This past week we poured the first bit of concrete in the giant rat slab foundation (or mat foundation) that sits, or will sit, at the bottom of One Delisle. At its deepest point, below the building's core, it will be over 4m tall. Meaning, the area occupied by the gentlemen in the above photo will be fully covered in concrete when it's complete. Note the height of the rebar in the middle of the photo. This picture doesn't even do it justice, though. You need to be on site and down in the bottom of the hole to really feel it. There's a lot of bar, and it's going to be very deep.
In our case, this raft slab foundation will, as it sounds, serve as the building's foundation. This is what the tower will rest on. However, raft slabs can also serve the function of withstanding hydrostatic pressures from below (groundwater). That is the case with the raft slab foundation at Junction House given that we have a watertight "bathtub" design for the underground. However, that's not the case here at One Delisle, as the groundwater levels aren't as high and this will not be a "bathtubbed" underground. So the job of this giant slab is as a mat foundation.
Disclaimer: I am not a structural engineer or a hydrogeological engineer. What do I know?