#57 Stone as Fill 2

[nbryan]

Could the use of #57 stone be placed under footings where
loose soils were removed? The argument would be that fines
could wash into the stone and potentially undermine the
foundation?

 

[KAM_imported]

Our firm often uses #57 stone as backfill beneath footings when soft cohesive soils are removed, and high groundwater conditions exist. The stone layer thickness does not normally exceed 12 inches. If the adjacent soil profile consists of cohesive soils, the possibility of soil washing into voids in the stone is probably remote. If the surrounding soils are clean sands, this is a possibility. This can be prevented by requiring that the contractor wrap the stone layer with a suitable geotextile fabric (similar to an aggregate underdrain). Even if ravelling of soil into voids in the stone does occur, it would probably not undermine the footing, but may cause subsidence of the ground surface adjacent to the footing. We typically compact each 12-inch thickness of stone using 3 passes of a suitable vibratory plate type compactor.

 

[jainslie]

It has been my experience that 57's do not compact well. We perfer to use DGA, CSB or in a pinch #9's

 

[72shortbox]

I would say #57 if fine under a foundation (geotextile is a good idea but not always needed.) I think infiltration of fines would be more problimatic if you had some type of cyclic loading like a pavement. I usualy call for #57 under cast inplace retaining walls not just for bearing but for added sliding resistnace

 

[amitg]

What woud be the recomended bed under road surface. We use compacted #57.