunnel wall,

so they are quite important in that respect.

It's really important that the segments get laid out

in the right sequence. As we are excavating,

I decide what orientation the next ring gets installed at.

I only started at the beginning of March,

so only two and a half months.

So all is extremely new to me.

I just hope I don't give them the wrong ring.

A tunneller's first breakthrough is an important rite of passage.

It's the highlight of the job.

Not only is it my first breakthrough, it's this project's

first breakthrough as well. It's a massive occasion

and we're just all hoping it all goes well

and we turn up at the right place at Canary Wharf.

The noise you can hear is Elizabeth, our first TBM.

She's currently boring her way through the concrete that'll

bring her in to the Canary Wharf box.

But with less than a metre to go, Elizabeth stops digging.

CAMERON: How bad is it?

There could be a dozen reasons for stopping cutting, you know?

It could be a belt issue, but we'll find out.

Elizabeth has a conveyor belt stretching all the way up to

the surface to carry away the excavated rock and soil.

Today, of all days,

this crucial link has broken - the belt has slipped.

Elizabeth can't break through until it's fixed.

Scott's shift is about to end.

There will be no first breakthrough for the young engineer.

The night shift get to claim the first breakthrough of this contract.

Devastated, to be honest.

They work into the night trying to fix the belt

on the other side of the wall.

Can't do anything more about it now. Just wait patiently.

Or impatiently.

We're going to repair the conveyor for the rest of this night shift,

and then we'll shove through between 7.30 and 8 tomorrow morning.

The drawn-out fix is good news for Scott, who is now back on shift.

Unfortunately it took nine hours.

It's up and running now, so all is well in the end.

We did the repairs overnight to the conveyor and we're now

looking forward to Elizabeth coming through.

Scott's, and Crossrail's, first breakthrough

is now just centimetres away.

Scott gets the honour of being second man through.

I was on the phone to my mum just as we broke through.

A bit sad, I know, but she was happy for me.

My very first one.

They let me come out at the end, one of the first ones,

so it were brilliant, yeah, I really enjoyed it.

Ecstatic, totally!

One, two three...

THEY CHEER

One, two, three...

THEY CHEER

One stop east at the Royal Docks,

Linda's team has been working around the clock to remove

the protruding arch inside the Connaught Tunnel.

They have just one day left to shore up its roof with steel

and concrete before they must re-flood this dock.

This will be the final act of the second part of the play.

And we're just waiting for the final sign off for the last pour.

The team had scheduled the concrete pour to start today at dawn.

But there's a glitch - they need to add more steel

to strengthen the roof.

6.30 this morning the steel wasn't right. Too narrow.

So it was a mutual agreed decision to stop.

This isn't going to work like it is, we need to get some more steel

in there, some more rebar.

We're here on the last day pouring concrete on the last minute

of the last hour.

And this is a complete departure from the original scheme.

With the steel finally in place,

the concrete pour begins - eight hours behind schedule.

Concrete has just started pumping, unfortunately,

here at three o'clock in the afternoon rather than

seven o'clock in the morning. Never a dull moment!

We've got the concrete pumps

and they're busy pumping the concrete up through this pipe.

It comes through here and then it goes up into the outside.

We had initially planned to do it this morning,

so it's now this afternoon,

but now we're finally getting it in and it's almost done.

The final push pays off and water streams back into the area on time.

There's one last challenge before boats can pass through here.

Divers need to cut away the huge steel props that have been

supporting the dock walls.

DIVER: OK, ready for main air

-DIVE SUPERVISOR:

-Roger, roger. Main air's coming on to the diver.

Anything underwater that needs to be done, we're here to

offer our assistance. It's not easy sort of work.

You can imagine trying to go down there

and work in completely black water.

The divers need to use heat-cutting tools to slice the props free.

When that's done, they will then start pumping air into the prop,

which will make it buoyant

and should enable it to float to the surface.

It'll be great to see the props come out because that then gives us

a free passage for when these battleships to come through

in September.

We have committed to the Royal Navy,

and to ExCel that we're going to make this passage free.

Any time you have divers down in the water, doing hot cutting works,

it's just by its nature, extremely hazardous, extremely perilous.

-DIVE SUPERVISOR:

-Roger, OK.

Roger, we'll send down the cutting rig and the rods.

Yeah, it's hot.

Make it cold.

That's cold.

The air line's ready for you.

Roger, roger.

Roger, up on your slack, you're coming back.

It's been a difficult job but we're getting there.

One stop east at Woolwich, it's a big day for the Bermingham family.

They are approaching the last few metres of their drive

under the Thames.

So at the moment we're just going to go in to the tunnel

where TBM 1 is actually still mining underneath the river Thames.

Nearly reached breakthrough point.

It took the Brunels 16 years to complete the first Thames tunnel.

Peter and Dan Bermingham have built theirs in just over eight months.

We're going to breakthrough into the new reception chamber

at North Woolwich. We'll be relieved to get through.

It's always nice to see the light at the end of the tunnel.

The Thames tunnel machine's cutting wheel is designed to work

under high pressure when she's digging under water.

So, just like a diver,

she must depressurise in a chamber before she can come up for air.

This is where all the action has been.

You can see here on the teeth how you've got the wear

at different levels. That's the full profile,

and you can see here that's worn all the way back there.

Been through some tough flints and geology, but er, yeah, made it.

For lifelong tunneller, Peter Bermingham, completing

the Crossrail Thames Tunnel is the culmination of a 50-year career.

No, this is me lot.

I'm now retiring. Looking forward to that.

My wife's got a nice little sports car

so we're talking about driving down the Amalfi coast in Italy.

Forget about tunnels, concentrate on an enjoyable retirement

with my wife and grandchildren right now.

It's good. Time to go.

Keep hoisting up.

The tunnel may be finished,

but this tunnelling machine's life isn't over.

Try and keep it square to the crane, lads.

Her components will be re-used to build other tunnels

around the world.

Keep coming down.

Keep coming down. Another 500 mill. Keep lowering off.

200 mill. Keep coming. Stop.

At the Royal Docks,

the waterway above the Connaught Tunnel has finally reopened.

Linda and the team have completed the tunnel just in the nick of time.

I can't believe you can see all the way through.

No-one's ever going to have been able to see that

all the way through.

-Doesn't it look fantastic?

-I know, it's mad!

I can't believe it's finally done.

Feels so good.

Like, we're directly below the docks right now and you wouldn't know.

I know. Hello, metres of water there above us.

Oh, my gosh, we were working like dogs, weren't we, 24/7?

It couldn't have been closer. It couldn't have been closer.

We've done it.

A couple of years ago

when I was standing in a steel-lined structure I had no idea, I couldn't

even envisage what it would be like when we were finished.

It just seemed like we had so much work ahead of us.

It was never ever, ever going to end.

For me to have it as my first job is amazing.

I think I'm going to disappointed at everything else I go to now.

This is the new Connaught Tunnel for the next 120 years.

You need to get out of the way here

because trains are going to start coming through!

The new £15-billion railway is due to be open to the public by 2018.

There's a huge amount of work still to do before a single train can run.

Workers must gouge out space beneath the city's crowded streets

for ten enormous new stations.

It's hard to imagine that in another five years this will be teeming

with passengers, there'll be swanky new trains coming through

and it will all be an architectural masterpiece.

Building these structures will not only be

a big engineering challenge...

Beautiful! Beautiful! Looking more than good, looking brilliant.

But it will also reveal lost secrets of London's past.

It's exciting, this is one of the first times within this

immediate area that we've actually found several skeletons together.