I had a vinyl lined in ground that I repaired many years ago. It was a concrete block which had to be re-laid to make it partially out of ground, actually only about 1 block out. I custom ordered a liner to fit from the local pool dealer, put padding under the vinyl (like thin styrofoam) and used a vermiculite/portland cement mix for the pool bottom. Also installed a new filter, skimmer (never had one originally) and new outlet. Laid up new block and set pressure treated 2x8 on top, had my brother mix vermiculite and cement in a mixer and wheel back to me to trowel in (easier than it sounds). Then taped foam to walls and set liner in. Need to start filling right away or vinyl will shrink. Stapled liner to rim boards, trimmed excess, then put 2x8 on top.