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Tappan Zee Bridge over the Hudson River

Tappan Zee Bridge over the Hudson River – Formwork & Shoring Systems

Building a custom suspended cofferdam that was part of the construction of a new Tappan Zee Bridge (the Governor Mario M. Cuomo Bridge) and replaced the existing Tappan Zee Bridge over the Hudson River in New York

Scope

Build two anchor pier foundations (35 feet by 326 feet by 14 feet deep) and two tower foundations (60 feet by 362 feet by 16 feet deep), with minimal water intrusion, for the more than 16,000-foot bridge

Challenge

The bridge’s structural integrity was dependent on key design features such as the 419-foot, inclined towers, geometrically aligned cables, girders, crossbeams and foundations.

Performance

To form the foundations, Aluma Systems designed and installed custom steel cofferdams with integrated walers and seal-welded face sheets. The system was fabricated with high-strength steel in panels (20 feet by 11 feet) and pre-cast soffits supported by caissons six feet in diameter. In total, the systems provided exceeded 50,000 square feet of formwork and nearly two million pounds of fabricated steel.

The forms remained in the Hudson River through two entire winter cycles, withstanding every conceivable challenge — ice flows, occasional drift material and a Nor’easter in which waves topped the forms.

The precast decks were assembled above the Hudson, and the Aluma cofferdam forms were bolted to the side of the precast soffits with heavy angle and bolts. All forms were water sealed with compressive joint material after all panels were assembled. Once secured, the entire system was lowered, using strand jacks, into the Hudson River in one uniform drop, which took nearly a day to complete. The forms were designed to restrain 8–14 feet of water from the Hudson River throughout construction.

Once in place, the concrete was poured in two lifts: the first from 10 feet and 6 inches above the water line and the second to the top of foundation. The concrete pours on the four mass foundations were completed with only minor water intrusion from the Hudson River.