All language subtitles for How.Did.They.Build.That.S01E04.Viaducts.and.Hotels.1080p.WEB-DL.DDP2.0.H.264-squalor_track3_[eng]

Narrator: How did engineering
innovation allow a bridge

to span this vast valley and
become the tallest in the world?

Man: Defying
gravity, defying nature.

Narrator: How did
engineers rip up the rulebook

to build this hotel upside
down in an abandoned quarry?

Man: When a building
is flipped like this,

then things that you would
normally take for granted

need to be completely
reconsidered.

Narrator: And what happens
when you attempt a world first,

to build a forest in the
sky in the middle of a city?

Woman: That is a huge
amount of extra weight

that the building
needs to absorb.

Narrator: This is the
age of the extraordinary...

Man: Where else can you swim

from one skyscraper to
the other 300 feet in the air?

Narrator: Where
ingenious engineers

have unleashed
unchecked creativity...

Woman: Everything
in this building

pushes at the boundaries
of what's possible.

Narrator: Building structures
so outrageous, they defy logic.

Woman: The forces on this thing

look like it should
be torn apart.

Narrator: Now their
secrets are revealed.

Discover the incredible
stories of their construction...

Woman: These are
extraordinary feats of engineering.

Narrator: To try and understand,

how did they build that?

What happens when a road

that carries up to
50,000 cars a day

needs to cross a river?

Corina kwami: Crossing
over a road, river, or valley,

that's easy... build a bridge.

Narrator: But what if
that river is in a valley

that's nearly 1,000 feet
deep, a mile and a half wide,

and located in one of France's

most beautifully
unspoiled regions?

The answer is to hire

one of the world's
most visionary architects

and assemble a team
of brilliant engineers

to construct the most
advanced bridge possible.

Nehemiah mabry:
You know something is

at the cutting
edge of engineering

if you have to design
a brand-new system

to deal with it.

Narrator: The millau viaduct
is the tallest structure in France

and the tallest
bridge in the world.

Michel virlogeux: Nothing
has been done exactly like this.

Each big bridge is a new bridge.

Narrator: It cost
300 million Euros

and took 15 years to
create a bridge so special

that people travel from
around the world to see it.

So, how did they build it?

It's quiet now, but
in the late 1990s,

the sleepy town of millau,
in the south of France,

was a bottleneck of
traffic on a tourist road

between Paris and the
mediterranean coast.

Lord foster: Imagine
peak holiday,

the route from Paris
to the mediterranean,

@and the traffic
just slows down.

You've got 20-mile
nose-to-tail pollution.

Narrator: Relief,
though, was on its way

in the shape of a new
autoroute to the mediterranean

that, 150 miles south of Paris,

would finally bypass
long-suffering millau.

But there was no way
around the massive tarn valley,

where the town lies.

The valley is a vast,

steep-sided
one-and-a-half-mile-wide split

in the massif central plateau.

Deciding exactly how
to cross it wasn't easy.

Michel virlogeux
was on the project

right from the first planning
stages in the late 1980s.

Michel virlogeux:
The first idea was to go

slightly down in the
valley and to come up.

And finally, somebody,
a road engineer said,

"why do you go
down in the valley?"

We could not answer,

and so we said
immediately, we'll look at it.

Narrator: So, architects
were asked to design a bridge

to span the whole
valley, and in 1996,

the plan from foster and
partners won approval.

Foster: Our
interpretation as a team

was to march across the valley

from plateau to plateau
with the most efficient,

the lightest impact
on the landscape

and create a series of spans,

and along the way, you
would bridge over the tarn.

Narrator: Building such
an extraordinary bridge

would turn the project
into a laboratory

of engineering innovation
on a massive scale.

The whole bridge
weighs 290,000 tons

and is made up of three
major components...

Seven giant concrete piers
rise up from the valley floor,

on which rests an
8,070-foot-long road deck.

