Grant Erwin wrote:
If there is a clear path so a truck can back up to it from the street,
then you can contact tree pruning/removal outfits and ask them if they
would divert their wood chip truckloads to the pool for awhile. Those
guys have to pay to dump those wood chips, and they just love it when
they find places willing to take them for free. They will rot down to
dirt in a couple of years and will then be entirely suitable as a
soil base. In essence, you don't do anything and just let them fill
it up. I bet it would be full in a year.

They will never rot to dirt, since dirt contains quartz sand particles. It
will never be a stable soil base.