Sand bottom inground pool

[Styxbb]

I am in the process replacing my inground pool liner. The old liner is out and I need to move some sand around due to washout. It seems that there is some type of hardener in the sand, more than just compaction. Is that a thing? If so, where do I get it?

Thanks in advance.

 

[ajw22]

Your pool bottom could be vermiculite.

Builders may mix some dry concrete mix in with the pool bottom to harden it.