I worked at several sites along the TransBay Corridor redevelopment, within stone’s throw of this tower. You are correct about the tiebacks, shoring and bracing of the excavations. If they were done improperly, other buildings around would be in distress, and the monitoring equipment in the excavation itself would show lateral displacement. Driven piles into the overburden are ridiculous for a load of that magnitude. They needed drilled shafts well into the Franciscan formation.
I agree.
I can’t speak for the local conditions, I was just making observations. I’d imagine you can’t possibly drill a shaft without slurry. For the novices, slurry is a soupy clay liquid holding the sides up in a drill hole, preventing them from caving in. Concrete is heavy than slurry, pump the concrete in at the bottom of a drilled shaft, the slurry floats on top of the concrete, the hole is filled with concrete as you collect the over flowing slurry -possibly reuse it.
Different places lend themselves better to different techniques, bed rock in Mangatten is very-very shallow. Chicago is known for drilled caissons, bed rock at 60-90 feet. Bed rock in Lousiana delta might be 1,000 feet, not friendly to skyscrapers.
In this case, I would guess, the owner gave a clear message to the construction inspection staff not to increase costs. Fighting with the contractor, they might claim those costs or stick it elsewhere in a change order.
The only inspection was what the owner consider “due diligence” and they were preoccupied with selling two bedroom condo’s at $2.1 million.
Buyer beware!