Original subtitles

In this episode... Look, it's multi -kilometres of nearly eight metres

tunnel through the centre of London. It's absolutely enormous.

A multi -billion dollar super sewer network.

Some of the things that we are doing here are cutting -edge technology, world

-class engineering.

And the groundbreaking innovations from history.

There's a really exciting piece of important engineering history somewhere

this building.

That make the impossible possible.

London. Spanning over 600 square miles.

This mighty metropolis is one of the world's busiest cities.

But danger lurks beneath these streets.

London's sewers have reached maximum capacity.

The underground network is full of waste from sinks, toilets, and washing

machines around the city.

Engineers tackle five blockages every hour.

It costs roughly $1 .3 million every month.

And the torrent of raw sewage is overflowing.

Archaeologist Kathy Newland is looking at the root of the problem.

London's original sewer system was built 150 years ago by Joseph Bazalgette. He

was considered an engineering genius.

But time and London has moved on.

We've grown from a population of 2 million people to more than 9 million

And the system just can't cope.

For centuries, London has been struggling to deal with its most basic

Before London got its first sewer system, the city's waste was dumped

into the River Thames.

And during the summer of 1858, the hot weather exacerbated the smell of

untreated human waste, causing a crisis known as the Great Stink.

Today, the mighty Thames is under threat once again.

London -born construction engineer Ray Cantwell lives near the river and knows

the extent of the problem.

My mum used to actually be able to swim across the River Thames from Bishop's

Park over to Putney. It probably wasn't recommended back in the day, but ever

since then it's getting worse and worse.

It's horrible to see, horrible to work around.

It's quite disgusting, actually, if I'm honest with you.

London's original sewer was designed for both sewage and rainwater.

the water carried the sewage away from the city.

Following heavy rain, combined sewage and water overflows, CSOs, prevented

sewage from backing into people's homes by discharging directly into the Thames.

The emergency CSOs were only designed to operate once or twice a year.

But today, with more people and more rainfall, London's overwhelmed system

discharges sewage almost every time it rains.

Whenever there's over two millimeters of rainfall in London, these CSOs release

tons of untreated sewage into the River Thames.

Approximately 34 million tons on a typical year.

Sometimes when you do have heavy rain the night before, you can come onto the

site and actually see the amount of sewage going into the river and the

discoloration of the River Thames. This is the main problem that we have to

tackle.

Something has to be done to save the Thames.

So engineers have started one of Europe's biggest construction projects.

The London super sewer.

This is a huge undertaking in the center of London.

The scale is just enormous.

A multi -billion dollar feat of engineering that will extend London's

sewer system.

This is exciting. This is the pinnacle of civil engineering.

It's the mega -project that get the attention.

That's really why I got into engineering.

Designed to transform the River Thames, it's truly groundbreaking.

Some of the things that we are doing here are cutting -edge technology, world

-class engineering.

So I'm pretty sure a lot of other countries will follow on from this and

as a set standard.

The super sewer will bring the existing network into the 21st century.

The combined sewer overflows, or CSOs, will be connected to 24 deep shafts.

Under the ground, approximately 20 miles of tunnels will thread their way

through the tangle of the city's subterranean infrastructure.

At the deepest shaft ever dug in London, sewage will be pumped the height of Big

Ben up to the largest wastewater treatment plant in Europe.

There are approximately 54 sewage outpoints across the River Thames.

The Thames Tideway Tunnel Project aims to intercept these worst offending CSOs,

send them into our tunnels and our shafts down to Beckton Sewage Treatment

Works. In essence, once the project is completed, we hope to reduce the amount

of untreated sewage that is released into the River Thames every year by

96%. But such an

ambitious project is full of challenges.

How do you prevent millions of tonnes of toxic sewage flooding the Thames?

How do you tunnel beneath London's underground rail network and the river

itself? How do you pump thousands of litres of sewage vertically to the

treatment plant?

And given how dense London is, how do you manoeuvre the enormous equipment

through such limited space?

It will take some of London's top engineers to pull it off.

Behind me, we can see the drop shaft construction in the background.

Engineer Josh Roy is overseeing one of the first stages of construction, the

drop shaft.

This is the viewing platform, which is the platform where the crane supervisor

or the banksman coordinates lifting into the shaft.

