Tuesday, May 18, 2010

Inside the Launch Box: a little detail

With this posting I present... more pictures from the inside the Second Avenue subway tunnel boring machine (TBM) launch box.

With this posting I'll be looking at some of the "under reported" areas of the launch box -- like, the vertical conveyor system, the muck tower, the side walls, the area under the decking, and the work that is taking place at the north end of the work site.

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

First let's start by taking another look at the TBM, from a few different angles.

This shot was taken from inside the stairwell, looking south towards the two starter tunnels and the TBM, which is on the right.

The image appears blurry only because it was shot through the protective plastic mesh that surrounds the stairwell. (If you left-click on the image, you can clearly see the mesh.)

This high angle shot was taken from a catwalk that is about 50 feet above the floor of the launch box. (In case you were wondering... I was escorted to this area by a member of the project team.)

Courtesy of The Robbins Company

This image, from the Robbins web site, details the different parts of a Main Beam TBM. (This is the type of TBM that is being used on this project.)

If you want to see how this particular TBM works then I suggest that you have a look at this brief video: Robbins Main Beam TBM Boring Cycle.

A closer look at a section of the front of the machine.

These is one of jacks that was used to move the 480-ton machine from the east to the west side of the launch box - to put it into position to bore the west tunnel.

The machine was initially assembled on the east side of the launch box because of the need to use the heavy lift crane at street level to position various parts, like the 61-ton cutterhead. Once the machine was assembled it was very carefully and very slowly jacked across the floor, from east to west.

This is a view from the front of the machine looking towards the rear. The wall on the left is the west side of the launch box.

This is the same wall - now about 100 feet further north. The west wall of the launch box (shown here on the left) is about 60 feet high.

This is a view (looking north) down the inside of the trailing gear of the TBM.

Crushed rock, or muck, that is produced by the tunneling operation will be brought back to this section of the TBM using a horizontal conveyor and deposited into small rail cars (called muck cars). The muck cars will then transport the crushed rock back to the launch box.

This is full view of the trailing gear of the TBM.


Now let's have a look at how the crushed rock that is produced by the TBM is removed from the work site.

Crushed rock will be transported from the TBM trailer gear back to the launch box using what are called muck cars. These cars will be moved through the tunnel on a set of tracks that will be laid behind the TBM.

Once back at the launch box, the crushed rock will then be dumped onto a conveyor system that will deposit the crushed rock into the hopper shown below.

Crushed rock from the tunneling operation flows into the hopper, in the direction shown by the larger arrow, and then the rock is transported to the surface on a vertical conveyor belt.

Once it reaches the surface it is immediately loaded into waiting dump trucks.

While the TBM can be in operation at all hours of the day, the vertical conveyor will only operate during the permitted hours of street level work - which are 7 a.m. - 10 p.m. M-F, and 10:00 a.m. - 6 p.m. Saturday.

During other times the rock brought out of the tunnels will be stored in the launch box until it can be taken to the surface.

Now some not so good news.

I did the math. It looks to me like it will take approximately 8,000 10,100 14,600 dump truck loads, over the next year or so, to take away all of the crushed rock that is produced by the TBM as it bores both tunnels. (If you're interested, you can check my math at the end of this posting.)


Now let's take a look a look at the launch box itself.

A few basic stats:
Its size is 56' (W) x 63' (H) x 815' (L).
(i.e. it's about 3 city-blocks long.)

The box extends from a point just south of East 92nd Street all the way to a point just south of East 95th Street.

I must admit that I was totally overwhelmed and awed by the size of the launch box once I was standing on the floor of it - 7 stories below Second Avenue.


The MTA said in a press release that 117,000 cubic yards (3.159 million cubic feet) of material (rock and soil) was removed during its construction. This is the amount of material that would fill over 5,000 dump trucks.

In these images you can have a close look at the utilities (gas, water, electric, telephone, cable, etc.) that have been suspended now from the ceiling of the launch box.

Note that the large horizontal beams (e.g. the beam marked with the digits "31" above) are not utility lines. These are the cross braces between the east and west walls of the launch box.


