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Specification for Organic Content in Fill

Specification for Organic Content in Fill

Specification for Organic Content in Fill

What do you consider a reasonable maximum organic content to specify for engineered fill placed under a building foundation?  Material in question is a silty clay bordering on a silt.  I am expecting 0 to 6 feet of fill under the footings (ie depth varies).  2 story wood frame construction for condominiums.  

RE: Specification for Organic Content in Fill

We traditionally recommend NOT using soil with more than 4% organics for engineered fill.

RE: Specification for Organic Content in Fill

Thanks.  Material in question came in at 3% and I was thinking a 2% limit was too strict but 5% seemed a bit too lax.  So that 4% limit works for me.  I'll consider your response standard of practice :).  Kidding.  But if anyone else has a comment I'd be interested.  

RE: Specification for Organic Content in Fill


We generally recommend 3% max by dry weight. Obviously, no large organics (stumps, branches, roots, leaves, lumber or construction debris, etc.).


Jeffrey T. Donville, PE
TTL Associates, Inc.

RE: Specification for Organic Content in Fill

DougB - why use a silty clay borderline silt as structural fill below a foundation?  Wouldn't a granular material be a better choice (for compaction and sturctural capacity).  Silt and silty clay are highly moisture sensitive and depending on the location of the job, the contractor could have serious compaction problems if the jobsite gets wet.  Of course, a good contractor could make the material work, but I've learned to plan for the worst case scenario (i.e., low bidder!j/k).

RE: Specification for Organic Content in Fill

I agree with the 3% under footings and maybe up to 6% under slabs that could tolerate a little settlement and cracking.

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