To top it off, seven huge
pylons tower above the piers,

with tensioned cables
supporting the road below.

Because these cables
send the load directly

back to the pylons,
which are balanced

by an equal load
from the opposite side,

the cable-stayed bridge
design is very efficient.

To realize the slim line,

elegant design
would take innovation

at every stage of construction.

@hayley loren oakes: That
demands a feat of engineering

@on a completely different
level, something extraordinary.

Narrator: At the start
of construction in 2001,

the first things to be built

were the seven huge
load-bearing towers, or piers.

Building a road
deck at this height

had never been attempted before.

They were so tall
that the engineers

had to turn to
skyscraper technology.

♪

The builders used a technique
known as climbing formwork.

Each pier had its
own platform and mold,

which would create a
13-foot section at a time.

Once one level of concrete
had been poured and set,

hydraulic Jacks
pushed the mold up

so that the next
level could be poured.

But as the piers grew,

getting the concrete
to the top to pour

became more and more difficult.

Corina: That's where
cranes come in,

but the piers were so high

that the cranes had to
be tied to them for stability.

Narrator: With
robot-like efficiency,

all seven piers grew
13 feet every three days.

They took 21 months to
reach road level, by which point,

each contained
16,000 tons of steel

and three million
cubic feet of concrete.

Next came the road.

Eight steel sections
were assembled on-site

at the valley's edge, but
lifting them into position

with the crane at this height
would be too dangerous.

Incredibly, despite
weighing 36,000 tons,

these sections would be slid
out across the top of the piers,

but this posed a
serious problem.

Michel: If you use a
classical technique,

you will have to push the piers,

and, in addition,
you have friction,

and so the piers would not
have resisted these forces

because they are very tall.

Narrator: The friction caused
by sliding the sections of road

over the piers could
cause them to fall over,

but the team came up
with an ingenious solution.

Michel: So, the idea was to
develop a launching system

which do not introduce any
horizontal force on the piers.

Hayley: What they used
to lay the bridge deck

of the millau viaduct
was a complete one-off.

Narrator: The team constructed
seven temporary metal piers.

On top of all of the piers,

computer-controlled
hydraulic platforms

would lift and move
each road deck along,

very slowly, out
towards the centre,

with the middle road decks
already rigged with two pylons.

Launched from both sides,

the road decks moved just
23 inches every four minutes,

five times slower than a snail,
until they met in the middle.

Hayley: Each piece would
move forward, inches at a time.

It took days to get the
whole thing into place.

Narrator: With each deck
taking up to three days

to reach its final position,

this process was vulnerable

to one of the region's
most unpredictable threats.

Winds in the tarn
valley had been recorded

at 125 miles per hour,
but even much lighter winds

would cause problems during
the critical deck launches.

Michel: Every morning, the site
received a weather prediction,

and we decide not to launch

if we have not five
days in front of us

with less than these
37 kilometres per hour.

Debbie sterling: Can you
imagine what would happen

if a giant piece of this roadúdeck
got caught up by the wind?

It would cause
really bad damage.

Narrator:

The clock for two days,

the central sections
of the millau viaduct,

complete with the
two middle pylons,

were finally within
touching distance.

Global positioning systems
had been used to plot their path.

Despite starting
at different heights

and with a gentle curve

throughout the one
and a half miles,

when the roads met,

they were within the
one centimetre tolerance.

The final component
was not entirely crucial

to the engineering,

but was a fitting
way to celebrate

an incredible
piece of innovation.

Foster: It was inventing how
you would make the bridge,

that magic moment
when, you know,

from one and a quarter
kilometres coming together

that two and a half kilometre,
and they magically touch.

Narrator: The road was complete,

but it wasn't designed to
solely rest on the seven piers.

It needed to be supported
at more regular intervals,

to be strong and rigid enough

to take the loads
of the bridge deck

and five million vehicles
a year traveling across it.

This would be done
by massive cables.

