All language subtitles for Impossible Engineering s06e04 Himalaya Mega Bridge.eng

In this episode...

Crossing chasms...

Bridging nature's
most challenging divides...

In winter, the water
just chucks it down this valley

through almost
impenetrable forests.

With the unique
engineering solutions...

Engineers weren't gonna let
earthquakes stop the railway.

That make
the impossible possible.

Captions by Vitac...
www.Vitac.com

captions paid for by
discovery communications.

Many of the world's greatest
railroads have defied nature,

overcoming its
most difficult terrain.

Whether scaling sheer heights
or navigating dense forest,

engineers have managed
to carve out routes

to create the most epic lines
imaginable.

But crossing chasms
tests them to their limits.

From ferocious rivers

to remote, windswept valleys...

Uniquely engineered bridges

crucially keep the world
connected.

But each of these crossings
raises individual challenges

that are often
seemingly impossible

for railroads to overcome.

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Well, the key challenge
is the tidal range.

The water flows in and out

of a quite constricted channel
very fast.

But, arguably,
the biggest obstacle

facing bridge engineers
is a hidden one.

Located on the notorious
ring of fire,

New Zealand's brooding volcanoes
are a stark reminder

it sits squarely
on a major fault line...

Where the Australian and pacific
tectonic plates collide.

Here, the devastating effects
of earthquakes

are an ever-present threat.

Heritage advisor Karen Astwood

has traveled
into its rugged interior

to see how engineering
played its part

in keeping a vital railroad
safe from seismic shifts.

What I'm approaching now

is one of the north island
main trunk original tunnels.

When the line was constructed
in the early 1900s,

it became incredibly important

because it connected
Auckland and Wellington,

which is the north island's
two major cities.

But by the 1960s,

this particular section
of the main trunk line

in the Rangitikei district was
putting the route in jeopardy.

Many of the tunnels built
were in danger of collapse.

Upgrading this section
simply wasn't practical.

The unstable ground

meant the tunnels
weren't feasible to strengthen,

and neither was creating
new ones.

Instead, engineers came up

with an ambitious plan
to reroute the original line,

known as
the Mangaweka deviation.

But in the way
lay what appeared to be

an insurmountable obstacle.

Here it comes. This is
the South Rangitikei viaduct.

It is immense.
What an amazing structure.

So impressive.

Opened in 1981

and measuring a staggering
1,030 feet in length,

the mammoth six-span viaduct

carries a single track
across twin-legged piers,

a vertigo-inducing
250 feet above the river.

Wow.

But to see what makes
this bridge truly revolutionary,

you need to look much closer
to the ground.

When designing
the South Rangitikei viaduct,

engineers had to consider
the earthquake conditions

it needed to operate under to
keep the critical north island

main trunk line functioning.

It was the groundbreaking work

of eminent earthquake scientist
and engineer Dr. Ivan Skinner

which provided the answer.

At the time the Mangaweka
deviation was being planned,

seismic engineering technology
was in its infancy.

So the designers of
the South Rangitikei viaduct

had to come up with
a completely new solution...

Base isolation.

The first of its kind
in the world,

the bridge's innovative design

features energy-absorbing
dampers in the foundations,

which allow it to step from side
to side when a tremor hits.

Okay, so,
we're just putting together

a really basic demonstration

to give you an idea
about how base isolation works.

To begin with,
we've got a shake board,

which is going to mimic

the horizontal forces
of an earthquake.

Now, usually, you'd build your
bridge straight onto the earth.

But the South Rangitikei
viaduct, however,

we've got the foundations,

and then we've got
the base isolation,

then we've got the pier.

Unlike traditional Bridges,

the foundations consist
of two sections...

One built into the ground

and the other fixed
to the bottom of each pier.

At the base of each pier
sits a set of rubber pads,

which act to absorb
a portion of the energy

created in the event
of an earthquake.

So, these tennis balls

are standing in
for the flexible bearings

or pads that are
in the base isolation.

And this is a platform that
the bridge pier is gonna sit on.

Okay, so, now that we've got
the foundation sorted out,

we're gonna build our piers.

