These lanes will close Sunday evening at 7 p.m. and are scheduled to reopen on Feb. 6.
The city says that westbound traffic won't be able to access University Avenue while the work is being completed.
John Kelly, the director of design and construction, linear underground infrastructure in the city's engineering and construction services division told CBC News that this work is part of an ongoing effort to replace a four-kilometre portion of a major watermain stretching from Spadina Avenue to River Street.
Kelly said the current shutdown at the downtown intersection is unavoidable.
"We'll be excavating a fairly significant pit in the east side of the [University Avenue and Elm Street] intersection. It is more than four metres wide, so that prevents us from actually installing steel plates to allow traffic to go over it during the peak periods of the day, otherwise we would have been doing that," he said in a telephone interview.
The wider project began in January 2012 and is expected to be completed this spring, Kelly said.