Ellie cosgrave:
The millau viaduct

is what we call a
cable-stayed bridge.

It makes use of
thick steel cables

to support the
weight of the bridge

and lock the structure
together at the same time.

Narrator: The cables would
be hung from 285-foot pylons,

each on top of a concrete pier.

The prefabricated steel
pylons, weighing 700 tons,

had to be installed
in one piece.

Loaded onto massive transporters
which crawled across the bridge,

the pylons were then
inserted into a frame

and pivoted into position.

The seven pylons
would share the job

of supporting their own
5,000-ton section of road,

each from just 22
tensioned steel cables.

Expected to have a
lifespan of at least 120 years,

the bridge needed to
be easily maintained,

so a secret tunnel was built
in, running under the road.

Camille baudel is a tour guide.

Camille baudel: We
are inside the deck

of the millau viaduct... [Thump]

and we are just underneath
the roadway joint.

That's why we can hear the
noise of the vehicles passing on it...

[Thump]

and the joints are here

to absorb the
movement of the deck

because when it's very
hot, the deck expands,

and when it's cold,
it's retracted, like this,

so the joints are here to
open and close all the time.

Narrator: Being a
bridge for vehicles,

accidents have to be considered,

especially a crash that causes
a sudden weight imbalance,

which could be catastrophic.

Camille: So,
these balls are here

because if there is an
accident on the traffic

and a lot of liquid
pours into the deck,

these balls will float so
the liquid can go down,

and there is no more
weight inside the deck.

Narrator: Finally,
in December 2004,

one month ahead of schedule,

the first cars rolled across
this stunning strip of tarmac.

Now, five million vehicles
pass over it a year,

and people even take detours
just to experience its magic.

Foster: Initially,
you couldn't cross

because everybody was stopping
their cars and photographing,

because a lot of people make
the journey just to see the bridge,

as well as to enjoy the
speed of the crossing.

Narrator: The millau viaduct
pioneered new ways of building

and did it in record time,

a remarkable achievement
for a proud team.

Foster: A three-year
adventure for 500 people.

Everybody coming
from different disciplines,

different backgrounds,

and wanting to achieve something
that was truly outstanding,

something that had
not been done before

and something that would
turn making a car journey,

a truck journey, across this
2 1/2 kilometres in the sky

a kind of ethereal experience.

Michel: Each
bridge is a prototype.

You use ideas which
generally already exist.

An engineer must know
what was done before

and must be able to reuse
good ideas which exist.

A colleague said,
engineers are climbing

on each other's shoulders.

♪

Narrator: Most
buildings in Shanghai

try to reach for the skies,
but just a few miles west,

designers and engineers have
flipped this habit on its head.

Here, they've gone down.

Nestled into a
300-foot-deep quarry

is an incredible new building

that offers a true
escape from reality.

Corina: This place
is part "thunderbirds,"

part bond villain lair.

It's even got a shark pool!

Narrator: But
this is no film set.

It's the world's first
underground hotel.

Creating this 500,000-
square-foot upside-down hotel

with underwater floors

meant turning
engineering on its head.

Hayley: When your
building's flipped like this,

everything that
you take for granted

is just thrown into the air.

Narrator: It took 12 years
and $300 million to engineer

a way around earthquakes,
floods, and crumbling rock.

The result...

The 336-room, subterranean
wonderland hotel.

So, how did they build it?

Back in 2005, before
the project started,

this deserted quarry, a
30-minute drive from Shanghai,

was earmarked to
become the exact opposite

of a tourist destination.

@hao zeng: The government
planned to make this place

as a treatment
place for the garbage.

Narrator: But a
developer had a vision,

to create a hotel with
a feature so unique

that people would travel
from around the world

to experience it.

Tasked with turning this site
from garbage can to gold mine

was architect Martin jochman.

Martin jochman: When
I visited the quarry,

actually it was
completely overgrown

and the water
level was quite high.