This is just
a standard old bridge...

Build it straight into
the ground onto the foundations.

And here is a pier from
the South Rangitikei viaduct.

But to show you the full effect
of how the base isolation works,

I've just got to duck off
and get some water.

Rather than
rigidly fixing the bridge,

the base isolators
effectively separate it

from the ground
for greater flexibility.

Okay, so,
here comes an earthquake.

And as you can see,
the one straight into the ground

is absorbing all of the energy
from the earthquake,

so it's more likely to fail
and the bridge collapse.

While the South Rangitikei
viaduct...

It's not absorbing as much
of the earthquake forces,

so it's less likely to fail
in the event of an earthquake.

Under most circumstances,

the bearing pads
absorb enough force

to keep the bridge
structurally intact,

but in a major earthquake,

the pier can lift up
by as much as 5 inches,

allowing it to step
from one leg to the other,

preventing
a catastrophic collapse.

And that's the genius
of base isolation.

Every day, Ivan Skinner's

inspired innovation enables
trains to traverse the length

of New Zealand's
rugged north island,

keeping the country moving

even when experiencing
the most terrifying tremors.

This is an ingenious piece
of engineering, and I love it.

But the ground
doesn't have to quake

to present
engineering challenges

to those audacious builders
behind the world's

most challenging
railroad projects.

Southern France's
rugged Auvergne region

isn't the most obvious place
to build a railroad.

But at the end
of the 19th century,

transporting wine
from the region's vineyards

to the capital of France
became a priority.

Forming a natural blockade,
however, was the massif central,

a sprawling landscape
of imposing peaks,

deep gorges,
and famously strong winds.

Historian Patricia Roch�s
is taking to the skies

and taking on
the notorious turbulence...

Wow!

To get a bird's-eye view

of why plans to build
the new line were stalling...

the immense Truy�re river gorge.

To combat the elements
and bridge the valley

would require a feat
of engineering ingenuity...

The breathtaking
Garabit viaduct.

At 1,850 feet long
and 400 feet high,

upon its completion,

Garabit was the tallest
and longest railroad bridge

the world had ever seen.

The iconic design
of the Garabit viaduct

was the work of one
of the 19th century's

most celebrated engineers,
Gustave Eiffel.

It would take
Eiffel's unique talents

to make Garabit viaduct
not only possible,

but one of the most spectacular
railroad Bridges in the world.

When France needed a bridge

to span the immense
Truy�re river gorge

and withstand its famous winds,

they turned to renowned engineer
Gustave Eiffel.

Today, Eiffel's solution to
withstanding the gusting winds

will be studied up close
by the team

tasked with maintaining
this mammoth structure.

The design is one that would
go on to earn him the nickname

"the magician of iron."

Instead of thick, solid girders,

Eiffel used smaller,
crisscrossing wrought-iron beams

with thousands
of triangular gaps.

His inspired design dramatically
reduces wind resistance

as it's buffeted by
the powerful gusts at Garabit.

Despite its
lightweight appearance,

the Garabit viaduct was designed
to carry a 400-ton train

and built to last.

The 540-foot-wide arch
was constructed from both sides,

as cranes at each end
extended it, piece by piece,

until the two halves
were joined.

Metal structures expert
Francois Milien

is part of the fearless team
responsible for ensuring

the bridge continues
to stand the test of time.

Taking five weeks to complete,

each of the bridge's

crisscrossed beams
and 600,000 rivets

are inspected for signs of wear.

Eiffel's little-known
masterpiece

of railroad engineering

remains a stunning example
of his signature style

that would later inspire
a Parisian icon,

the Eiffel Tower.

The Truy�re river gorge
inspired Eiffel

to use an innovative
new structural strategy,

but for other great crossings,
the location has inspired

the use of groundbreaking
new materials.

Home to the towering
alps mountain range,

Switzerland's impenetrable peaks

would make train
travel impossible...

were it not for the ingenuity
and resourcefulness

of its railroad pioneers.

Nowhere are the challenges
they faced more obvious

than the spectacular
Rhaetian railway.

