Tuesday, October 4, 2011

Beyond the Pilot Cut

This posting contains images of work that has taken place underground in various project locations during August and September.

All of the photographs shown below were taken by the MTA and/or its contractors. The MTA gave me permission to reproduce them on this blog.

Note: The brown lines of text directly under the image indicate, first, the source (i.e. MTA) and second, the unedited caption that MTA Capital Construction applied to the image.

MTA - 8/10/11
C4B - 72nd Street center cut south - looking S

This first image, from early August, appears to show work on the so-called pilot cut for the 72nd Street station cavern. The pilot cut, along the roof of the cavern, is the first section of the station cavern that is mined.

This work is being performed by the MTA's contractor, SSK Constructors, a joint venture of Schiavone Construction, J.F. Shea Construction, and Kiewit Infrastructure Corp.

You can see the basic keystone shape of the pilot cut, above in the mined cavern, and then also below in diagram 2.

(left-click on the image for a closer look)

The set of diagrams above summarizes the steps taken to mine an underground rock cavern like the one being built for the new 72nd Street station.

SSK started their work at the top of the cavern, while S3 Tunnel Constructions was mining the east and west tunnels below using the TBM. SSK first mined the pilot cut (diagram 2), and is now in the process of mining the two subsequent slash cuts to the right and left (diagrams 3 & 4).

Since the cavern is so wide, slash cuts are used to allow the arch to be supported safely in increments. Only when the slash cuts are complete and the arch fully supported is the cavern mined down to the cavern floor (diagrams 5 & 6).

MTA - 9/29/11
C4B - Underground looking north from the base of the 69th Street shaft

This recent image shows the pilot cut and a section of the slash cut on the left that has been mined.

MTA - 9/29/11
C4B - Station Cavern - Looking south from base of 72nd Street shaft

A recent image of the 72st Street station cavern.


MTA - 8/3/11
C4B - G3S1 Cavern 2 - looking south

This image, from early August, shows a different area: the location of the future "G3S1 Cavern 2".

This cavern is being built in support Phase 3 of the project. The cavern provides room for the future S1 tunnel (shown in red in the diagram below) to connected to the G3 tunnel (shown in blue) that is being built as part of Phase 1.

From this cavern, SSK has been mining the continuation of the west tunnel to the upper level of the north side of the Lexington Avenue/63rd Street station. (Readers may recall that the TBM only mined the west tunnel to a point just south of 65th Street. They had to stop there because the bend of the tunnel into the station was just too sharp for the TBM to mine.)

Note - Look carefully on the right in the image above and you can see one of the steel ribs that apparently was left by the Sandhogs when they finished the west TBM tunnel in early February 2011. So what you are looking at is the point where the west TBM tunnel ends and the G3S1 Cavern 2 starts.

G3/G4 Tunnels and 72nd Street Station
Second Avenue Subway
(left-click on the image for a closer look)

This diagram details the current and planned subway tunnels just to the east of the Lexington Avenue/63rd Street station.

The G3 & G4 tunnels (shown in blue and green) are being built as part of Phase 1 of the project. The tunnels designated as S1 & S2 (shown in red), for the future "T Line", will be built during Phase 3 of the project.

MTA - 8/19/11
C4B - G3S1 Cavern 2 - Drilling for blast holes

MTA - 8/3/11
C4B - North TBM escape niche looking north

This interesting shot shows a small tunnel that was mined in the event that the Sandhogs, working in TBM tunnel 2, needed to exit the east tunnel during an emergency.


MTA - 8/29/11
C3 - Demolition work existing platform

This image shows demolition work that is taking place on the upper level of the north side of the Lexington Avenue/63rd Street station, i.e. behind the existing orange wall that separates the north side and south (active) side of the station.

The work is being performed by the MTA's contractor Judlau Contracting.

MTA - 8/29/11
C3 - Demolition work existing station platform

Update - 10/11/11
The MTA told me this afternoon that a portion of the upper and lower platforms are being removed, as shown in the 2 images above, to create space for new stairways that will connect to one another.


MTA - 8/11/11
C1 - Concrete and waterproofing work in the west tunnel

Work being performed in the west TBM tunnel by the MTA's contractor, S3 Tunnel Constructors.

MTA - 8/27/11
C1 - Invert concrete work in the west tunnel

Workers in this image are pouring the permanent tunnel invert (i.e. the floor) of the tunnel concrete liner. The tunnel invert is the floor structure that will support the running track. The image also shows the forms, and the concrete pump lines.

The contractor is also in the process of installing concrete cast-in-place tunnel lining in the west tube. (not shown in this image.)

Please remember, I didn't take any of these shots. They are courtesy of the MTA.


Jim Kingdon said...

What is the approximate size of the G3/S1 and G4/S2 caverns? Or to ask it another way, when/if phase 3 is built, will it be a tight fit to have enough room to work in? I assume any phase 3 TBM would come from the south, from a future launch box. If so, will there be room to assemble a crowd of onlookers like they did near 63rd street station a few weeks ago?

Anonymous said...

Ok Jim lets get to stage 2 first.

mdh said...

Another great post, Ben. You do an excellent job describing aspects of the construction process that a vast majority of people don't see or even consider when they think about this project.

Surprisingly, I still find myself explaining to friends that the current work is simply an extension of the Q Train up 2nd Avenue... not a new "T Train" all the way up/down 2nd Avenue, as most people believe. The MTA should do a better job of advertising that fact, because otherwise there will be a TON of disappointed New Yorkers when Phase 1 completes.

Chet- NYC said...

The photos are really amazing. I doubt that 99 out of any 100 people have any clue just how much work it is to build a subway in NYC.

Arverne By The Sea said...

Wow! my father worked for a coal mine for over 30 years, there were some underground tunnels where his team used to work. He has always been sharing with me all about such machines, i was never really interested in knowing about them and was too claustrophobic to visit those tunnels even once!

Don Anon said...

Do you know why the demolition work on the platform at 63d St. station is needed?

The Launch Box said...


The MTA told me this afternoon that a portion of the upper and lower platforms, on the north side of the Lexington Ave/63rd Street station, are being removed to create space for new stairways that will connect to one another.