And effectively, it's the only position you can see down into the drop shaft

during construction.

The internal diameter of the drop shaft when it's complete will be 15 meters.

And currently, we've excavated to approximately 12 meters below ground

And we are continuing to 32 meters below ground level in total depth.

This is just one of the 24 shafts engineered to tackle the biggest sewage

overflows along the river.

Crucially here, during a normal year, a number of overflow events occur, which

means that pollution obviously goes straight into the Thames.

So here we're providing a drop shaft, and in the future, a series of

interception chambers will take any overflows directly into the tunnel

than into the Thames.

By connecting the existing sewage overflows to vertical shafts, engineers

start to remedy the most problematic areas.

But buried underground and flooded with tons of sewage, much of the network will

be inaccessible for servicing.

To ensure it functions maintenance -free for decades to come, engineers must

tackle a fundamental problem.

At this site in particular, beyond a depth of four meters, we are well past

groundwater level, and therefore we can expect to have some kind of water

ingress as we construct.

and that's one of the biggest challenges on this site and other sites across the

project in London.

The shafts are reinforced with concrete, but over time they can be corroded by

the water outside and the sewage within.

Under the microscope, concrete is laced with tiny capillary channels.

Water and sewage can permeate these capillaries, causing irreparable damage.

Engineering a network to withstand sustained attack from water and sewage

of the biggest challenges.

And buried so far underground, this project must be designed to last.

To make it happen, engineers will need to draw inspiration from the pioneers of

the past.

Engineers in London are hard at work extending the city's underground sewer

system.

But buried below the earth, regular maintenance will be a challenge.

And this super sewer is going to need to last for generations to come.

To find long -term solutions.

Archaeologist Cassie Newland has traveled to the ancient city of Knathos

Greek island of Crete to see a 4 ,000 -year -old Minoan marvel.

This is Europe's oldest city, the London of its day.

This was home to up to 100 ,000 people.

But sustaining so many people in this landscape wasn't easy.

So the great challenge of a city like this is getting enough fresh water for

people to drink.

It's very hilly, it's very rocky, the weather is very seasonal, so you have

great dry periods followed by torrential winter storms.

And all the fresh water has got to come from springs on the opposite side of the

valley. Once it's in the city, the real challenge is moving it around to where

it's needed.

Sometimes the water's going downhill, but sometimes you've got to pull it up.

The Minoans thrived here because they understood a basic principle of water.

always finds its own level.

By using a stream on the nearby hill, they were able to direct the water down

and up again across the city.

This allowed the Minoans to build networks not just for water, but also

drainage and sewage.

At the bottom of this hole are in -situ terracotta pipes.

Now, the pipes are designed to bring the fresh water in for drinking.

They're a very special shape, sort of like a very long, thin cone. So the

entrance at one end is slightly wider than the exit at the other. This allows

them to fit together really snugly, excluding air and making sure that water

pressure is maintained within the system.

Pericot is a fabulous material because it doesn't matter what you're putting

through it, whether it's acid or alkali, it will remain unchanged for thousands

of years.

The pipes laid down here are as good today as they were when they were first

laid.

And the Minoans' networks were built to last.

I'm standing on the oldest road in Europe.

4 ,000 years ago, when engineers constructed this, they put in a huge

drain. Take all the water from the palaces and the courts above it. The

amazing thing is, it all still works.

All thanks to meticulous engineering.

It's got this lovely sinuous line as the drain makes around the hill. And that's

for a very specific reason. It's all about controlling the flow of the water.

While you want it free -flowing so you can avoid blockages, you don't want it

just shooting off down the hill too fast because that would erode the bottom of

your drains and cause it to collapse.

What we have here is very careful management of that flow rate.

I mean, this is really very clever.

And the system is still draining water from the city today.

This city -wide network is remarkable.

Hydraulic engineering began here, and it's the basis of everything we do

For London's super sewer, engineers must ensure the buried network will remain

as maintenance -free as Knossos.

The sheer capacity of the shafts will help control any surges.

But the bigger problem is waterproofing.

Existing methods can be challenging for such giant and complex structures.

To apply a sheet membrane waterproofing system is quite labor intensive.

