If I recall correctly from a previous article about this, one issue in this case is that after the building was built there was excavation in an adjacent lot.
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?