vermiculite floor gone

i have an 18x36 in ground pool, the first liner i got lasted quite a while, over 10 yrs, and in the last 4 yrs, ive went through 2 liners. the installers said that they would dig a route around the pool so that the ground water wouldnt b and issue,but they never did. so now the floor of my pool is just a mess, wher the vermiculite is all but gone. the only place wher its not is around floor drain and up about 3 ft. the rest of the pool floor is like a sandy mix, and the deep end wher the vermiculite ends its all rutted up from ground water erosion. what i was wanting to know is what can i use to fill in wher the lloor is rutted up from the ground water before i spread the vermiculite.

Pretty much anything that is firm and won't shift. In my area, people would use a type of clay-ey soil called locally "chert", and tamp it in. But I don't know what's available in your area.

You probably could use a light sand-cement mix. That's what used to be used in stead of vermiculite and cement.