It requires access at a later stage along all sides of the shaft and at

so it becomes a safety risk.

At the shaft, there's a revolutionary solution.

A chemical treatment is added directly to the concrete mix.

Reacting to the water and cement in the mix, the chemicals grow into crystals.

filling the capillaries.

As the crystals duplicate, they create a network that stops water from passing

through. The impermeable barrier will hopefully be as effective as the

terracotta used by the Minoans.

And because it simultaneously strengthens and waterproof,

this innovative treatment will protect the site for years to come.

Okay, so we're now batching the concrete mixture, but just behind me you can see

two silos that are both batching at the same time into one pump. The material

goes into the hopper behind me, and the pump then pumps the concrete mixture in

this line all the way to the drop shaft for use in the spray concrete lining

construction.

The exposed ground in the shaft is unstable.

so the mix is designed to set quickly.

With excavation temporarily halted and emergency breathing apparatus on hand,

it's safe to enter.

Each four -foot vertical lining requires 130 tons of the mix.

But there's a risk the mixture will set before the work is completed.

The solution is an ultra -high -pressure pneumatic hose.

Don't cross the red and white line, basically.

Simple as that.

The mixture is propelled at 4 ,000 psi, enough pressure to cause serious harm.

So here we are at the bottom of the drop chart.

We've tested the mixture at the surface, and now the concrete mixture is being

applied as a spray concrete lining, incorporating the crystallizing agent as

waterproofing measure.

With the pump working at full power, it takes just minutes to protect the

section.

It's great to see the spray concrete lining application in person.

It's really quite a challenge that has been overcome here.

With its longevity assured, the super sewer network can start to grow.

But building miles of tunnel directly under the Thames will be a massive

engineering challenge.

Just beyond me is the earth.

Our purpose is the river.

This is a huge undertaking in the center of London.

And experts will have to bring in some cutting -edge technology to get the job

done.

Extending above and below the River Thames, London's super sewer is one of

biggest engineering projects in Europe.

At over 20 sites across London, engineers are digging tunnels in

directions, creating a network nearly 20 miles long to keep up with the city's

growing population.

But tunneling below one of the biggest, busiest and oldest cities in the world

comes with a number of challenges.

Just finding space for a start.

Here we're surrounded by listed buildings,

architectural gems and historic monuments.

And that's just above the surface.

When you get below ground, it's even more complicated.

You've got all your existing infrastructure. So that's the Victorian

system. It's your water main, your gas main.

It's your electric cables and your telecoms cables.

It's the tube and all the pedestrian walkways that go with that.

And that horrible tangled network is set inside 2 ,000 years' worth of

archaeology. And then there's the river, without which none of this will be

here, but which makes the whole of the subsoil completely waterlogged and

difficult to dig through.

And they're not just digging any old tunnels.

These tunnels are big, big enough to drive a double -decker bus through.

Engineers need a machine that can work under the most difficult circumstances.

With the weight of London above them, the team is facing a seemingly

challenge.

The solution can be found below the battlefields of the past.

On England's south coast, Engineer Katie Tom is searching for a location that's

been all but forgotten.

I'm really excited.

This place is normally closed to public, but I've got special permission to have

a look inside, so I can't wait to see what's in there.

Extending almost 600 feet into the chalky earth, this

is the Windchelsea Tunnel.

Lots of graffiti on the walls down here, lots of initials, which is quite nice

to see the history of it, really.

The tunnel's origins stretch back to World War I.

In the trenches of Flanders, Allied forces devised a plan to dig tunnels

enemy lines.

Once dug, huge caches of explosives could be detonated inside them.

The Windchelsea tunnel was the secret test site for this plan and was dug by

extraordinary new machine.

So you can look at the shape of the tunnel and the length of it.

It's almost a perfect circle. I can track the movement of what the machine

have been doing.

all the way around to here to take out the material.

It must have been a big beast of a kit for its time, really quite

so it's really exciting to learn about it.

The mysterious machine used here could hold the key for London's super sewer.

And Katie has managed to track down the only example left in existence.

I have exclusive access to the Science Museum group collection.

No one is allowed back here.

But I've been told there's a really exciting piece of important engineering

history somewhere in this building, and I can't wait to find it.

It's like an Aladdin cave.

