Sunday, January 23, 2011

A View Down Below, Part 1

Let's take a walk down Second Avenue in a way you never have before - underground, inside the west tunnel of the Second Avenue Subway.

A few notes before you start this journey:

- The work that you see here is part of Contract 1 (referenced as Contract C-26002 by the MTA) of Phase I of the Second Avenue Subway project. This contract was awarded in January, 2007, to Skanska USA Civil, Schiavone Construction, and J.F. Shea Construction, in a joint venture under the name S3 Tunnel Constructors.

- The work in the tunnels is performed by members of
Laborers' Local Union No. 147 (a.k.a. the New York City Sandhogs).

- All of the images shown below were taken on January 18, 2011,
unless otherwise noted.

Note that you can left-click on any image
to view it in high-definition format.

An aerial view of a portion of the Tunnel Boring Machine (TBM) launch box site - looking south towards the tunnels. (The launch box extends from a point just south of East 95nd Street to a point just south of East 92th Street.)

The west tunnel, which is currently being mined by the TBM, is visible in this image on the right.

The tunnel on the left is the starter tunnel for the east tunnel. Mining of this tunnel, with the TBM, should start in March 2011.

The narrow gauge tracks that you see in this photo are not the tracks of the future Second Avenue subway. These tracks are used by the muck trains that transport the rock produced by the mining operation.

This is a another view of the launch box, looking north. The wall to the north in this image is about three blocks away.

The cylindrical struts that you see in this image help to support the east and west walls of the launch box.

This shot shows the launch box as seen from ground level, looking south.

Notice the tall rubber boots being worn by the workers. These boots are necessary for journeys into the tunnel because the tunnel is very muddy, as you will see in the images that follow.

At the moment, this tunnel extends from a point just south of 92nd Street to approximately 67th Street - a distance of just over one mile.

This is a view just inside the tunnel looking south. The tunnel has been mined to a diameter of 22 feet. At this location, the floor of the tunnel is about 75 feet below the street level.

The large yellow pipe on the ceiling carries fresh air to the head of the tunnel.

The cables on the right carry electricity for the TBM, and for the tunnel lighting. Additional cables are used for communications.

This is a view from deeper inside the west tunnel, now looking north back towards the launch box. This photo was taken roughly underneath 84th Street.

Notice how smooth the walls of the tunnel are in this area. This is very high quality rock which means it was probably quite easy for the TBM to cut through.

Note the three pipes on the right side of the tunnel in this image. Two of the pipes are used to carry water and air towards head of the machine, and one of the pipes is used carry water back out of the tunnel.

Also note the spray painted notation, "84th," on the left hand side of the tunnel. The cavern for the 86th Street station will eventually be mined just north of this location.

Clearly some of the Sandhogs on this project are New York Giants fans - but a reliable source has told me that most of them are actually New York Jets fans.

This is interesting shot. It shows an area in the tunnel with weak rock.

To buttress the weak rock, a set of steel ribs and mesh has been setup at this location to provide additional stability, and to protect the workers.

When the workers come across rock like this they must move the TBM forward very slowly, sometimes just a few feet per day.

When the TBM finally finishes its job and is backed out of the tunnel, the contractor will add a one foot thick precast concrete lining. The will be achieved by using a traveling form.

The contractor will pour the concrete for the tunnel invert and when the required strength has been achieved they will strip the forms and move them ahead.

Then another traveling form will be erected in place for the arch, the concrete will be pumped in, and when the strength is obtained the form will be stripped and moved ahead. (Stripped is a term in the industry to remove the forms, whether they be wood or steel, and move them ahead for the next concrete placement or pour.)

The material you see on the right, which looks somewhat like clay, is made up of fine rock particles that have fallen from the muck train that travels on this track.

The sandhogs regularly must shovel this heavy, wet material out of the bottom of the tunnel in order to keep the track bed clear. They generally do this during periods when maintenance is being performed on the TBM (i.e. when there are no muck trains moving on this track).

Now you are standing at a point that is approximately under 80th Street. The small engine that you see here is used to pull the muck train.

Note the very high quality rock in this section of the tunnel - no steel ribbing in sight.

Here on the left you can see some of the hopper cars that are used to transport rock out of the tunnel.

In the distance, you can see a muck train that has been positioned inside the TBM - waiting to be loaded loaded with rock from the mining operation.

Here is another view of the hopper cars waiting to be backed into the TBM.

Notice the steel ribs in this section of the tunnel. They must have hit lots of weak rock in this area.

This is the end of the conveyor belt, mounted on the TBM, that transports mined rock to the waiting hopper cars.

This is a close-up shot of the muck produced by the mining operation.

This is a view, looking north, from inside the TBM.

The front of the TBM, where the cutterhead is located, is now starting to come into view - on the left.

In the foreground, you see part another part of the conveyor system.

This is one of the Total Stations that allow the TBM operators know exactly where they are, and the precise direction that they are headed.

The stations are able to calculate distances and angles with a very high level of accuracy by shooting a laser toward a set of retroreflector targets that are mounted on the front of the TBM.

You can be sure that nothing like this was being used when the first tunnels of the New York City subway system were constructed over 100 years ago!

Courtesy of The Robbins Company

Before going any further, here is a diagram that details the main elements of the machine.


And this image, which was taken about seven months ago inside the launch box, provides you with a clear view of the front of the TBM .

Back in the tunnel, you can see here on the left a Sandhog working on the left gripper shoe of the machine.

And here you are -- right behind the cutterhead of the Second Avenue subway TBM.

The Sandhogs here are clearing away loose rocks while the machine is not in operation.

Note the propel cylinders on the upper left. These cylinders are used to push the cutterhead, with incredible force, into the rock face in front of the TBM.

A closer view of these cylinders.

And in this shot, you again see a group of Sandhogs working to install steel ribs right behind the cutterhead of the machine.

You have scene here that, in some ways, resembles an operating room: intense overhead lighting and a very experienced team focused on a single task.

It's almost as if the Sandhogs do not need words to communicate with one another. It is similar perhaps to the way that track gangs on the railroads used to work together in the days before machines did most of the heavy work.


The 2nd half of this image set can be found on this link:
A View Down Below, Part 2 - January 30, 2011


Anonymous said...

Ben, this is great. Did you get an actual tour below?

The Launch Box said...

For the time being I can't discuss or reveal the source of these images. At some point I will, just not at the moment.


Ted said...

These are awesome photos. Great images of men and machines! Look up shot-crete to see what they spray on the walls to make them more solid.
-- ETB

Anonymous said...

Very impressive shots! Glad to see NYC expanding its public transit system.

Michelle said...

Ben, your posts are so informative and interesting! It is great to be able to see and understand what is going on right under our feet. Thank you for all the effort you have put into this great blog!