But is there any bedrock under all the landfill or just sand ?
I had a friend who was a civil engineer in Norfolk, VA. He told me that they drive piles until they stop moving a certain deflection per hammer strike. You do not need bedrock.
The piers on the Brooklyn Bridge sit on clay. They ran out of money about two thirds of the way to bedrock, and the clay is compacted as hard as rock under a couple hundred feet.