Lershac said:Dirt will settle like mad unless it's applied in small lifts and compacted between lifts mechanically....and even then it may settle.
You want that concrete deck (likely the single most expensive part of your build ) to last a long time without settling, separation and cracking, then go with gravel backfill.
Just my .02$
Melt In The Sun said:congratulations! Time for a quick swim, no?