It was more like a lake
which was surrounded

by old industrial buildings
and overgrown vegetation.

Narrator: Martin used the
location's natural assets

as a starting point
for his design.

Martin: The inspiration
for the design

came from the quarry
and from the greenery,

from the rocks,
from the waterfalls,

and it needed to span
between the ground level

and the bottom
of the quarry itself.

This was what would make it

really outstanding
and spectacular.

Narrator: Martin was
keen to create a building

that fitted naturally and
seamlessly into the environment.

What appears to
be just a two-story,

grass-covered
complex at ground level

is only the tip of the
structural iceberg.

Hidden below is the main
16-story hotel room section

of the building,

the design embracing
shapes from within the quarry.

One half curves
in, the other out.

Between them is a
waterfall-like glass atrium,

which houses the elevator
shafts and services,

but it's at water level where
things are most unusual.

Here, huge
16-foot-deep aquariums

hold over 300 tons of water,

so the lowest two floors of
restaurants and guest suites

have huge windows onto an
extraordinary underwater world.

Martin: What I tried to do
is to create a building mass

that joined with the quarry
and became part of it.

It became part of the overall
character of the quarry itself.

Narrator: In 2011,

as the 5,000-strong
construction team began work,

this challenging site threw up
its own unique set of problems.

Before the engineers
could start building the hotel,

they had to prepare
the quarry itself,

which had been
abandoned for years.

Zeng: Before we start
building construction,

we had to make sure
the condition is okay

for building works,
and, as you see,

the cliff here is
not very stable,

so we had to solve this problem.

Narrator: So, how do you
prepare a giant hole filled with water

for an underground hotel?

First, the team drained
the quarry of 30 feet of water

before turning
to the rock faces,

which would need to
fit the hotel structure.

Martin: The quarry had to follow

the shape of
the building itself,

but also, because of
the safety requirements,

we needed to do
some stabilization

of the rock faces themselves.

Some of the rock faces had
to be blasted, but not too many.

Narrator: The quarry is
comprised of andesite,

a type of rock formed
during a volcanic eruption.

It's solid in places but can
be crumbly and unstable,

creating dangerous
conditions for anyone below.

Ellie: It is pretty amazing
to see behind this building

because it looks
from the outside

as if it's all
fixed to the wall,

but actually there's a huge
cavernous space behind it,

and it's really only fixed at
the top and at the bottom.

Narrator: The team
came up with a solution.

49-foot steel bolts were
driven deep into the rock

at six-and-a-half foot
intervals, creating a huge grid.

The compressive force
of these 6,000 bolts

knitted together the loose rock.

For added security, a metal
mesh was anchored across the bolts

and sprayed with a
thin layer of concrete.

All this is still visible
from the inner atrium.

Ellie: It is pretty amazing
to me how well the concrete

has weathered to colour match
the original walls over time.

Narrator: Only once
this was all done

could they begin work on
the massive foundations.

They would require 2.1
million cubic feet of concrete,

into which steel trusses
would be embedded.

But pumping all that concrete
from ground level down 300 feet

wasn't as easy as
you might imagine.

@joshua macabuag: Until it
sets, concrete is a delicate mix

of materials of different
sizes and weights,

and it has to be
continually mixed.

Martin: Getting
the concrete down

was probably the most important
and most difficult to solve.

We all know how to pump
concrete high to build skyscrapers,

but pumping it down 90 meters
is a different story altogether

because gravity can separate
the parts of the concrete

and can weaken the concrete.

Narrator: The
upside-down structure

of Shanghai's wonderland hotel

meant the foundation's
concrete had to be pumped down,

which risked
weakening the material.

As its components
vary in size and weight,

the concrete could separate
out by the time it reached

the bottom of the quarry,

so the team came
up with a simple

but incredibly
effective solution

to ensure that the
concrete stayed mixed.

