One of my friends is preparing to install at 18 foot ABG pool. He has removed the sod and top soil from the location. After checking for level, he has found out that the high section cannot be lowered any further as it was previously (Years Ago) a driveway and garage location. The dirt is packed very well in this location, it stalls a roto tiller when trying to loosen it.
Can he make this his lowest grade by building the other areas up to level with masonary sand? This would make the sand depth 2 inches over the packed hard ground and a little over 4 inches in some other locations. Will having a 4 inch depth of sand in some locations around the perimeter of the pool cause it to wash out?
He will be using a pad between the vinyl liner and the sand with a preformed cove system if that makes any difference.