The MBTA shut the Silver Line tunnel through the Seaport on Wednesday after construction on Congress Street caused concrete to fall onto the platform at the World Trade Center Station.
The T will run buses on city streets along that portion of the Silver Line while it conducts an engineering assessment of the tunnel.
“Out of an abundance of caution for T customers and employees, the MBTA has closed the Silver Line tunnel from South Station to Silver Line Way until that assessment is complete,” the agency said in a statement. “There were no known injuries as a result of this incident.”
The MBTA believes the concrete was dislodged by construction on the Waterside Place apartment complex near the station.
MBTA spokesman Joe Pesaturo declined to provide a timeline for the engineering assessment or the tunnel closure, saying, “Engineers will take the time necessary to perform a thorough and complete inspection.”
But Waterside Place developer John Drew said it could be completed as soon as Wednesday night. He said his company would handle any needed repairs to the tunnel.
“We’re expecting the repair is something that can be done in the matter of a day or two,” he said. However, he cautioned that he could not make any definitive assessment until after the engineering review.
It’s not clear when the concrete fell. Drew’s team met with MBTA officials earlier Wednesday after noticing that piledriving work had raised the sidewalk outside the World Trade Center Station on Congress Street. Further inspection showed that concrete had fallen from an underground support column, Drew said, leading to the tunnel closure.
The Silver Line tunnel was built during the Big Dig highway project, which also included the Ted Williams highway tunnel to East Boston. In 2006, a Jamaica Plain woman was killed when several massive slabs of concrete fell from the ceiling of the Williams tunnel, crushing the car she was traveling in. A review revealed the wrong adhesive material was used to secure the concrete panels.
The MBTA did not provide further details Wednesday about the concrete that fell in the Silver Line. But Drew said he was told the piece of concrete was small, about 3 or 4 inches long. “I don’t think it was chunks,” he said.
The T suspended service through the tunnel around 2:15 p.m. and quickly announced the buses would run along an above-ground route instead. Passengers on the Silver Line, unique for its bus-only roadway between South Station and the congested Seaport District, will instead have to contend with commuting on crowded city streets during rush-hour traffic.
The detour through Seaport streets threatens to considerably slow service on a line that is often jam-packed at rush hour. During the morning commute, passengers bound for the Seaport from South Station often must wait for multiple buses to pass by before being able to board.
The Silver Line is just weeks away from adding new service, when a new branch to Chelsea will launch. The first leg of that trip will run through the tunnel from South Station.