As I mentioned in my previous post, the soil under the old house was quite loose and full of organic material. From what I have been told by neighbours, this area used to have a stream or an underground stream running through the backyard and may also have been a floodplain for the Ottawa river long ago before the entire area was developed. That would certainly explain the large amount of organic material in the soil - it was almost like peat.
So, to ensure that the new house would not settle, the builder had to remove all of the organic soil until they reached undisturbed mineral soil - about 60 cm below the level of the bottom of the footings on the new house. Then, about 160 metric tonnes of engineered fill were dumped in the hole, spread and compacted to create a firm flat surface to build on.
Now the surface is ready to build on and the next step is to pour the concrete footings.