Monday, October 20, 2008

October 18, 2008 - A Big Hole

92nd, NW corner - looking S
Finally, after 15 months of hard work, we see the start of the "big hole" (in 2nd Avenue) that will become the launch box for the Tunnel Boring Machine.

Workers began digging out the hole, and decking over 2nd Avenue, about two week ago. They will continue decking over 2nd Avenue, moving up the west side of the avenue - and then they will repeat the process on the east side.

Here workers can be seen positioning new sections of concrete decking. The decking is supported by a grid of steel beams.

Another view of the decking.

92nd - looking SW
Workers have completed decking over 2nd Avenue at this location, except for one section.

Here's another view of the same access hole at this location. Obviously this hole will need to be closed before traffic is shifted back to the west side of the avenue...

What I find interesting is that the decking was installed before large quantities of earth underneath was removed. My guess is that they will completely deck over most of 2nd Avenue and only then will they excavate the hole to it's full depth of 70 or so feet. (Note: A reader just left a comment that appears to explain why they need to do more work before digging the launch box any deeper. You can click on the comment at the end of this posting.)

btw. 92nd and 93rd, W side - looking N
Here's picture of a set of the large pipes that are used to drill out the secant piles.

Here we have an typical New York City apartment building (on the east side of the avenue) framed by two of the drilling pipes.

Here you see two of the steel I-beams that form the outer edge of the launch box, with a secant pile drilling pipe in the middle. Keep in mind that these I-beams are about 77 feet in length.

btw. 94th & 95th - looking S
Here workers are positioning a new piece of the temporary pipeline that's used to transport the slurry concrete mix, from the plant on 96th street, to the job site.

Same location - looking N

This a portable screw pump for the concrete slurry. It's called a Screwsucker, and if you're really interested you can read more about this machine on this web link.

94th, near the NW corner - looking S
The worker in this picture is cleaning a piece of equipment that's sitting on top of one of the deep rectangular holes that has been dug out for a section of the slurry wall.

Same location - looking NE
This, I believe, is another one of the rectangular slurry wall holes. Workers have installed a steel rebar cage inside the hole and the next step, I believe, is to pour in the concrete slurry mixture.

I think these funny looking things are a kind of funnel that is used when concrete is poured into one of the secant hall holes. They are laying on their side at the moment.

btw. 92nd and 91st, W side - looking N
I found this large colored panel down near 91st street, in an area of the job site that is mostly used for storage at the moment. I've recently learned (from a comment that was left on the blog) that this is a welding screen. It's used to protect people walking by from the intense light and UV radiation put out by a welder.

btw. 92nd and 93rd, W side - looking S
These large blue panels are used to protect pedestrians, from flying pieces of mud, when the rotary drilling rig is working on the job site.
(This picture is sort of out of place, I know, but I thought it would go nicely after the orange panel in the previous shot. )

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

Regional Plan Association:
“Tomorrow’s Transit: New Mobility for the Region’s Urban Core”
Press Release
Report (12 Mb)
"RPA Releases Transit Blueprint for Urban Core.
A new study by the Regional Plan Association lays out a comprehensive plan for new and upgraded transit for New York City and Northern New Jersey. The 53-page, in-depth report entitled “Tomorrow’s Transit: New Mobility for the Region’s Urban Core” outlines new subway, bus, commuter rail, light rail and ferry projects for the Region's ‘Urban Core,’ which includes the five boroughs of New York City and urban portions of Northern New Jersey. The nearly forty recommendations focus on providing service to underserved and impoverished areas, better connections within the existing transit network and short- and long-term transit solutions with varying price tags."


Josh said...

The large orange panel is a welding screen. It protects people walking by from the intense light and UV radiation put out by a welder.

I think the reasoning behind leaving so much dirt in the areas to be excavated when they're decked over is to return the surface to normal as fast as possible. As long as their is enough room for the excavating equipment, to start working, it can be decked over.

jmp said...

It seems pretty obvious to me why they can't dig deeper where they're installing the decking.

The decking is held up by large beams. The beams are held up by the newly constructed slurry wall on one side and the concrete splice box under the center of the avenue. The slurry wall keeps the dirt under the sidewalk (and the buildings' foundations) from sliding into the hole as it gets deeper. There's nothing currently on the other side of the street to keep the dirt under the part of the avenue currently in use from sliding into the hole.

Furthermore, the splice boxes themselves, which currently support one end of each beam, are resting on nothing but dirt, so digging too deep would undermine that and cause the decking to collapse. Once they finish this side of the street, they'll switch back to the east side of the street and build out the slurry wall there. As that goes in place, they'll put in the other halves of the beams. I assume that they'll splice the beams together inside the splice boxes in such a way that the beams can span the width of the avenue without the splice box being supported from underneath. Once that happens digging should be able to go pretty quickly, as there will be little or nothing to get in the way...