Church pool RE-construction

[Poolsean]

It may be as easy as pouring cement, although that's a lot of cement. Perhaps gravel then cement over it, or compacting dirt then cement. I think in either case, you're better off going with the opinion of an expert structural engineer.
I would think that you'd want to grid rebar on the new floor and tie it into the existing pool rebar.
I wish I knew more on this.

[Sumo1]

Thanks, Sean. Maybe one of the PBs will chime in....
Hal