And here it is.

The Whitaker Tunnel Boring Machine was the brainchild of English engineer

Douglas Whitaker.

So this is the cutting base, as you can see here.

You've got the buckets on the outside. There's the cutters here, which would

have excavated the material.

The buckets, as it moved, would have collected it.

But Whitaker's amazing machine got off to a rough start.

The ambitious plan in the World War I trenches failed, and his machine was

buried under the battlefield in France.

This example was part of a cancelled attempt to dig a channel tunnel between

England and France in 1921.

This one is a little bit larger than the one that would have cut the Winchelpey

Tunnel. But the size of the buckets is similar, and that would have given the

uniformity of the markings that we saw in the chalk, caused by this large

movement that would have helped the machine advance out of the tunnel.

But despite its failings, Whitaker's extraordinary tunneling beast did

vital innovation.

Rock contains cracks, faults, and folds.

When tunneling underground, it's crucial to keep the pressure balanced.

If the excavated material or spoil is removed too quickly, the sudden change

pressure can cause a collapse.

Whitaker had the solution.

What Whitaker came up with is this corkscrew conveyor which takes the

collected from the bucket all the way down the length of the machine.

This is a very simple mechanism, really.

The material goes in as it's being excavated and then as it moves... around

material is taken along the whole end of the machine and then is collected

right at the end.

It's simple.

Whitaker's corkscrew technique meant that he could remove just the right

of spoil at any given time.

The corkscrew and the cutting mechanism were calibrated at the same rate to make

sure that that was balanced correctly to stop the tunnel from caving in.

Whitaker's Tunnel Boring Machine, or TBM, was the forerunner of a technique

used all over the world.

Whitaker's combination of the rotating cutting base and the screw conveyor

really has become the blueprint of all future TBMs. This is such an amazing

piece of engineering.

And today, engineers will need to use the principles put in place by Whitaker

dig the massive tunnel network that will make up London's super sewer.

Engineers in London are hard at work on a new super sewer to accommodate the

city's rapidly growing population.

Using principles originally engineered by Douglas Whittaker, seven giant tunnel

boring machines, or TBNs, will dig the tunnel network.

Some of these machines have a diameter the length of a London bus.

and weigh up to nearly 1 ,500 tons.

And here she is.

Each TVM has been specially engineered for the job.

This is Rachel, our tunnel boring machine, 8 .1 meters in diameter.

With all the backup gantries, it's going to be 147 meters long when complete.

Engineer Mark Shepard is doing a final inspection of this machine's cutting

before it's deployed under London.

So this is the cutting wheel of the machine.

It's around 100 tons on its own.

This will do all the cutting, so we're mining through mostly London clay in

section of Tideway.

This is an earth pressure balance machine, so this cutter head will be

mined clay at pressure.

The red screw at the bottom there will rotate, and that will take the muck out.

Like the Whitaker machine, the screw helps maintain pressure at the tunnel

It runs right through the heart of the machine.

And because it's so long, that can keep a plug of material as we're excavating

and hold the pressure in the face.

That's rotating full of material, and we can control the speed of that.

We have a guillotine door as well on the end so we know exactly how much muck is

coming out. We're not taking too much out.

Because there are so many underground obstacles to work around.

The TBMs will excavate deeper than all existing infrastructure directly under

the river.

Lowering them down the drop shafts is a precision operation.

But once in position, they'll advance 26 feet per day to connect all the shafts

together.

The project is just enormous.

Site manager Paul Hallows is venturing down to one of the biggest tunnels on

project to check out one of the mega machines in action.

It's absolutely enormous.

So, we're at the front of the TBM now.

Just beyond me, you can see, that's the bulkhead.

Just beyond the furthest away part, you can see the TBM.

That's where the cutting disc is, which is turning about 2 RPM.

Beyond that is the earth.

Our purpose is the river.

We're at the business end.

All the spoil in front of the TBM, that's being cut away, then dropping

into the invert in the front of the machine there, coming up this screw

here,

dropping down into the conveyor, then it's away all the way down the tunnel on

conveyor belt, up to the surface, and gone from sight.

As the cutter moves forward, Paul and the team build giant concrete rings to

support the new tunnel.

The further the TBMs travel, the more segments are needed.

