Bridge piers generally don’t float. River beds are by definition “bedrock”.
depends on where they are geograpically.
Ideally, yes, the steel piles or auger cast piles (A hole drilled in the ground and filled with concrete, also called caissons), are taken to rock or "driven to refusal".
However, not all bedrock is lying close enough to the surface to do this. Thats why we have geo-structural engineers to determine bearing capacity and how big the cassions (Auger cast piles) have to be and how deep they have to go to hit adequate bearing.
This was not a foundation issue.
This was a structural/mechanical failure. Either anchor bolts failed or the brige was point loaded beyond design capacity, which is frankly irelevant due to the construction/repair work.It's referred to as "moments". Time and distance travelled. It may only be a fraction of an inch of travel and milliseconds of time, but it's going on constantly, and if it's interuppted for any reason, it can be catastrophic.
We’ll see. The “bedrock” layer can be pretty far down.