Neighborhood Archeological Dig?

We have no idea what is actually going on across the street but it looks much like an archeological dig of some sort. We know they are converting the long ago closed Polyclinque into apartment units and also building a new apartment building just to the right of the to-be-renovated Polyclinique building.

We watch the mystery dig unfolding across the street and take photos. This has been going on for several months now.

At first they seemed to just be moving dirt around. 

Next, they started digging big holes.

At this point they had created terraced holes and we could see what looked like a very old stone wall.

It looks like they are removing items and wrapping them in plastic bags and also laying down some sort of tags next to where items are found. In this photo, items that were spread all around have been collected into one area. We noticed survey equipment being used quite a lot, so maybe they are mapping the locations of items being removed?

In this shot, the hole had been dug even deeper so they finally put up a fence at the base of the wide pre-existing staircase. They also dug out a deep trench towards the right. B likes to call the dig workers ants. For example, he'll say, "The ants are out!"

The deep trench runs just behind the fence along the sidewalk. 

And there are more holes! The one in the foreground is terraced and is very deep. They have dug out the area of the to-be-constructed apartment building to be called Les Terrasses. What looks like an old cement wall was exposed and then they removed the wall. We have no idea what this tiered deep hole in the foreground is all about. 

I worry about the trees. I expect that most of these won't make it after the disruption to the root systems. Maybe that's the plan anyway.

With warmer temps the sun shades popped up. I've even seen some of the folks trying to work under an umbrella. We've were having a lot of rain. In the event of a sudden downpour, the pop up sun shades and umbrellas were helpful!

In this photo, can you see the round hole just inside the gated entrance?

If you compare the photo above to the next 3 photos you can clearly see a few new long trenches and squarish areas have been added.

The round hole holds rainwater pretty well. 

While the "dig" is going on new construction is going ahead on the right.

Large metal supports are being driven deep into the ground and wooden slats have been inserted between the supports. Soil has been backfilled behind the wooden slats/supports. It looks like they are maintaining a roadway across the middle of this area. We see them driving trucks of dirt in/out across this, though at some point that will have to stop as the new building will span this whole area. 

It is interesting to watch but so many questions...