The Assassin (Sha ren zhe Tang Zhan)

Today on "Impossible engineering,"

the Kansai airport,

the most ambitious land reclamation project

in modern history.

Built in the middle of Japan's Osaka bay...

...it took revolutionary engineering...

Some of the best of Japanese technology was required

to strengthen that ground below the island.

Otherwise, it would have just vanished.

...To make the impossible possible.

captions paid for by Discovery communications

the island nation of Japan

has some of the most densely populated cities in the world.

Over 127 million people are competing for precious space.

Geography is that Japan is a very heavily populated island.

It's double the population of the u.K.

And although the island is bigger than the u.K.,

75% of it is mountainous,

and about 50% of it is at a 45-degree slope,

so you can't live on that.

So everybody's crammed into the coastal areas

and the big cities.

So when Japan announced that they would be building

their first 24-hour international airport,

it was easier said than done.

Their solution...

Create more land in the middle of Osaka bay.

They had no choice.

If you wanted the airport to be where people could get to it,

it had to be within reach of Osaka.

The logical conclusion to that was to go to the difficult place

of the Osaka bay.

Engineers would attempt to make the largest man-made island

in the world for their proposed airport.

There was risk, real risk,

in trying to build something so big

and on such an ambitious scale.

But building a massive, man-made island wasn't

the only challenge builders of the Kansai airport faced.

And earthquakes are a constant threat.

There were also unexpected obstacles

hidden beneath Osaka bay.

Perhaps the biggest challenge of all is the weak ground.

The ground under the sea at the site that was chosen

was so weak

that divers would sink into it if they stood on it.

Despite all this, engineers still decided to move forward

with the most ambitious land reclamation project

in modern history.

Every project is a challenge, but there is an edge to it

when you're stepping out of the known into the unknown.

It took centuries of innovation to make the bold idea

of raising an island from the sea a reality.

Creating land in open water has always been a challenge.

Prehistoric tribes in Scotland built huts in lochs,

called crannogs, to house large families.

They worked pretty well until the stilts rotted away.

In Peru, the uros people of lake titicaca

built villages on rafts of reeds

to prevent attacks by their neighbors, the incas,

but their anchoring system was unreliable.

In the pacific ocean, the rulers of the ancient saudeleur dynasty

built offshore islands to rule from,

but they took their secrets of construction to the grave.

Thankfully, a more reliable strategy for creating land

was on the horizon.

Today, the Netherlands has some of the most sophisticated water

drainage systems in the world,

but it wasn't always this way.

Over the centuries, the Netherlands

has suffered a number of catastrophic floods.

The country is constantly fighting to keep the north sea

at bay.

One third of the nation's land is below sea level,

and 65% of it is vulnerable to flooding.

By the 17th century, the growing population

was running out of dry, usable land to produce food.

The nation had a crisis on its hands.

Then, in 1609, engineer jan adriaanszoon leeghwater

came up with an ingenious solution...

...one that would change

the face of the Netherlands forever.

Water engineer nanco dolman has come to beemster polder

to see leeghwater's innovation firsthand.

The area nanco is visiting was at one time

a 27-square-mile, 10-foot-deep lake.

In the 17th century, windmills were used for water drainage,

but they had their limits.

Beemster lake was too deep for leeghwater's windmill to drain,

so he had to come up with a different solution.

Leeghwater dug a 24-mile ring canal around beemster lake.

He used the excavated soil from the canal

to create a barrier, or dyke.

Then he installed his first windmill.

It pulled water from the lake

and distributed it into his recently-dug ring canal.

What leeghwater did next was a stroke of engineering genius.

He constructed a series of windmills.

As the water level in the lake dropped,

another windmill was constructed 3 feet below it.

The dyke leeghwater constructed protected his new land

from future flooding.

It took three years

and 42 windmills to completely drain the lake,

and in 1612,

the first reclaimed piece of land in the Netherlands

was ready for cultivation.

These areas of land became known as polders.

Today, 50% of the Netherlands is made up of reclaimed land

protected by 7,500 miles of dykes and sea defenses.

But to build the largest man-made island

in the world, the designers of the Kansai airport

are going to need more than a few windmills.

The best case scenario is that all would work well

and the island would stand.

And the worst case scenario was that the whole thing

would vanish into the seabed and just keep going.

The Kansai international airport

is Japan's first 24-hour airport.

It's also located on the largest man-made island

in the world.

In the 17th century, engineers in the Netherlands

reclaimed farmland by using windmills to drain flooded land.

But Kansai's builders couldn't drain Osaka bay,

so, instead, they raised the earth above the bay.

The soft clay bottom of Osaka bay

is one of the last places on earth

you'd want to build an airport.

The clay holds water like a sponge.

If you place a heavy object on top,

the clay will compress as water is forced out,

causing the object to sink.

Some of the best of Japanese technology

was required to strengthen that ground below the island.

Otherwise, it would have just vanished.

Engineers knew that the island would sink

under the weight of their proposed airport.

The question was how much?

If they couldn't control how far the island sank,

the project would fail.

Their solution... The sand drain.

Sand drains provide water in the ground

with a shortcut to the surface.

Here's how it works.

First, engineers spread sand across the soft, clay bottom.

Then, they drive pipes into the sea floor

and fill them with sand.

They remove the pipes, leaving sand columns behind.

The idea is that the weight of the airport and island

will compress the clay.

The sand columns will help channel excess water up and out

through the sand layer.

The island will still sink,

but it will do so in a much more controlled way.

Engineers installed one million sand drains in Osaka bay.

An operation of this scale had never been attempted before.

The best case scenario is that all would work well,

and the island would stand.

And the worst case scenario

was that the whole thing would vanish into the seabed

and just keep going.

But before they could make the island,

engineers had to construct a sea wall

to protect it from the pounding waters of Osaka bay.

To keep the island from washing away,

engineers are using a decades old,

but ingenious engineering solution.

In the 1950s, engineer Pierre Danel

developed a system that would become the gold standard

in sea erosion defenses...

The tetrapod.

At Tokyo's waseda university, engineer John Batchelor

has come to see a demonstration of how tetrapods work.

Well, there will be waves at least three meters high

in a big typhoon, and they pack a lot of punch.

So it's very important

that the edge of the island is not scoured away by the waves.

This tank can simulate waves of around 10 feet,

which are a common occurrence in Osaka bay.

Two students down there are putting the model together.

They're putting pink pebbles on one side

to represent boulders,

which would be a very traditional way of protection.

And on the other side they're putting tetrapods, like this,

that link together.

It's simulating waves that are about three meters high,

which is what we'd expect from a big typhoon in the Osaka bay.

So we can see clearly from here that,

even just with one wave,

quite a few of the pink boulders have been washed,

some of them right over the island,

whereas the tetrapods have all stood firm.

And that's because the tetrapods,

even though they were lifted by the waves,

couldn't be pulled apart because of their shape.

Tetrapods also dissipate the force of the waves

because water flows around rather than against it.

Since the 1950s, Danel's tetrapods

have been protecting the world's coastlines.

And at the Kansai airport, tetrapods