Located beneath three active rail lines at Rotterdam Junction, N.Y., the 107-ft-long reinforced concrete pedestrian tunnel is among the last components to complete the 750-mile Empire State Trail. To keep the rail corridor fully operational during construction, the project team adapted the box-jacking method to pull the cast-on-site tunnel through the embankment. The innovative approach minimized the magnitude of rail embankment deformation by applying roughly equal and opposite forces to each side. Six sets of steel tendons were installed through the embankment and connected to hydraulic jacks affixed to the far end of the box. On the other side of the embankment, the tendons were connected to a cellular cofferdam designed to resist the anticipated jacking load. With less than 8 ft of cover separating the tunnel roof and the tracks, a row of grout-filled steel pipes installed directly above the tunnel prevented settlement. Other major elements included a soil nail headwall through which the box entered the embankment and a lubrication system to reduce friction along the walls.
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