"Scott M. Petty" wrote in message ...
I'm planning to mount a telescope pier (Astro Pier) on a to be poured
concrete slab. The slab would be on a slope (although the slab obviously
would be level) and would vary between 1 and 5 feet in depth, being at least
4 feet deep under the telescope pier. The overall size of slab would be
approximately 8 x 13 feet.

I think you're implying that the slope of the hill is 1/2; that is a
verticle drop of 4' over 8' of ground; quite steep. Such a slope is
plastic and will tend to flow, especially when wet and supporting the
weight of a concrete slab.

Since you want to level the ground, hire a landscaping/patio
contractor and build a proper retaining wall and fill the hole with
rock and dirt as he suggests. Then pour a proper slab ( depending on
your temperature zone and subsoil - you'll probably only need 6" -
streets are built with 9" concrete and highways with 12") over
aggregate & sand, isolated from the pier as others have described.
Expect to pay $100 per cubic yard for the concrete,