While frigid weather conditions have limited river work in recent weeks, Tappan Zee Constructors, LLC (TZC) has been forging ahead with the parts of the bridge that anchor it to the land: the abutments. Located at each end of the crossing, the stout abutments will serve as solid foundations for the bridge and the land-side highway.
TZC is currently constructing the abutments for the northern span of the twin-span bridge. The southern span’s abutments will be constructed in 2017, after traffic is shifted onto the northern span and the landing of the existing bridge is removed.
Construction of the abutment in Rockland began with the strengthening of loose soil through the installation of aggregate piers, which are tubular, subterranean masses of stone. After the aggregate piers were completed, forms were installed to create the shape of the foundation. Next, the area inside the form was filled with reinforcing steel and concrete to create a robust foundation to support the abutment.
A different approach is being utilized in Westchester, due to slopes and rocky subsoil soil conditions. These abutments are being supported by 4-foot diameter drilled shafts in which steel shells are drilled into the rock and filled with reinforced concrete. The Westchester abutment is being poured today, Mar. 13, and the work is readily visible from this project construction camera.
TZC contracted with Iron Lady Enterprises, one of many woman-owned small businesses on the project, to perform the steel work. The firm’s founder, Dianna Montague, was on site every day to oversee her iron workers as they overcame often-harsh winter conditions to assemble cages of rebar within the abutment forms. Quality assurance engineers also were on hand to ensure the work met specifications.
“It’s challenging work, especially this year with all the snow that we have had,” said Montague. “But TZC has been great to work with and our team is proud to be a part of this major project.”
With the steel reinforcements installed, each abutment will be completed when the forms are filled with over 950 cubic yards of concrete. With each cubic yard (a block that measures 1 yard deep, 1 yard wide and 1 yard high) weighing approximately 4,200 pounds, the weight of the concrete that will be poured into each abutment is equal to that of approximately 1,000 average-weight cars.
The challenge of pouring that large a volume of concrete into the relatively confined space inside the abutment form requires precise timing. TZC’s concrete teams work quickly to fill the form at a constant rate to ensure the concrete cures properly, enabling it to withstand the stresses of many future generations of traffic.
You can learn more about other foundation elements, such as the approach span and main span pile caps, and the geotechnical investigations that helped inform their design.
