Not a geologist, but I suspect that'll depend on how liquid the 120' of sand between the piles and the bedrock gets.

I'm sure the engineers ran the calculations and deemed it 'safe enough'

Or some investor did.

Investors will always want things cheaper, and they don't understand engineering. The responsibility of ensuring that the design is safe falls on the engineer who stamped the drawing. Situations like this are covered in engineering ethics classes, which most civil engineers in the US would have taken.

Plus, depending on the state, a Professional Engineer (a certification earned) has to sign off on this stuff and is liable in the event of something catastrophic happening, like the building falling over.

Because Millennium is on reclaimed land, they cannot determine whether or not they have drilled into bedrock. They drill into what's called the 'point of refusal'; a point where they can no longer drill deeper. Whether this is bedrock or even stable soil is somewhat vague.

Almost nothing in this comment is accurate:

- You CAN determine the type of rock you are drilling through as well as it's relevant characteristics. Pieces of the material are brought to the surface with the drilling mud and instruments are put down the hole.

- Builders DO NOT just stop drilling when their drill won't drill no further. (This made me laugh!) There is testing, design, design review, more testing during construction, more design review and perhaps modification based on conditions. If a particular drill could not drill to design depth, they would likely change the bit or drill.

- While there will always be some uncertainty, engineers require more than a vague understanding of soil conditions to design the foundation of a building like this. Any remaining uncertainty should be taken into account in the design.

Maybe I have a poor definition of 'point of refusal', but this is the term developers use. Most developers in SF don't tell you whether they drilled down to bedrock or not.

It's a real term. This is not how the pile depth is decided but a maximum depth.

It's awfully hard to believe that they literally can't tell what the soil is like at the point of refusal. Sending down a camera and a light is child's play compared to actually running a drill string.