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.