I skipped the second week of construction behind my house because nothing progressed except for delivery of materials.
In this third week, ironworkers formed rebar cages to be dropped into a bore hole to reinforce foundation piers. This weekend they drilled the first borehole with a diameter of between half to one meter to a depth of 20 meters. Watching the nature of the soil brought up, I noticed that the soil noticeably changed at that last meter with solid clay compared with the muck brought up for the first 19 meters.
The first six meters of the borehole has a steel casing. The remainder of the hole is stabilized by pumping a bentonite slurry into the hole, which keeps out ground water and puts pressure on the side wall to keep it from falling in. Then the reinforcing bar cage was dropped into the hole in three sections and welded together.
Tomorrow it is likely they will pump concrete down a pipe installed within the rebar cage. The concrete will displace the slurry from the bottom up.