Thursday, July 8, 2010

TBM Probe Breaks Ground on 2nd Ave

-- Updates (3) can be found below

A drill that was connected to the Second Avenue subway TBM went off course at about 3 a.m. this morning and broke through the surface of 2nd Avenue at East 90th Street.

No injuries were reported and luckily the drill did not pierce the 30-inch gas main, the 36-inch water main or any of Con Edison's cables below the surface of Second Avenue in this area. If the drill had pierced a gas main, the consequences clearly could have been tremendous.

During the TBM mining operation, which is taking place about 60 feet below street level, the sandhogs perform a process known as "probing" using a rock drill to determine ground conditions and water inflows ahead of the TBM. Apparently one of the probes that they drilled went in an unintended direction and ended up bursting out into the open air at East 90th Street.

The divot in the road surface that was produced by the 2-inch drill was patched up before the start of the morning rush hour.

The first public report of this incident was made by John Del Signore on the the Gothamist blog and was based on an anonymous tip (shown below) that was posted on their website :

"Construction Accident Units Operating With A Subway Boring Machine That Accidentally Bored Through 2nd Avenue And Collapsed A Verizon MANHOLE. All Utilities Requested To Respond And Check For Further DAMAGE. Road Closures In EFFECT. Manhattan, NY 7/8/2010 4:38 a.m" reporter Gabriela Resto-Montero was on the scene this morning and shot this picture as part of her report, "Second Avenue Subway Construction Drill Pops Up on East 90th Street."

Courtesy of Gabriela Resto-Montero/

The hardhats being worn by the two men on the left would suggest that they are sandhogs. The man on the right, with the white hardhat, probably works for Parsons Brinckerhoff, the consulting firm responsible for the construction management aspect of the project.

I took these two pictures of the incident location at about 6:30 p.m. this evening with my cell phone camera.

East 90th Street & 2nd Avenue - NW corner - looking East

The location where I believe that the drill popped through the road surface is shown with the blue arrow - at a location that is about 6 feet west of the center line of Second Avenue.

The actual hole that was produced by the drill is no longer visible because it has been filled in and covered with an asphalt road patching material.

I concluded that this was the location of the drill hole because it's the only road patch in this intersection that looks like it has been freshly applied.

East 90th Street & 2nd Avenue - looking SE

This is a closer view of the asphalt patch that was applied over the hole.

Other news sources have reported that the MTA has placed the drilling of probes (for the TBM) on hold until they can determine why this morning's probe went so far off course.

This most likely means that the tunneling must also now be placed on hold since they can't safely move the TBM forward without first probing the rock ahead of the machine.

An Update - 7/9/10:
A spokesperson in the MTA's press office told me late this afternoon that the contractors at the site have a enough probe information so that the TBM can continue to mine the new tunnel while the investigation is taking place.

The diagram below shows the location of the 36-inch water main (shown in Blue) and a 30-inch gas main (shown in Green) that run under Second Avenue between 92nd and 95th streets. These mains almost certainly extend south along the avenue and pass through the intersection of East 90th Street and Second Avenue.

Source: Presentation to the CB8 Second Avenue Subway Task Force - 1/26/10 - p.5

If you assume that the location of these two mains at 90th Street are in the same location, then one could estimate that drill came up just to to the right of the 36-inch water main.

An Update - 7/13/10:

East 90th Street - looking N

I had another look at the intersection on Second Avenue and East 90th Street on my way home this evening. The spray painted notations here apparently confirm that a 30-inch gas main is present underneath this intersection.

An Update - 7/16/10:

The MTA told me this afternoon that the investigation of this incident is now complete and that the tunneling contractor has resumed probe drilling, as of today.

As an outcome of the investigation the contractor will now limited the length of probe drilling in front of the TBM cutterhead to a maximum of 80 feet. This limit will vary depending upon the elevation of the cutterhead drill point vs. the lowest elevation of utilities in the area.

I was also told that the high-speed horizontal conveyor, that transfers tunnel muck from the dump station to the muck bin, had a mechanical failure on July 9. (This explains why no tunnel muck has been carted away from the site this week.) All of the mined material is currently being stored in the muck bin (down in the launch box) until the horizontal conveyor repairs are complete.

: : : : :

In other developments...

When I passed by the launch box work site this morning I found the workers preparing to lower a set of muck cars down into the launch box, so I stopped to take a few pictures.

The muck cars are used to transport the mined rock, or muck, from the TBM working location back to the launch box work site between 92nd and 95th streets.

East 92nd Street - looking SE

: : : : :

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

"Second Avenue Subway Construction Drill Pops Up on East 90th Street"
By Gabriela Resto-Montero - 7/8/10

"Subway Drill Pierces Second Avenue; MTA Investigates" (0:51)
NY1 - 7/8/10

NYC Water Tunnel No. 3
By Chris Corbett
Via Flickr
This incredible collection of more than 1,000 images documents the work of the sandhogs who are building New York City Water Tunnel No. 3. If you want to get an idea of what it probably looks like down in the new Second Avenue subway tunnel then have a look at these images.


Samay said...

How did the probe come up on 90th if the tunnel has already been dug south of 90th?

The Launch Box said...

Thank you for the excellent question.

The short answer:

The location of the TBM noted on this blog was wrong. The TBM (as of July 1st) was between 90th and 91st Street - not "80' south of 90th Street" as was mistakenly noted on this blog for the past 10 days or so.

The long answer:

In early July the MTA told me that the TBM had mined approximately 300' as of July 1st. I used this information to calculated the street location of the TBM, but I somehow screwed up the calculation when I used incorrect assumptions for the distance between, and width of, the streets in this part of the city.

This evening I went on Google Maps and used their "Distance Measurement Tool" to approximate the location of the TBM (on July 1st) at a point 400' south of the southern edge of 92nd Street. (i.e. 400' = 300' of TBM mining + 40' "starter tunnel" + 60' of launch box south of 92nd Street.)

This put the TBM at a point about halfway between 90th and 91st streets.


Anonymous said...

This probing incident rests sqaure on the shoulders of the construction management (CM) team. It indicates a either a lack of supervision during a critical function, or lack of experienced personnel assigned to monitor it, most likely the case if it was on a night shift. When probing, one carefully monitors the drill feed pressure, wash color, and rate of penetration. It should be clearly evident when passing from sound rock into decomposed rock or soil. The Sandhogs will keep probing until told to stop by the CM, so in my opinion, the fault lies with them. Regardless, a very dangerous situation.

Core Drill Bits said...

It indicates either a lack of supervision during a critical function, or lack of experienced personnel assigned to monitor it..