The part between the Fontanka and the Troitskiy Prospekt was closed down for roadworks. But the public could still walk on the street. Unlike you might be used to in some European or US streets the safety for the public was close to nothing.
You see that pothole cover lying there? There were more like that, right next to an open hole without any fences. Look the wrong way, walk the wrong line and down you go. :)
At any site I saw most of the workers don't do a lot. Yeah, lot of talking, smoking, looking at girls and stuff like that.