For a Frost Protected Shallow Foundation how do I compact gravel? – GreenBuildingAdvisor

I’m looking at a frost protected shallow foundation for a zone 6a garage. Code calls for a 12″ thickened edge for the “footing”, and then I intend to use a 5″  slab for the center. The guides require 6″ of free draining gravel (#57 is often suggested), at the bottom of the thickened edge and also in the field.

All the guides I’ve found specify free draining gravel, this include the Revised Builders Guide to Frost Protected Shallow Foundations as well as ASCE 31-01.  They also specify that it must be compacted, but everywhere I look, it says that free draining gravel doesn’t really compact because of the lack of fines.

So, how do I compact the gravel under the insulation as the guides say?

Do I need gravel on the slope from the bottom of the thickened edge to the center of just in the center?

If it’s just in the center, how do I keep the gravel in the center from sliding down the slope? I saw a suggestion of geogrid to contain the drainage gravel, but that source seemed suspicious.