Original subtitles

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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