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.
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 Rochés 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 Truyère 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 Truyère 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 Truyère 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.