Martin: The builder had
to create remixing stations

on the way down the quarry,

where the mix of the
concrete would be collected,

remixed, and sent down
again so that when the mix

got to the bottom
where it needed to get to,

it was the right consistency.

Narrator: This innovation was
just one of the ideas pioneered

as engineers tried to overcome
the site's unique challenges.

Martin: This method
was patented,

so it's one of the, I
think, 38 or so patents

that the, the
builder had to create

to, to realize this building.

Narrator: By 2015,

the foundation and
substructure were completed

and work had begun
on the next levels,

but the build faced
another challenge.

Seven years prior,

the devastating
sichuan earthquake

that left 87,000 dead
and 5 million homeless

prompted the Chinese government

to enforce strict
seismic building codes

across the country.

Joshua: But when you
have an earthquake,

then what's happening
is that the ground

is shaking violently
from side to side,

and it's that sideways force
that has to be carried down

into the foundations,

so if a structure is in
an earthquake zone,

then it has to have a way to
resist that sideways motion,

or it will fall down.

Narrator: To prevent
a catastrophic collapse,

buildings in earthquake zones

are often set apart from the
ground using isolator pads.

Ellie: Base isolators are
essentially like suspension

but for a whole building.

This means that when the earth
moves because of the earthquake,

the base isolators
absorb that movement,

leaving the rest of the
building completely undisturbed.

Narrator: The
wonderland hotel, though,

couldn't use this technique
in the traditional way,

as it had a
fundamental difference.

Corina: Normal buildings
have one point of contact

with the earth, at the bottom.

Here you need to connect
the top, where people enter,

with the bottom, where
the weight of the structure is.

The problem is, is that
during an earthquake,

these might move in
the opposite direction,

and when that happens, well,
you have a hotel falling in a hole.

Narrator: To prevent
the top of the building

from tearing away from the
bottom during an earthquake,

both ends of the structure

needed to move
independently of each other,

so a radical
solution was needed.

First, a series of inverted
l-shaped steel trusses

were embedded into
the concrete base,

rooted to the quarry floor.

This created a rigid joint
at the bottom of the building

that reduces lateral
movement during a quake.

It was, in fact, at
the top of the building

where traditional isolator
pads would be used.

Martin: The worst-case
scenario, if it was fully rigid,

would be that the
whole building collapses,

and it's a major disaster.

The way it's been designed
was a rigid connection at the base

and then at the top
had to sit quite loosely

on the edge of the quarry

so that it would
enable any movement

in case of earthquake.

Narrator: So, the
engineers turned

seismic isolation
technology upside down.

Joshua: They have used
a form of seismic isolation,

which means they've
taken that top section,

they've sat it on a series of
separation joints, steel plates,

which means that the sections
can move independently.

Narrator: 16
floors up at the top,

the building isn't
fixed onto the rock.

Instead, the upside-down
l-shaped trusses

of the structure

rest on the concrete lip that
runs around the quarry wall.

A set of steel isolators sit
between the trusses and the lip,

allowing the building
to slide back and forth

in the event of an earthquake.

Martin: This is to allow for
minimal damage to the building

rather than the whole
building collapsing.

Narrator: Water was key to
the design of this complex,

and in 2018, one of the
last phases of construction

was refilling the quarry

with over 50 million
gallons of water.

It would take six months
but would also pose

one of the biggest threats
to the hotel and its guests...

Flooding.

Corina: You've got twice
the annual rainfall of London

coming down into a
waterproof rock hole.

Plus, there's a
waterfall pouring water in

and a river and a canal, all
within overflowing distance.

Narrator: Prone to
typhoons and monsoons,

this coastal region
is one of the world's

most vulnerable to flooding,

so the team came
up with a solution

that could instantly address
the smallest increase in water.

Martin: In order to
maintain this water level,

we have a very powerful
emergency pump,

and this will come
into operation

if there's too much water
coming into the quarry.

