Sunnyray is right on about the drilling for the ventilation here; on Sunday they had the northbound curb lane blocked with pylons (you can see them in Jivey's picture) and concrete curbs to allow room for the rig and the associated equipment--the work was going on at the time.
I was not by there today, but it looked like this work will be taking place for a while; the sidewalk on the east side of Yonge was also blocked with instructions for pedestrians to use the west side sidewalk. I imagine that the northbound traffic from 401 to Sheppard will be backed up the morning and afternoon rush hours.
On Sunday afternoon it looked like rush hour on Yonge going north[added Tuesday]--but today there was nothing, all of the work was completed. The shoring rig was back on the Emerald Park site.
Maybe it was Emerald work, not Hullmark work.