It was sheer coincidence that I got this photo at the time I did. The angle of the crane's arm perfectly matches the angle of the shadow on the side wall of 235 Laurier at O'Connor. I had been tipped off that mid-June morning that they were removing the floor of the Rideau Winter Club.
The crane was supporting a green rig, which is a vibratory driver/extractor, according to this California PDF manual on foundations (28MB), specifically pages 7-21 to 7-23.
After piles were installed and the dirt removed from between the piles and the neighbouring building's garage structure, excavation could begin on the site. In this shot, taken the same day as the tip I mentioned in the first photo, they're about halfway through extracting the soil under the former Rideau Winter Club. You can see the former cooling tubes that are still present, nearly a century after first installed, and decades after they were last used.
In this photo sent to me earlier the same morning, you can get a better idea of the layering. Above the pipes was concrete, wood, reinforced concrete and/or fill, then the asphalt of the parking surface we'd known for many years. Beneath the pipes is soil infill, likely added when the rear of the building was decommissioned. Also note the hefty foundation walls on the far side.
Here's another one of those giant concrete foundation blocks, reminiscent almost of Stonehenge. It's hard to get scale, but judging by those stacks of what I suspect are four-by-eights, it's at least a couple feet thick.
By the end of June, digging out was mostly finished. these large white blocks have been installed along the top edge of the neigbouring building's underground garage, behind the piles for 150 Slater's retaining wall.
In early July, they were removing the soil from the lower level. Presumably they had run out of room to dig away from above. Behind this digger, you can see the retaining wall had been built up more. There's also a hole in the neighbouring parking garage. Maybe that was an "oops".
Here's a similar shot showing just the wall. I really like the layers in this shot. The white blocks are acting as the footing for a wooden barrier wall. Little triangles have been installed on the piles for the installation of tiebacks (incidentally, that's the page where I found the link to the Foundation manual. A good illustration of tiebacks is on page 194 of the PDF). I guess the neighbouring garage only goes down a storey or two, otherwise there wouldn't be any space for the tiebacks.
As I was going through my old photos, I found this one I took during this year's St. Patrick's Day parade. I had never before noticed that space between the two buildings, looking all the way to the World Exchange Centre, with its rooftop ball clock. Instinctively I took this photo. At the time, I had been oblivious that the Laurier Computer building (partial view on the left) was to be demolished. I guess my instincts were correct.
Lastly, here's a more square shot of the area from July 23rd. They've added a black tarp over the white blocks. They've also filled in behind the retaining wall (whose tiebacks have now been installed), and it has become a little catwalk, the negative space becoming a positive one. The spray-painted "EXIT" sign and the ladder gives it a Donkey Kong feel.
For all photos of 150 Slater's development, see previous posts marked with the "150 Slater" label.