Question Concrete Pool was emptied to clean and paint .
Concrete pool popped 5" on deep end. What is dyi way to fill void between pool bottom and ground?
What material should be used?
Answer From what you written I assume water table is above the deep end of the pool.
Its surprising that the pool has popped up.Since all the pools are designed for empty and filled situations.The other problem I foresee is leakage since from what you have written its the case of failure of concrete since concrete is a monolith structure and it cannot bend like steel. And if you observe closely inside it would have cracks in concrete.
Best option would be to fill sand around the pool but if you provide a pictures of pool inside and around the outside. I will be in better position to advice you.