This iconic network of 10 lines

clings to the steep slopes
and valleys

of the Swiss Graubunden canton.

Today, bridge specialist
Karl Baumann

is taking to the tracks
en route to a spot

where early 20th-century
innovation

helped conquer this
most mountainous terrain.

At its heart
lies the Arosa line,

a 16-mile single-track railroad

which climbs
a dizzying 3,280 feet

through the Schanfigg valley.

Karl's destination is Langwies,

where the forbidding alpine
setting presented rail engineers

with what seemed like an
impossible obstacle to overcome.

To make matters worse,
here at Langwies,

it also has to cross
the vast river Plessur gorge.

For trains to cross that valley

would take a feat of engineering
on a truly epic scale.

The daunting task fell to
civil engineer Hermann Schurch.

He not only needed to design

a structure strong enough
to span the huge chasm...

It would call for
a groundbreaking approach

to how it was built, too.

Given the steep terrain,

transporting large sections
of solid steel

was out of the question.

The solution was the mighty
Langwieser viaduct.

Constructed from a material
which had never been used

to build a railroad viaduct
on this scale before...

Reinforced concrete.

At 930 feet long,

with a central arching span
330 feet wide,

when it was completed in 1914,

it was the longest concrete
railroad bridge

ever constructed.

To build a bridge
strong enough to sustain

the weight of trains
across the valley

in a single arching span,
Schurch embedded steel

within the concrete members
of his structure.

By reinforcing the concrete
in this way,

he could make use of
both materials' strength...

Steel to resist
tensile or twisting forces

and concrete to resist
compressive forces.

Using a huge framework of
wooden scaffolding for support,

up to 200 men toiled
on this project,

ensuring its completion
took just two years.

Thanks to the vision and skill

of the men who built
the Langwieser viaduct,

reinforced concrete
conquered the giant gorge...

and changed the way rail Bridges

were built forever
in the process.

But, of course, even
the most exquisite rail Bridges

are born of necessity.

In the 19th century,
engineers faced the challenge

of building a faster route
connecting London and Dublin.

In order to connect
the two capitals,

a new rail line would be needed

that would run along
the north coast of wales.

But to achieve this ambition

would involve bridging
a deceptively difficult

stretch of water...

The gaping Conwy river
estuary...

And its complex tidal flows.

The obvious place for a crossing

was at the river's
narrowest point.

Here, Conwy's imposing castle
had been strategically built

around 600 years earlier.

But as civil engineer
John Chilton appreciates,

turning the idea into a reality

would test engineers
to their limits.

Well, the key
challenges for building a bridge

in this sort of situation
is a very fast-flowing river.

The tidal range means
that the water flows in and out

of a quite constricted channel
very fast.

Adding to the Titanic challenge,

it would need
to bridge the entire river

in a single,
self-supporting span,

a feat seemingly impossible

for the technology of the 1800s.

If the engineers were going to

put a bridge across
at this point,

then they would have to have

a particularly revolutionary
solution

to take these
heavy loads across.

So, what would it take
for this intrepid team

to make an impossible bridge
a reality?

The Conwy river estuary

presented a nearly
insurmountable challenge

to engineers...
An impossibly wide crossing

with a strong and
often unpredictable current.

Their answer
was the groundbreaking.

Conwy railway bridge.

The first box-girder bridge
ever constructed.

Complete with formidable towers

designed to blend seamlessly
with its medieval neighbor.

This pair of wrought-iron
tunnel-like structures

weigh in at a massive
1,320 tons apiece

and stretching
over 420 feet long.

When it opened in 1849,

it was the longest single-span
rail bridge in the world.

The key thing here is that

you're taking the railway bridge
to much larger dimensions.

It certainly was a groundbreaker
at the time.

It was the brainchild

of two of Victorian Britain�s
most eminent engineers...

Robert Stephenson
and William Fairbairn.

To eliminate the need
for central supports,

Stephenson's inspired idea
was to carry trains

through his bridge
rather than over the top of it.

But the size of the span needed
would push the boundaries

of Victorian engineering
like never before.

To show the principle
of a girder,

we've got two piers
of the bridge here.

