installing pool on unlevel ground need advice

[BigDave]

What kind of pool? Traditional steel wall Above Ground or soft sided?

[mwatson61]

traditional steel wall

[BigDave]

The sand really goes inside the pool wall - the wall holds it in.
You are right, sand can shift. I have also seen the 45 degree rule CarlD mentioned.
It's best to dig down to undisturbed soil, if you must build up, a block retaining wall filled with compacted base material (crushed concrete comes to mind) would be the way to go.
You can also dig to level then hold the high side back with a retaining wall. You'll probably have to dig quite a bit larger than you already have to build the wall.

[CarlD]

A popular material up here for filling, like BigDave's crushed concrete is called Quarry Product, known to the trades as "QP". QP is dirty large gravel. It's unwashed and has fairly large chunks of stone (1") mixed with dirt. It's significantly less expensive than washed gravel, drains virtually as well, and has a very high friction coefficient which makes it less prone to shifting under the immense weight of a pool. It's really one of the best products for backfilling behind retaining walls.

My base rises about 2 1/2' at the ground's lowest point and using QP and retaining block (and an engineer ) I was able to make the base smaller than the rule of thumb. It hasn't shifted at all in 12 years.

If you REALLY want to ensure it works great, install a French Drain first, underneath it to drain away any water that passes through the QP.