The Assassin (Sha ren zhe Tang Zhan)

In this episode,

the world's urban railroads,

the unique challenges of laying tracks in the city...

To do 2,500 blasts under grand central

required a lot of coordination

to make sure that we didn't disturb anything above.

And the ingenious solutions...

This port is just such an impressive operation,

and the whole thing is running on rails.

Without the cable cars, it would be really difficult

to get around.

To make the impossible possible.

captions paid for by discovery communications

despite being able to weave their way across the planet,

covering colossal distances on cross-continental journeys,

trains are in a league of their own

when serving the world's cities.

Many of our busiest metropolises thrive

on the existence of the railroad,

transporting the population on its daily commute,

getting goods to market, and visitors to great landmarks.

But the urban environment poses some remarkable challenges

for railroad engineers, from grueling inclines...

You can see the challenges that are faced,

and you can see the undulating territory

and how steep these hills are.

To keeping supply on par with demand...

Our biggest challenge is the new generation of vessels.

It is one challenge to work the vessel,

other challenge to get them into the hinterland.

And delivering vital services.

The post office was gonna have to find a faster

and more efficient way to get that mail around town

if the capital was gonna stay connected.

And it's one such seemingly impossible challenge

that has been facing engineers in New York for decades.

New York City, a Metropolis that relies heavily on its railroads.

With around 90 million passengers a year

traveling westward from long island

to the heart of the city, Manhattan,

the busiest commuter line in the us is desperately overstretched.

To relieve the strain, engineers and construction workers

are at work in the central hub of the city's rail network.

Although few passersby would even notice.

We're here in the heart of grand central terminal.

This is where hundreds of thousands of passengers a day

come through to take the trains.

Mike Pujdak is part of a team working in near secret

to solve New York's commuter problems.

Given how packed and congested midtown Manhattan is,

we have to work like a stealth project.

All of our materials and all of our equipment still,

to this day, has to come in from queens and the Bronx

to feed this job.

Despite the challenges, the city's nonstop transit system

is operating undisturbed.

It's remarkable that hundreds of thousands

of tourists and commuters come into grand central

every day into this iconic structure

and don't have any idea of the magnitude of the construction

that's going on right below their feet.

The east side access project,

with ambitions to completely transform

the transit network in New York.

It's an undertaking on a truly grand scale.

This is one of the largest infrastructure projects

ongoing in the us right now.

This is incredibly important for New York.

This project is $11.1 billion,

and we have, right now, currently,

about 1,600 people working on it.

And at one point, we peaked out at 2,600 people

a day working on this project.

Connecting one of the world's

largest railroad commuter stations

with the busiest commuter railroad in the us

via more than 7 miles of tunnel,

east side access will carry trains

along a network of new and refurbished tunnels

into a four-platform, eight-track terminal directly

under grand central terminal and park Avenue.

It's a giant space that must be constructed from scratch.

And that's easier said than done when you're operating

under some of the most expensive real estate on the planet.

So, we're in the east side access caverns here,

and we're 150 feet below park Avenue

and grand central terminal.

If you don't carefully plan what you got to do down here,

you will wind up creating a situation

where you could disturb the ground

'cause you could influence some of the structures above.

With the consequences of any errors

adding to a potentially multi-billion-dollar disruption,

it's a scenario that had to be avoided at all costs.

We could not interrupt this economic area

and the traveling public coming into grand central,

'cause that's a lifeline for the economy in this area.

To create this vast underground terminal, Mike and his team

utilized an appropriately awe-inspiring solution.

Fire in the hole!

Just to set the stage here, this is all Manhattan bedrock.

There was nothing here.

And then we used drill blast methods

to basically carve out the balance of the structure.

It's controlled blasting,

so you basically calculate the amount of powder

you're gonna use to control how much rock you want to remove,

and then you measure the vibrations,

so that way, you don't impose any issues to the buildings

and the structures above.

When finally excavated, this space was 1,150 feet long,

which is larger than the Chrysler building is tall,

and it was 60 foot high by 60 foot wide,

and we have two caverns.

I mean, to do 2,500 blasts under grand central

and not impact them

required a lot of coordination with Metro north.

Work on this supersized city railroad

began in 2007 with the launch of a pair

of giant tunnel boring machines under Manhattan.

Using powerful cutting heads to burrow

through the layers of dense rock,

the tunnel boring machines

were set on course towards grand central.

As tunnel engineer Jeff rice recalls,

operating in the heart of New York caused complications.

If we were in a burgeoning city somewhere

where there wasn't already an overfilled Penn station

and a historic grand central in the way,

a completely developed Manhattan,

heavily traveled train-traffic areas within the project limits,

the project would've been much simpler.

The huge volumes of rock and debris generated

by the tunneling process made removing it

a challenging logistical dilemma.

Since we couldn't bring muck up through grand central

and it was not viable to bring it up

by train out of grand central, we needed to bring it out

where it could be handled for trucking.

With working out of the overcrowded center of Manhattan

out of the question, the team had no alternative

but to take the wreckage the long way around.

The rock removed from the tunnels

was then brought back entirely through the second tube

of the existing tunnel on a conveyor system out to queens.

The sheer volume of rock that was removed through

the length of all the tunnels, it's time-consuming.

Stretching for over 1.2 miles, the giant conveyor

fed out to a construction yard

where rubble was loaded onto trucks.

Thousands of tons of material was brought out.

The tunnel has become pretty much a highway

for all the resources in and out of the tunnel.

But one section of tunnel under queens

poses east side access' engineers

with a particularly tricky set of problems.

There you go.

With soft ground, a high water table,

and dense, active city infrastructure to contend with,

inspired engineering solutions are required.

What we're approaching is

one of the greatest challenges on the east side access project

is the northern boulevard crossing.

So, you can see northern boulevard at midday

is still a heavily traveled truck route.

Here comes a Astoria-line train on the elevated structure.

On top of the elevated structure at northern boulevard,

underneath northern boulevard is a five-track subway structure,

one of the heaviest traveled lines in all of New York City.

To get the trains for east side access to their destination,

the route must cross directly

below these three major transport links.

But the challenging ground conditions

leave only a small area of viable material

to tunnel through and little margin for error.

All the traditional methods, and particularly methods

that were tried and true here in New York City

and in north America, in general, they met defeat.

We didn't want to do something innovative.

We had to do something innovative here.

With just under 10 feet of soil between the subway

and the new tunnel,

the engineering required to solve this problem

had to be bold.

This is one of... It's not necessarily the first,

but this was the first time for a tunnel in north America

where we're able to horizontally freeze the ground.

Freeze pipes basically carried tubes that ran back

and forth to a freeze plant.

The freeze plant used a chilled brine to pump the chilled brine

through all of the pipes individually

and freeze the ground slowly.

Creating this frozen layer of earth

helped to strengthen the ground

sufficiently to tunnel in safety.

The frozen arch performed better than we expected.

That provided the initial support to allow us

to actually perform our sequential tunneling.

It's very high stakes, but in the end,

it was a very big success and very proud of it.