It could be through
exceptional rainfall

or if there is some,
some breakage

into the quarry from the canal,

so this can then deal
with that situation.

Narrator: Fully automated
and computer-controlled,

the emergency water
pumping system is programmed

to keep the water level
within a 20-inch tolerance.

Six pumps are at
the ready to evacuate

3,500 gallons per minute
into the surrounding canals.

The next challenge was to
create a suitable ecosystem

for exotic fish like these.

The two underwater floors
needed to have spectacular views

to warrant the
$3,000-a-night price tag

for its exclusive suites.

But the quarry lake
was too dark and vast

to guarantee guests
a worthy sight.

Martin: The client envisaged
that part of the building

would be underwater,

but no real instructions
as to how to deal with it,

so I suggested that
we put aquariums

below the water level

to face the guest
rooms or the restaurants,

so the client really
agreed that we should put

themed tropical aquaria
with some sharks in it, as well.

Narrator: Separate from the
main body of water in the quarry,

these self-contained
aquariums would be huge...

16 feet long and
over 16 feet deep,

containing 40 tons of water.

The engineers needed a material
that would be strong enough

to withstand the
pressure of the water

and clear enough for the
guests to see the display.

Normal glass
wasn't up to the job.

Joshua: Glass is perfect
for small aquariums,

but when you're
trying to hold back

many tons of water
like you are here,

then it's just too brittle,

meaning that a small
crack could be catastrophic.

Narrator: Upping the depth
of the glass was pointless.

The thicker the glass, the
more opaque it becomes.

The solution was to use acrylic.

Martin: Acrylic can be as
thick as 200 millimetres,

300 millimetres, and you
can still see clearly through it.

Narrator: The largest of
the acrylic aquarium windows

the engineers installed
weighed over four tons

but revealed the underwater
paradise in all its glory.

♪

In 2018, the intercontinental
wonderland hotel

finally opened its
doors to the public.

It had taken 12 years of hard
graft and amazing engineering

to overcome an array
of complex problems,

but against the odds,

Martin and his team created
this extraordinary building,

the world's first
underground luxury hotel,

an outstanding achievement
for a site once earmarked

for a garbage dump.

Corina: This project
is an example

of taking a scarred
piece of land

and turning it into
something beautiful, luxurious,

and even natural.

But above all, it's an
amazing piece of engineering.

♪

Narrator: Cities are growing
more crowded by the day.

Greenery is being pushed
back to make room for concrete,

but what if it didn't
have to be this way?

In Italy, radical designers
and engineers are pioneering

a new approach to
both urban expansion

and environmental regeneration.

Manfredi catella: This
idea was a bit crazy,

like having trees on a building.

Narrator: These
trailblazers have rethought

how city life could be,
lifting a forest into the sky,

creating a stunning,
life-giving sculpture.

Debbie: It feels like
this futuristic version

of what buildings should be.

Nehemiah: What many of
our cities and urban areas

are crying out for is
more green space.

This could be the solution.

Narrator: Engineers had to
create a structure strong enough

to hold two and a
half acres of forest

and tough enough to
withstand high winds,

all while battling vibrations
from subway trains.

So, how did they build it?

Milan is a city of
70 square miles,

almost all of it
dense urban sprawl,

but packing people in has meant
sacrificing something important.

Ellie: Green spaces
are an essential part

of the city's ecosystem.

Not only do they
do the obvious thing

of absorbing carbon
dioxide and emitting oxygen,

but they give us
humidity, they collect dust,

and create an ecosystem
for insects and animal life.

All of these things
together make the city

a more hospitable
and pleasurable place.

Narrator: Starved of the space
to create a traditional garden,

a developer decided
to think outside the box.

Manfredi: Developers love
challenges, so the big thing was

how can we reintegrate the
neighbourhood into the city

and having the opportunity
to do it through the nature.

There was a strong
commitment by all of us

@in making a
sustainable project.

