Such a hole is not coming over night O.o
Don’t know what happened or why you built there but I don’t know where it is smooth and because of structure integrity it’s a risky job.
If you can let me know the coordinates which are smooth I can try it.
Regarding the structural integrity concern if needed don’t change ANY blocks, make pier legs down to the ground and it will survive. BUT in this picture it is to far for the string of added blocks to reach and it will collapse if you try. Highly recommend emptying mats into a CV storage before anything is touched either by you or an NPC. Moving it will be much safer then