Could it really be 16 inches thick? That seems awfully thick for just a
patio. Anyone know what that would support, weight wise?

I have looked at putting in a garage slab, an 4, 5, or 6 inches is
normal around here. 16 would be rediculous.

I don't know what this thing looks like, but might it just be a
floating edge-thinkened slab? They would have mounded up dirt and fill
in a rough shape of the patio, then poured concrete on it to make a 4
inch layer on top, and about 8 inches or so on the sides.

But it seems like the buildter really needs to take care of this. Small
claims court might help, perhaps? And lifting 8tons of anything by hand
is no fun. I did a few tons of dirt by hand last summer, over the
course of several weeks. The payoff was a nice garden for my wife. Your
payoff will be a nice hole where once there was brand new patio. If you
really have to do this yourself, wouldn't it be worth it to take down
the fence and get a bobcat in there? (At least, I've been looking for
an excuse to rent one, and your situation seems like a great excuse).

-Kevin