New York City Transit awarded Skanska USA Civil a $37 million contract to construct two new vent plants for the 1/9 7th Avenue subway line in Lower Manhattan. Constructing the two new vent plants required extensive underground utility relocation and restoration, design and installation of excavation support systems (steel sheeting) and roadway decking, soil stabilization, concrete and steel construction and extensive mechanical, electrical and plumbing components.
Located a few blocks from Ground Zero, the Park Place plant features three 150 HP fans and the Albany Street plant has two 200 HP fans. The joint venture designed and installed the protective shielding between the fan plants and the subway tunnels. The shielding was installed during night and weekend track outages. In order to facilitate airflow in the subway tunnel, the project team will be installing approximately 115 natural ventilation dampers along the 1 and 9 subway line street grating. The scope of work also included demolition and rebuilding of the existing ventilators along West Broadway which were damaged during the terrorist attacks of 9/11. Both of these activities were performed during general orders.
Since both plants are totally below the city streets and surrounded by commercial and residential buildings, stability of the existing subsurface was a great concern. There was extensive use of steel sheeting, bracing, decking and chemical grouting to control the ground water and soil. The project was extremely complicated because the streets, surrounding buildings and ground water level had to be safeguarded. Every conceivable utility is located within the footprint of the plants such as water, sewer, gas, steam, telecom and electrical lines and they all had to be maintained and in operation for the entire construction period. This was accomplished by providing temporary utility service outside of the main cuts and/or hanging existing utilities from below the decking system. Heavy vehicular and pedestrian traffic in and around the work sites had to be maintained throughout the project. A project of this nature normally takes four years but because of community and other constraints, an aggressive schedule was required to complete work in half the time. Both plants were under construction simultaneously in order to meet the project completion milestone dates of 16 months for the restoration of both streets.