Up at the surface, a seemingly endless supply keeps the TBMs fed.

Since London streets can be difficult to navigate, the segments are transported

by barge along the Thames.

Once safely on site, they're craned down the shaft to join the TBM's automated

production line.

Each tunnel ring gets brought into the tunnel by the loco.

It's put on the storage cassette.

From the storage cassette, it's picked up, carried up to the front.

At the front of the machine, the segments are picked up by suction,

where they need to be, and secured in place.

We excavate in 1 .8 -meter increments.

So every time we've advanced 1 .8 meters, we retract the rams, we build

these concrete rings.

These concrete rings, 1 .8 meters wide.

There's eight of these sections make a complete ring.

There's over 40 tons per ring.

Once a complete ring is then built, then we can excavate, start again, start

another 1 .8 meters.

This is what we're going to be doing for the next 4 ,500 meters.

The giant tunnel boring machines are the solution to the London super sewers

seemingly impossible engineering challenge.

They can quickly and accurately thread their way through London's web of

underground obstacles.

And it's all thanks to tunneling pioneers like Douglas Whitaker.

The engineers of the past, you can only be impressed by them.

Everything we're doing now is as mechanized as possible.

Now we're just concrete lines, rapid progress.

Much better environments to work in, but hats off to them.

I wouldn't have liked to have been around then.

But now the super sewer team faces perhaps their greatest challenge.

So this is the lowest point in London. So this project is unique in terms of

depth. They'll need to invent a way to remove the sewage from deep below

The super sewer is one of the most ambitious networks in the world.

By extending London's old sewer sit, engineers are planning to prevent

of tons of sewage from flooding the Thames.

The Lee Tunnel pump shaft in East London is the final stage of the tunnel

network. At nearly 125 feet wide and 288 feet below ground, it's

the network's lowest point.

and is the deepest shaft in all of London.

The shaft is so deep, it could swallow a big bend here. And there's a really

good reason for that.

It's about creating the perfect self -cleaning velocity.

And you do that by controlling gradients.

Too shallow, nothing goes anywhere.

Too steep, and the liquids separate out from the solids, leaving them behind to

accumulate and form blockages.

So we're now on the west side of the pumping station.

At the pumping station, engineer Jad Budiya is venturing all the way down to

bottom.

So this is the lowest point in London that you can physically and safely get

From here, accumulated sewage must now be pumped to the treatment plant for

processing. But pumping tons of semi -solid material almost 300 feet

upwards is a huge challenge.

To find a solution, engineers looked to another region that was once drowning in

problems of their own.

The Friesland region in Holland is a 2 ,100 square mile area of flat land

bordering the North Sea.

Its history is punctuated with fierce storms and devastating floods.

Marine engineer Keith Storm has seen the damaging effects on the land.

Friesland is one of the wettest areas, and that's because north, west, and

south, we are surrounded by water.

So that was always our biggest problem.

So with a couple of days of storms,

the enormous amounts of water inland, which could be millions and millions of

cubic meters, would take months to get rid of. So you really need a significant

engineering solution to do that.

Saving this land seemed an impossible challenge, but one Dutch engineer

he had the answer.

In the early 20th century, Dirk Frederick Wouda perfected the pump

And in 1920, he built this.

The Wouda Pumping Station.

At the time, the largest and most technologically advanced steam pumping

in the world.

And it could hold the key to the super sewers problem.

I love coming in here, and it's a beautiful time to see the machine

smoothly and steadily.

The heart of the station was the centrifugal pump.

Inside a centrifugal pump, a shaft -driven blade called an impeller

As the impeller accelerates, fluid is sucked through the inlet port at the

center. The velocity propels the fluid to the edges and out through the

discharge port at the top.

Well, as a marine engineer, on board a ship, we use also centrifugal pumps.

But I've never seen a size like this.

The giant pumps are driven by enormous steam engines.

And these steam engines were originally fed by eight large boilers.

So these massive pumps require a lot of horsepower, and that's why we require

each engine to have 500 horsepower, which is equivalent to a beautiful

car.

Just to give you an idea of the capacity of all the eight pumps, if you fill up

this whole building... up to the rooftop with water.

And all the pumps are running like now on a steady speed.

