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NATM breakthrough on East Side Access Oct 2012
Peter Kenyon, TunnelTalk
For the first time a continuous tunnel connects Queens and Manhattan on New York's US$8 billion East Side Access subway project.
The Schiavone Construction and Kiewit Corp joint venture has completed complex NATM excavations on the top drift of a challenging 120ft section of tunnel that now completes a continuous link.
Hole through CQ026 slurry wall on Drifts 1 and Drift 3

Hole through CQ026 slurry wall on Drifts 1 and Drift 3

A tunnel now runs more than 3.5 miles from a cavern 12 stories underneath Grand Central Terminal to four concrete-lined, 22ft diameter tunnels just feet below the Sunnyside rail yard in Queens that will soon be connected to the Long Island Rail Road main line (Fig 1).
The connection between the Manhattan and Queens tunnels took place directly underneath Northern Boulevard in Long Island City, Queens. The US$96.8 million CQ039 contract to excavate this vital 120ft x 64ft (36m x 19.5m) segment of tunnel was handled separately from the other tunneling contracts because the proximity and weight of existing infrastructure presented a host of ground support and structural challenges.
"For the first time since the East Side Access project began, there is now a continuous path through newly built tunnel from Queens to the East Side of Manhattan," said MTA Chairman and CEO Joseph J. Lhota. "This is the path Long Island Rail Road trains will follow when this project is completed."
Construction of the short section was complicated by a number of structural issues. Not only does it need to bear the weight of Northern Boulevard, a busy six-lane truck route leading to the Ed Koch-Queensboro Bridge, it also needs to support the four-track IND subway trunk line underneath the roadway that carries the E, M and R subway trains. It also needs to support the weight of the elevated BMT Astoria Line, which carries the N and Q subway trains.
  • Fig 1. East Side Access alignment

    Fig 1. East Side Access alignment

  • Michael Horodniceanu at the breakthrough location

    Michael Horodniceanu at the breakthrough location

Project workers had to drive a new set of foundation pilings into the ground to temporarily support the Astoria Line tracks and elevated structure during the construction of the tunnel. They then jacked up the line ever so slightly in order to relieve its permanent foundation supports of the line's weight, and shift the weight to the temporary supports.
Then they cut into the permanent foundation, which had been protruding into the right-of-way where the new tunnel is being built. In later phases of construction, workers will restore the subway line to its permanent foundation, which has been modified to rest on top of the newly completed section of LIRR tunnel.
  • New foundation pilings

    New foundation pilings

  • Elevated Astoria Line

    Elevated Astoria Line

  • Ground freezing to assist stability

    Ground freezing to assist stability

"The first challenge that we faced was to resupport the elevated subway structure and shift its weight onto a temporary structure and then physically lift the elevated line up off its foundation and place it on temporary struts all without disrupting existing subway service," explained Michael Horodniceanu, President of MTA Capital Construction.
Fig 2. Excavation is completed in a series of drifts

Fig 2. Excavation is completed in a series of drifts

"Once we completed that we have then frozen the ground and excavated and created a new tunnel. Between that and the freezing a piece of tunnel this challenging has never been attempted in this region before. What happened here is a true milestone. This is the most complicated and challenging 120 feet of tunnel we've built on any of our construction mega-projects."
"That it is being completed as intended is a testament to human ingenuity and perseverance."
In order to further ensure the continued stability of the nearby ground, the tunnel has been divided up into seven horizontal drifts which are arranged length-wise and stacked into three columns. Each frozen drift is being excavated separately, and the first one completed is the southernmost, topmost one (Fig 2).
Work on Contract CQ039 will continue, with completion of this stage of the project scheduled for April 2013. Workers will complete adjacent drifts in the coming weeks before breaking down the concrete walls separating the drifts from one another, thereby creating a single tunnel 60ft wide and 40ft high, capable of carrying three tracks. The outer tunnel walls will then be structurally reinforced and lined with concrete.
References
East Side Access slippage forces new contract - TunnelTalk, February 2012
Tunnel worker loses his life in New York - TunnelTalk, November 2011
Slurry TBMs ready to tackle New York ground - TunnelTalk, March 2011
East Side Access soft ground tunnels awarded - TunnelTalk, October 2009
East Side Access optimization - TunnelTalk, October 2009

           

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