By Kevin Zawacki
Though ground-breaking for the new Tappan Zee Bridge isn’t expected to take place until late summer, about 20 workers are on the Hudson River each day, gathering soil samples and running tests in the crossing’s shadow.
The boat captains, firemen, engineers and other professionals on the water are prepping for the construction of the new span, which is expected to open in 2017 and cost taxpayers an estimated $5.2 billion.
“The smart, earlier work is underway,” explained Tom Madison, the executive director of the New York State Thruway Authority, Tuesday afternoon before leading some two-dozen journalists and lawmakers on a tugboat tour of the research currently underway.
Madison said the biggest risk factors in building the new span are the geotechnical conditions, or soil and rock on the river bottom that will support the crossing and 145,000 vehicles it serves daily.
Now, a handful of barges are carrying out boring and analysis of materials at the river’s floor; the findings will guide the construction conglomerate with the lowest bid who is tasked with carrying out the billion-dollar infrastructure overhaul.
“We’ll have a solid understanding of the engineering principals for putting together the foundation,” Madison said.
The following step, slated to stretch from April to June, is test pilings. Seven cylindrical structures close to 200-feet long will be driven into the river’s soil and rocks, and their strength tested. The test piles will be removed before construction begins, but the findings will be used for the final project.
“They will indicate conditions across the river,” said Kristine Edwards, a bridge design development manager, during the tour.
Edwards added that precautions are being taken during the test piling process to protect river life, especially the endangered Hudson sturgeon. Since some fish and mammals are particularly susceptible to sound, engineers will drive the piles into the river with air compression technology that creates an insulation zone with bubbles and limits loud noise.
A team of biologists will also monitor nearby fish populations during the test piling project, Edwards added.
The cost of current testing and research—financed by the New York State Department of Transportation and New York State Thruway Authority—reaches into the millions. The test piling aspect costs $17.8 million, officials said, and the current boring costs $3.5 million.
The state will select the conglomerate tasked with building the span in late August, Morley said, after bids come in this July. The design team and construction team will work in tandem per a new design-build law passed last year.
“It shifts the risk back to the private sector,” Madison said, noting a design-build formula means quicker built time, less bureaucracy and likely lower prices. The project is expected to cost about $5.2 billion, but the final price tag could “swing significantly in either direction,” according to Madison.
No concrete plan for financing has been presented yet, though officials said toll-backed Thruway bonds are an option. Federal loans and toll hikes are also possibilities.