Single Size Backfill
Single Size Backfill
(OP)
Can you help me please,
I keep being told that 'single size stone backfill is self-compacting'. Do they mean 'single size backfill requires no compaction', is there a subtle difference between the two phrases?
What I specifically need to know is that if the surround material is "clean, single size angular granular material from within the range 20mm to 70mm", what settlement is there likely to be, I need to traffic over it.
If the installation (perforated pipe, wrapped in geotextile) is within the single size material, within a prepared trench, does the backfill 'compact' in a way that minimizes settlement?
Thank you.
I keep being told that 'single size stone backfill is self-compacting'. Do they mean 'single size backfill requires no compaction', is there a subtle difference between the two phrases?
What I specifically need to know is that if the surround material is "clean, single size angular granular material from within the range 20mm to 70mm", what settlement is there likely to be, I need to traffic over it.
If the installation (perforated pipe, wrapped in geotextile) is within the single size material, within a prepared trench, does the backfill 'compact' in a way that minimizes settlement?
Thank you.





RE: Single Size Backfill
RE: Single Size Backfill
If I understand the situation this stone is being placed around a perforated pipe in a trench and then this trench will have traffic loads on it. Depending on the type of pavement, if there is any, and the type of traffic; the trench could settle and require some maintenance quicker if there is no compactive effort.
It is always better to compact, but in this case the risk appears to be fairly low if you do not compact.
Mike Lambert
RE: Single Size Backfill
the fine grained material can migrate into the voids of the rock and that will both clog the drain rock and cause additional settlement. It should not be considered "containment"
RE: Single Size Backfill
1) Use a washed uniformly graded aggregate and wrap the whole thing in permeable geotextile filter fabric, or
2) Use clean, washed sand, and no filter fabric.
Professionally I've always seen/used option 1, but a guy on engtips made a very compelling argument for option 2 last time around, and I've been considering specifying that for my next job requiring a french drain, to see how it works.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Single Size Backfill
An estimate can be made using AASHTO T19 (ASTM C29) by comparing the volume of voids in both loose and rodded samples of the same material. Consolidation under compactive effort can be estimated to be at least as much (and probably more) than occurs by rodding.
RE: Single Size Backfill