Above ground pool into hole with concrete walls

[crgregersen]

I'm planning to dig a hole for a 16foot (488cm x 122cm) round above ground pool.

I'll make a stone walls of height 100cm with 10cm sand in the bottom.
I'm planning a inside diameter for the wall of 500cm which gets me 6cm on each side.

The idea is to be able to drop in a pool in the summertime and a trampoline in the spring/autumn/winter time.

Any recommendations, warnings, etc.?
I cannot find information about anyone who has done this.. and I don't understand why not?
I live in the northern Europe so I believe this is optimal since the summertime is so short.. so I don't want to have a real stationary pool.