I'd put the dirt that you CAN pack in the hole about 8" deep, then pack the snot out of it with the bucket on the excavator, keep repeating the process. If you really wanted to compact it good, I believe there are sheepsfoot rollers that you can get to go on the excavator in place of the bucket. Roll it back and forth with down pressure.
You can't put a thicker layer down THEN try to compact it because you won't transfer the PSI of the compacter to the bottom of thicker dirt.
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