If it was a deep excavation I can’t imagine it was done without “tying back” the sides. A slurry wall, injection grouting and alike. No way it was so deep as to undermine 60-90 foot piles.
Honestly, I really don’t think there would be speculation at this late date if the design was flawed. I, you, anybody could walk into the building department and request access to the plans. It would be clear rather quickly if the design was seriously flawed.
So...next we ask, was what was designed actually installed and properly inspected. This is a private building, it was the owner perogative to hire and pay for the inspection services they deemed necessary. The original design firm may well have no involvement in the construction inspection, if fact, it’s common for design firms to be undercut ($) by construction inspection firms.
You can’t get a 90 foot H-pile delivered to downtown San Franciso and welding H-Piles end to end is hugely expensive in both welding labor and productivity cost.
Did the contractor pay an inspection to say a 17 foot piece of scrap
Driven in 5 minutes is actually a 90 footer?
Where the inspectors even watching and keeping the appropriate records?
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.