Back in the 1990s, I worked in a skyscraper a couple blocks away at the Embarcadero wharf, and had an office looking across the bay towards the Bay Bridge. The City sold some land next to us, and I watched as a developer built a hotel. Noisy as heck for a long time as they drove piles into the ground, and very deep. Not only that, but they then drove steel piles at angles around every vertical pile, perhaps seven angled for each vertical pile at the basement level, and these were all welded together with brackets. They made sure that building would not sink. And it was a seven-story hotel. That leaning Millennium Tower is 58 stories in height.
It's well known that much of this land is former bay, filled in with sediment, shipwrecks and garbage from the 1800s. The original bay shore actually extended many blocks inland. So driving piles to bedrock should be mandatory (but isn't).
If piles aren’t driven to bedrock, they are driven to a “level of resistance” or “refusal” (refusal to advance). The level of resistance is a function of the hydraulic hammer force and blows per inch of advancement. (Literally how many hammer blows on the pile per inch of additional advancement, 50-60 might be considered “refusal”.). Having said that, some reasonably conservative assumptions about the underlying soil need to be made to be defined the required “level of resistance”. Propped hammer sizing is critical, propped pile shoes (protective end treatment) and construction inspection is critical.
Contractors have been indicted for collusion with inspectors to “pass” piles. There was a huge case in NY some years back.
Whom did the owner hire to do construction inspection and did they have any experience in pile driving?
(Structural Engineer, I’ve worked in both design and construction.)