Foundations on Organic Materials 6

[pelelo]

Experts,

I got few questions about foundations on organics Materials:

1 - What is the allowable Organic content percentage that a material on which the foundation is resting on, can be considered ok?. I ask this, because I have read several reports and it is stated vague conclusions such as "foundation materials have high or some amount of organics, therefore they are not appropriate for these purposes", but it is not specified how much is high or low, or simply what is the organic content percentage value that could trigger some settlement effects in the future?.

2 - Anyone knows any reference (paper, book, DOT manual), that could provide some information about this?

3 - How is the moisture content related to the organic content?, if both are similar, or if both are "high" or "low", does that have any meaning?

Please let me know,

Thanks

 

[SlideRuleEra]

See this US Federal Highway Administration Report on "Classification of Organic Soils".

...many state DOTs (Departments of Transportation) in the United States have strict limits on the maximum value of the organic content (2-7%) that can be present in soils to be used as subgrades and backfills.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[geomane]

Rule of thumb that I was taught is 5% max in structure areas and 10% max in pavement areas. Organic soils/Peat typically have a relatively high water content.

 

[dik]

and tend to be more compressible and break down to lose their bulk.

Dik

 

[oldestguy]

I'd look at the density oof the material. If cohesive and in the "hard" category, that may be OK even at somewhat higher loss on ignition level.

 

[fattdad]

In embankment fill, we'd limit the organic content to 5 percent. In native materials, you can't really limit anything. If it's there, it's there and you have to gauge performance, use a deep foundation or remove it.

The real reason I write is to make the distinction between, "Organic Content" and, "Organic Soils." Organic content is based on some laboratory test such as, "Loss on Ignition." Organic soils, as defined by ASTM D2487 are based on contrasting the liquid limits from wet prep to oven-dry prep. If that LL-w/LL-od ratio exceeds 1.33 you call the soil either an OH or OL. These soils may have no discernible (i.e., visible) organic content. They may feel lightweight, they may have very low strength, they may have VERY high moisture contents and they will present huge problems in secondary compression. Cv may actually show quick primary consolidation, but the secondary will kill the project. These can be mitigated for earthwork using preloads/surcharges intended to drive out the secondary compression.

Sandy soils with organic content that reside below the water table may be just fine for small load changes. Organic soils - not so true!

f-d

ípapß gordo ainÆt no madre flaca!

 

[dik]

Thanks f-d...

Dik

 

[pelelo]

Gents,

Thanks a lot for your replies. They were all very helpful.