I am getting estimates on large fiberglass pools. I have had two builders come out so far and say they backfill with "wet sand". They say that's the only way to backfill all the voids. But most of what I have researched say that sand is not the preferred method anymore as they have found that two things happen with sand. 1. It causes more pressure on the side walls than small gravel 2. If it gets wet, it will settle. Think of a sandcastle on the beach and what happens when the sand gets water on it, it sorta melts down from the shape it was in before it got saturated with water.
My research on the net says that the preferred method is small gravel because it will lock into place, but if it gets wet, it will not change shape. The gravel also does don't exert the same pressure on the sidewalls as the sand does. So I am throwing this out there to see what experience you have had or what you know first hand as a builder. This pool will be in the 16x40 range in size and with the decking (850 sq ft pavers), fence, electrical, plumbing, filter, pump all included, I'm looking at about 45K to 50K and I don't want to make a big mistake on the install. Thanks!!