Standard Dry Density vs Design Density for #57

We have used 120 pcf in the past for AASHTO No. 57. but honestly, it's probably a little high.

I know field techs have attempted to check compaction on stone and failed miserably to get consistent results, leading me to believe the density is highly variable.

98pcf is 15kn/m3 - i think that is definitely too low. It may be variable as it is a difficult material to assess, but I would take a higher value to be conservative as this will increase your earth pressures

Are you sure the 98 isn't 98%?

I agree with MTNClimber. I use and have often seen 120 PCF used for clean, crushed stone.

Various on-line sources report a bulk density of 87 to 105 pcf.
It will of course vary, depending on gradation and rock specific gravity.
Seems about right to me, as that fairly uniform material (1" to No. 4) has high voids.
I suspect the reported lab value is correct for that sample.

I don't see the density increasing much in-place, as it's unlikely to have a moisture content of even 3%. Maybe go with 110 pcf.

migration of fines is the big unknown here and could increase the density a lot - unless you use geotextile to prevent it. soil migration is the main reason i dont use open graded rock as backfill

cvg - I agree that filter fabric should
be used with the stone. The nice thing about using crushed stone for backfill is that it reduces the size of the retaining wall. So if you’re close to the property line, it buys the owner some more functional space. It’s also recommended for MSE and segmental retaining walls that are exposed to water (seawalls, detention ponds, walls within flood plans, ext.). We have used it extensively in these scenarios. Haven’t gotten a call back yet.