Filling in swimming pool

[Stimw]

Back in the mid 70's I drove a dump truck for the digging crew and sometimes helped the installation crew with this style of pools.
The steel wall was set and panels bolted together with angle braces. Then the bottom of the wall was poured with concrete and later back filled.
The inside was just fine sand troweled smooth to the liner shape.
The liner was then snapped into the top coping which was bolted to the top of the walls. We used an old torpedo vaccuum cleaner in the skimmer hole to suck the air out from under the liner.
Then carefully filled with water so the pressure would not damage the troweled sand under the liner.
If it had a bottom drain you might be able to pump in out with the pool pump. Once you get the liner out you should be able to push the walls in and break the concrete. (my best guess) The panels were bolted together with 3/8" bolts.

 

[Verticaltrx]

Be sure to either bust up the concrete in the bottom or remove it completely. My uncle filled in an in-ground concrete pool some years ago by just filling it with soil and compacting as they went up. All was well until they got a lot of heavy rain, the water that soaked into that area had no where to go, the soil became saturated and it ended in a badly stuck tractor when someone drove across it.