The progress of the East Side Access construction in Long Island City, Queens, as of December 20, 2012.
This photo shows 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 (E/M/R), and the elevated subway (N/Q).
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 in some views 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.
Photo: Metropolitan Transportation Authority / Patrick Cashin.