Now let's take a walk to the north end of the launch box, where they are still removing virgin soil from the site.

This is a view from a point that I would guess is under East 94th Street, looking north. Workers in the distance are moving soil into piles, so that it can be lifted using a clam shell bucket to the surface.

The red clam shell bucket that is shown in these two images is attached to a crane that is located on Second Avenue between East 94th and 95th streets.

If you look carefully you can see a video camera that has been mounted on the left-hand side of this glory hole. The camera allows the operator of the crane to see what is going on down in the hole from the cab of the crane.


And this last set of images is a collection of miscellaneous shots that I thought were also noteworthy.

This is a view looking south from a point under East 94th Street. The front of the TBM can be seen off in the distance.

Note the reflection in the standing water.

In this image you can see the sparks that were produced by a worker who was doing some welding while we were in the hole.

This is a close-up view of a section of Manhattan bedrock. The pipes shown are part of the de-watering system. (This is the system that continuously removes the ground water from the site during construction.)

This is an image of the glory hole that is located near East 92nd Street.

Look closely at this image. In it, you can see the demarcation line between the point where the bedrock ends and the secant walls begin.

And this, the last image in this set, is a reflection of the glory hole at east 92nd Street in a pool of standing water on the floor

If you would like to look at more images from inside the launch box, then I suggest that you have a look at this link:
Inside the Second Ave. Subway Launch Box
Where you can find 90 hi-resolution images that were taken by Benjamin Kabak of 2nd Ave. Sagas.


And finally -- here's the math that was used to figure out the approximate number of truck loads that will be required to take away the rock from the two tunnels:

Volume = Length x PI (3.14159) x Radius x Radius

TBM Run No. 1 (West Tunnel)
92nd Street to 74th Street [Note 1]
5,006 linear feet x 3.14159 x 11' x 11' ≈ 1.903 million cubic feet of rock

TBM Run No. 2 (East Tunnel)
92nd Street to 63rd Street
7,830 linear feet x 3.14159 x 11' x 11' ≈ 2.976 million cubic feet of rock

Total Amount of Rock, before excavation:
4.879 million cubic feet x 0.037 ≈ 180,500 cubic yards

Estimated Number of Truck Loads
(based on the weight of the rock)
4.879 million cubic feet (volume before excavation)
x 150 pounds per cubic foot / 2,000
365,900 tons of rock
≈ 14,600 dump truck loads
(assuming 25 tons of rock per truck load)

14,600 truck loads / (12,836 linear feet / 50 feet per day [TBM mining] / 7 days per week [TBM mining] * 6 days per week truck loading [M-Sa] )
≈ 60 - 70 truck loads per day (M-Sa)

These calculations have been updated twice since they were first posted, based on the input that I've received from various readers of this blog.

Note 1:
The east tunnel will be extended from 74th Street to the existing stub tunnel at 63rd Street as part of Contract 4A.


Here's a listing of the recent additions
to the right-hand column of The Launch Box

Tunneling Begins Under Second Avenue
MTA Press Release - 5/14/10

"Massive Machine Carves Out 2nd Ave. Subway Line" (2:20)
By Matthew Rivera
The Wall Street Journal - 5/14/10

"Drill Baby Drill at Future 2nd Avenue Tunnel" (1:44)
New York Post via YouTube - 5/14/10

"MTA Launches Second Avenue Subway Boring Machine" (2:13)
By Rebecca Spitz
NY1 - 5/14/10

"Second Avenue Subway Excavation Begins:
Tunnel Boring Machine Digs Phase 1" (2:31)
By Tai Hernandez
Fox 5 News - 5/14/10

"Second Ave. Subway Construction Starts Again" (1:37)
By Adam Siff
WNBC-TV News 4 New York - 5/14/10


JRC said...

What's amazing is to recall the tangle of various utilities lines as they were being excavated early in the project. Now the lines are tidily ordered and suspended above the launch box (nice picture!). I remember one of the workers told me once that that aspect of the project was, for him, the most satisfying of all of his team's accomplishments.

Hank said...

I'd hope they're using this essentially clean fill for other projects in the city, such as the Fresh Kills and Bloomfield landfill reclamation.