The limits depend on the type of soil, water conditions, and the size of the vibrator(roller or otherwise). For expample if you are using a small walk behind roller compacting a damp sand (i.e. near optimum) then you may be able to compact up to 12 inches, although 6 to 9 inches is more likely. In the same conditions, a plate compactor might get 6 inches with 4 to 8 passes.
If you could be more specific, we might be able to help you better. But in general terms, vibratory compaction equipment will penetrate less than 1 foot unless very large equipement is used in which case 2 to 3 feet might be possible.
In general,
Soil dumped out of a truck is about 88% SPDD compaction. With about 3 passes of compaction, relative to type and depth, you will get up to 92% SPDD, 5 passes 95% SPDD, 8 passes 98-100% SPDD.
At optimum moisture, the lower the density the less compactive effort needed.
That has been my experience in the field.