The whole building is empty in two minutes only.

The ability to shift such volumes so quickly is thanks to the gravity

engineering inside the pump.

The first thing we will do is build the impeller.

And we do it very simply by attaching the tube onto the pencil.

Like this.

Cutting the envelope.

And then attach the impeller into the drill.

So now my impeller is ready.

Now we are going to prime the pump as we do in the main unit.

To prime the pump, water is sucked into the tube.

The pump is now primed.

And if we start rotating... Oh, there he goes.

The centrifugal furnace has overcome the gravity, and the pump has started

pumping and getting very wet.

The brilliant simplicity of this ingenious system allows WUTA to continue

pumping vast amounts of water, even today.

So even 100 years old, these pumps are still doing their job.

and are very important to keep the country dry.

And in order to keep their super sewer running smoothly, engineers in London

will have to adopt some of these same techniques with the modern -day twist.

Deep below the ground in London, engineers have installed the solution to

super sewers pump problem.

Dwarfing even those at the Wouda pumping station in Holland.

These centrifugal pumps are so large and so powerful, they must be encased

within concrete 13 feet thick.

The technology of centrifugal pumps has been around for a long time.

The only difference with the lead tunnel project is that the size of them are

unique in the sense that they've never been made to this size.

The pumps are really big here. They're effectively two stories high.

Weighing over 50 tons with a 7 .2 -foot diameter impeller,

one pump can move the equivalent of 3 ,000 liters per second, and there are

pumps.

The centrifugal pump can actually cope with a lot of solid material, and it

would be very difficult to actually take this up to ground level without pumping

and using the pumps that we have.

No other pumps would have the capacity or the duty to pump out the lead tunnel.

Like Wouda in Holland, the pumps need a lot of energy to drive them.

On the next floor are six motors weighing more than 30 tons each.

These motors generate 3 .5 megawatts, so very large power usage for the motors

to drive the pumps.

These motors have a central shaft, which then is connected to the impeller

itself.

These giant motors are power -hungry, and part of the solution to this problem

is above ground.

This is Becton Sewage Treatment Works, the largest plant in Europe.

We're standing on the flow collection chamber where the six pumps pump up it

this level. They then transfer the flows through steel pipes up to the inlet

works for distribution into the sewage room it works.

At the sewage works, the wastewater settles in giant sedimentation tanks

bacteria breaks down and removes impurities, including ammonia.

The process releases natural gas, some of which can be recycled for energy

production across the site.

With the pumps running at full capacity, Becton processes 2 .3 billion liters of

wastewater each day.

Enough to fill Wembley Stadium twice.

And all this cleaned wastewater is returned safely to the Thames.

It was a brilliant experience to see the pumps operating for the first time

three years ago.

So it's a great feeling working to clean up the River Thames.

And I feel proud.

Since its inception in 2010, the Super Tour has grown 30 kilometers from west

east London.

This megaproject is one of the biggest infrastructure works in Europe,

six of the biggest waste water pumps ever used in Britain and the biggest and

deepest shaft ever sunk in London.

It has a storage capacity of 600 Olympic swimming pools worth of fluid.

By the time it's completed in 2024 and the 34 worst polluting overflows are

collected, pollution in the temps should be reduced by up to 97%.

By connecting the most polluting CSOs to 24 new shafts, the super sewer will

revolutionize the existing Victorian network.

Millions of tons of sewage will be carried along nearly 20 miles of

ending at London's deepest shaft, 288 feet below ground.

After being pumped up to the largest treatment works in Europe, billions of

liters of safe wastewater can be returned to the Thames.

The new super sewer has pushed the boundaries of construction.

The feeling now is when we come into the tunnel, both myself and all our team,

immensely proud of where we've got to.

It's a very empowering position to be in.

By drawing on the innovators of the past and conquering the many challenges, the

project will improve the lives of 9 million Londoners.

I want to have an impact on the London area, the local residents, and being a

Londoner myself, I have a clear passion for making sure this project is a

successful one.

And its success will be far -reaching.

The new super sewer will serve this city for the next century and beyond.

It will reconnect the people of London with their river.

The success of the project will stand as testimony for the ingenuity of today's

engineers.

The Super Sewer team has succeeded in making the impossible possible.

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