These lanes will be closed for three weeks, scheduled to reopen on Feb. 6.
The city says that westbound traffic on Elm Street won't be able to access University Avenue while the work is being completed.
John Kelly, the director of design and construction for linear underground infrastructure in the city's engineering and construction services division said this work is part of an ongoing effort to replace a four-kilometre portion of a major water main 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.
This work is only part of the project to restore water mains from D'Arcy Street to Gerrard Street. The entire project is expected to be completed in October 2015.