This photo shows work as of February 12, 2013, on tunnels leading into caverns underneath Grand Central Terminal that will house a future concourse for arriving and departing Long Island Rail Road trains. The entire project is slated to be complete in 2019. #

An overhead view of the construction pit and tunnel access chamber, in Sunnyside, Queens, near Queens Plaza station. At lower left is the muck staging area for material removed while tunneling. See this view on Google Maps. #

Work underway on one of the most challenging parts of the entire project -- excavating a tunnel under Northern Boulevard, while simultaneously supporting the overhead roadway, the overhead underground subway, and the elevated subway. To ensure stability, the tunnel was excavated in seven separate horizontal segments, or "drifts." And because the ground is soft at this site and difficult to control during excavation, it was frozen to allow for increased control and rigidity. Workers had to drive a new set of foundation pilings into the ground to temporarily support the elevated structure during construction. They then jacked up the line a fraction of an inch to shift the weight to the temporary supports, which you can see running vertically through the newly built tunnel. Those supports will be removed after the weight of the elevated subway is shifted back to the walls of the tunnel, which has been engineered to carry the load. Photographed on December 20, 2012. #

The progress of the East Side Access construction in Long Island City, Queens, as of December 20, 2012. This photo shows an overview of the site, between Northern Boulevard and the Sunnyside Rail Yard. The horizontal beams are supporting a large construction pit. #

The project will connect the Long Island Rail Road with a new concourse underneath Grand Central Terminal. This photo shows construction underway on September 19, 2011. #

Work on tunnels leading into caverns underneath Grand Central Terminal that will house a future concourse for arriving and departing Long Island Rail Road trains, photographed on February 12, 2013. #

Looking east from underneath Northern Boulevard, this photo shows what will be a track bed leading toward four newly excavated tunnels underneath Sunnyside Yard, on December 20, 2012. #

Operating Engineer Patricia McQuillia operates a locomotive carrying workers and reporters from the Tunnel Boring Machine below Second Avenue and 63rd St., on November 8, 2007. #

This photo shows work on the caverns underneath Grand Central Terminal that will house a future concourse for arriving and departing Long Island Rail Road trains, on February 12, 2013. Eight tunnels will allow trains to reach four platforms in two adjacent caverns. #

This photo shows work on the caverns underneath Grand Central Terminal that will house a future concourse for arriving and departing Long Island Rail Road trains, on February 12, 2013. #