Yeah - Toronto and GTA is pretty much all this fractured shale (which is prone to swelling) - further north you go, will see more limestone (i think it's mainly limestone) and harder rock and they are much closer to the surface (or above) - good old Canadian shield territory
Had to google what this meant. Fascinating stuff. Here is an short and sweet article on the Toronto bedrock swelling for anyone interested:
Wow, standing below an unsupported rock wall with lose boulders 10 feet above their head would be completely disallowed in the mining industry. Do that everyday and you'd be guaranteed a LTI eventually. All they need to do to remediate the hazard is drap a curtain over the rock wall from the lip. With the right tools and materials a 10 min job.
It's not unsupported rock with loose boulders - this is a treated cut rock face reviewed by geotechnical engineers and the safety team. There are no boulders. The whole site is cut into rock and precautions are taken prior to allowing workers into the space. Maybe the photo makes it look different than it actually is on site. Safety is a huge priority on site - no shortcuts here.
If this isn't the construction industries definition of unsupported lose ground I have no idea what would be. Every mine I've been in would not need any wire mesh based on constructions definition than. In a mine basically every rock wall 2.0m above the ground needs to be bolted and screened, almost no exceptions.
... and with a thick transfer slab right over top of the opening to support the columns above.