Narrator: The answer
was to create a building

that could hold all the
plants of a park on the ground

within a vertical structure.

This would be bosco
verticale, or the vertical forest.

Structural engineer Luca buzzoni

was brought in to
make it possible.

Luca buzzoni: As a
structural engineer,

what I was, I must admit
I was skeptical about it.

You typically don't put
big trees on tall buildings

because of additional
weight, because of wind forces

and all sort of things.

Narrator: Luca's doubts
were well-founded.

No building like this
had ever been attempted.

On these structures,
plants came first,

and they would impact the way
the buildings were constructed,

so an unusual
collaborator was needed.

Laura gatti is an agronomist,

or in layman's terms,
a plant whisperer.

Laura gatti: This building
has been designed for trees.

We make calculation on what

@the trees is
needing to survive,

thinking to be a tree
and thinking like a tree.

This is not a building
in which the greening

is put just for decoration.

Joshua: Normally the landscaping
is the last part of the project,

but here the plants are actually

built into the fabric
of the structure,

@and the design of the structure

is led by the
needs of the plants,

and that's pretty
standard for a greenhouse

or an arboretum,
but it's not that usual

for an inner city
block of flats.

Narrator: This unusual brief
for up to 27-story apartments

that were half giant plant pots

would result in a
unique and complex plan.

The ambitious design called
for two residential towers

that would rise 360 feet
and 250 feet from the ground.

Cantilevered
terraces would extend

11 feet from the structures.

These would have to be
strong enough to hold 900 trees

and allow them to grow
up to 20 feet in height.

In addition, 16,000 other plants

would act as cladding
for the building.

Construction began in 2009,
with 6,000 workers on site.

Their first challenge came from
Milan's public transport system.

Luca: The buildings on
this project have been built

either on top or very close
to existing Metro tunnels,

so it was quite the challenge
to, to build big buildings

on top of those tunnels.

Narrator: 27-story
buildings like these

would normally
need concrete piles

drilled deep into the
bedrock for stability,

but with the subway

carrying 1.4 million commuters
every day right underneath,

the engineers had to find
a way to give their buildings

a strong base without
touching the tunnels,

and they inadvertently
struck gold.

Luca: It was possible to
design shallow foundations

even if the buildings are
pretty tall and pretty big

because the soil in this
part of the town is very good.

It's made of sand and gravel,

so the capacity of the
ground is pretty high.

Narrator: Although the
ceilings of the subway tunnels

were as little as 11
feet below ground level,

the engineers could
cautiously build on top of them.

During construction, a
24-hour monitoring station

was set up to keep
an eye on any stresses

exerted on the tunnels below.

Though bosco verticale's

wouldn't interfere
with the subway,

the vibrations from
the trains could still ruin

the living conditions for
the buildings' occupants,

so the engineers
turned to a solution

often used to protect
buildings in earthquake zones.

Luca: So, basically,
what this system makes

is very similar to what you have

in a normal car with
a shock absorber,

so in the same way shock
absorbers take vibrations

from the irregularities in the
roads and damp them down.

Narrator: The vast
buildings were floated

on a bed of base isolators
made up of steel Springs.

The Springs act as a dampers
for the vibrations from the trains,

so the earth is free to
move below the building,

while the structure
remains insulated

from the subway line underneath.

With the buildings and trains

effectively isolated
from each other,

the engineers could tackle

the most unique
challenge of this project.

They had to design a structure

to cope with the hundreds
of plants and trees,

and the soil they live in,

whose weight and
size constantly change.

To complicate things,
many of these plants

would live around the edges
of huge cantilevered balconies.

Cantilevers are a
trick of engineering.

These reinforced concrete slabs

look like they're
suspended in space,

when they are, in
fact, internally fixed

to support columns
within the main structure.

But they are usually designed
to bear a limited weight.

