BY JANIE ROSMAN
New Tappan Zee Bridge project authorities gave reporters a boat tour of the beginnings of the new bridge project last week. Twenty percent of the steel piles are now in place and are being cleaned.
“Pile installation of the two main towers of the bridge has been completed, all piles are in the group in place,” NYS Thruway Authority Construction Compliance Engineer Tom McGuinness told us.
The new bridge will have 43 approach span piers — each formed by groups of piles — compared to 196 on the current bridge. Additionally, the first five approach span piers near the Westchester shoreline have piling completed.
Hollow inside, the piles fill with river muck as they’re installed in two sections, vibrated and field welded. Once in place, a giant clamshell bucket excavates the muck, and each pile is reinforced with concrete and rebar (reinforced steel).
Variations in the river bed require pile lengths from 100 to 330 feet long, and from 3 to 6 feet in diameter. TZC is prepping and installing piles at four locations simultaneously.
Next comes capping to ensure a more stable foundation. The main tower concrete pile cap forms are onsite and being prepped prior to installing. Approach span pier caps, made offsite, will be shipped to the construction site.
Two 1,000-foot work trestles on each shoreline support equipment and prevent excessive shoreline dredging that could harm the river and shorelines. Part of the Rockland trestle will be dismantled, and part will remain in place as the Thruway Authority’s permanent maintenance dock.
Installation, reinforcement and capping continue through next year (spring 2015), McGuinness said.
The project is on time, and on budget thus according to project overseers. “The attention to detail, accuracy, scheduling, documentation for the size and scope of this project is impressive,” special project advisor Brian Conybeare commented.
Last June, TZC leased space at Hudson Harbor, where it manages daily project activities. Westchester-based construction staff is ferried to work sites from an adjoining pier in Sleepy Hollow, and no heavy equipment or building materials are located at Hudson Harbor, or taken to work sites from the shore in this area.
TZC also began placing acoustic receivers near the construction zone last year to locate endangered Atlantic and shortnose sturgeon that were
tagged by other researchers. Dredging the remaining areas will be between August 1 and October 31 this year.
Stone placement via conveyor and chute armors (protects) the river bottom in dredged areas from machinery used to make the pile caps, piers, and to lift girder sections.
The 90 to 100 vessels and barges in the river will become more than 130 as the project ramps up. GPS trackers are being placed on construction equipment, and a geo (electronic) fence will be placed around the work zone.
Details about the Coast Guard’s expanded Regulated Navigation Area (RNA) 500 yards north and 500 yards south of the span, and boating safety information, are listed on the New NY Bridge website.