We have a girder,
this piece of paper,

which is very thin and wide.

And if we put it across
between the piers, it sags

and won't even carry
its own weight.

The strength of the girder

depends principally
on its depth.

To construct
a girder strong enough,

Stephenson and Fairbairn

experimented with
different-shaped tubes.

So, the circular section
already holds its own weight,

and it will carry this
little pot at the bottom here.

I'm going to add some pennies

to demonstrate
how the beam works.

1, 2, 3, 4, 5...

70, 71, 72.

And as you can see,

the tubular beam has failed
by crumpling.

With only a small point of
contact between beam and piers,

load stresses cause it
to squash at the ends.

So, now we're going to take
this rectangular tube

and see if it outperforms
the circular tube,

which failed at 71 pennies.

72, 73, 74, 75...

101, 102, 103, 104.

Having a larger
surface area in contact

with the supports
on each side of the river

meant Stephenson
and Fairbairn's box girders

could carry
significantly more weight

over a longer single span.

But overcoming
the monumental challenge

of crossing the river Conwy

didn't stop
at the bridge's design.

Constructing the enormously
heavy spans in midair

over the water wasn't an option.

If you have the high-tidal range

and you have fast-flowing water,

it makes it difficult
to put temporary supports

in the channel.

Instead,
its engineers turned to nature

and ingeniously used
the Conwy's treacherous tides

to their own advantage.

The girder made of
wrought-iron sheets

was riveted together, was
constructed on a beach nearby

between the high-
and low-tide marks.

Once complete, large
pontoons were floated underneath

so it could be towed
into position

and lifted into place
with hydraulic pumps.

The high-tidal range
was actually used

for the benefit
of the construction process.

For its time, the Conwy bridge

was a radical piece
of railroad engineering.

By introducing
the new box-girder technology,

it pushed the boundaries
of what was thought possible

and changed the face
of bridge-building forever.

The Conwy bridge certainly
moved the technology forward

because this
forward bridge construction

has gone on to influence

the design of long-span
bridge beams worldwide.

And this
groundbreaking feat of ingenuity

is still part of Britain�s
busy rail network today.

The Conwy bridge is
a magnificent achievement.

The fact that it is still
standing here after 170 years

is a testament to the quality
of the Victorian engineering,

and this certainly
has stood the test of time.

When it comes to Bridges,

railroad engineers must overcome
problems of all kinds,

the most fundamental of which

is often how to transport
materials to a build site.

At the start
of the 20th century,

the global market for timber
was sky-high.

While Canada's densely forested
Vancouver island

offered apparently endless
resources to meet the demand,

transporting vast loads
of lumber

from this remote spot
to the mainland and beyond

presented
an impossible challenge...

A problem islander and master
carpenter Gord MacDonald

understands well.

This is Cowichan bay,

and Cowichan bay
is really the gateway

for logs for this island,

and it has been for centuries.

It's getting them to here
is the tough part.

In 1911, a railroad
was commissioned to carry wood

from the logging camps
to the coast,

but building it would prove
to be anything but easy.

After extensive surveys,

the most strategic route
was finally chosen,

one which left engineers facing

what seemed like
an impassable obstacle...

The plunging
Koksilah river gorge.

Even on a summer day like today,

you can hear the river below.

And in winter, the water
just Chucks it down this valley

along the riverbeds, through
almost impenetrable forests.

But trees had brought
railroad builders to the island,

and it would be trees
which provided a solution

to bridging the huge ravine.

It's just sensible
that you would prefer

to use materials
which are locally available.

Conquering nature with
the simple resources on hand

would take a truly remarkable
feat of engineering.

The Koksilah
river gorge in Vancouver

presented an enormous challenge

to the engineers tasked
with building a railroad

that could transport
valuable lumber to the coast.

But in the early 20th century,

they came up with a solution...

The monumental Kinsol trestle.

Standing 145 feet high

and spanning 615 feet in length,

the Kinsol trestle
took an incredible

1.2 million board-feet of timber
to construct,

making it one of the largest
wooden Bridges in the world.

I must say, even though I've
been here hundreds of times,

it always is a real treat
to come back.

