Tterribilis

I need some help, guys. I think i'm in over my head. Yes, that was a pool pun =) We're building a pool on the side of a fairly steep mountain, in central Mexico. We've dug down to bedrock, and built a concrete and rebar reinforced stone box . All of the walls are interconnected, and are 5 feet thick at the base, and 2 feet thick at the tops. The columns in the walls are connected to concrete and rebar cross members in the floor.base of the box. and the box is about 6 feet deep at it's leading edge. The plan is to fill that with 30' X 30" box with crushed stone and then put a fiberglass pool in it. The problem is that I don't know anything about the weight distribution of crushed stone and when i sit a 70 ton bowl of water on it....what the outward pressure on those walls will be. I know that if you build a mound of crushed stone...you can drive a 40 ton excavator onto it and the sides of the mound don't move at all.....but that's not in a box...and it's not 70 tons. If we were home in the states, i could rely on code enforcement to help me with his problem....but there's no such thing as code where we are, and there's no yellow pages to just dial up a civil engineer. Can anyone tell me anything about the weight distribution of crushed stone as a base aggregate?