I don't think they came close to properly compacting the lower support. SGW2009 descrbed the process he observed. Souded like they built ~ 10 ft x 18 foot wire mesh boxes, open at the top. Fill it with raw material that OEM said each piece was 92% air by volume, not counting the voids when filled to a 2 foot depth in the wire boxes.
He said the compaction was a bit hap hazzard.
I think over time, with occasional bumper to bumper 20-30,000 lb semis riding over with relatively resricted slow traffic on 3 lanes each way, steady setteling will be an issue.
From my prior comments from OEM about recommended compaction:
For roadway support (not an overpass), appears to be bulk thicknes limited to 12" max if using a push compactor, but it appeared to be used on the full 24" deep blocks.
And for the full 24", 600-1000 psf, 2 passes "with a tracked excavator or dozer"
Kevin Kelleher, PEME
Internal Mechanical Eng'g Consultant DuPont ESD Specialists