Rockery Design with broken stone backfill

[chuck22044]

Re: Thread 255-322322; I'm familiar with FHWA CFL/TD-06-006; I've a contractor that want's to use granite blast rubble for backfill behind an 18ft tall rockery. Very angular but randomly graded (4in to 24in pieces). Any ideas about weight and lateral pressures or potential problems? (I'm always tentative about rockeries because they depend so heavily on the contractor's experience in construction them.)

 

[dirtsqueezer]

You'd certainly have good drainage! I gave up my FHWA manual a few years ago, but I do remember being allowed to use blast rubble for backfill on a road washout in about '03. We couldn't test for compaction obviously, but there were visual and roll count methods for ensuring it was to spec. That's vertical pressure, which obviously works for material like quarry spall. My concern would be the question of whether that granite blast rubble would provide lateral support to your cut slope.
I would call your guy with the FHWA and talk to him about it. That's a pretty serious wall at 18 feet, and if you're dealing with them, you're probably dealing with roadwork, which means traffic, which means safety. Just sayin'.