Dear OP (Zzyzx)_

Something thing defintely wrong with your description of the situation
or the situation itself

54' x 58' x 3' tapered to 11' is approx 800 yds of concrete (3.3
milliton lbs)

Think would be ~90 trucks! I don't think so.

A massive multi-lane concrete overpass can be on the order of 1500 yds


The structural engineering test lab where I worked had a floor 50' x
80' x 2' thick & a reaction wall 80' x 21' x 3' thick

Even at only $100 yd monolithe you're talking would be about ~$80k just
for the mud.

Perhaps the real situation is end wall & side walls then back filled &
covered with a slab; a much more cost effective way to generate that
geometry.

Assuming 6" slab & walls the same configuation would be about 80 yds,
much more resaonable

I have never seen residential detail as you describe



cheers
Bob