The Assassin (Sha ren zhe Tang Zhan)

Today on "Impossible engineering,"

the Rion-Antirion bridge...

A colossal structure built in the heart of an earthquake zone.

Spanning 2 miles across open water,

it took revolutionary engineering...

...and a look back at some hard lessons from the past...

The energy release was massive,

and now the specimen has just catastrophically failed.

...To make the impossible... Possible.

Captions by vitac

captions paid for by Discovery communications

August 2004, the Rion-Antirion bridge

opens to traffic for the first time.

It's an engineering masterpiece of the modern age.

This massive structure

spans almost 2 miles across the Gulf of Corinth in Greece.

It boasts the longest fully suspended deck

and deepest foundation piers of any bridge on earth.

For chief engineer Panayotis Papanikolas,

it was the project of a lifetime...

...but for centuries,

building a bridge across the Gulf of Corinth was just a dream

due to a long list of environmental challenges.

But wind isn't the only threat to the bridge.

The two land masses on either side of the Gulf of Corinth

are constantly drifting apart.

This, along with frequent earthquakes, high winds,

and deep water meant that

building a bridge across the Gulf would be a daunting task...

...but the need for a safe crossing was desperate.

The perilous waters of the Gulf of Corinth

often made ferry crossings impossible

and cut the peninsula off from important services.

So in the 1990s, the government embarked

on one of the most ambitious engineering projects

in modern history.

The first challenge was to design a bridge

that could span

the almost 2-mile gap across the Gulf of Corinth.

The distance was too great for a single-span bridge,

so engineers has to build support towers in water

that's over 200 feet deep.

To overcome the water-depth issue,

Panayotis and his fellow engineers

would need to look

to history's great engineering innovations for the solution.

Building in water has always been a challenge.

Early builders relied on conveniently placed rocks

for the foundation of their structures.

Fine for lighthouses, useless for bridge building.

Creating artificial islands

was time-consuming and impractical in deep water.

In the 19th century, pressurized structures called case-ins

were developed to create underwater building sites.

But they were difficult to build...

And dangerous.

Fortunately, in the 20th century,

a new technique was on the horizon.

In the 1940s, engineer guy Maunsell

came up with a solution

that finally conquered the challenge of building at sea.

Professor Luke Bisby is heading far out into the English channel

to see the remains

of Guy Maunsell's bold creation firsthand.

Maunsell's influence on contemporary engineering

I don't think really can be overstated.

This was really the first time

that this had ever been attempted,

and so it was really quite a daring feat of engineering.

Maunsell's innovation

was triggered by the second world war.

It became clear the river thames was a prime target

for German bombers during the war.

The Germans wanted to destroy London's docks

and lay mines to disrupt allied shipping.

So Maunsell came up with a radical new design

for off-shore sea defense...

...naval forts consisting of two 80-foot high concrete towers

each containing four floors of accommodations

topped with a gun deck.

But the ingenious part of Maunsell's design

wasn't the layout of the fort...

It was how it would be constructed

and deployed at sea.

Knock John here was towed out 3 to 6 miles

from where it was constructed on land,

and then it was sunk in place exactly where you see it.

Maunsell designed the bases of his forts

as huge hollow concrete barges.

Despite their enormous weight,

they had enough buoyancy to float.

Maunsell built the forts

on top of these large concrete barges

and then calculated how large the barges needed to be

in order to hold the weight of the fort

so they could be taken out and then sunk in place.

The massive 4-1/2 ton concrete forts

were constructed in a dry dock,

then towed out to sea with a 100-man crew already on board.

When they had it in the place where they wanted it,

they essentially just pulled out a stopcock at one end

and let the water flow in.

As the water was flowing in,

the barge started to list in the water.

Eventually, the nose dipped under the water.

All 100 men were hanging on

as the fort was sinking at 35 degrees.

Despite the rough submersion,

Maunsell's groundbreaking design worked perfectly.

The bottom of the barge basically filled up with water,

and eventually the entire barge sunk to the bottom

and flattened out.

Maunsell's forts helped British forces shoot down

22 enemy aircraft and 30 flying bombs.

They protected London from attack

and made engineering history.

The influence of this type of construction you can see

in all different facets of engineering today.

You can see it in the off-shore-oil-and-gas industry

with oil platforms.

You can see it being used as foundations for wind turbines.

And, of course, you can see it being used

as a way of placing foundations

for large bridge structures around the world.

But the most impressive use

of Maunsell's revolutionary floating concrete design

is at the Rion-Antirion bridge.

The Rion-Antirion bridge

spans an incredible 2 miles

across the deep waters of the Gulf of Corinth.

To support this massive structure,

engineers used principles

first exploited by Guy Maunsell in the 1940s

and super-sized them.

In 1998, construction begins on 4 enormous pier foundations.

Each one is larger than a football field

and weighs almost 80,000 tons.

The hollow pier footings are built in a dry dock

just as guy Maunsell did

but on a scale he couldn't have imagined.

Before the footings can be taken out into the Gulf of Corinth,

engineers need a solution to a serious problem...

A problem Maunsell never had to deal with.

The Gulf of Corinth lies in the heart

of one of the most active seismic zones in the world.

In an earthquake, the soft seafloor would liquify

causing the piers to sink and the bridge to collapse.

Unless an answer was found, the project was over.

The engineers came up with a radical solution.

They would drive hundreds of long tubes deep into the soil

where the four piers will sit.

This ingenious idea stabilized the soft seafloor.

Bridge footings are usually

anchored directly into the ground.

But for the Rion-Antirion,

they were placed on top of a 10-foot layer of gravel.

This allowed the footings to shift with the earth

during an earthquake.

With a solution to the earthquake problem,

the engineers are now ready to begin

one of the most audacious parts of the build...

...maneuvering the half-constructed piers

into the Gulf.

Engineers continued to build up the massive structures

while they were still floating.

Each layer of heavy concrete that was added

sunk the pier further down,

pushing it closer to its final resting place

200 feet below on the seafloor.

The end result was four enormous hollow foundation piers.

They're the first of their kind...

A series of massive concrete underwater caverns.

The pier footings for the Rion-Antirion

can survive an earthquake,

but what about its nearly 2-mile long suspended deck?

The builders of this massive structure will need to produce

even more impossible engineering.

The Rion-Antirion bridge in Greece

is a modern engineering marvel.

Over 11 million cubic feet of concrete,

more than 100,000 tons of steel, and 39 miles of cabling

make up the longest fully suspended cable-stayed bridge

on the planet.

Panayotis Papanikolas and his fellow engineers

had to overcome a long list of obstacles

before their dream

of a bridge spanning the Gulf of Corinth

could be realized.

The Gulf of Corinth

is one of the busiest trade routes in Europe.

Its shipping lanes cannot be disrupted.

To design a bridge capable of spanning this gap

without interfering with shipping,

engineers would need to turn

to the great innovators of the past for inspiration.

It was the romans who first engineered solid Bridges

using stone and a simple but revolutionary shape... the arch.

However, the wider the gap,

the more arches were needed and the heavier the bridge became.

For hundreds of years, inca communities in the high andes