It's such a great bridge.

The wooden trestle
was a vital part

of Vancouver island's
valuable logging industry

for nearly 60 years.

Kinsol is really
a unique bit of engineering.

You've got this
quite ambitious crossing,

the deep side here,
complexity of the shape.

A problem made worse each spring

as the river levels swell
with melting snow and ice,

putting the timber to the test.

You can tell
just by looking at it

that it was really built
to perform heavy work.

There's a section of the bridge
which is quite long

and has to be kept up
above the highest water.

That section of the bridge has
to be entirely self-supporting.

They can't build in the in-canal
section or in the river section

because, of course,
it would just be swept away.

To see
just how the wood was engineered

to conquer the river

requires burrowing
to the very heart of the bridge.

Ah, all the bears around here
are vegetarians, I think.

We should be... Reasonably safe.

So, where we are now

is down in the very working guts
of the trestle.

We are...

We're just making our way out
into the Howe trusses.

First patented
by American bridge builder

William Howe in 1840,

his ingenious design
made it possible

to build bigger spans
using wood,

something in
plentiful supply here.

Howe trusses were
great for these logging Bridges

because not only did they use
a lot of wood

but you could use
relatively small pieces

or, you know,
short pieces of wood.

In a truss,
the three sides work together

to give it strength.

In a Howe truss,
the diagonal wooden beams

leaning towards the center
of the bridge are in compression

while the vertical metal Poles
are in tension.

So, generally,
in the web of the truss,

the timber is doing
what it's best at.

It's working hard
in compression.

The other big advantage
of a truss like this

is that it's also capable

of a great deal of work
over that long span.

So it can carry a heavy load
above and make a big crossing.

Today,
Gord is going to check out

just how well they're holding up
after almost a century.

So, this is a tool
called a resistograph,

and it's a very slender drill.

And as the drill advances,
the onboard computer

takes measurements
of resistance.

And we know that resistance is
an indicator of wood's strength.

Boring into the
timbers at key locations

reveals if they are sound
or suffering from decay.

Imagine that
that scale represents

the path of the drill bit.

And these peaks are measurements
of high resistance,

and the flat spots like that,

that's probably
the very center of the tree,

the pith...
Would be less resistance.

So, clean bill of health.

Though it was
still standing strong

when the bridge closed in 1979,

it quickly fell into
serious disrepair.

And in 2006,
it was set for demolition.

But it was determined
that a feat of engineering

this remarkable
and so historically significant

was too important to destroy,

so this impossible bridge

was destined
for an important second act.

After the Kinsol
trestle was retired in 1979,

it was decided that
this elaborate piece of history

was too important to demolish.

So after four years
of painstaking restoration,

the trestle was reopened

as the centerpiece
of one of Vancouver island's

most popular and educational
hiking trails.

People come from all over
the world to see the bridge.

They get an insight into

just that age
in the development of the west

when no task was too big

and no undertaking
too formidable.

And nearly 100 years
after its completion,

the Kinsol trestle remains

a towering achievement
in rail engineering.

These sorts
of Bridges were just...

They're just a critical part
of the railway,

getting things from "a" to "b,"

and one of the reasons
we love them so much

is because they just speak
to that challenge overcome.

The world's engineers

are continuously
pushing boundaries,

and in the 21st century,

there's one mega bridge
in the making

that will be capable
of conquering all.

India.

Home to some of the world's
remotest communities.

None more so than a region
within Jammu and Kashmir,

bordering Pakistan at
the foothills of the Himalayas.

And it's here that a
record-breaking railroad project

of epic proportions
is under way.

The region
around Bakkal and Kauri

is very, very remote,

and it's very difficult
to get around there.

And so, for a long time,

there's been this will or this
need to create a railway link.

The Kashmir railway project

is a 215-mile line
that will connect communities

amidst some of the most hostile
terrain on earth.

That rail line has to go through
tunnels and above Bridges

because of the really
mountainous topography

that we experience
in the Himalayas.

But in its path to completion

lies a ferocious obstacle.

