Rehabilitation of Whitehall Street Fan Plant

Rehabilitating a fan plant for New York City Transit is an intricate job, requiring rigorous testing, tight construction specifications and difficult logistics.

It's all part of the work list for the project team rehabilitating the fan plants at Whitehall Street and Furman Street in the Montague Street Tunnel.

Asked to work on only one at a time, the project team focused first on the Whitehall Street fan plant, turning it over to NYCT's Operation Division in April. Completion entailed passing a 100-hour endurance test, clearing it to provide life-safety emergency ventilation service for the tunnel.

It was "a very difficult project that had a zero tolerance for mistakes," a jury member said.

The $23.5 million project scope involved demolition of an existing street-level building, construction of a new building and installation of new electrical power and ventilating equipment. It also entailed reconstruction of 250 lin. ft. of transition tunnel, 85 ft. of vertical shaft and 15,000 lin. ft. of fireline replacement.

Constructing the building's foundation involved installing a sheet-pile bulkhead in the East River around three sides of the new building's footprint. It also required the installation of cast-in-place piles with steel casings.

Work on this piece of the project was conducted from barges in the river, which offered mobility for the piling equipment.

While surveying to replace deteriorated sheet piling, the project team found a 36-in. cooling water intake pipe and a 48-in. outfall pipe that served the HVAC systems for several downtown buildings. The pipes were below the mud line and in an area where the team planned to install barge spuds.

To eliminate the risk of hitting those pipes during installation, or of a barge resting on the cast iron pipes at low tide, the team quickly redesigned project specifications, losing no time on the schedule.

Congestion and tight spacing at the site provided broader challenges for the

project team. The site had trailers on the north side, the historic but deteriorating Battery Maritime Building on the south and South Street traffic and pedestrian lanes to the west.

That forced the team to work from the building footprint, and to make a careful decision to use an existing 25-ft. diameter shaft, with its 4-ft.-thick walls, as part of the support for a 200-ton crawler crane - so it wouldn't block South Street traffic.

The tight spacing also impacted the topside work of installing the reinforced concrete building foundation, steel erection and final architectural cladding. That work was done in an area only large enough to accommodate a tractor-trailer.

Meanwhile, the team simultaneously handled steel erection, electrical work, fireline work and ventilation equipment installation in the tunnel.

Another delicate task came in removal of sheet piling on the structure's north side, adjacent to the pipes and near the vertical shaft. The team used a vibratory hammer to prevent vibration from stressing the Maritime Building or the shaft already in use as support for the crane.