I have been going to South Padre with my family since I was a kid in the 1960s.
South Padre is one long sand bar. I have no idea how many hundreds of feet you would have to go to hit bedrock. There is only so much you can build on compacted sand. I don’t know how they were able to build the few skyscraper condos that are there now.
“I have no idea how many hundreds of feet you would have to go to hit bedrock.”
Model the sand more like a fluid than a solid; and drill lots of piles. Think of the ground level foundation as a platform. (I have lots of engineers in my family who have worked on designs much more complicated than this hotel.)