Monday, January 17, 2011
A View from Above
On Saturday afternoon, I was invited to visit the rooftop of 233 East 69th Street to take, for this blog, a few pictures of one of the active work sites on Second Avenue.
The images that follow were taken from the the rooftop terrace of this 16-story apartment building, which is located on the west side of Second Avenue between 69th and 70th streets.
The contractor working at this location, SSK Constructors JV, is preparing to start mining the underground cavern for the new 72nd Street station. SSK Constructors is a joint venture made up of Schiavone Construction, J.F. Shea Construction, and Kiewit Infrastructure Corp.
Click on the picture above to view a larger copy of this stitched image. To view the original high-definition image, which is 6,834 x 2,444 pixels, click on this link to my account on Flickr.
In this image, you can see the active work site - with 69th Street on the right and 70th Street on the left.
If you look closely, you can see three groups of SSK workers on the job site.
This is closer view of the southern end of the work site at this location. (69th Street is on the right in this image.)
Underneath the steel decking (shown above) is one of the two 60-foot deep access shafts that was dug out by S3 Tunnel Constructors earlier. The other access shaft is located just north of 72nd Street.
SSK will use these two shafts for access to a cavern that eventually will be blasted out of the bedrock below Second Avenue.
I'm told that they will mine the cavern for the station by first blasting out a pilot cut at the top of the cavern. Next, they will mine 2 slash cuts on the right and left of the pilot cut.
Then, after the TBM has mined the 2nd (east) tunnel, later this year, they will mine the station cavern down to the floor level of the track tunnels.
This is a closer view of the northern end of the work site at this location. (70th Street is on the left in this image.)
This is a view looking north on Second Avenue. The 72nd Street access shaft is located just to the north of the crane shown in this image.
This is a closer shot of the 72nd Street access shaft work site, to the north on Second Avenue.
If you enlarge the image you can also see work sites between 78th and 79 (in the middle of Second Avenue) and near 83rd Street (on the west side of the avenue).
And up on 92nd Street...
92nd Street, NE corner - looking E
This is the recently activated ground freezing plant that is just to the east of Second Avenue.
The plant produces a chilled calcium chloride brine that is pumped through a network of pipes that has been installed in the drilled holes on Second Avenue near 91st Street. The ground near 91st Street & Second Avenue must be frozen before the TBM can mine the east tunnel because of the weak rock structure below ground.
A brief presentation explaining, in general, how the ground freezing process works can be found on this link to the University of Washington's web site.
btw. 91st and 92nd streets - looking SW
This image shows some of the drilled pipes that have been installed near 91st Street.
In this image you can see the top of two of the vertical pipes that have been connected to the ground freezing plant. The pipes are white, not because of the snow, but because they are now covered with frost.
One could imagine that it will take quite some time for the snow in this area to melt.
Posted by Ben H on 1/17/2011 11:00:00 PM