One of the trickiest
segments of the entire line

is where the railway
has to actually cross over

the river Chenab,
and that's because the gorge

is very, very deep there.

So the distance from
where the railway line is,

down to the surface
of the river,

is over 300 meters.

The only way of
spanning this enormous chasm

is with the world's highest
railroad crossing...

The audacious Chenab bridge.

At a staggering 4,300 feet long,

and towering 1,080 feet
above the river,

once completed, the Chenab

is set to be
a true giant of engineering.

The Chenab bridge
is a record in the making,

because once it's finished,

it will be the highest
railway bridge in the world.

But the most crucial
phase of this epic project

has taken place
more than 320 feet below

the valley's edge...

Preparing its foundations,

no mean feat for a bridge
of this magnitude.

The bridge itself
is only as strong and stable

as the foundations
upon which it's built.

Engineering geologist Phil ward

knew building
this railroad bridge

would be the challenge
of a lifetime

when he saw the site where the
Chenab bridge would one day be.

These are the largest cut slopes
I've ever been involved in.

Between the slope,

the area's propensity
for landslides,

and its incredibly remote
build site,

the Chenab bridge
would prove to be

the most impossible piece
of this railroad puzzle.

Engineering geologist Phil Ward

has firsthand experience
dealing with the challenges

facing the construction
of the Chenab bridge,

not least because
of its remote location.

When I first visited the site,

it was a six-hour Jeep drive

from Jammu
up to the bridge site.

The access roads
were subject to landslides.

The Chenab bridge is crossing
the Chenab river at a location

where the slope angles
are particularly steep.

And surrounding
the area of the bridge,

there's a lot of evidence
of big landslides,

so slope instability
along the river gorge.

It took two critical years

of boring into the steep slopes

to analyze the condition
of the rock

before engineers were satisfied

that the bridge foundations
could be constructed.

Then the colossal process

of stabilizing the rock faces
began.

These are the largest cut slopes
I've ever been involved in,

and a great deal of rock
had to be excavated,

and very, very large numbers
of rock bolts

had to be installed
to stabilize those cut slopes.

Rock bolts are formed
from grids of steel bars,

some up to 130 feet in length,

that are driven into the rock
face and secured in position.

Once inserted,
the bolts help to stabilize

and strengthen
the valley's walls,

creating a surface that's
secure enough to build on.

These reinforced the rock mass

and gave us assurance
that we could provide

an adequate factor of safety
on slope stability.

Over a decade
since its conception,

the vast gorge is almost ready
for the arch to span the river.

However, this project
still has years ahead of it

and many more obstacles
to overcome before the bridge

and this ambitious
railroad line is complete.

The giant arch
will need to withstand

all that this volatile region
can throw at it,

from earthquakes to destructive
winds and monsoon rains.

But once complete,

this monumental structure
will dwarf the Eiffel Tower

and set a new benchmark for
mega Bridges around the globe.

For me, this has been one of
the most exciting projects

I've ever worked on.

The scale of the project is
mind-boggling, in actual fact,

and it always amazes me
every time I visit the site,

as I come around the corner
on the access road

and see these massive rock faces

dwarfing
the tiny little vehicles

that are traversing the faces.

This project is
testing engineers to the limit

and will surely
continue to do so.

Meanwhile, the world watches

challenge after challenge
overcome.

I think it is so fascinating
watching the progress

of a record-breaking bridge
like the Chenab bridge.

And I also think
it's a real Jewel in the crown

for structures in India
because it's had

so many different
complex challenges solved

that it will
almost set a precedent.

Once this bridge is finished,

I think it'll be one of the most
impressive Bridges in the world.

It's a really, really
impressive structure.

Since the birth
of the railroads,

Bridges have opened up
the world to trains...

allowing them to cross
seemingly unconquerable chasms.

I hope at some point
in the future,

I can travel
across the Chenab bridge

and feel privileged that
I was involved in the design.

Thanks to inspired solutions...

The base isolation used
in the South Rangitikei viaduct

was completely innovative
at the time.

Engineers continue to build

their impossible railroads.

Every time we push a boundary,

we then aspire to push
that boundary even more,

to break that next record.

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