Dcarrill said:
That's the thread that actually started making me question what to do. I assume the reason they suggest not backfilling is because undisturbed ground is compacted naturally. However the ground I plan on setting this pool on has been turned over and is not at all compacted. I'm just not sure if tamping is enough.
Going to get a little technical here, but this is what I went to school for and did for a number of years (not pool installation, Civil Engineering - specifically earthworks)
Every soil has its own particular maximum density. That maximum density can only be acheived at a specific water content. Too much or too little water and you will never compact that soil to its maximum density. What then happens is, if the water content changes to closer to optimum, either from drying or from rain/groundwater, the soil may further compact on its own.
Some soils have very sharp compaction curves. If you stray a little bit from the perfect amount of water you are only going to get maybe 80% compaction. Other soils are more forgiving, their curves are flatter. You have more leeway and can still be within the %95 of maximum density that we look for.
As the other thread suggests, QP, Crusher Run, Quarry Process, 3/4 + fines, or whatever you want to call it (it varies from locale to locale) is a very forgiving medium. It is 3/4" crushed stone, fines, and stone dust. If compacted correctly, it will set up almost like concrete. It's compaction curve is very flat. You can vary by a couple of percentage points and still be fine.
You can recompact excavated soil, but to do it right you would have to compute compaction curves for it. It's not rocket science but you do need some equipment that really serves no other purpose and is not exactly cheap.
Your best bet to excavate down to virgin udisturbed soil, and then backfill with QP first and then sand or stone dust as a top layer (QP can be a bear to screed and get level)
You want to compact the backfill in lifts. If you are using a jumping jack type compactor, no more than 6" lifts (and really, the jumping jacks are useless unless you are in a trench). A vibratory plate compactor is better. The heavier you can handle, the better. Keep your lifts small - 8" or so, and compact them well.
Topsoil is not used for structural fill, as it contains a lare amount of organic material. Organic material rots, leaves voids, and voids collapse.
If you have large rocks you are burying, you also do not want to nest them. Spread them out and make sure there are no voids around them. Fill will eventualy infiltrate into voids.
-dave