Photo by Jeff Rubenstone / ENR

Disruption: One of two floating concrete batch plants (above, in a September photo) at the New NY Bridge site partially collapsed on Dec. 16.

A barge-mounted concrete batch plant at the new Tappan Zee Bridge jobsite in New York partially collapsed on Dec. 16. Project representatives reported no injuries and say project concrete placement operations have been halted until an investigation is complete.

State Thruway Authority engineers and safety experts "are monitoring the situation to ensure that [contractor] Tappan Zee Constructors conducts a thorough investigation into exactly what caused this equipment failure," says Brian Conybeare, special adviser to Gov. Andrew Cuomo for the replacement bridge, officially called the New NY Bridge Project. "We will also review any corrective action plan presented by [Tappan Zee Constructors] to prevent similar accidents in the future."

New York State Dept. of Environmental Conservation media-relations director Tom Mailey described the incident to ENR, saying, "On the morning of Dec. 16, one silo tipped over, knocking over two other silos. No liquid or mixed cement was spilled into the river."

According to Mailey, when one of the silos fell, it was torn open and emitted a plume of cement dust that may have deposited some material in the Hudson River. The department is continuing to monitor the river site for possible environmental impacts, he says.

Mounted on a 200-ft barge, the batch plant was being used for concrete placement during pile-cap installation. It was removed from the site after the collapse.

In a Dec. 16 statement, contractor spokeswoman Carla Julian said that, although concrete work has been halted, all other construction activities continue at the site.

In addition to the installation of pile caps, some piles are still being driven for the new dual-span bridge.

The New NY Bridge is a $3.9- billion replacement for New York's 59-year-old Tappan Zee Bridge.

Joint-venture contractor Tappan Zee Constructors is pursuing an aggressive schedule for the project and is looking to finish work on the bridge's foundation in 2015, with an eventual project completion date set for 2018.