Nehemiah: So, when I
think about these balconies,

I think about the fact
that they are essentially

experiencing cantilever
action, so not only is it carrying

the weight of the
plants and the soil,

but any moisture
that's in the air

that gets trapped into the
soil is just adding to the load

and therefore increasing
the amount of reaction

that the attachment
has to resist

on the exterior of the building,

and so the
fluctuations of the loads

or the weight on these
balconies really does change

as the seasons and
the humidity changes.

Narrator: The engineers
came up with a way

to make the balconies
incredibly strong

to counter the weight
of the trees and plants.

Luca: We have
post-tensioned slabs,

and what that means
is that in concrete slabs

we normally only
have steel rebars.

In this case, we also
have steel cables,

and those steel
cables are pre-stressed

so that the presence
of the cables in the slabs

provide additional resistance
and additional stiffness.

Narrator: So, as well
as predictable, stable

steel and concrete,

these towers would
also be shape-shifting

organic structures,

with dynamic loads that
needed to be understood

and controlled as
much as possible.

Luca: This is a live building.

It changes season after season,
and it grows year after year,

so it's not something
that's normal on a project,

so what we did first of all,

we tried to
understand how to cope

with the changing
life of the buildings.

Narrator: It was crucial
the experts identified plants

that gave the engineers

a chance to design a
building that could cope.

Laura: We select trees
that are not allergenic

or not messy tree,

and we understand which
are the position on the building

in which the wind is
higher than other parts,

and we select the trees
to thrive in this condition.

Narrator: That wind
was the biggest concern.

A large tree in a strong wind

could put serious
strain on the building,

and the wrong trees could
badly damage the structure.

The team needed to know as
much detail as possible before

choosing these potentially
destructive elements.

A selection of trees were
tested in a wind tunnel

to assess if they were
suitable for high-rise living.

Luca: First of all,
we had a set of tests

in the wind tunnel here in Milan
to understand the behaviour

of the trees together with
the behaviour of the building

to see if the
presence of the trees

was introducing additional
forces on the building

and to understand the magnitude

of the additional
forces on the building.

And then we had a second
set of tests in Florida.

Ellie: At Florida
international university,

they have built
the wall of wind.

Here they can
build whole buildings

and blast them with
hurricane force wind

to see how they stand up.

Narrator: The tests helped
determine which trees

were the perfect weight
and shape for the building,

but there was another,
more basic worry

that had to be addressed.

If a small tree on the ground
is knocked over by the wind,

it can be a small problem.

If a tree falls from
a large building,

then you've got a
very big problem.

Hayley: If a tree falls
from the 27th floor,

everyone is going
to know about it.

Narrator: With six-foot
trees planted 27 stories high,

no one wanted to
take any chances.

Luca: For most of the trees

and all the medium
and tall trees,

we have cables
that basically provide

an additional anchor for
the trees in case they break

so that they cannot fall over
during windstorms, for instance.

And then for all the big trees

and especially
for all the positions

that we identified
as possibly critical

because of high wind
velocity during windstorms,

we provided an additional
anchoring system

that basically connecting
the root ball of the trees

to the concrete structure
so that they cannot fall over.

Narrator: It took three years
to create this tower block oasis,

which was officially
opened in 2014.

These two buildings are proof
that people can have it all...

Enjoy life in the Metropolis

and a taste of nature right
outside their high-rise window.

Nehemiah: I
think it's also great

that a person can
look out their window

and see what looks like a
forest growing on their balcony,

when, in fact, they're in
the middle of an urban area.

Narrator: The engineers
who built bosco verticale

overcame new challenges

and achieved the
best of both worlds,

pushing sustainable
green spaces skyward

and offering a glimpse of
the future for city dwellers.

Luca: It's a brave example

that shows that something
different is possible,

that healthier cities
are possible for us.

@manfredi: The strong
commitment and passion by all of us

@made a project
that, at the end,

has become today a
symbol, an icon for sure.