Buses replacing trains along stretch of Green B Line

Police and MBTA workers responded to a hole found in the ground at the intersection on Commonwealth and Essex on Friday.Harrison Hill for The Boston Globe

Repairs to the Commonwealth Avenue Bridge are expected to be completed by Saturday morning and commuters can expect the Green Line’s B branch to operate on a normal schedule, officials said.

Problems began on Friday when a piece of debris fell off the bridge that carries Commonwealth Avenue over the Massachusetts Turnpike, MBTA spokesman Joe Pesaturo said. The chunk, which was about 2 feet by 3 feet, landed on a work site below.

One westbound travel lane on Commonwealth Avenue was closed, he said, though there was no disruption to travel on the Turnpike or the commuter rail.

Green Line service was interrupted in the area between Babcock and Blandford streets as a result of the debris. Buses replaced trains on a stretch of Green Line’s B branch as crews inspected and worked on the bridge, MBTA officials said.

The Green Line will be operating on its normal Saturday schedule, Pesaturo said.

A number of T stops were affected by the bridge incident, including Blandford Street, Boston University East, Boston University Central, Boston University West, Saint Paul Street, Pleasant Street, and Babcock Street.

Michael Verseckes, a spokesman for MassDOT, said workers are in the midst of a project to rebuild the substructure, or foundation, of the bridge. Heavy construction is scheduled to begin next year on a separate project to replace the deck and superstructure that carry the roadway.